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.
Salivary Gland Cancer
There are hundreds of minor salivary glands lining parts of the mouth and larynx and can be seen only though a microscope. Many of the salivary gland tumors are non cancerous and they do not spread to other tissues. Salivary gland cancer is a type of head and neck cancer. Advancing age, radiation therapy to head and neck and exposure to cancer-causing chemicals at work are largely factors that cause salivary gland cancer.
Causes and risk factors
Risk of getting salivary gland cancer increases as one gets older. Most develop it in their 50s and 60s. A person is at higher risk of developing salivary gland cancer if exposed to radiation. One may also come in contact with radioactive substances through work. In case of childhood cancer and treatment with radiotherapy, there is increased risk for at least 20 years post treatment. Skin cancer in the past also slightly increases the risk of cancer of salivary glands. Smoking tobacco tends to increase the risk. Human papilloma virus has been noticed in some types of salivary cancer and efforts are on to confirm this. Investigation into the low level radiation from mobile phones is also being done.
Signs and symptoms
While salivary gland cancer may not cause any symptoms, it is sometimes found during a regular dental check up. As symptoms caused by salivary gland cancer may also be caused by other conditions, consult a doctor if any of the following problems occur:
CT and MRI are used to determine if salivary gland cancer has spread to other tissues. An examination of the patient to check signs of health, in the neck, mouth and throat areas is vital. History of patient's health, habits and past illnesses and treatments is recorded. A small amount of glucose is injected into the vein and the PET (Positron Emission Tomography) scanner rotates around the body and takes images where glucose is used in the body. Malignant cells show up brighter in the picture because they are more active and take up more glucose than normal cells do. Endoscopy and biopsy are also done to test for salivary gland cancer. As salivary gland cancer is hard to diagnose, it is recommended to have tissue samples checked by a pathologist who has expertise in diagnosing salivary gland cancer.
Treating salivary gland cancer
Stage I is when cancer is confined to the salivary glands and is 2 cm or smaller; Stage II is larger than 2 cm but not larger than 4 cm; stage III is when it has spread to a lymph node or to soft tissues around the affected gland and stage IV has spread further.
There are three types of standard treatment used for salivary gland cancer – surgery, radiation therapy and chemotherapy. Some may receive more than one type of treatment. Therapy depends upon the stage the patient is in and the higher the stage, more the therapy and aggressive and multiple therapies are given.
If the tumor is small and located in an easy-to-access spot, surgeon may remove it and a small portion of healthy tissue that surrounds it. Removing the entire salivary gland is done if the tumor is large and if the cancer extends to nearby structures such as facial nerves, ducts that connect to salivary glands, facial bones and skin may also be removed.
If the cancer has spread to lymph nodes in the neck, the surgeon may remove most of the lymph nodes. Reconstructive surgery is done by a plastic surgeon to improve the ability to chew, swallow, speak and breathe after the surgery. The patient may need grafts of skin, tissue or nerves from other parts of the body to rebuild areas in the mouth, throat and jaw.
Radiation therapy using neutrons which are more effective in treating certain salivary gland cancers is used. Post surgery, this therapy is used to kill cancer cells that might still remain. In case surgery is not possible and tumor is large and located in a place that makes removal too risky, radiation alone is used to treat salivary gland cancer.
Although this is not currently used as a standard treatment for salivary gland cancer, Chemotherapy is a drug treatment used to kill cancer cells. This may be an option for people with advanced salivary gland cancer that has spread to distant areas in the body.
Those who undergo radiation therapy to the head and neck often experience dry mouth which can be uncomfortable. This can lead to frequent infections in the mouth, cavities and pose problems in teeth and difficulty eating, swallowing and speaking. If such complications arise then:
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Bibliography / Reference
Collection of Pages - Last revised Date: November 17, 2019