Radiation therapy

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Radiation therapy or radiotherapy , often abbreviated RT , RTx , or XRT , is therapy using ionizing radiation, generally as part of cancer treatment to control or kill malignant cells and is usually delivered by a linear accelerator. Radiation therapy can be curative in some cancers if they are localized to one area of ​​the body. It may also be used as part of adjuvant therapy, to prevent tumor recurrence after surgery to remove primary malignant tumor (eg, early stage of breast cancer). Radiation therapy is synergistic with chemotherapy, and has been used before, during, and after chemotherapy in susceptible cancers. The oncology subspecialty associated with radiotherapy is called radiation oncology .

Radiation therapy is generally applied to cancerous tumors because of its ability to control cell growth. Ionizing radiation works by damaging DNA from cancer tissue causing cell death. To save normal tissue (such as the skin or organs that have to pass through radiation to treat the tumor), beam-shaped radiation is directed from multiple exposure angles to intersect the tumor, giving the absorbed dose far greater than in the surrounding, healthy. tissues. In addition to the tumor itself, the radiation field may also include diluted lymph nodes if they are clinically or radiologically involved with the tumor, or if there is considered a subclinical malignancy risk. It is necessary to enter normal tissue margins around the tumor to allow for uncertainty in the daily set-up and internal tumor movements. This uncertainty can be caused by internal motion (eg, respiration and bladder filling) and movement of external skin marks relative to tumor position.

Radiation oncology is a medical specialty related to radiation, and differs from radiology, the use of radiation in medical imaging and diagnosis. Radiation may be prescribed by a radiation oncologist with a view to healing ("curative") or for adjuvant therapy. It can also be used as a palliative treatment (where cure is not possible and the goal is for local disease control or symptom relief) or as therapeutic therapy (where therapy has survival benefits and can be curative). It's also common to combine radiation therapy with surgery, chemotherapy, hormone therapy, immunotherapy or some mixture of four. The most common types of cancer can be treated with radiation therapy in several ways.

Appropriate treatment intentions (curative, adjuvant, neoadjuvant therapy, or palliative) will depend on the type of tumor, location, and stage, as well as the patient's general health. Total body irradiation (TBI) is a radiation therapy technique used to prepare the body to receive bone marrow transplantation. Brachytherapy, where radioactive sources are placed inside or next to areas that require treatment, is another form of radiation therapy that minimizes exposure to healthy tissue during procedures to treat breast, prostate, and other cancers. Radiation therapy has several applications in non-malignant conditions, such as the treatment of trigeminal neuralgia, acoustic neuroma, severe thyroid eye disease, pterygium, pigment villonodular synovitis, and the prevention of keloid scarring, vascular restenosis, and heterotopic ossification. The use of radiation therapy in non-malignant conditions is limited in part by concerns about the risk of radiation-induced cancer.

Video Radiation therapy

Medical use

Different cancers respond to radiation therapy in different ways.

The cancer response to radiation is illustrated by its radiosensitivity. Highly radiosensitive cancer cells are rapidly killed by simple radiation doses. These include leukemia, most lymphomas and germ cell tumors. The majority of epithelial cancers are only slightly radiosensitive, and require a much higher radiation dose (60-70 Gy) to achieve radical healing. Some types of cancer are primarily radioresistant, ie, much higher doses are required to produce radical healing than may be safe in clinical practice. Kidney cancer cells and melanoma are generally considered radioresistant but radiation therapy is still a palliative choice for many patients with metastatic melanoma. Combining radiation therapy with immunotherapy is an active area of ​​investigation and has shown some promise for melanoma and other cancers.

It is important to distinguish the radiosensitivity of a particular tumor, which to a certain extent is a laboratory measure, from the "cancer" cancer radiation in actual clinical practice. For example, leukemia is generally incurable with radiation therapy, as they are disseminated through the body. Lymphoma can be radically curable if it is localized to one area of ​​the body. Similarly, many of the usual, radioresponsive tumors are routinely treated with curative doses of radiation therapy if they are at an early stage. For example: non-melanoma skin cancer, head and neck cancer, breast cancer, non-small cell lung cancer, cervical cancer, anal cancer and prostate cancer. Metastatic cancer is generally incurable with radiation therapy because it is impossible to treat the whole body.

Prior to treatment, CT scans were often performed to identify tumors and surrounding normal structures. Patients receive small skin marks to guide the placement of the treatment area. Positioning of the patient is very important at this stage because the patient should be set in the same position during treatment. Many patient positioning devices have been developed for this purpose, including masks and printable pillows for patients.

The tumor response to radiation therapy is also related to its size. Because of its complex radiobiology, very large tumors respond poorly to radiation compared with smaller tumors or microscopic disease. Various strategies are used to overcome this effect. The most common technique is surgical resection before radiation therapy. This is most often seen in breast cancer treatment with extensive local excision or mastectomy followed by adjuvant radiation therapy. Another method is to shrink the tumor with neoadjuvant chemotherapy before radical radiation therapy. The third technique is to increase the radiosensitivity of cancer by giving certain drugs during radiation therapy. Examples of radiosensitizing drugs include: Cisplatin, Nimorazole, and Cetuximab.

The effects of radiotherapy on cancer control have been shown to be limited in the first five years after surgery, especially for breast cancer. The difference between breast cancer recurrence in patients receiving radiotherapy vs. those who are not seen is mostly within the first 2-3 years and no differences are seen after 5 years. This is explained in detail here.

Maps Radiation therapy

Side effects

Radiation therapy itself does not cause pain. Many low-dose palliative treatments (eg, radiation therapy for bone metastasis) cause minimal or no side effects, although short-term pain may occur in the days following treatment because of compression nerve edema in the treated area. Higher doses may cause various side effects during treatment (acute side effects), within months or years after treatment (long-term side effects), or after treatment (cumulative side effects). The nature, severity, and longevity of the side effects depend on the organ receiving the radiation, the treatment itself (type of radiation, dosage, fractionation, concurrent chemotherapy), and the patient.

Most side effects can be predicted and expected. Side effects of radiation are usually limited to the area of ​​the body of the patient being treated. Side effects depend on the dose; eg higher doses of head and neck radiation can be associated with cardiovascular complications, thyroid dysfunction, and pituitary axis dysfunction. Modern radiation therapy aims to minimize side effects to a minimum and to help patients understand and deal with unavoidable side effects.

The main side effects reported are fatigue and skin irritation, such as mild to moderate sunburn. Fatigue often occurs during mid-treatment and may last for weeks after treatment ends. The irritated skin will heal, but may not be as elastic as before.

Acute side effects

Nausea and vomiting

This is not a common side effect of radiation therapy, and is mechanically associated only with abdominal or abdominal care (which usually reacts several hours after treatment), or by radiation therapy to a particular nausea-producing structure in the head. during the treatment of certain head and neck tumors, most commonly the inner ear vestibules. As with any troubling treatment, some patients vomit immediately during radiotherapy, or even to anticipate, but this is considered a psychological response. Nausea for any reason can be treated with antiemetics.

Epithelial surface damage

Epithelial surface can sustain damage from radiation therapy. Depending on the treated area, this may include skin, oral mucosa, pharynx, intestinal mucosa and ureter. The rate of damage and recovery onset depends on the rate of epithelial cell turnover. Usually the skin begins to become pink and sore a few weeks after treatment. The reaction can become more severe during treatment and up to about one week after the end of radiation therapy, and the skin can be damaged. Although this wet desquamation is uncomfortable, recovery is usually rapid. Skin reactions tend to get worse in areas where there are natural folds in the skin, such as beneath women's breasts, behind the ears, and in the crotch.

Oral, throat and abdominal wounds

If the head and neck areas are treated, temporary pain and ulceration usually occur in the mouth and throat. If severe, this can affect swallowing, and patients may require painkillers and nutritional/dietary supplements. The esophagus may also become ill if treated directly, or if, as usual, it receives a collateral radiation dose during lung cancer treatment. When treating malignancy and liver metastasis, it is possible for collateral radiation to cause peptic ulcers, stomach or duodenum. This collateral radiation is generally caused by the non-targeted delivery (reflux) of the infused radioactive agent. Methods, techniques and tools are available to reduce the occurrence of these types of adverse effects.

Uncomfortable

The lower bowel may be treated directly with radiation (anal or rectal cancer treatment) or exposed by radiation therapy to other pelvic structures (prostate, bladder, female genital tract). The typical symptoms are pain, diarrhea, and nausea. â € <â € <

Swelling

As part of the common inflammation that occurs, soft tissue swelling can cause problems during radiation therapy. This is a concern during the treatment of brain tumors and brain metastases, especially where there is pre-existing intracranial pressure or where the tumor causes total lumen obstruction (eg, trachea or major bronchus). Surgical intervention may be considered before treatment with radiation. If surgery is deemed unnecessary or inappropriate, patients may receive steroids during radiation therapy to reduce swelling.

Infertility

Gonads (ovaries and testes) are very sensitive to radiation. They may not be able to produce gametes after direct exposure to most normal doses of radiation treatment. Care planning for all body sites is designed to minimize, if not completely exclude doses to the gonads if they are not the primary care area.

Late side effects

Late side effects occur months to years after treatment and are generally confined to the treated area. They are often due to damage to blood vessels and connective tissue cells. Many of the effects are late reduced by fractional treatment into smaller parts.

Fibrosis

Irradiated tissue tends to become less elastic over time due to scattered scarring.

Epilation

Haircut (hair loss) can occur in any hair skin with doses above 1 Gy. It just happens inside the radiation field. Hair loss may be permanent with a single dose of 10 Gy, but if the dose is fractionated permanent hair loss may not occur until the dose exceeds 45 Gy.

Drought

The salivary glands and tear glands have a radiation tolerance of about 30 Gy in the 2 Gy fraction, a dose exceeded by the most radical head and neck cancer treatments. Dry mouth (xerostomia) and dry eye (xerophthalmia) can interfere with long-term problems and greatly reduce the quality of life of patients. Similarly, sweat glands in the treated skin (such as the armpits) tend to stop working, and the moist natural vaginal mucosa is often dry following pelvic irradiation.

Lymphedema

Lymphedema, a condition of localized fluid retention and tissue swelling, may result from damage to the lymphatic system maintained during radiation therapy. This is the most frequently reported complication in patients with breast radiation therapy who receive adjuvant axillary radiotherapy after surgery to clear the axillary lymph nodes.

Cancer

Radiation is a potential cause of cancer, and secondary malignancies are seen in a small proportion of patients - usually less than 1/1000. Usually occurs 20-30 years after treatment, although some haematological malignancies may develop within 5 - 10 years. In most cases, this risk is very proportional to the reduction in risk provided by treating primary cancer. Cancer occurs within the area of ​​the patient's care.

Heart disease

Radiation has the potential risk of excess mortality from heart disease seen after several RT regimens of breast cancer in the past.

Cognitive impairment

In the case of radiation applied to head radiation therapy may cause cognitive decline. Cognitive impairment is especially noticeable in young children, between the ages of 5 and 11. The study found, for example, IQs of 5-year-olds dropping every year after treatment by some IQ points.

Radiation enteropathy

Gastrointestinal tract can be damaged after abdominal and pelvic radiotherapy. Atrophy, fibrosis and vascular changes result in malabsorption, diarrhea, steatorrhea and bleeding with bile acid diarrhea and vitamin B12 malabsorption commonly found due to ileal involvement. Pelvic radiation diseases include radiation proctitis, producing bleeding, diarrhea and urgency, and can also cause radiation cystitis when the bladder is affected.

Radiation-induced polineuropathy

Radiation treatment is indispensable but can damage nerves near target areas or in delivery paths because nerve tissues are also radiosensitive. Nerve damage due to ionizing radiation occurs gradually, the initial phase of microvascular injury, capillary damage and nerve demyelination. The subsequent damage occurs due to vascular constriction and nerve compression due to the uncontrolled growth of fibrous tissue caused by radiation. Radiation-induced polineuropathy, ICD-10-CM Code G62.82, occurs in about 1-5% of those receiving radiation therapy.

Depending on the irradiated zone, the effect of late neuropathy may occur in the central nervous system (CNS) or peripheral nervous system (PNS). In CNS, for example, cranial nerve injuries usually appear as loss of vision 1-14 years post-treatment. In civil servants, injury to the plexus nerve appears as radiation-induced brachial plexopathy or radiated induced lumbosacral plexopathy that appears up to 3 decades post-treatment.

Cumulative side effects

The cumulative effect of this process should not be confused with long-term effects - when short-term effects are lost and long-term effects are subclinical, re-irradiation can still cause problems. This dose is calculated by a radiation oncologist and many factors are taken into account before the next radiation occurs.

Effects on reproduction

During the first two weeks after conception, radiation therapy is lethal but not teratogenic. High radiation doses during pregnancy cause anomalies, growth disturbances and intellectual disabilities, and there may be an increased risk of leukemia in childhood and other tumors in offspring.

In men who had previously undergone radiotherapy, there appeared to be no increase in genetic defects or congenital malformations in their children conceived after therapy. However, the use of assisted reproductive technology and micromanipulation techniques may increase this risk.

Effects on the pituitary system

Hypopituitarism generally develops after radiation therapy for sellar and parasellar neoplasms, extracellar brain tumors, head and neck tumors, and follows the entire body irradiation for systemic malignancy. Hypopituitarism induced by radiation mainly affects growth hormone and gonad hormone. In contrast, the hormone adrenocorticotrophic (ACTH) and thyroid stimulating hormone (TSH) deficiency are the most common among people with radiation-induced hypopituitarism. The change in prolactin secretion is usually mild, and vasopressin deficiency appears to be extremely rare as a consequence of radiation.

Accident radiation therapy

There are strict procedures to minimize the risk of overexposure of unintentional radiation therapy in patients. However, errors occasionally occur; for example, the Therac-25 radiation therapy machine was responsible for at least six accidents between 1985 and 1987, where patients were given up to a hundred times the intended dose; two people were killed directly by a radiation overdose. From 2005 to 2010, a hospital in Missouri overexposed 76 patients (mostly with brain cancer) over a five-year period because new radiation equipment was incorrectly arranged. Although medical errors are very rare, radiation oncologists, medical physicists and other members of the radiation therapy therapy team are working to eliminate them. ASTRO has launched a safety initiative called Safe Target which, among other things, aims to record national mistakes so doctors can learn from every mistake and prevent it from happening. ASTRO also publishes a list of questions for patients to ask their doctors about radiation safety to ensure every treatment is as safe as possible.

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Used in non-cancerous diseases

Radiation therapy is used to treat early-stage disease of Dupuytren and Ledderhose disease. When Dupuytren disease is in the nodule and the stage cord or fingers are at a minimum deformation stage of less than 10 degrees, radiation therapy is used to prevent further progression of the disease. Radiation therapy is also used post-surgery in some cases to prevent disease continues to grow. Low-dose radiation is usually used three gray radiation for five days, with a three-month break followed by another phase of three gray radiation for five days.

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Technique

Action mechanism

Radiation therapy works by damaging the DNA of cancer cells. This DNA damage is caused by one of two types of energy, photons or charged particles. This damage is the direct or indirect ionization of the atoms that make up the DNA chain. Immediate ionization occurs as a result of ionizing water, forming free radicals, especially hydroxyl radicals, which then damage DNA.

In photon therapy, most of the effects of radiation are through free radicals. Cells have mechanisms to repair single strand DNA damage and double-stranded DNA damage. However, double-stranded DNA damage is much more difficult to repair, and can lead to dramatic chromosome abnormalities and genetic deletions. Targeting a double-stranded break increases the likelihood that the cell will experience cell death. Cancer cells are generally less differentiated and more like stem cells; they reproduce over the most healthy different cells, and have a reduced ability to repair sub-lethal damage. Single strand DNA damage is then passed through cell division; damage to the DNA of cancer cells accumulates, causing them to die or to reproduce more slowly.

One of the major limitations of photon radiation therapy is that solid tumor cells become oxygen deprived. Solid tumors can overcome their blood supply, causing a low state of oxygen known as hypoxia. Oxygen is a powerful radiosensitizer, increasing the effectiveness of the given radiation dose by forming free radicals that damage DNA. The tumor cells in the hypoxic environment may be as much as 2 to 3 times more resistant to radiation damage than cells in normal oxygen environments. Much research has been devoted to overcoming hypoxia including the use of high-pressure oxygen tanks, hyperthermia therapy (thermal therapy that dilates blood vessels to the tumor site), blood substitutes that carry increased oxygen, radiosensitizer cell hyposselel drugs such as misonidazole and metronidazole, and hypoxic cytotoxins tissue poison), such as tirapazamine. More recent research approaches are being studied, including preclinical and clinical investigations into the use of oxygen diffusion enhancement compounds such as trans sodium crocetinate (TSC) as radiosensitizers.

Charged particles such as protons and boron, carbon, and neon ions can cause direct damage to cancer cell DNA through high LET (linear energy transfer) and have antitumor effect independent of tumor oxygen supply because these particles act mostly through direct energy transfer usually. causing a double-stranded DNA break. Because of their relatively large mass, protons and other charged particles have few side edges that spread in the tissues - the bundles do not widen much, stay focused on the shape of the tumor, and provide small dose side effects to the surrounding tissue. They also more precisely target tumors using the Bragg peak effect. See proton therapy for a good example of the different effects of intensity-modulated radiation therapy (IMRT) versus charged particle therapy. This procedure reduces damage to healthy tissue between the charged particle's radiation source and the tumor and sets a limited range for tissue damage once the tumor has been reached. In contrast, the use of uncharged charged particles of IMRT causes its energy to damage healthy cells when out of the body. This outcome damage is not therapeutic, may increase the side effects of treatment, and increase the likelihood of secondary cancer induction. This difference is particularly important in cases where the proximity of other organs makes wild ionization particularly destructive (eg, head and neck cancer). This x-ray exposure is very bad for children, because of their growing body, and they have a 30% chance of a second malignancy after 5 years after the initial RT.

Dose

The amount of radiation used in photon radiation therapy is measured in gray (Gy), and varies depending on the type and stage of the treated cancer. For curative cases, typical doses for solid epithelial tumors range from 60-80 Gy, while lymphomas are treated with 20 to 40 Gy.

The prevention dose (adjuvant) is usually about 45-60 Gy in the 1.8-2 Gy fraction (for breast, head, and neck cancer.) Many other factors are considered by radiation oncologists when choosing a dose, including whether patients receive chemotherapy, comorbidity patient, whether radiation therapy is administered before or after surgery, and the rate of successful surgery.

The specified dose delivery parameters are determined during the treatment planning (part of the dosimetry). Treatment planning is generally performed on specialized computers using specialized care planning software. Depending on the radiation delivery method, multiple angles or sources may be used to add up to the total required dose. The planner will try to devise a plan that provides a uniform dose of prescription to the tumor and minimizes the dose to surrounding healthy tissue.

In radiation therapy, a three-dimensional dose distribution is often evaluated using a dosimetry technique known as dosimetry gel.

Fractionation

The total dose is fractionated (spread over time) for several important reasons. Fractionation allows normal cell time to recover, while tumor cells are generally less efficient at repair between fractions. Fractionation also allows tumor cells that are in a relatively radio-resistant phase from the cell cycle during one treatment to cycle into the sensitive phase of the cycle before the next fraction is given. Similarly, chronic or acute hypoxic (and therefore more radioresistant) tumor cells may reoxygenate between fractions, increasing the killing of tumor cells.

Fractionation regimens are individualized between different radiation therapy centers and even between individual doctors. In North America, Australia, and Europe, the typical fractionation schedule for adults is 1.8-2 Gy daily, five days a week. In some cancers, prolonged fractional scheduling may allow tumors to regenerate, and for this type of tumor, including squamous cell cancer of the head and neck and cervix, radiation treatment should be completed in a certain amount. time. For children, typical fractional sizes may be 1.5 to 1.8 Gy per day, since smaller fractional sizes are associated with decreased incidence and severity of late-onset side effects on normal tissue.

In some cases, two fractions per day are used near the end of treatment. This schedule, known as concurrent increase regimen or hyperfractionation, is used on tumors that regenerate faster when they are smaller. In particular, tumors in the head and neck show this behavior.

Patients receiving palliative radiation to treat painful bone metastases should not receive more than one radiation fraction. One treatment provides comparable relief of pain and morbidity for multi-fraction treatment, and for patients with limited life expectancy, one of the best treatments to improve patient comfort.

Schedule for fractionation

One of the increasingly used and ongoing fractionation schedules is hypofractionation. This is a radiation treatment in which the total dose of radiation is divided into large doses. The common dose varies significantly by type of cancer, from 2.2 Gy/fraction up to 20 Gy/fraction. The logic behind hypofractionation is to reduce the chances of cancer returning by not giving enough time cells to reproduce and also to exploit the unique biological radiation sensitivity of some tumors.

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Type

Historically, the three main divisions of radiation therapy are:

• external beam radiation therapy (EBRT or XRT) or teleterapy;
• brachytherapy or sealed source radiation therapy; and
• systemic radioisotope therapy or non-sealed source radiotherapy.

The difference is related to the position of the radiation source; Externally outside the body, brachytherapy using closed radioactive sources is placed right in the area under treatment, and systemic radioisotopes are administered via infusion or oral consumption. Brachytherapy may use temporary or permanent radioactive source placement. The temporary source is usually placed by a technique called afterloading. In vacuum tube afterloading or applicators are placed surgically in the organ to be treated, and the source is loaded onto the applicator after the applicator is implanted. This minimizes radiation exposure to health care personnel.

Particle therapy is a special case of external beam radiation therapy in which particles are protons or heavier ions.

External beam radiation therapy

The following three sections refer to the treatment using x-rays.

Conventional external beam radiation therapy

Conventional external beam radiation therapy (2DXRT) is delivered via a two-dimensional ray using a x-ray kilovoltage therapy unit or a medical linear accelerator that produces high-energy X-rays. 2DXRT consists mainly of one radiation beam that is sent to the patient from several directions: often front or back, and both sides. Conventional refers to planned or simulated treatment methods on a special calibrated diagnostic x-ray machine known as a simulator because it re-creates a linear accelerator action ( or sometimes with the eye), and the normally established arrangement of the radiation beam to achieve the desired plan . The purpose of the simulation is to accurately target or localize the volume to be treated. This technique is well established and generally fast and reliable. The concern is that some high-dose treatments may be limited by the radiation toxicity capacity of healthy tissue located close to the targeted tumor volume. An example of this problem is seen in the radiation of the prostate gland, where adjacent rectal sensitivity limits the dose that can be safely prescribed using 2DXRT planning in such a way that tumor control may not be easy to achieve. Prior to the invention of CT, physicians and physicists had limited knowledge about the actual radiation dose delivered to both cancer and healthy tissue. For this reason, 3-dimensional conformal radiation therapy becomes the standard treatment for a number of tumor sites. More recently other forms of imaging are used including MRI, PET, SPECT and Ultrasound.

Stereotactic radiation

Stereotactic radiation is a special type of external beam radiation therapy. It uses a focused radiation beam that targets a well-defined tumor using very detailed imaging scans. Radiation oncologists perform stereotactic treatments, often with the help of neurosurgeons for tumors in the brain or spine.

There are two types of stereotactic radiation. Stereotactic radiosurgery (SRS) is when doctors use a single or multiple stereotactic radiation treatment from the brain or spine. Stereotactic body radiation therapy (SBRT) refers to one or more stereotactic radiation treatments with the body, such as the lungs.

Some doctors say the advantage of stereotactic treatment is that they provide the right amount of radiation for cancer in a shorter time than traditional treatments, which can take 6 to 11 weeks. Plus treatments are given with extreme accuracy, which should limit the effects of radiation on healthy tissue. One problem with stereotactic treatments is that they are only suitable for certain small tumors.

Stereotactic treatment can be confusing because many hospitals call treatment by the manufacturer's name rather than call it SRS or SBRT. The brand names for this treatment include Axesse, Cyberknife, Gamma Knife, Novalis, Primatom, Synergy, X-Knife, TomoTherapy, Trilogy and Truebeam. The list is changing when equipment manufacturers continue to develop new technologies specifically to treat cancer.

Virtual simulation, and 3-dimensional conformal radiation therapy

Planning of radiation therapy therapy has been revolutionized by the ability to describe tumors and adjacent normal structures in three dimensions using specialized CT and/or MRI scanners and planning software.

Virtual simulation, the most basic form of planning, allows the more accurate placement of radiation rays than is possible using conventional X-rays, where soft tissue structures are often difficult to assess and normal tissue is difficult to protect.

Improved virtual simulations are 3-dimensional conformal radiation therapy (3DCRT) , in which the profile of each radiation beam is formed to fit the target profile of the eye view (BEV) using a multileaf collimator (MLC) and a number of variable blocks. When the volume of treatment corresponds to the shape of the tumor, relative radiation toxicity to the surrounding normal tissue is reduced, allowing higher radiation doses to be sent to the tumor than conventional techniques would allow.

Intensity-modulated radiation therapy (IMRT)

Intensity-modulated radiation therapy (IMRT) is an advanced type of high precision radiation that is the next generation of 3DCRT. IMRT also enhances the ability to adjust the treatment volume to the shape of a concave tumor, for example when a tumor is wrapped around a vulnerable structure such as the spinal cord or major organs or blood vessels. Computer-controlled x-ray accelerator distributes the right dose of radiation to malignant tumors or specific areas within the tumor. The radiation delivery pattern is determined using highly customized computing applications to optimize and simulate care (Maintenance Planning). The radiation dose is consistent with the 3-D form of the tumor by controlling, or modulating, the intensity of radiation emission. The intensity of the radiation dose increases near the volume of the gross tumor while the radiation between normal neighboring tissues decreases or is completely avoided. This results in better tumor targeting, reduced side effects, and improved treatment outcomes than even 3DCRT.

3DCRT is still widely used for many body sites but the use of IMRT grows on more complex body sites such as CNS, head and neck, prostate, breast, and lung. Unfortunately, IMRT is limited by its need for additional time from experienced medical personnel. This is because doctors must manually describe a CT picture one tumor at a time through an entire disease site that can take longer than 3DCRT preparation. Then, medical physicians and dosimetris should be involved to make a proper treatment plan. In addition, the new IMRT technology was used commercially since the late 1990s even in the most advanced cancer centers, so radiation oncologists who did not learn it as part of their residency program had to find an additional source of education before implementing IMRT.

Evidence of increased survival benefits from either of these two techniques versus conventional radiation therapy (2DXRT) develops for many tumor sites, but the ability to reduce toxicity is generally accepted. This is particularly the case for head and neck cancer in a series of important trials conducted by Professor Christopher Nutting of Royal Marsden Hospital. Both techniques allow dose escalation, potentially increasing usability. There are some concerns, especially with IMRT, about the increased exposure of normal tissues to radiation and the potential consequences for secondary malignancies. Over-belief in imaging accuracy may increase the likelihood of missing lesions not seen in the planning scans (and therefore not included in the treatment plan) or who move between or during treatment (eg, due to inadequate patient respiration or immobilization). New techniques are being developed to better control this uncertainty - for example, real-time imaging combined with real-time adjustment of therapeutic rays. This new technology is called image-guided radiation therapy (IGRT) or four-dimensional radiation therapy.

Another technique is real-time tracking and localization of one or more implantable electrical devices implanted inside or near the tumor. There are various types of medical implant devices used for this purpose. It can be a magnetic transponder that senses the magnetic field generated by multiple transmission reels, and then sends the measurement back to the positioning system to determine the location. The implant device can also be a small wireless transmitter sending out an RF signal which will then be received by the sensor array and used for localization and real-time positioning of tumor tracking.

volumetric modulated arc therapy (VMAT)

Volumetric modulated arc therapy (VMAT) is a radiation technique introduced in 2007 that can achieve highly conformible dose distribution across target volume coverage and normal network sparing. The specificity of this technique is to modify three parameters during treatment. VMAT provides radiation by rotating the gantry (usually 360 Â ° spinning field with one or more arcs), changing the speed and shape of the beam with multileaf collimator (MLC) (sliding window transfer system) and the fluence output rate (dose rate) of the linear accelerator medical. VMAT has an advantage in patient care, compared to the intensity of conventional static field modulation radiation (IMRT), reducing radiation delivery time. Comparison between conventional VMAT and IMRT to save healthy tissue and Organs at Risk (OAR) depends on the type of cancer. In the treatment of nasopharyngeal carcinoma, oropharyngeal and hypopharyngeal, VMAT provides equivalent or better OAR protection. In the treatment of prostate cancer, OAR protection results are mixed with some studies that support VMAT, others like IMRT.

Particle therapy

In particle therapy (proton therapy being one example), energetic ionizing particles (protons or carbon ions) are directed at the target tumor. Dosage increases when particles penetrate the tissue, to a maximum (Bragg peak) occurring near the end of the particle range, and then down to (almost) zero. The advantage of this energy deposition profile is that less energy is stored into healthy tissue around the target tissue.

Auger Therapy

Auger therapy (AT) uses a very high ionizing radiation dose in situ that provides molecular modification at the atomic scale. AT differs from conventional radiation therapy in several aspects; it does not depend on radioactive nuclei to cause cellular radiation damage to cellular dimensions, or involves some external pencils from different directions to zero-in to provide doses to targeted areas by reducing doses outside the targeted tissue/organ location. In contrast, in situ delivery of extremely high doses at the molecular level using AT aims for in situ molecular modification involving molecular breakdown and molecular regulation such as changes in the stacking structure and cellular metabolic functions associated with the molecular structure..

Contact x-ray brachytherapy

Brachytherapy x-ray contact (also called "CXB", "electronic brachytherapy" or "Papillon Technique") is a type of radiation therapy using X-rays applied near the tumor to treat rectal cancer. This process involves inserting an x-ray tube through the anus into the rectum and placing it in the cancerous tissue, then high doses of X-rays transmitted directly to the tumor at two weekly intervals. This is usually used to treat early rectal cancer in patients who may not be candidates for surgery. The NICE 2015 review found major adverse events of haemorrhage occurring in about 38% of cases, and radiation-induced ulcers occurring in 27% of cases.

Brachytherapy (sealed source radiotherapy)

Brachytherapy is delivered by placing a radiation source inside or next to an area requiring treatment. Brachytherapy is commonly used as an effective treatment for cervical cancer, prostate, breast, and skin and can also be used to treat tumors in many other body sites.

In brachytherapy, a precise radiation source is placed directly at the site of a cancerous tumor. This means that irradiation affects only very localized areas - radiation exposure to healthy tissues away from reduced sources. Characteristics of brachytherapy provide an advantage over external radiation therapy - tumors can be treated with very high local radiation doses, while reducing the possibility of unnecessary damage to surrounding healthy tissue. Travel brachytherapy can often be completed in less time than other radiation therapy techniques. This can help reduce the likelihood of living cancer cells splitting and growing in intervals between each dose of radiation therapy.

As one example of the local nature of breast brachytherapy, SAVI devices provide radiation doses through multiple catheters, each of which can be individually controlled. This approach reduces exposure to healthy tissue and the resulting side effects, compared with external beam radiation therapy and older breast brachytherapy methods.

Unsupported source radiology (systemic radioisotopic therapy)

Systemic radioisotope therapy (RIT) is a form of targeted therapy. Targeting can be caused by the chemical properties of isotopes such as radioiodine which is specifically absorbed by the thyroid gland a thousand times better than any other organ. Targeting can also be achieved by installing a radioisotope to the antibody molecule or the other to aim it at the target tissue. Radioisotopes delivered intravenously (into the bloodstream) or ingestion. An example is the infusion metaiodobenzylguanidine (MIBG) to treat neuroblastoma, oral iodine-131 to treat thyroid cancer or thyrotoxicosis, and lutetium-177 and yttrium-90 bound hormone to treat neuroendocrine tumors (therapeutic peptide receptor radionuclide).

Another example is the injection of yttrium-90 radioactive glass or resin microspheres into the hepatic artery for radioembolisation of liver tumors or liver metastases. This microsphere is used for a treatment approach known as selective internal radiation therapy. The microspheres are about 30 μm in diameter (about a third of human hair) and are sent directly to the arteries that supply blood to the tumor. This treatment begins by guiding the catheter through the femoral artery in the legs, navigating to the desired target site and managing the treatment. The blood that feeds the tumor will bring the microspheres directly to the tumor allowing a more selective approach than traditional systemic chemotherapy. There are currently two different types of microspheres: SIR-Spheres and TheraSphere.

The main use of systemic radioisotopic therapy is in the treatment of bone metastases from cancer. Radioisotopes travel selectively to the damaged area of ​​the bone, and remove normal undamaged bones. The common isotopes used in the treatment of bone metastases are strontium-89 and samarium ( ¹⁵³ Sm) lexidronam.

In 2002, the United States Food and Drug Administration (FDA) approved the ibritumomab tiuxetan (Zevalin), which is a conjugated anti-CD20 monoclonal antibody to yttrium-90. In 2003, the FDA approved a tositumomab/iodine ( ¹³¹ I) tositumomab (Bexxar) regimen, which is a combination of labeled iodine-131 labeled monoclonal antibodies and unlabeled anti-CD20 antibodies. These drugs are the first agents of what is known as radioimmunotherapy, and they are approved for the treatment of refractory non-Hodgkins lymphoma.

Intraoperative radiotherapy

Intraoperative radiation therapy (IORT) is applying therapeutic levels of radiation to target areas, such as cancerous tumors, while the area is exposed during surgery.

Rationale

The rationale for IORT is to provide a high radiation dose right into the targeted area with minimal exposure of surrounding tissue displaced or sheltered during IORT. Conventional radiation techniques such as external beam radiotherapy (EBRT) after surgical removal of the tumor have several disadvantages: The tumor bed in which the highest dosage should be applied is often missed due to localization of the wound cavity complex even when modern radiotherapy planning is used. In addition, the usual delay between surgical removal of the tumor and EBRT allows for the repopulation of tumor cells. These potentially harmful effects can be avoided by providing more precise radiation to the target tissue leading to the immediate sterilization of residual tumor cells. Another aspect is that the wound fluid has a stimulating effect on the tumor cells. IORT was found to inhibit the effects of wound fluid stimulation.

Deep breath-resistant inspiration

Deep breath-hold inspiration (DIBH) is a method of radiotherapy delivery while limiting the exposure of radiation to the heart and lungs. It is used primarily to treat left breast cancer. This technique involves a patient holding his breath during treatment. There are two basic methods of performing DIBH: breath free-breathing and spirometry are monitored in a continuing inspiratory breath.

src: www.franciscanhealth.org

History

Medicine has been using radiation therapy as a treatment for cancer for more than 100 years, with the earliest roots traced from the discovery of x-rays in 1895 by Wilhelm RÃÆ'¶ntgen. Emil Grubbe from Chicago was probably the first American doctor to use x-rays to treat cancer, beginning in 1896.

The field of radiation therapy began to grow in the early 1900s largely due to the work of innovative Nobel Prize winning scientist Marie Curie (1867-1934), who discovered the radioactive elements of polonium and radium in 1898. It started a new era in the medical world. treatment and research. Throughout the 1920s the danger of radiation exposure was not understood, and little protection was used. Radium is believed to have extensive curative strength and radiotherapy is applied to many diseases.

Before World War II, the only practical radiation sources for radiotherapy were radium and emanation, radon gas, and x-ray tubes. External beam radiotherapy (teleterapy) begins at the turn of the century with a relatively low x-ray (& lt; 150 kV) machine. It was found that while superficial tumors can be treated with low-voltage x-rays, more penetration, higher energy required to reach the tumor in the body, requires higher stress. X-ray Orthovoltage, which uses 200-500 kV tube voltages, began to be used during the 1920s. To reach the deepest tumor buried without exposing the skin and tissues that are intervened into a dangerous dose of radiation requires a beam with energy of 1 MV or more, called "megavolt" radiation. Producing megavolt x-rays requires tension on a x-ray tube of 3 to 5 million volts, which requires a very large expensive installation. Megavoltage x-ray units were first built in the late 1930s but due to limited costs to some institutions. One of the first, installed at St. Bartholomew, London in 1937 and used until 1960, using a 30-foot long x-ray tube and weighing 10 tons. Radium produces megavolt gamma rays, but is extremely rare and expensive because of its low incidence in ores. In 1937, the entire world providing radium for radiotherapy was 50 grams, valued at £ 800,000, or $ 50 million in 2005 dollars.

The discovery of a nuclear reactor at the Manhattan Project during World War 2 enabled the production of artificial radioisotopes for radiotherapy. Cobalt therapy, a teleterapi machine using gamma megavolt rays emitted by cobalt-60, radioisotopes produced by ordinary cobalt metal irradiation in reactors, revolutionized the plane between the 1950s and early 1980s. Cobalt machines are relatively inexpensive, powerful and easy to use, although due to the age of 5.27 years cobalt must be replaced every 5 years.

The medical linear particle accelerator, developed since the 1940s, began replacing x-ray and cobalt units in the 1980s and older therapies are now declining. The first medical linear accelerator was used at Hammersmith Hospital in London in 1953. Linear accelerators can produce higher energy, have more collimated rays, and produce no radioactive waste with their accompanying disposal problems such as radioisotope therapy.

With the discovery of tomography (CT) by Godfrey Hounsfield in 1971, three-dimensional planning became a possibility and created a shift from the delivery of 2-D radiation to 3-D. CT-based planning allows physicians to more accurately determine dose distribution using anatomical axial tomographic images of patients. The emergence of new imaging technologies, including magnetic resonance imaging (MRI) in the 1970s and positron emission tomography (PET) in the 1980s, have transferred radiation therapy from 3-D according to intensity-modulated radiation therapy (IMRT) and for guided radiation (IGRT) thermal therapy. These advances allow radiation oncologists to better see and target tumors, which have resulted in better treatment results, more organ pickling and fewer side effects.

Source of the article : Wikipedia