There are several ways of giving radiation dosage to a cancerous tumor. The most common method is to deliver the required dosage from an external beam of radiation produced outside the body. In this case the source of radiation beam is located 80-100 cm from the body of the person receiving radiation. Sometimes placing the source of radiation within the tumor might have advantages over delivering radiation from an external source. This method of delivering required radiation from an internal source embedded within the tumor is called brachytherapy.
If you are aware of the inverse square law in physics you would know the dosage of radiation therapy delivery changes by a great proportion depending upon the distance of the radiation source to the intended target. In brachytherapy the source of radiation is within the tumor volume and the proper placement of these sources of radiation within the tumor is of crucial importance.
There are several radioactive isotopes used in the brachytherapy. These include radium-226, cesium-137, cobalt-60, iridium192, iodine-125, gold-198 and palladium-103. Radium has a longer half-life compared to some of the other radioactive isotopes. In the past radium was the primary isotope used in brachytherapy, but recently radium has been largely replaced by cesium, gold and iridium, which have relatively shorter half-life and lower energies and because of this the radiation from these isotopes can be easily shielded.
Brachytherapy can be delivered with devices known as implants. These devices may be in the form of needles or seeds or ribbons. Brachytherapy can be delivered with permanent or temporary implants. These implants might be temporary or permanent. Temporary implants usually have a longer half-life and higher energies compared to the permanent implants. All temporary implants are inserted into the tumor during surgery. The duration of treatment for the temporary implant is usually 1-3 days.
Interstitial low-dose rate (LDR) brachytherapy is usually used for cancers involving the mouth and oral cavity, pharynx. This mode of treatment is often used in the treatment of sarcomas. Prostate cancer treatment is the most common form of LDR brachytherapy using seeds. Uterine cancer is the most common application of intracavitary LDR treatment. These patients are often isolated to prevent radiation exposure to nursing and other supportive staff during the care of the person.
The most common uses of high-dose rate (HDR) brachytherapy includes treatment of esophageal cancer, lung cancer and recently breast cancer and prostate cancer. Most HDR treatments are done as outpatient procedures allowing the patients to return to home the same day as treatment. Patients who are receiving treatment for prostate cancer is an exception who may remain in the hospital for 2-3 days during the treatment.
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