Radiation therapy,
Radiotherapy is a method of locoregional cancer treatment using radiation to destroy cancer cells by blocking their ability to multiply. Irradiation is designed to destroy all tumor cells while sparing the surrounding healthy tissue.
Radiotherapy is used in more than half of patients with cancer. It is with surgery, treating the most common cancers and may lead to a cure by itself. It can be used alone or combined with surgery and chemotherapy. Its indications are related to the type of tumor, its location, its stage and the overall condition of the patient. It can be done on an outpatient basis, that is to say, without hospitalization, because the sessions are short and fewer side effects than during chemotherapy.
There are four major techniques of radiotherapy:
* External radiation therapy: it is the best known and most used source of radiation is outside the patient. The cobalt bombs, which use a radioactive source of cobalt-60 γ, have virtually disappeared, at least in developed countries, in favor of linear particle accelerators of high energy X-rays and electron beams. There are three main techniques: conventional radiotherapy, conformal radiotherapy and helical tomotherapy or radiotherapy, but is uncommon.
* Brachytherapy: the radioactive source is placed for a limited time (usually several hours) or permanently within the patient, the tumor or into a cavity in contact. Three main techniques, even they are divided into sub-techniques according to their dose rate (low-speed and broadband) and type of loading (manual or delayed). These interstitial brachytherapy, intracavitary brachytherapy and brachytherapy endoluminal
* The metabolic radiotherapy vector: the radioactive source is a liquid, injectable, unsealed, and will bind to target cells.
* The radiosurgery: close to external radiotherapy, its principle and its indications are however different from other radiotherapy techniques, approaching those of surgery, she uses one or more ultra-focused beams. Two types of apparatus are used: the Gamma Knife and Novalis and Cyberknife.
Indication
Depending on the type of tumor, its location, its size, its extension and its stage, the patient's general condition and symptoms, there are three very different situations in which we will use in radiotherapy for very specific purposes:
The curative radiotherapy
As its name implies, the goal is to irradiate all the cancerous cells to cause the control or cure cancer. This implies the absence of lesions at a distance. It is in about half of the radiation. It can be used alone or in combination with surgery or chemotherapy.
The dose required depends on the type and volume of the tumor, some are very radiosensitive, while others are radioresistant. We must ensure that the dose to the tumor control is less than the tolerance dose of critical organs, implying a rigorous technique may not deliver a sufficient dose and have local recurrence or otherwise deliver an overdose and cause side effects. The usual protocol delivers a dose of 10 Gy per week for 5 sessions of 2 Gy per day. The total dose varies depending on the case 30 to 70 Gy.
Palliative radiotherapy
The objective here is not to cure the cancer but to relieve the patient of small doses to alleviate pain resulting from cancer too advanced for treatment.
It is for cancer too locally advanced or metastatic.
The treatment is palliative, it should be short and not very aggressive, to cause the least possible inconvenience to the patient. For example, irradiation of type "split-run", will retrieve between 2 series of irradiation.
Radiotherapy symptomatic
Its aim is to relieve a symptom particularly embarrassing for the patient. Its efficiency is:
* Analgesic: The analgesic effect of radiation is almost constant and occurs rapidly in a few days. It is often used in the pain of bone metastases. The disappearance of pain is the early sessions, sometimes after a painful rise due to radiation-induced inflammation.
* Haemostatic: In the case of persistent bleeding that sometimes found in cancers of the rectum, bladder, head and neck or gynecological few sessions of radiotherapy result in the drying and the bleeding stops.
* Decompression: In cancers with signs of cord compression - which is an emergency, or root, radiotherapy may be an effective treatment, provided they start early signs of compression. It should be short, often just a few sessions to limit spinal irradiation. Moreover, the edema by lymphatic or venous compression are also much improved by radiotherapy.
Application
Depending on the location and stage of tumors, radiation may be used alone, but it is most often combined with surgery and / or chemotherapy and / or hormonal therapy.
Most cancers can be treated with radiation to some extent. This includes breast, prostate, lung, rectum etc..
This therapy is mostly applied to treat a localized region around a tumor. The field of radiation often covers the lymphatic network draining the tumor.
To reach the tumor area and its possible extensions without harming healthy tissue surrounding the target is irradiated successively at different angles, so that the radiation fields are superimposed on the area to be treated. The maximum radiation is then localized to the tumor area.
Before the development of immunosuppressive drugs, this technique was used to prevent unwanted immune reactions in organ transplantation.
Dosage
The radiation dose delivered by radiation is measured in Gray (Gy). The doctor prescribed dose radiation oncologist to deliver in a given area (usually tumor) and the fractionation used (dose per session). It defines the appropriate dose constraints should not be exceeded in the surrounding areas (organs at risk). The dose and fractionation depends on the location and nature of the disease. Usually one dose from 45 to 80 Gy is delivered to the target by a fraction of 2 Gy / day (order of magnitude). The breast is treated with such doses of 45-50 Gy and lung tumors at doses higher than 65 Gy dose can be delivered by beams of photons or electron energy of 1.25 MeV ( cobalt bomb) and several MeV for linear accelerators. More rarely neutrons, protons, pions or photons of lower energy are also used. The radiation physicist then proposes a planning process which will then validated by the radiation oncologist. This is to establish the number and arrangement of beams that will help deliver the dose to the target by limiting the dose to healthy tissue.
Here the maximum permissible doses of certain organs:
Spinal cord: 45 Gy,
Brainstem: 54 Gy,
Optic chiasm: 54 Gy,
Optic nerve: 60 Gy,
Brain: 60 to 70 Gy,
Parotid: 40 to 60 Gy,
Larynx: 60 to 64 Gy,
Lung: 20 Gy,
Liver: 20 Gy,
Os: 50 Gy,
Prostate: 75-80 Gy,
Heart: 45-50 Gy,
Lens: 12 Gy,
Thyroid: 20 Gy,
Read also Cancer
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