Provides radiation for oncology. Radiation therapy - radiotherapy

Radiation therapy as a method of treating cancer has been widely used for several decades. It ensures the preservation of the organ and its functions, reduces pain, improves survival rates and the patient’s quality of life. The essence of radiation therapy is the use of high-energy ionizing radiation (wave or corpuscular). It is directed to the area of ​​the body affected by the tumor. The principle of radiation is to disrupt the reproductive abilities of cancer cells, as a result of which the body gets rid of them naturally. Radiation therapy damages cancer cells by negatively affecting their DNA, making them unable to divide and grow.

This treatment method is the most effective for destroying actively dividing cells. The increased sensitivity of malignant tumor cells to ionizing radiation is caused by 2 main factors: firstly, they divide much faster than healthy cells, and secondly, they cannot repair damage as effectively as normal cells. Radiation therapy is carried out using a radiation source - a linear accelerator of charged particles. This device accelerates electrons and produces gamma rays or x-rays.

Some types of radiation therapy

Radiation for cancer is possible using sources of radioactive radiation placed in the patient's body (so-called internal radiation therapy or brachytherapy). In this case, the radioactive substance is located inside catheters, needles, and special conductors that are implanted inside the tumor or placed in close proximity to it. Brachytherapy is a fairly common method of treating prostate, cervical, uterine, and breast cancer. The radiation acts so accurately on the tumor from the inside that the negative impact on healthy organs is minimal.

Some patients are given radiotherapy instead of surgery, for example for laryngeal cancer. In other cases, radiation therapy is only part of the treatment plan. When radiation for cancer is given after surgery, it is called adjuvant. It is possible to perform radiotherapy before surgery, in which case it is called neoadjuvant, or induction. This type of radiation therapy makes the operation easier.

Radiation therapy is the effect on the patient’s body of ionizing radiation of chemical elements with pronounced radioactivity in order to cure tumors and tumor-like diseases. This research method is also called radiotherapy.

Why is radiation therapy needed?

The basic principle that formed the basis of this section of clinical medicine was the pronounced sensitivity of tumor tissue, consisting of rapidly multiplying young cells, to radioactive radiation. Radiation therapy is most widely used for cancer (malignant tumors).

Goals of radiation therapy in oncology:

1. Damage, followed by death, of cancer cells when exposed to both the primary tumor and its metastases to internal organs.
2. Limiting and stopping the aggressive growth of cancer into surrounding tissues with the possible reduction of the tumor to an operable state.
3. Prevention of distant cell metastases.

Depending on the properties and sources of the radiation beam, the following types of radiation therapy are distinguished:

It is important to understand that a malignant disease is, first of all, a change in the behavior of various groups of cells and tissues of internal organs. Various variations in the relationship between these sources of tumor growth and the complexity, and often unpredictability, of cancer behavior.

Therefore, radiation therapy for each type of cancer gives a different effect: from complete cure without the use of additional treatment methods, to absolutely zero effect.

As a rule, radiation therapy is used in combination with surgical treatment and the use of cytostatics (chemotherapy). Only in this case can you count on a positive result and good prognosis for life expectancy in the future.

Depending on the location of the tumor in the human body, the location of vital organs and vascular lines near it, the choice of irradiation method occurs between internal and external.

• Internal irradiation is carried out when a radioactive substance is introduced into the body through the alimentary tract, bronchi, vagina, bladder, by introduction into blood vessels or by contact during surgical intervention (incision of soft tissues, spraying of the abdominal and pleural cavities).
• External irradiation is carried out through the skin and can be general (in very rare cases) or in the form of a focused beam on a specific area of ​​the body.

The source of radiation energy can be both radioactive isotopes of chemicals and special complex medical equipment in the form of linear and cyclic accelerators, betatrons, and gamma installations. A banal X-ray machine used as a diagnostic equipment can also be used as a therapeutic method for some types of cancer.

The simultaneous use of internal and external irradiation methods in the treatment of a tumor is called combined radiotherapy.

Depending on the distance between the skin and the source of the radioactive beam, the following are distinguished:

• Remote irradiation (teletherapy) – distance from the skin 30-120 cm.
• Close-focus (short-focus) – 3-7 cm.
• Contact irradiation in the form of application to the skin, as well as external mucous membranes, of viscous substances containing radioactive drugs.

How is the treatment carried out?

Side effects and consequences

Side effects of radiation therapy can be general and local.

Common side effects of radiation therapy:

• Asthenic reaction in the form of deterioration in mood, the appearance of symptoms of chronic fatigue, decreased appetite with subsequent weight loss.
• Changes in the general blood count in the form of a decrease in red blood cells, platelets and leukocytes.

Local side effects of radiation therapy include swelling and inflammation at the sites of contact of the beam or radioactive substance with the skin or mucous membrane. In some cases, the formation of ulcerative defects is possible.

Recovery and nutrition after radiation therapy

The main actions immediately after a course of radiation therapy should be aimed at reducing intoxication that can occur during the breakdown of cancer tissue - which is what the treatment was aimed at.

This is achieved using:

1. Drink plenty of water while maintaining the excretory functions of the kidneys.
2. Eating foods rich in plant fiber.
3. The use of vitamin complexes with sufficient amounts of antioxidants.

Reviews:

Irina K., 42 years old: Two years ago I underwent radiation after I was diagnosed with cervical cancer in the second clinical stage. For some time after treatment there was terrible fatigue and apathy. I forced myself to go to work earlier. The support of our women's team and work helped me get out of depression. The nagging pain in the pelvis stopped three weeks after the course.

Valentin Ivanovich, 62 years old: I underwent radiation after I was diagnosed with laryngeal cancer. I couldn’t talk for two weeks – I had no voice. Now, six months later, hoarseness remains. No pain. There is still a slight swelling on the right side of the throat, but the doctor says that this is acceptable. There was a slight anemia, but after taking pomegranate juice and vitamins, everything seemed to go away.

• Introduction
• External beam radiotherapy
• Electronic therapy
• Brachytherapy
• Open radiation sources
• Total body irradiation

Introduction

Radiation therapy is a method of treating malignant tumors with ionizing radiation. The most commonly used therapy is high-energy X-rays. This treatment method has been developed over the past 100 years and has been significantly improved. It is used in the treatment of more than 50% of cancer patients and plays the most important role among non-surgical methods of treating malignant tumors.

A brief excursion into history

1896 Discovery of X-rays.

1898 Discovery of radium.

1899 Successful treatment of skin cancer with X-rays. 1915 Treatment of a neck tumor with a radium implant.

1922 Cure of laryngeal cancer using x-ray therapy. 1928 The X-ray was adopted as the unit of radioactive exposure. 1934 The principle of radiation dose fractionation is developed.

1950s. Teletherapy with radioactive cobalt (energy 1 MB).

1960s. Obtaining megavolt X-rays using linear accelerators.

1990s. Three-dimensional planning of radiation therapy. When X-rays pass through living tissue, the absorption of their energy is accompanied by the ionization of molecules and the appearance of fast electrons and free radicals. The most important biological effect of X-rays is DNA damage, in particular the breaking of bonds between two of its helical strands.

The biological effect of radiation therapy depends on the radiation dose and duration of therapy. Early clinical studies of the results of radiation therapy showed that daily irradiation with relatively small doses allows the use of a higher total dose, which, when applied simultaneously to tissues, turns out to be unsafe. Fractionation of the radiation dose can significantly reduce the radiation dose to normal tissues and achieve tumor cell death.

Fractionation is the division of the total dose during external beam radiation therapy into small (usually single) daily doses. It ensures the preservation of normal tissues and preferential damage to tumor cells and makes it possible to use a higher total dose without increasing the risk for the patient.

Radiobiology of normal tissue

The effects of radiation on tissue are usually mediated by one of the following two mechanisms:

• loss of mature functionally active cells as a result of apoptosis (programmed cell death, usually occurring within 24 hours after irradiation);
• loss of cell division ability

Typically, these effects depend on the radiation dose: the higher it is, the more cells die. However, the radiosensitivity of different cell types is not the same. Some types of cells respond to irradiation primarily by initiating apoptosis, these are hematopoietic cells and salivary gland cells. In most tissues or organs there is a significant reserve of functionally active cells, so the loss of even a significant part of these cells as a result of apoptosis is not clinically manifested. Typically, lost cells are replaced by proliferation of progenitor cells or stem cells. These may be cells that survived after tissue irradiation or migrated into it from non-irradiated areas.

Radiosensitivity of normal tissues

• High: lymphocytes, germ cells
• Moderate: epithelial cells.
• Resistance, nerve cells, connective tissue cells.

In cases where a decrease in the number of cells occurs as a result of the loss of their ability to proliferate, the rate of cell renewal of the irradiated organ determines the time frame during which tissue damage manifests itself and can range from several days to a year after irradiation. This served as the basis for dividing the effects of radiation into early, or acute, and late. Changes that develop during radiation therapy up to 8 weeks are considered acute. This division should be considered arbitrary.

Acute changes during radiation therapy

Acute changes mainly affect the skin, mucous membrane and hematopoietic system. Although cell loss during irradiation initially occurs in part due to apoptosis, the main effect of irradiation is the loss of cell reproductive capacity and disruption of the process of replacing dead cells. Therefore, the earliest changes appear in tissues characterized by an almost normal process of cellular renewal.

The timing of the effects of radiation also depends on the intensity of radiation. After a single-stage irradiation of the abdomen at a dose of 10 Gy, death and desquamation of the intestinal epithelium occurs within several days, while when this dose is fractionated with 2 Gy administered daily, this process extends over several weeks.

The speed of recovery processes after acute changes depends on the degree of reduction in the number of stem cells.

Acute changes during radiation therapy:

• develop within weeks after the start of radiation therapy;
• skin suffers. Gastrointestinal tract, bone marrow;
• the severity of the changes depends on the total radiation dose and the duration of radiation therapy;
• therapeutic doses are selected in such a way as to achieve complete restoration of normal tissues.

Late changes after radiation therapy

Late changes occur primarily in, but are not limited to, tissues and organs whose cells are characterized by slow proliferation (eg, lung, kidney, heart, liver, and nerve cells). For example, in the skin, in addition to the acute reaction of the epidermis, late changes may develop after several years.

Distinguishing between acute and late changes is important from a clinical point of view. Since acute changes also occur with traditional radiation therapy with dose fractionation (approximately 2 Gy per fraction 5 times a week), if necessary (development of an acute radiation reaction), the fractionation regimen can be changed, spreading the total dose over a longer period in order to preserve more stem cells. The surviving stem cells, as a result of proliferation, will repopulate the tissue and restore its integrity. With relatively short-term radiation therapy, acute changes may appear after its completion. This does not allow the fractionation regimen to be adjusted based on the severity of the acute reaction. If intensive fractionation causes the number of surviving stem cells to decrease below the level required for effective tissue repair, acute changes may become chronic.

According to the definition, late radiation reactions appear only a long time after irradiation, and acute changes do not always predict chronic reactions. Although the total radiation dose plays a leading role in the development of a late radiation reaction, the dose corresponding to one fraction also plays an important role.

Late changes after radiation therapy:

• the lungs, kidneys, central nervous system (CNS), heart, connective tissue are affected;
• the severity of the changes depends on the total radiation dose and the radiation dose corresponding to one fraction;
• recovery does not always occur.

Radiation changes in individual tissues and organs

Skin: acute changes.

• Erythema resembling sunburn: appears at 2-3 weeks; Patients note burning, itching, and soreness.
• Desquamation: First, dryness and desquamation of the epidermis are noted; later weeping appears and the dermis is exposed; Usually within 6 weeks after completion of radiation therapy, the skin heals, residual pigmentation fades within several months.
• When healing processes are inhibited, ulceration occurs.

Skin: late changes.

• Atrophy.
• Fibrosis.
• Telangiectasia.

Oral mucosa.

• Erythema.
• Painful ulcerations.
• Ulcers usually heal within 4 weeks after radiation therapy.
• Dryness may occur (depending on the radiation dose and the mass of salivary gland tissue exposed to radiation).

Gastrointestinal tract.

• Acute mucositis, manifested after 1-4 weeks by symptoms of damage to the gastrointestinal tract exposed to irradiation.
• Esophagitis.
• Nausea and vomiting (involvement of 5-HT 3 receptors) - with irradiation of the stomach or small intestine.
• Diarrhea - with irradiation of the colon and distal small intestine.
• Tenesmus, mucus secretion, bleeding - during irradiation of the rectum.
• Late changes - ulceration of the mucous membrane, fibrosis, intestinal obstruction, necrosis.

central nervous system

• There is no acute radiation reaction.
• Late radiation reaction develops after 2-6 months and is manifested by symptoms caused by demyelination: brain - drowsiness; spinal cord - Lhermitte's syndrome (shooting pain in the spine, radiating to the legs, sometimes provoked by flexion of the spine).
• 1-2 years after radiation therapy, necrosis may develop, leading to irreversible neurological disorders.

Lungs.

• After a single exposure to a large dose (for example, 8 Gy), acute symptoms of airway obstruction are possible.
• After 2-6 months, radiation pneumonitis develops: cough, dyspnea, reversible changes on chest x-rays; improvement may occur with glucocorticoid therapy.
• After 6-12 months, irreversible fibrosis of the kidneys may develop.
• There is no acute radiation reaction.
• The kidneys are characterized by a significant functional reserve, so a late radiation reaction can develop after 10 years.
• Radiation nephropathy: proteinuria; arterial hypertension; renal failure.

Heart.

• Pericarditis - after 6-24 months.
• After 2 years or more, cardiomyopathy and conduction disturbances may develop.

Tolerance of normal tissues to repeated radiation therapy

Recent studies have shown that some tissues and organs have a pronounced ability to recover from subclinical radiation damage, which makes it possible to carry out repeated radiation therapy if necessary. The significant regenerative capabilities inherent in the central nervous system make it possible to repeatedly irradiate the same areas of the brain and spinal cord and achieve clinical improvement in recurrent tumors localized in or near critical zones.

Carcinogenesis

DNA damage caused by radiation therapy can cause the development of a new malignant tumor. It can appear 5-30 years after irradiation. Leukemia usually develops after 6-8 years, solid tumors - after 10-30 years. Some organs are more susceptible to secondary cancer, especially if radiation therapy was performed in childhood or adolescence.

• Induction of secondary cancer is a rare but serious consequence of irradiation characterized by a long latent period.
• In cancer patients, the risk of induced cancer recurrence should always be weighed.

Repair of damaged DNA

Some DNA damage caused by radiation can be repaired. When administering more than one fractional dose per day to tissues, the interval between fractions must be at least 6-8 hours, otherwise massive damage to normal tissues is possible. There are a number of inherited defects in the DNA repair process, and some of them predispose to the development of cancer (for example, in ataxia-telangiectasia). Radiation therapy at normal doses used to treat tumors in these patients can cause severe reactions in normal tissues.

Hypoxia

Hypoxia increases the radiosensitivity of cells by 2-3 times, and in many malignant tumors there are areas of hypoxia associated with impaired blood supply. Anemia enhances the effect of hypoxia. With fractionated radiation therapy, the tumor's response to radiation may result in reoxygenation of areas of hypoxia, which can enhance its harmful effect on tumor cells.

Fractionated radiotherapy

Target

To optimize external radiation therapy, it is necessary to select the most favorable ratio of its parameters:

• total radiation dose (Gy) to achieve the desired therapeutic effect;
• the number of fractions into which the total dose is distributed;
• total duration of radiation therapy (determined by the number of fractions per week).

Linear-quadratic model

When irradiated at doses accepted in clinical practice, the number of dead cells in tumor tissue and tissues with rapidly dividing cells is linearly dependent on the dose of ionizing radiation (the so-called linear, or α-component of the irradiation effect). In tissues with a minimal rate of cell turnover, the effect of radiation is largely proportional to the square of the dose delivered (the quadratic, or β-component of the radiation effect).

An important consequence follows from the linear-quadratic model: with fractionated irradiation of the affected organ with small doses, changes in tissues with a low rate of cell renewal (late responding tissues) will be minimal, in normal tissues with rapidly dividing cells the damage will be insignificant, and in tumor tissue it will be greatest .

Fractionation mode

Typically, tumor irradiation is carried out once a day from Monday to Friday. Fractionation is carried out mainly in two modes.

Short-term radiation therapy with large fractionated doses:

• Advantages: small number of irradiation sessions; saving resources; rapid tumor damage; lower likelihood of tumor cell repopulation during treatment;
• Disadvantages: limited possibility of increasing the safe total radiation dose; relatively high risk of late damage in normal tissues; reduced possibility of reoxygenation of tumor tissue.

Long-term radiation therapy with small fractionated doses:

• Advantages: less pronounced acute radiation reactions (but longer treatment duration); lower frequency and severity of late damage in normal tissues; the possibility of maximizing the safe total dose; the possibility of maximum reoxygenation of tumor tissue;
• Disadvantages: great burden for the patient; high probability of repopulation of cells of a rapidly growing tumor during the treatment period; long duration of acute radiation reaction.

Radiosensitivity of tumors

For radiation therapy of some tumors, in particular lymphoma and seminoma, a total dose of 30-40 Gy is sufficient, which is approximately 2 times less than the total dose required for the treatment of many other tumors (60-70 Gy). Some tumors, including gliomas and sarcomas, may be resistant to the highest doses that can be safely administered to them.

Tolerant doses for normal tissues

Some tissues are particularly sensitive to radiation, so the doses delivered to them must be relatively low to prevent late damage.

If the dose corresponding to one fraction is 2 Gy, then the tolerable doses for various organs will be as follows:

• testicles - 2 Gy;
• lens - 10 Gy;
• kidney - 20 Gy;
• lung - 20 Gy;
• spinal cord - 50 Gy;
• brain - 60 Gy.

At doses higher than specified, the risk of acute radiation damage increases sharply.

Intervals between fractions

After radiation therapy, some of the damage caused by it is irreversible, but some undergo reverse development. When irradiated with one fractional dose per day, the repair process is almost completely completed before irradiation with the next fractional dose. If more than one fractional dose per day is administered to the affected organ, then the interval between them should be at least 6 hours so that as much damaged normal tissue as possible can be restored.

Hyperfractionation

By delivering multiple fractionated doses of less than 2 Gy, the total radiation dose can be increased without increasing the risk of late damage to normal tissues. To avoid increasing the total duration of radiotherapy, weekend days should also be used or more than one fractional dose per day should be given.

In one randomized controlled trial in patients with small cell lung cancer, CHART (Continuous Hyperfractionated Accelerated Radiotherapy), in which a total dose of 54 Gy was delivered in fractionated doses of 1.5 Gy three times daily for 12 consecutive days, was found to be more effective compared to the traditional radiation therapy regimen with a total dose of 60 Gy, divided into 30 fractions with a treatment duration of 6 weeks. There was no increase in the incidence of late lesions in normal tissues.

Optimal radiation therapy regimen

When choosing a radiation therapy regimen, one is guided by the clinical features of the disease in each case. Radiation therapy is generally divided into radical and palliative.

Radical radiation therapy.

• Usually carried out at the maximum tolerated dose to completely destroy tumor cells.
• Lower doses are used to irradiate tumors that are highly radiosensitive and to kill microscopic residual tumor cells that are moderately radiosensitive.
• Hyperfractionation in a total daily dose of up to 2 Gy minimizes the risk of late radiation damage.
• Severe acute toxicity is acceptable given the expected increase in life expectancy.
• Typically, patients are able to undergo daily radiation for several weeks.

Palliative radiotherapy.

• The goal of such therapy is to quickly alleviate the patient's condition.
• Life expectancy does not change or increases slightly.
• The lowest doses and number of fractions are preferred to achieve the desired effect.
• Prolonged acute radiation damage to normal tissue should be avoided.
• Late radiation damage to normal tissues has no clinical significance

External beam radiotherapy

Basic principles

Treatment with ionizing radiation generated by an external source is known as external beam radiation therapy.

Superficially located tumors can be treated with low-voltage X-rays (80-300 kV). Electrons emitted by the heated cathode are accelerated in the X-ray tube and. hitting the tungsten anode, they cause X-ray bremsstrahlung. The dimensions of the radiation beam are selected using metal applicators of various sizes.

For deep-lying tumors, megavolt X-rays are used. One of the options for such radiation therapy involves the use of cobalt 60 Co as a radiation source that emits γ-rays with an average energy of 1.25 MeV. To obtain a sufficiently high dose, a radiation source with an activity of approximately 350 TBq is required

However, much more often, linear accelerators are used to produce megavolt X-rays; in their waveguide, electrons are accelerated to almost the speed of light and directed at a thin, permeable target. The energy of the X-ray radiation resulting from such bombardment ranges from 4-20 MB. Unlike 60 Co radiation, it is characterized by greater penetrating power, higher dose rate and is better collimated.

The design of some linear accelerators makes it possible to obtain beams of electrons of various energies (usually in the range of 4-20 MeV). With the help of X-ray radiation obtained in such installations, it is possible to uniformly influence the skin and tissues located underneath it to the desired depth (depending on the energy of the rays), beyond which the dose quickly decreases. Thus, the depth of exposure at an electron energy of 6 MeV is 1.5 cm, and at an energy of 20 MeV it reaches approximately 5.5 cm. Megavolt irradiation is an effective alternative to kilovolt irradiation in the treatment of superficial tumors.

The main disadvantages of low-voltage X-ray therapy:

• high dose of radiation to the skin;
• relatively rapid dose reduction as penetration deepens;
• higher dose absorbed by bones compared to soft tissues.

Features of megavoltage X-ray therapy:

• distribution of the maximum dose in the tissues located under the skin;
• relatively minor skin damage;
• exponential relationship between the decrease in absorbed dose and penetration depth;
• a sharp decrease in the absorbed dose beyond a given irradiation depth (penumbra zone, penumbra);
• the ability to change the beam shape using metal screens or multi-leaf collimators;
• the ability to create a dose gradient across the beam cross-section using wedge-shaped metal filters;
• possibility of irradiation in any direction;
• the possibility of delivering a larger dose to the tumor by cross-irradiation from 2-4 positions.

Radiotherapy planning

Preparation and conduct of external beam radiotherapy includes six main stages.

Beam dosimetry

Before clinical use of linear accelerators begins, their dose distribution should be established. Taking into account the peculiarities of absorption of high-energy radiation, dosimetry can be performed using small dosimeters with an ionization chamber placed in a tank of water. It is also important to measure calibration factors (known as output factors) that characterize the exposure time for a given absorption dose.

Computer planning

For simple planning, you can use tables and graphs based on beam dosimetry results. But in most cases, computers with special software are used for dosimetric planning. Calculations are based on beam dosimetry results, but also depend on algorithms that take into account the attenuation and scattering of X-rays in tissues of different densities. This tissue density data is often obtained using a CT scan performed with the patient in the same position as during radiation therapy.

Target Definition

The most important step in planning radiation therapy is identifying the target, i.e. volume of tissue to be irradiated. This volume includes the volume of the tumor (determined visually during a clinical examination or based on CT results) and the volume of adjacent tissues, which may contain microscopic inclusions of tumor tissue. Determining the optimal target boundary (planned target volume) is not easy, which is associated with changes in the patient’s position, movement of internal organs and the need, therefore, to recalibrate the device. It is also important to determine the position of critical bodies, i.e. organs characterized by low tolerance to radiation (for example, spinal cord, eyes, kidneys). All this information is entered into the computer along with CT scans that completely cover the affected area. In relatively uncomplicated cases, target volume and position of critical organs are determined clinically using plain radiographs.

Dose planning

The goal of dose planning is to achieve a uniform distribution of the effective radiation dose in the affected tissues so that the radiation dose to critical organs does not exceed their tolerable dose.

The parameters that can be changed during irradiation are:

• beam dimensions;
• beam direction;
• number of bundles;
• relative dose per beam (“weight” of the beam);
• dose distribution;
• use of compensators.

Verification of treatment

It is important to direct the beam correctly and not cause damage to critical organs. For this purpose, radiography on a simulator is usually used before radiation therapy; it can also be performed during treatment with megavolt X-ray machines or electronic portal imaging devices.

Selecting a radiation therapy regimen

The oncologist determines the total radiation dose and creates a fractionation regimen. These parameters, together with the beam configuration parameters, fully characterize the planned radiation therapy. This information is entered into a computer verification system that controls the implementation of the treatment plan at the linear accelerator.

New in radiotherapy

3D planning

Perhaps the most significant development in the development of radiotherapy over the past 15 years has been the direct use of scanning methods (most often CT) for topometry and radiation planning.

Computed tomography planning has a number of significant advantages:

• the ability to more accurately determine the location of the tumor and critical organs;
• more accurate dose calculation;
• True 3D planning capability to optimize treatment.

Conformal radiotherapy and multileaf collimators

The goal of radiation therapy has always been to deliver a high dose of radiation to a clinical target. For this purpose, irradiation with a rectangular beam was usually used with limited use of special blocks. Part of the normal tissue was inevitably irradiated with a high dose. By placing blocks of a certain shape, made of a special alloy, in the path of the beam and taking advantage of the capabilities of modern linear accelerators, which appeared thanks to the installation of multileaf collimators (MLC) on them. it is possible to achieve a more favorable distribution of the maximum radiation dose in the affected area, i.e. increase the level of conformity of radiation therapy.

The computer program provides such a sequence and amount of displacement of the blades in the collimator, which allows obtaining a beam of the desired configuration.

By minimizing the volume of normal tissue receiving a high dose of radiation, it is possible to achieve distribution of the high dose mainly in the tumor and avoid an increased risk of complications.

Dynamic and intensity modulated radiation therapy

It is difficult to effectively treat targets that are irregularly shaped and located near critical organs using standard radiation therapy. In such cases, dynamic radiation therapy is used when the device rotates around the patient, continuously emitting X-rays, or modulates the intensity of the beams emitted from stationary points by changing the position of the collimator blades, or combines both methods.

Electronic therapy

Despite the fact that electron radiation has a radiobiological effect on normal tissues and tumors that is equivalent to photon radiation, in terms of physical characteristics electron rays have some advantages over photon rays in the treatment of tumors located in some anatomical areas. Unlike photons, electrons have a charge, so when they penetrate tissue they often interact with it and, losing energy, cause certain consequences. Irradiation of tissue below a certain level turns out to be negligible. This makes it possible to irradiate a volume of tissue to a depth of several centimeters from the surface of the skin without damaging critical structures located deeper.

Comparative features of electron and photon radiation therapy electron beam therapy:

• limited depth of penetration into tissue;
• the radiation dose outside the useful beam is negligible;
• especially indicated for superficial tumors;
• for example skin cancer, head and neck tumors, breast cancer;
• the dose absorbed by normal tissues (eg, spinal cord, lungs) underlying the target is negligible.

Photon radiation therapy:

• high penetrating ability of photon radiation, allowing to treat deep-seated tumors;
• minimal skin damage;
• Beam features make it possible to achieve greater compliance with the geometry of the irradiated volume and facilitate cross-irradiation.

Generation of electron beams

Most radiation therapy centers are equipped with high-energy linear accelerators capable of generating both X-rays and electron beams.

Since electrons are subject to significant scattering as they pass through air, a guide cone, or trimmer, is placed on the radiation head of the device to collimate the electron beam near the surface of the skin. Further adjustment of the electron beam configuration can be achieved by attaching a lead or cerrobend diaphragm to the end of the cone or by covering the normal skin around the affected area with leaded rubber.

Dosimetric characteristics of electron beams

The effect of electron beams on homogeneous tissue is described by the following dosimetric characteristics.

Dependence of dose on penetration depth

The dose gradually increases to a maximum value, after which it sharply decreases to almost zero at a depth equal to the normal penetration depth of electron radiation.

Absorbed dose and radiation flux energy

The typical penetration depth of an electron beam depends on the energy of the beam.

The surface dose, which is usually characterized as the dose at a depth of 0.5 mm, is significantly higher for the electron beam than for megavolt photon radiation, and ranges from 85% of the maximum dose at low energy levels (less than 10 MeV) to approximately 95% of the maximum dose at high energy level.

At accelerators capable of generating electron radiation, the radiation energy level ranges from 6 to 15 MeV.

Beam profile and penumbra zone

The penumbra zone of the electron beam turns out to be slightly larger than that of the photon beam. For an electron beam, the dose reduction to 90% of the central axial value occurs approximately 1 cm inward from the conventional geometric boundary of the irradiation field at the depth where the dose is maximum. For example, a beam with a cross section of 10x10 cm 2 has an effective irradiation field size of only Bx8 cmg. The corresponding distance for a photon beam is approximately only 0.5 cm. Therefore, to irradiate the same target in a clinical dose range, the electron beam must have a larger cross-section. This feature of electron beams makes coupling of photon and electron beams problematic, since dose uniformity at the boundary of irradiation fields at different depths cannot be ensured.

Brachytherapy

Brachytherapy is a type of radiation therapy in which the radiation source is located in the tumor itself (the radiation volume) or near it.

Indications

Brachytherapy is performed in cases where it is possible to accurately determine the boundaries of the tumor, since the irradiation field is often selected for a relatively small volume of tissue, and leaving part of the tumor outside the irradiation field carries a significant risk of relapse at the border of the irradiated volume.

Brachytherapy is applied to tumors whose localization is convenient both for the introduction and optimal positioning of radiation sources, and for its removal.

Advantages

Increasing the radiation dose increases the effectiveness of suppressing tumor growth, but at the same time increases the risk of damage to normal tissues. Brachytherapy allows you to deliver a high dose of radiation to a small volume, limited mainly by the tumor, and increase the effectiveness of its treatment.

Brachytherapy generally does not last long, usually 2-7 days. Continuous low-dose irradiation provides a difference in the rate of recovery and repopulation of normal and tumor tissues, and, consequently, a more pronounced destructive effect on tumor cells, which increases the effectiveness of treatment.

Cells that survive hypoxia are resistant to radiation therapy. Low-dose radiation during brachytherapy promotes tissue reoxygenation and increases the radiosensitivity of tumor cells that were previously in a state of hypoxia.

The radiation dose distribution in the tumor is often uneven. When planning radiation therapy, proceed in such a way that the tissues around the boundaries of the radiation volume receive the minimum dose. Tissue located near the radiation source at the center of the tumor often receives twice the dose. Hypoxic tumor cells are located in avascular zones, sometimes in foci of necrosis in the center of the tumor. Therefore, a higher dose of radiation to the central part of the tumor negates the radioresistance of the hypoxic cells located here.

If the tumor has an irregular shape, rational positioning of radiation sources allows one to avoid damage to the normal critical structures and tissues located around it.

Flaws

Many radiation sources used in brachytherapy emit y-rays, and medical personnel are exposed to radiation. Although the radiation doses are small, this should be taken into account. Exposure to medical personnel can be reduced by using low-level radiation sources and automated administration.

Patients with large tumors are not suitable for brachytherapy. however, it can be used as an adjuvant treatment after external beam radiation therapy or chemotherapy when the tumor size becomes smaller.

The dose of radiation emitted by the source decreases in proportion to the square of the distance from it. Therefore, to ensure that the intended volume of tissue is sufficiently irradiated, it is important to carefully calculate the position of the source. The spatial location of the radiation source depends on the type of applicator, the location of the tumor and what tissues surround it. Correct positioning of the source or applicators requires special skills and experience and is therefore not possible everywhere.

Structures surrounding the tumor, such as lymph nodes with obvious or microscopic metastases, are not subject to irradiation with implanted or intracavity radiation sources.

Types of brachytherapy

Intracavitary - a radioactive source is introduced into any cavity located inside the patient’s body.

Interstitial - a radioactive source is injected into the tissue containing the tumor focus.

Surface - the radioactive source is placed on the surface of the body in the affected area.

The indications are:

• skin cancer;
• eye tumors.

Radiation sources can be entered manually or automatically. Manual administration should be avoided whenever possible as it exposes medical personnel to radiation hazards. The source is administered through injection needles, catheters or applicators previously embedded in the tumor tissue. The installation of “cold” applicators is not associated with irradiation, so you can slowly select the optimal geometry of the irradiation source.

Automated introduction of radiation sources is carried out using devices, for example, Selectron, commonly used in the treatment of cervical and endometrial cancer. This method involves computerized delivery of stainless steel granules containing, for example, cesium in glasses, from a leaded container into applicators inserted into the uterine cavity or vagina. This completely eliminates exposure to radiation to the operating room and medical personnel.

Some automated injection devices work with sources of high-intensity radiation, for example, Microselectron (iridium) or Catetron (cobalt), the treatment procedure takes up to 40 minutes. With low-dose radiation brachytherapy, the radiation source must be left in the tissue for many hours.

In brachytherapy, most radiation sources are removed after the target dose has been achieved. However, there are also permanent sources; they are injected into the tumor in the form of granules and, after they are depleted, are no longer removed.

Radionuclides

Sources of y-radiation

Radium has been used for many years as a source of y-rays in brachytherapy. It has now fallen out of use. The main source of y-radiation is the gaseous daughter product of the decay of radium, radon. Radium tubes and needles must be sealed and frequently checked for leakage. The γ-rays they emit have relatively high energy (on average 830 keV), and a fairly thick lead shield is needed to protect against them. During the radioactive decay of cesium, no gaseous daughter products are formed, its half-life is 30 years, and the energy of y-radiation is 660 keV. Cesium has largely replaced radium, especially in gynecological oncology.

Iridium is produced in the form of soft wire. It has a number of advantages over traditional radium or cesium needles when performing interstitial brachytherapy. A thin wire (0.3 mm in diameter) can be inserted into a flexible nylon tube or hollow needle previously inserted into the tumor. Thicker hairpin-shaped wires can be inserted directly into the tumor using a suitable sheath. In the USA, iridium is also available for use in the form of granules enclosed in a thin plastic shell. Iridium emits γ-rays with an energy of 330 keV, and a 2 cm thick lead shield can reliably protect medical personnel from them. The main disadvantage of iridium is its relatively short half-life (74 days), which requires the use of a fresh implant in each case.

An isotope of iodine, which has a half-life of 59.6 days, is used as permanent implants for prostate cancer. The γ-rays emitted by it are of low energy and, since the radiation emanating from patients after implantation of this source is insignificant, patients can be discharged early.

β-Ray Sources

Plates emitting β-rays are mainly used in the treatment of patients with eye tumors. The plates are made of strontium or ruthenium, rhodium.

Dosimetry

Radioactive material is implanted into tissues in accordance with the radiation dose distribution law, depending on the system used. In Europe, the classic Parker-Paterson and Quimby implant systems have been largely replaced by the Paris system, particularly suitable for iridium wire implants. When dosimetric planning, a wire with the same linear radiation intensity is used, radiation sources are placed parallel, straight, on equidistant lines. To compensate for the “non-overlapping” ends of the wire, they take 20-30% longer than needed to treat the tumor. In a volumetric implant, the sources in the cross section are located at the vertices of equilateral triangles or squares.

The dose to be delivered to the tumor is calculated manually using graphs such as Oxford charts or on a computer. First, the base dose is calculated (the average value of the minimum doses of radiation sources). The therapeutic dose (for example, 65 Gy for 7 days) is selected based on the standard dose (85% of the baseline dose).

The normalization point when calculating the prescribed radiation dose for superficial and in some cases intracavitary brachytherapy is located at a distance of 0.5-1 cm from the applicator. However, intracavitary brachytherapy in patients with cervical or endometrial cancer has some peculiarities. Most often, when treating these patients, the Manchester technique is used, according to which the normalization point is located 2 cm above the internal os of the uterus and 2 cm away from the uterine cavity (the so-called point A) . The calculated dose at this point allows one to judge the risk of radiation damage to the ureter, bladder, rectum and other pelvic organs.

Development prospects

To calculate the doses delivered to the tumor and partially absorbed by normal tissues and critical organs, sophisticated three-dimensional dosimetric planning methods based on the use of CT or MRI are increasingly used. To characterize the radiation dose, exclusively physical concepts are used, while the biological effect of radiation on various tissues is characterized by a biologically effective dose.

With fractionated administration of high activity sources in patients with cervical and uterine cancer, complications occur less frequently than with manual administration of low activity radiation sources. Instead of continuous irradiation with low activity implants, you can resort to intermittent irradiation with high activity implants and thereby optimize the radiation dose distribution, making it more uniform throughout the entire irradiation volume.

Intraoperative radiotherapy

The most important problem of radiation therapy is to deliver the highest possible dose of radiation to the tumor so as to avoid radiation damage to normal tissues. A number of approaches have been developed to address this problem, including intraoperative radiotherapy (IORT). It consists of surgical excision of tumor-affected tissue and a single remote irradiation with orthovoltage X-rays or electron beams. Intraoperative radiation therapy is characterized by a low complication rate.

However, it has a number of disadvantages:

• the need for additional equipment in the operating room;
• the need to comply with protective measures for medical personnel (since, unlike a diagnostic X-ray examination, the patient is irradiated in therapeutic doses);
• the need for a radiological oncologist to be present in the operating room;
• radiobiological effect of a single high dose of radiation on normal tissue adjacent to the tumor.

Although the long-term effects of IORT have not been well studied, results from animal experiments suggest that the risk of adverse long-term effects from a single dose of up to 30 Gy is negligible if normal tissues with high radiosensitivity (large nerve trunks, blood vessels, spinal cord, small intestine) are protected. from radiation exposure. The threshold dose of radiation damage to nerves is 20-25 Gy, and the latent period of clinical manifestations after irradiation ranges from 6 to 9 months.

Another danger to consider is tumor induction. A number of studies conducted in dogs have shown a high incidence of sarcomas after IORT compared with other types of radiotherapy. In addition, planning IORT is difficult because the radiologist does not have accurate information regarding the volume of tissue to be irradiated before surgery.

The use of intraoperative radiation therapy for selected tumors

Rectal cancer. It may be appropriate for both primary and recurrent cancer.

Stomach and esophagus cancer. Doses up to 20 Gy appear to be safe.

Bile duct cancer. Perhaps justified in cases of minimal residual disease, but in unresectable tumors it is not advisable.

Pancreas cancer. Despite the use of IORT, its positive effect on treatment outcome has not been proven.

Head and neck tumors.

• According to individual centers, IORT is a safe method, well tolerated and produces encouraging results.
• IORT is warranted for minimal residual disease or recurrent tumor.

Brain tumors. The results are unsatisfactory.

Conclusion

Intraoperative radiotherapy and its use are limited by the unresolved nature of certain technical and logistical aspects. Further increase in the conformity of external beam radiotherapy will offset the advantages of IORT. In addition, conformal radiotherapy is more reproducible and does not have the disadvantages of IORT regarding dosimetric planning and fractionation. The use of IORT remains limited to a small number of specialized centers.

Open radiation sources

Achievements of nuclear medicine in oncology are used for the following purposes:

• clarification of the location of the primary tumor;
• detection of metastases;
• monitoring the effectiveness of treatment and identifying tumor relapses;
• conducting targeted radiation therapy.

Radioactive tags

Radiopharmaceuticals (RPs) consist of a ligand and an associated radionuclide that emits γ-rays. The distribution of radiopharmaceuticals in oncological diseases may deviate from normal. Such biochemical and physiological changes in tumors cannot be detected using CT or MRI. Scintigraphy is a method that allows you to monitor the distribution of radiopharmaceuticals in the body. Although it does not make it possible to judge anatomical details, nevertheless, all three methods complement each other.

Several radiopharmaceuticals are used for diagnostics and therapeutic purposes. For example, iodine radionuclides are selectively absorbed by active thyroid tissue. Other examples of radiopharmaceuticals are thallium and gallium. There is no ideal radionuclide for scintigraphy, but technetium has many advantages over others.

Scintigraphy

A γ-camera is usually used to perform scintigraphy. Using a stationary γ-camera, plenary and whole-body images can be obtained within a few minutes.

Positron emission tomography

PET scans use radionuclides that emit positrons. This is a quantitative method that allows you to obtain layer-by-layer images of organs. The use of fluorodeoxyglucose, labeled with 18 F, makes it possible to judge the utilization of glucose, and with the help of water, labeled with 15 O, it is possible to study cerebral blood flow. Positron emission tomography can differentiate primary tumors from metastases and assess tumor viability, tumor cell turnover, and metabolic changes in response to therapy.

Application in diagnostics and long-term period

Bone scintigraphy

Bone scintigraphy is usually performed 2-4 hours after injection of 550 MBq of 99 Tc-labeled methylene diphosphonate (99 Tc-medronate), or hydroxymethylene diphosphonate (99 Tc-oxidronate). It allows you to obtain multiplanar images of bones and an image of the entire skeleton. In the absence of a reactive increase in osteoblastic activity, a bone tumor on scintigrams may appear as a “cold” focus.

The sensitivity of bone scintigraphy is high (80-100%) in the diagnosis of metastases of breast cancer, prostate cancer, bronchogenic lung cancer, gastric cancer, osteogenic sarcoma, cervical cancer, Ewing's sarcoma, head and neck tumors, neuroblastoma and ovarian cancer. The sensitivity of this method is somewhat lower (approximately 75%) for melanoma, small cell lung cancer, lymphogranulomatosis, kidney cancer, rhabdomyosarcoma, myeloma and bladder cancer.

Thyroid scintigraphy

Indications for thyroid scintigraphy in oncology are the following:

• study of a solitary or dominant node;
• control study in the long-term period after surgical resection of the thyroid gland for differentiated cancer.

Therapy with open radiation sources

Targeted radiation therapy using radiopharmaceuticals selectively absorbed by the tumor dates back about half a century. A ratiopharmaceutical used for targeted radiation therapy must have a high affinity for tumor tissue, a high focus/background ratio, and remain in the tumor tissue for a long time. The radiopharmaceutical radiation must have sufficiently high energy to provide a therapeutic effect, but be limited mainly to the boundaries of the tumor.

Treatment of differentiated thyroid cancer 131 I

This radionuclide allows you to destroy the thyroid tissue remaining after a total thyroidectomy. It is also used to treat recurrent and metastatic cancer of this organ.

Treatment of neural crest derivative tumors 131 I-MIBG

Meta-iodobenzylguanidine, labeled with 131 I (131 I-MIBG). successfully used in the treatment of neural crest derivative tumors. A week after the appointment of a radiopharmaceutical, a control scintigraphy can be performed. With pheochromocytoma, treatment gives a positive result in more than 50% of cases, with neuroblastoma - in 35%. Treatment with 131 I-MIBG also provides some effect in patients with paraganglioma and medullary thyroid cancer.

Radiopharmaceuticals that selectively accumulate in bones

The incidence of bone metastases in patients with breast, lung, or prostate cancer can be as high as 85%. Radiopharmaceuticals that selectively accumulate in bone have similar pharmacokinetics to calcium or phosphate.

The use of radionuclides that selectively accumulate in bones to eliminate pain in them began with 32 P-orthophosphate, which, although it turned out to be effective, was not widely used due to its toxic effect on the bone marrow. 89 Sr was the first patented radionuclide approved for systemic therapy of bone metastases in prostate cancer. After intravenous administration of 89 Sr in an amount equivalent to 150 MBq, it is selectively absorbed by skeletal areas affected by metastases. This is due to reactive changes in the bone tissue surrounding the metastasis and an increase in its metabolic activity. Suppression of bone marrow functions appears after approximately 6 weeks. After a single injection of 89 Sr, in 75-80% of patients, pain quickly subsides and the progression of metastases slows down. This effect lasts from 1 to 6 months.

Intracavitary therapy

The advantage of direct administration of radiopharmaceuticals into the pleural cavity, pericardial cavity, abdominal cavity, bladder, cerebrospinal fluid or cystic tumors is the direct effect of radiopharmaceuticals on the tumor tissue and the absence of systemic complications. Typically, colloids and monoclonal antibodies are used for this purpose.

Monoclonal antibodies

When monoclonal antibodies were first used 20 years ago, many began to consider them a miracle cure for cancer. The goal was to obtain specific antibodies to active tumor cells that carry a radionuclide that destroys these cells. However, the development of radioimmunotherapy currently faces more challenges than successes, and its future appears uncertain.

Total body irradiation

To improve the results of treatment of tumors sensitive to chemotherapy or radiation therapy, and to eradicate the remaining stem cells in the bone marrow, increasing doses of chemotherapy drugs and high-dose radiation are used before transplanting donor stem cells.

Whole body irradiation goals

Destroying remaining tumor cells.

Destruction of residual bone marrow to allow engraftment of donor bone marrow or donor stem cells.

Providing immunosuppression (especially when the donor and recipient are HLA incompatible).

Indications for high-dose therapy

Other tumors

These include neuroblastoma.

Types of Bone Marrow Transplant

Autotransplantation - stem cells are transplanted from blood or cryopreserved bone marrow obtained before high-dose radiation.

Allotransplantation - HLA compatible or incompatible (but with one identical haplotype) bone marrow is transplanted, obtained from related or unrelated donors (bone marrow donor registries have been created to select unrelated donors).

Screening of patients

The disease must be in remission.

There must be no significant impairment of the kidneys, heart, liver, or lungs in order for the patient to cope with the toxic effects of chemotherapy and whole body radiation.

If a patient is receiving drugs that can cause toxic effects similar to those caused by whole body irradiation, the organs most susceptible to these effects should be especially examined:

• CNS - during treatment with asparaginase;
• kidneys - when treated with platinum drugs or ifosfamide;
• lungs - when treated with methotrexate or bleomycin;
• heart - when treated with cyclophosphamide or anthracyclines.

If necessary, additional treatment is prescribed to prevent or correct dysfunction of organs that may be particularly affected by whole-body irradiation (for example, the central nervous system, testes, mediastinal organs).

Preparation

An hour before irradiation, the patient takes antiemetics, including serotonin reuptake blockers, and is given intravenous dexamethasone. Phenobarbital or diazepam may be prescribed for additional sedation. In young children, general anesthesia with ketamine is used if necessary.

Methodology

The optimal energy level set on the linear accelerator is approximately 6 MB.

The patient lies on his back or on his side, or alternating the position on his back and on his side, under a screen made of organic glass (Perspex), which provides irradiation of the skin with a full dose.

Irradiation is carried out from two opposing fields with the same duration in each position.

The table together with the patient is placed at a distance greater than usual from the X-ray therapy machine so that the size of the irradiation field covers the entire body of the patient.

The dose distribution during irradiation of the whole body is uneven, which is due to the inequality of irradiation in the anteroposterior and posteroanterior direction along the entire body, as well as the unequal density of organs (especially the lungs compared to other organs and tissues). For a more uniform dose distribution, boluses are used or the lungs are shielded, but the irradiation regimen described below in doses not exceeding the tolerance of normal tissues makes these measures unnecessary. The organ at greatest risk is the lungs.

Dose calculation

Dose distribution is measured using lithium fluoride crystal dosimeters. The dosimeter is applied to the skin in the area of ​​the apex and base of the lungs, mediastinum, abdomen and pelvis. The dose absorbed by midline tissues is calculated as the average of dosimetry results on the anterior and posterior surfaces of the body, or a whole body CT scan is performed and the computer calculates the dose absorbed by a particular organ or tissue.

Irradiation mode

Adults. Optimal fractional doses are 13.2-14.4 Gy, depending on the prescribed dose at the point of rationing. It is preferable to focus on the maximum tolerated dose for the lungs (14.4 Gy) and not exceed it, since the lungs are dose-limiting organs.

Children. Children's tolerance to radiation is slightly higher than that of adults. According to the scheme recommended by the Medical Research Council (MRC - Medical Research Council), the total radiation dose is divided into 8 fractions of 1.8 Gy each with a treatment duration of 4 days. Other whole-body irradiation schemes are also used, which also give satisfactory results.

Toxic manifestations

Acute manifestations.

• Nausea and vomiting usually appear approximately 6 hours after irradiation with the first fractional dose.
• Swelling of the parotid salivary gland - develops in the first 24 years and then goes away on its own, although patients remain dry in the mouth for several months after this.
• Arterial hypotension.
• Fever controlled by glucocorticoids.
• Diarrhea - appears on the 5th day due to radiation gastroenteritis (mucositis).

Delayed toxicity.

• Pneumonitis, manifested by shortness of breath and characteristic changes on chest x-rays.
• Drowsiness due to transient demyelination. Appears at 6-8 weeks, is accompanied by anorexia, and in some cases also nausea, and resolves within 7-10 days.

Late toxicity.

• Cataract, the frequency of which does not exceed 20%. Typically, the incidence of this complication increases between 2 and 6 years after irradiation, after which a plateau occurs.
• Hormonal changes leading to the development of azoospermia and amenorrhea, and subsequently sterility. Very rarely, fertility is preserved and a normal pregnancy is possible without an increase in the incidence of congenital anomalies in the offspring.
• Hypothyroidism, developing as a result of radiation damage to the thyroid gland in combination with or without damage to the pituitary gland.
• In children, growth hormone secretion may be impaired, which, combined with early closure of the epiphyseal growth plates associated with whole body irradiation, leads to growth arrest.
• Development of secondary tumors. The risk of this complication after whole body irradiation increases 5 times.
• Long-term immunosuppression can lead to the development of malignant tumors of lymphoid tissue.

Radiation therapy - radiotherapy

Radiation therapy (radiotherapy) is a generally safe and effective treatment for cancer. The advantages of this method for patients are undeniable.

Radiotherapy ensures the preservation of the anatomy and function of the organ, improves the quality of life and survival rates, and reduces pain. For decades now, radiation therapy ( LT) is widely used for most cancers. No other cancer treatment is as effective as RT in killing the tumor or relieving pain and other symptoms.

Radiation therapy is used to treat almost all malignancies, in whatever tissues and organs they arise. Radiation for cancer is used alone or in combination with other methods, such as surgery or chemotherapy. Radiation therapy may be used to cure cancer completely or to relieve symptoms when the tumor cannot go away.

Currently, complete cure is possible in more than 50% of cases of malignant tumors, for which radiotherapy is extremely important. Typically, about 60% of patients treated for cancer require radiology at some stage of the disease. Unfortunately, this does not happen in Russian reality.

What is radiotherapy?

Radiation therapy involves treating malignant tumors using high-energy radiation. A radiation oncologist uses radiation to completely cure cancer or relieve pain and other symptoms caused by a tumor.

The principle of action of radiation for cancer is to disrupt the reproductive capabilities of cancer cells, that is, their ability to reproduce, as a result of which the body naturally gets rid of them.

Radiation therapy damages cancer cells by negatively affecting their DNA, causing the cells to no longer divide and grow. This method of cancer treatment is most effective in destroying actively dividing cells.

The high sensitivity of malignant tumor cells to radiation is due to two main factors:

1. they divide much faster than healthy cells and
2. they are not capable of repairing damage as effectively as healthy cells.

A radiation oncologist may perform external (external) radiation therapy using a linear particle accelerator (a device that accelerates electrons to produce X-rays or gamma rays).

Brachytherapy - internal radiation therapy

Radiation for cancer is also possible using sources of radioactive radiation that are placed in the patient's body (so-called brachytherapy, or internal radiation therapy).

In this case, the radioactive substance is located inside needles, catheters, beads or special conductors that are temporarily or permanently implanted inside the tumor or placed in close proximity to it.

Brachytherapy is a very common method of radiation therapy for prostate, uterine, and cervical or breast cancer. The radiation method so accurately affects the tumor from the inside that the consequences (complications after radiation therapy on healthy organs) are practically eliminated.

Some patients suffering from a malignant tumor are prescribed radiotherapy instead of surgery. Prostate cancer and laryngeal cancer are often treated in this manner.

Adjuvant treatment with radiotherapy

In some cases, RT is only part of a patient's treatment plan. When radiation for cancer is given after surgery, it is called adjuvant.

For example, a woman may be prescribed radiation therapy after breast-conserving surgery. This makes it possible to completely cure breast cancer and preserve breast anatomy.

Induction radiotherapy

In addition, it is possible to carry out radiotherapy before surgery. In this case, it is called neoadjuvant or induction and can improve survival rates or make it easier for the surgeon to perform the operation. Examples of this approach include radiation treatment for cancer of the esophagus, rectum, or lungs.

Combined treatment

In some cases, before surgical removal of cancer, RT is prescribed to the patient along with chemotherapy. Combination treatment can reduce the amount of surgery that might otherwise be required. For example, some patients suffering from bladder cancer, with the simultaneous administration of all three treatment methods, manage to completely preserve this organ. It is possible to simultaneously conduct chemotherapy and radiotherapy without surgery in order to improve the local tumor response to treatment and reduce the severity of metastasis (tumor spread).

In some cases, such as lung, head and neck, or cervical cancer, this treatment may be sufficient without the need for surgery.

Since radiation also damages healthy cells, it is very important that it is targeted specifically at the area of ​​the cancerous tumor. The less radiation affects healthy organs, the less likely the negative consequences of radiation therapy. That is why, when planning treatment, various imaging methods are used (imaging the tumor and its surrounding organs), which ensures accurate delivery of radiation to the tumor, protection of nearby healthy tissues and a reduction in the severity of side effects and complications of radiotherapy later.

Intensity modulated radiotherapy - IMRT

A more accurate match of the radiation dose to the tumor volume is provided by a modern method of three-dimensional conformal radiation therapy called intensity-modulated radiotherapy (IMRT). This method of radiation for cancer allows higher doses to be safely delivered to the tumor than with traditional radiation. IMRT is often used in conjunction with image-guided radiotherapy (IRT), which provides extremely precise delivery of the selected dose of radiation to the malignant tumor or even a specific area within the tumor. Modern developments in the field of radiology in oncology, such as RTVC, make it possible to adjust the procedure to the characteristics of organs prone to movement, such as the lungs, as well as tumors that are located close to vital organs and tissues.

Stereotactic radiosurgery

Other methods of ultra-precise delivery of radiation to the tumor include stereotactic radiosurgery, during which three-dimensional imaging is used to determine the precise coordinates of the tumor. After this, targeted X-rays or gamma rays converge on the tumor with the goal of destroying it. The Gamma Knife technique uses cobalt radiation sources to focus multiple beams into small areas. Stereotactic radiation therapy also uses linear particle accelerators to deliver radiation to the brain. In a similar way, it is possible to treat tumors and other localizations. This radiation therapy is called extracranial stereotactic radiotherapy (or body SR). This method is of particular value in the treatment of lung tumors, liver and bone cancer.

Radiation therapy is also used to reduce blood flow to tumors located in vascular organs such as the liver. Thus, during stereotactic surgery, special microspheres filled with a radioactive isotope are used, which clog the blood vessels of the tumor and cause it to starve.

In addition to being an active treatment for cancer, radiotherapy is also a palliative treatment. This means that RT can relieve the pain and suffering of patients with advanced forms of malignancy. Palliative radiation for cancer improves the quality of life of patients experiencing severe pain, difficulty moving or eating due to a growing tumor.

Possible complications - consequences of radiation therapy

Radiation therapy for cancer can cause significant side effects later. As a rule, their occurrence is due to damage to healthy cells during irradiation. Side effects and complications of radiation therapy are usually cumulative, that is, they do not occur immediately, but over a certain period of time from the start of treatment. The consequences can be mild or severe, depending on the size and location of the tumor.

The most common side effects of radiotherapy include irritation or damage to the skin near the radiation area and fatigue. Skin manifestations include dryness, itching, peeling, or blistering or blistering. Fatigue for some patients means only mild tiredness, while others report extreme exhaustion and are asked to undergo post-radiotherapy recovery.

Other side effects of radiation therapy generally depend on the type of cancer being treated. Such consequences include baldness or sore throat during radiology in oncology: head and neck tumors, difficulty urinating during irradiation of the pelvic organs, etc. You should talk in more detail about the side effects, consequences and complications of radiation therapy with your oncologist, who can explain what to expect during a particular treatment. Side effects can be short-term or chronic, but many do not experience them at all.

If the patient has undergone long-term complex treatment, then recovery after courses of radiation therapy may be required, for example, in case of general intoxication of the body. Sometimes proper nutrition and enough rest are enough to restore. For more serious complications, recovery of the body requires medical assistance.

What can a patient expect during treatment?

The battle with cancer (malignant tumor) is a great challenge for any patient. The following brief information about radiotherapy will help you prepare for this difficult battle. It addresses the main difficulties and problems that any patient may encounter during a course of radiotherapy or stereotactic radiosurgery. Depending on the specific case of the disease, each stage of treatment may acquire its own differences.

Preliminary consultation

The very first step in fighting cancer with radiotherapy is a consultation with a radiation oncologist who specializes in radiation therapy for malignant tumors. The patient is referred for consultation to this specialist by the attending oncologist, who diagnosed the cancer. Having analyzed the case of the disease in detail, the doctor chooses one or another method of radiotherapy, which, in his opinion, is best suited in this situation.

In addition, the radiation oncologist determines additional treatment if required, for example, chemotherapy or surgery, and the sequence and combination of courses of therapy. The doctor also tells the patient about the goals and planned results of therapy and informs him of possible side effects that often occur during a course of RT. The patient should make a decision about starting radiotherapy soberly and carefully, after a detailed conversation with the attending oncologist, who should tell about other options alternative to radiation therapy. Preliminary consultations with a radiation oncologist are an excellent opportunity for the patient to clarify all questions about the disease and its possible treatment that remain unclear.

Preliminary examination: tumor imaging

After a preliminary consultation, the second, no less important stage begins: examination using imaging techniques, which allows you to accurately determine the size, contours, location, blood supply and other features of the tumor. Based on the results obtained, the doctor will be able to clearly plan the course of radiation therapy. As a rule, at this stage the patient will undergo a computed tomography (CT) scan, as a result of which the doctor receives a detailed three-dimensional image of the tumor in all details.

Special computer programs allow you to rotate the image on the computer screen in all directions, which allows you to view the tumor from any angle. However, in some cases, the examination at the planning stage of radiotherapy is not limited to CT alone. Sometimes additional diagnostic options such as magnetic resonance imaging (MRI), positron emission tomography (PET), PET-CT (a combination of PET and CT) and ultrasound (ultrasound) are required. The purpose of additional examination depends on various factors, including the location of the tumor in a particular organ or tissue, the type of tumor, and the general condition of the patient.

Each radiotherapy session begins with the patient being placed on the treatment table. In this case, it is necessary to recreate with absolute accuracy the very position in which the preliminary examination was carried out using visualization methods. That is why in the preliminary stages, in some cases, marks are applied to the patient’s skin using a special permanent marker, and sometimes tiny tattoos the size of a pinhead.

These markings help medical staff ensure the patient's body is positioned accurately during each radiotherapy session. At the preliminary examination stage, measurements are sometimes taken for the manufacture of auxiliary devices for radiotherapy. Their type depends on the exact position of the tumor. For example, for cancer of the head and neck organs or brain tumors, a fixing rigid head mask is often made, and for lesions of the abdominal organs, a special mattress is made that exactly matches the contours of the patient’s body. All these devices ensure that the patient's position is maintained during each session.

Making a radiotherapy plan

After completing the examination and analyzing the obtained images, other specialists are involved in drawing up a radiotherapy plan. Typically this is medical physicist and dosimetrist, whose task is to study the physical aspects of radiation therapy and the prevention of complications (compliance with safety procedures) during treatment.

When drawing up a plan, specialists take into account a variety of factors. The most important of them are the type of malignant neoplasm, its size and location (including proximity to vital organs), data from additional examination of the patient, for example, laboratory tests (hematopoiesis, liver function, etc.), general health, the presence of serious concomitant diseases, experience with RT in the past and many others. Taking into account all these factors, specialists individualize the radiation therapy plan and calculate the radiation dose (total for the entire course and the dose for each radiotherapy session), the number of sessions required to receive the full dose, their duration and intervals between them, the exact angles at which the X-rays should hit the tumor, etc.

Positioning the patient before starting a radiotherapy session

Before each session, the patient must change into a hospital gown. Some radiation therapy centers allow you to wear your own clothes during the procedure, so it is better to come to the session in loose clothing made of soft fabrics that does not restrict movement. At the beginning of each session, the patient is placed on the treatment table, which is a special couch connected to a radiotherapy machine. At this stage, auxiliary devices (fixing mask, fastening, etc.), which were made during the preliminary examination, are also attached to the patient’s body. Fixation of the patient's body is necessary to ensure conformity of radiotherapy (exact match of the radiation beam to the contours of the tumor). The level of possible complications and consequences after radiation therapy depends on this.

The treatment table can be moved. In this case, medical personnel are guided by marks previously applied to the patient’s skin. This is necessary to accurately target the tumor with gamma rays during each radiation therapy session. In some cases, after placing and fixing the patient’s body position on the couch, an additional photograph is taken immediately before the radiotherapy session itself. This is necessary to detect any changes that may have occurred since the first examination, such as an increase in size of the tumor or a change in its position.

For some RT machines, a pre-treatment control image is mandatory, while in other cases it depends on the preference of the radiation oncologist. If at this stage specialists detect any changes in the behavior of the tumor, then an appropriate correction of the patient’s position on the treatment table is carried out. This helps doctors make sure the treatment is correct and the tumor receives the exact dose of radiation needed to kill it.

How does a radiation therapy session work?

A device called a linear medical accelerator of charged particles, or simply a linear accelerator, is responsible for the production of X-rays or gamma rays. Most devices of this kind are equipped with a massive device called a gantry, which during the session continuously rotates around the patient's table, emitting radiation that is invisible to the eye and in no way felt. A special and very important device is built into the gantry body: a multi-leaf collimator.

It is due to this device that a special shape of the gamma ray beam is formed, which allows targeted treatment of the tumor with radiation from any angle, practically without going beyond its limits and without damaging healthy tissue. The first few radiation therapy sessions are longer than the subsequent ones and take about 15 minutes each. This is due to technical difficulties that may arise when initially placing the patient on the couch or due to the need for additional imaging. Time is required to comply with all safety rules. Subsequent sessions are usually shorter. Typically, a patient's length of stay at a radiation therapy center is 15 to 30 minutes each time, from the time they enter the waiting room to the time they leave the facility.

Complications and need for follow-up

Radiation therapy is often accompanied by the development of side effects (complications), the nature and severity of which depend on the type and location of the tumor, the total dose of radiation, the patient’s condition and other factors. The effects of gamma radiation are cumulative, that is, they accumulate in the body, which means that most often unwanted and side effects, such as the consequences of radiation therapy, appear only after several sessions. That is why it is necessary to always maintain contact with the radiation oncologist, both before the procedure and during it, telling the doctor about all subsequent health problems that accompany radiotherapy.

Recovery after radiation therapy for complications

After completing a course of radiation therapy, the body may need to be restored, so the oncologist must draw up a follow-up schedule, which will allow tracking the effects of the treatment and preventing complications and tumor recurrence. As a rule, the first consultation with a specialist is required 1-3 months after completion of RT, and the intervals between subsequent visits to the doctor are about 6 months. However, these values ​​are arbitrary and depend on the behavior of the tumor in each specific case, when consultations may be required less often or more often.

Observation by a specialist after the end of radiation therapy makes it possible to timely identify a possible relapse of the tumor, which can be indicated by certain symptoms that worry the patient, or objective signs that the doctor identifies. In such cases, the oncologist will order appropriate testing, such as blood tests, MRI, CT or ultrasound, chest x-ray, bone scan, or more specific procedures.

The extent of measures to restore the body after radiation therapy depends on the degree of complications and intoxication of healthy tissue exposed to radiation. Medication is not always required. Many patients do not experience any effects or complications after radiation therapy, other than general fatigue. The body recovers over several weeks with a balanced diet and rest.

In modern oncology, internal radiation therapy, which consists of exposure to highly active radiological rays that are generated in the patient’s body or directly on the surface of the skin.

The interstitial technique uses x-rays originating from the cancerous tumor. Intracavitary brachytherapy involves placing a therapeutic substance into a surgical cavity or chest cavity. Episcleral therapy is a special method of treating malignant neoplasms of the ophthalmological organs, in which the radiation source is placed directly on the eye.

Brachytherapy is based on a radioactive isotope, which is introduced into the body using tablets or injections, after which they spread throughout the body, damaging pathological and healthy cells.

If no therapeutic action is taken, the isotopes decay after a few weeks and become inactive. Constantly increasing the dosage of the device ultimately has a very adverse effect on the neighboring unmodified areas.

Radiation therapy in oncology: methodology

1. Low-dose radiation therapy takes several days and exposes cancer cells to continuous exposure to ionizing radiation.
2. Treatment with ultra-high doses of X-ray radiation is carried out in one session. A robotic machine places a radioactive element directly on the tumor. In addition, the location of radiological sources can be temporary or permanent.
3. Permanent brachytherapy is a technique in which radiation sources are surgically sutured into the body. The radioactive material does not cause any particular discomfort in the patient.
4. To carry out temporary brachytherapy, special catheters are connected to the pathological focus, through which the emitting element enters. After influencing the pathology with moderate doses, the device is moved away from the patient to a comfortable distance.

Systemic radiation therapy in oncology

In systemic radiation therapy, the patient takes an ionizing agent through injections or tablets. The active element of the treatment is considered to be enriched iodine, which is mainly used in the fight against thyroid cancer, the tissues of which are especially susceptible to iodine preparations.

In some clinical cases, systemic radiation therapy is based on a combination of a monoclonal antibody compound and a radioactive element. A distinctive feature of this technique is its high efficiency and accuracy.

When is radiation therapy performed?

The patient undergoes radiation therapy at all stages of surgery. Some patients are treated alone, without surgery or other procedures. For another category of patients, simultaneous use of radiation therapy and cytostatic drugs is envisaged. The duration of exposure to radiation therapy depends on the type of cancer being treated and the goal of treatment (radical or palliative).

Radiation therapy in oncology which is performed before surgery is called neoadjuvant. The goal of this treatment is to shrink the tumor to create favorable conditions for surgery.

Radiological treatment given during surgery is called intraoperative radiotherapy. In such cases, physiologically healthy tissues can be protected by physical means from the effects of ionizing radiation.

Radiological therapy after surgery is called adjuvant treatment and is carried out to neutralize possible residual cancer cells.

Radiation therapy in oncology - consequences

Radiation therapy in oncology may cause both early and late side effects. Acute side effects are observed immediately during surgery, while chronic side effects can be detected several months after completion of treatment.

1. Acute radiation complications occur due to damage to rapidly dividing normal cells in the area of ​​radiation. These include skin irritations in damaged regions. Examples include dysfunction of the salivary gland, hair loss, or problems with the urinary system.
2. Manifestations of late side effects may occur depending on the location of the primary lesion.
3. Fibrous changes in the skin (replacement of normal tissue with scar tissue, which leads to limited movement of the affected area of ​​the body).
4. Intestinal damage that causes diarrhea and spontaneous bleeding.
5. Disorders of brain activity.
6. Inability to have children.
7. In some cases, there is a risk of relapse. For example, young patients have an increased risk of formation after radiation therapy, since the tissues of this area are very sensitive to the effects of ionizing radiation.