Brachytherapy for treatment of mesothelioma
Brachytherapy is a form of radiotherapy and considered an advanced form of cancer treatment. This therapy has been in use for more a century; doctors used it in some circumstances as an alternative to external radiotherapy and surgical treatment.
Radiotherapy is the use of ionizing radiation like x-rays to treat cancers by killing the cancer cells. About 40% of cancer patients have radiotherapy as part of their cancer treatment, including those with malignant mesothelioma. Radiotherapy is used both to treat the cancer and to provide symptomatic relief, if a cure is not possible. There are two types of radiotherapy:
- External radiotherapy or tele-radiotherapy in which the radiation is delivered from a radioactive source outside the body, usually a linear accelerator.
- Brachytherapy or internal radiotherapy
Brachytherapy is a form of radiotherapy in which the radiation if given by putting the radioactive source inside the body. ”Brachy” means short and hence brachytherapy means therapy given at short distance – ‘localized’ to be precise. It is also called internal radiotherapy, sealed source radiotherapy, seed implantation radiotherapy or endocurietherapy. The radioactive source is usually placed inside the cancer tissue or near to it. The radioactive source emits ionizing radiation which kills the surrounding cancer cells. The ionizing radiation can penetrate only a small distance of about 1 cm. So the ionizing radiations of the radioactive source (radio-active seeds) which is placed in the cancer tissue attack only the surrounding cancer cells and never attack the normal cells outside the cancer tissue. The radioactive seeds that are used in brachytherapy are – Iodine 125, Iodine 131, Palladium 103 and Iridium 192.
Types of brachytherapy
Temporary brachytherapy: The radioactive material is placed for a specific period of time and then removed. The radioactive material is placed inside the cancer tissue or near it and a high dose rate (HDR) or a low dose rate (LDR) radiation is given.
Permanent brachytherapy: The radioactive seeds or pellets which are about the size of rice grains (4 mm by 0.8 mm in dimension) are implanted in the cancer tissue or near it. These seeds are left permanently in the tissue. The seeds slowly emit radiation which kills the surrounding cancer cells. Up to 100 radioactive seeds are implanted. The radioactivity of the seeds diminishes gradually over a period of time and eventually ceases to emit any radiation. The seeds remain in the place of implantation for life harmless foreign bodies.
Preparing the patient for brachytherapy
Since brachytherapy is given under anesthesia, a few tests are done to assess the fitness of the patient to undergo anesthesia. These tests include a few blood tests, chest x-ray and electrocardiography. The results of these tests allow the anesthesiologist to determine the type of drug to be used while giving anesthesia. Imaging studies like ultrasound scan are then done to determine the location, size and extent of the tumor. This allows the radiotherapist to decide the location where the radioactive seeds will be placed.
Radiation oncologist – Evaluates the patient and determines the type of treatment. Responsible for deciding the overall treatment plan which includes the area to be treated and the dose to be delivered
Radiation physicist – Calculates the dose to be prescribed and determines the technique to be used to deliver the prescribed dose
Dosimetrist – Calculates the dose to be prescribed and helps in delivering the prescribed dose
Radiation therapist – Operates the equipment and delivers
the prescribed dose
Imaging methods like x-rays, ultrasound scan and CT scan are used to determine the area to be treated and a computer is used to calculate the time of exposure to radiation and to assist in the introduction of the radioactive seeds.
The person who manually does the procedure (usually an oncologist) is also exposed to some amount of radiation. The manual after-loading is now usually replaced by remote, reducing the risk of exposure of the oncologist to radiation.
Brachytherapy can be either a temporary or a permanent brachytherapy. And again based on the rate and duration of the therapy, it could be a high dose rate brachytherapy or a low dose rate brachytherapy.
High dose rate brachytherapy
In high dose rate (HDR) brachytherapy, thin catheters are first introduced in to the tumor to be treated. These catheters are connected to afterloader. The afterloader contains the radioactive seeds at the end of a wire. The seeds are pushed one by one in to the catheters. The computer decides the time and place of delivering the radiation.
High dose rate brachytherapy is an outpatient procedure. The delivery of each dose may last for a few minutes. Multiple such doses are given. Patients may receive up to 12 separate HDR brachytherapy treatments over one or more weeks. High dose rate brachytherapy is usually a temporary brachytherapy. After a series of treatment, the catheters are removed.
Low dose rate brachytherapy
In low dose rate brachytherapy, the patients receive continuous radiation over a period of hours or days. It is done as an inpatient procedure to allow the device to work over a longer period of time. If it is a temporary therapy, the device is removed after series of treatments. In permanent brachytherapy, the seeds are left in place which slowly lose the radioactivity over a period of time.
Side effects of brachytherapy
Though brachytherapy is a safer alternative to external radiotherapy and surgical treatment of cancer, there are a few side effects associated with this procedure.
Immediately after the procedure, the patient may feel soreness and pain at the site of the procedure. The treated area may also be swollen causing discomfort for the patient. Short term side effects may last for a couple of days and include bleeding from the site.
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