Intensity Modulated Radiation Therapy
Intensity modulated radiation therapy or IMRT is one of the most effective and precise methods of therapy administered in the treatment of cancer and tumors of various origins. This method was first employed in San Francisco at PAMF - Palo Alto Medical Foundation center in California. PAMF used this technique for the treatment of cancers of neck and prostate soft tissues.
Mechanism and clinical aspects of IMRT
Intensity modulated radiation therapy is an advanced version of the three dimensional conformal radiation therapy. The technique is administered with the integrated software and hardware to determine the amount of radiation required on a specific target. The IMRT team consists of clinicians, radiologists and physicists to evaluate the specific site and the radiation dose on the cancer cells in the specific location. The doses of radiation are determined by the clinicians after identifying the location of the target and also the normal tissues adjacent to it. These factors are further evaluated by the physicist through a specified computer software to calculate the effective dose proportion and also to reduce the side effects. IMRT technique involves the usage of dynamic multi leaf collimators (DMLC) which determine size and shape of the target site in relation to therapy that can be administered.
DMLC enables the radiation to be administered in different intensity levels through variations created in the single beam. This method helps in calculated release of radiation based on the requirement, whether high or low on the target site. The IMRT technique avoids the speculations of trial and error methods through its inverse planning technique in association with computer programmed release of the radiation. This prevents the normal surrounding tissues from getting damaged. IMRT technique has gained in importance because of its effective tumor control and cost saving factor. This method is also efficient as it not does involve different energies derived from photons or combinations associated with photons and electrons.
IMRT technique involves important requirements such as patient immobilization. This is to prevent the missing of target site during radiation therapy. IMRT for moving organ systems is considered as a sensitive and significant factor as the moving organs can affect the delivery of radiation to the target sites. Immobilization tools of invasive fixation systems (peacock talon system) and non-invasive fixation systems (reinforced mask) are used in the IMRT technique. In case of head cancer and neck cancer, oral stents and bite blocks are used to prevent the surrounding tissue damage. In conditions such as prostate cancer, patient immobilization is very difficult and hence, immobilization box is used.
Advantages of the IMRT technique
IMRT has potentially produced many advantages in the field of radiation therapy and oncology. It enables in the identification of multiple target sites in conditions such as brain metastases. The therapy affects the target sites while avoiding other normal tissues of the brain. This facilitates the prevention of CNS toxicity. The radiation thresholds of the IMRT are effective in the determination of normal tissue tolerance surrounding the target area. This helps minimizing complications such as vision loss and impairment associated with sensory organs.
Side effects of IMRT
The side effects of IMRT are predominantly associated with the equipment. These leakages often affect the intensity of the radiation related to the target site. The most common leakage are found in the multi leaf collimators. Another factor is the administration IMRT in children. Children are extremely sensitive to radiation therapies and subsequently if radiation therapies are administered in children, there may be incidences of mutated genes which may cause other complications. Studies specify the increase in the onset on secondary cancers in elderly population. This is predominantly noticed in case of prostate cancers.
Radiation therapy is usually part of cancer treatment administered under the guidance of an oncologist. It is used along with other treatments such as chemotherapy and surgery to control malignant cells. Radiation controls cell growth and plays a vital role in destroying cells or keep them from multiplying. The oncologist will decide on the kind of radiation and dosage of radiation. Some amount of healthy cells are likely to be targeted in the radiation therapy. There are two forms of radiation therapy.
External beam radiation: High powered x-rays are directed into or near the tumor from outside the body.
Internal beam radiation: Here the radiation is done from inside or near the tumor.
The side-effects of radiation therapy are hair loss, nausea, vomiting, skin problems, increased susceptibility to infection and low blood counts. Radiation therapy cannot be used on a pregnant woman.
Brachytherapy is a radiological method for treating tumors and cancers. It is also referred to as internal radiation and endocurie therapy. It is a conventional technique of radiation which is specifically administered into the body to treat cancers and also reduce or shrink tumors. Brachytherapy is used in the treatment of cancers in the liver, rectum, eye, prostate, breast, cervical and other soft tissues. In some cases brachytherapy is done in combination with the other cancer treatment methods to obtain accurate results. The source of radiation during brachytherapy appears as seeds and ribbons. These radioactive implants are administered in the patient's body.
Before a brachytherapy procedure, oncologists evaluate the patient through CT scans and X-rays. Patients are counseled about the procedure and side effects involved in brachytherapy. Since brachytherapy involves the administration of implants, patients are generally catheterized. There are two types of brachytherapy treatment methods. They are classified on the location of the implants and dosage of the implants administered in the body.
Intracavitary brachytherapy: In this procedure, the implants are placed in close proximity of the tumor or the cancer in the body. Intracavitary brachytherapy is a temporary mode of treatment which is again associated with the dosage. In some cases, low dose rate implants are given and the patient is advised to remain in the therapy room for some time. This period of stay may vary from few hours to few days. The patient is kept in an isolated section until the radioactive implants are removed. The other method is by administering high doses. In this case the patient is advised to stay back in the treatment room for a few minutes. The patient is allowed to move out of the room after the radioactive substances are completely removed from the body.
Interstitial brachytherapy: The implants are placed within the zone of cancer or the tumor. This method may be temporary or permanent depending upon the type of cancer or tumor and the stage of metastases. In case of a permanent implant, the radiation subsides gradually. Dosage of the radioactive implants is a very significant factor in brachytherapy as it is directly associated with the results and risk factors that may emerge. Appropriate dosage of the radioactive implant either through intracavitary or interstitial methods, will prevent the damage of healthy tissue that is close to the cancerous tissue. The accuracy of this procedure is mainly due to the positioning of the radioactive implants near the cancerous region. Brachytherapy has lesser side effects when compared to external beam radiation therapies.
Risk factors of Brachytherapy
Dosage and positioning of the implants are very important factors as failure in one of the techniques can lead to damage of the adjacent tissues. Patients generally express discomfort during the procedure and some patients experience swelling and tenderness in the respective area after the procedure. Precautions in appropriate catheterization during implants can avoid normal tissue damage.
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Bibliography / Reference
Collection of Pages - Last revised Date: April 20, 2021