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.
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Bibliography / Reference
Collection of Pages - Last revised Date: January 26, 2020