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Radiation and Duration of Treatment

  1. How long do radiation treatments typically last? Is there a difference between external versus internal radiation therapy?
  2. There seem to be so many types of radiation therapy options. How does the doctor determine the best radiation treatment option for the patient?

There are three major forms of radiation therapy

1. External radiation therapy

2. “Internal” radiation therapy or brachytherapy

3. Systemic radiation therapy.

External Radiation therapy consists of using different forms of radiation including photons, protons or electrons to irradiate a tumor in the body from outside in. That is the radiation is generated by a machine which is outside of the patient’s body and would be pointed towards the tumor or cancer. Obviously this means that the radiation has to go through the normal tissues between the external source of radiation and the tumor/cancer inside the body. We use different energies of photon or electron beams, to optimize focusing the radiation on the tumor and minimize radiation to the surrounding normal tissues. Proton beam is a unique form of radiation which would only deposit radiation at a certain point in the body i.e. tumor/cancer without radiating the normal tissue between the external source and the target of radiation.

“Internal” radiation or brachytherapy involves use of a variety of radioactive isotopes which are either temporarily or permanently placed inside or near the tumor/cancer. By doing so, radiation does not have to go through the normal tissue between an external source and the target of radiation. The most common form of permanent brachytherapy is prostate seed implant. In this form of treatment either Palladium (Pd-103) or Iodine (I-125) seeds are implanted inside the prostate. These seeds would irradiate the prostate gland and the cancer inside it as long as they are radioactive but eventually become inert. The most common example of temporary brachytherapy is the use of either Low Dose Rate (LDR) or High Dose Rate (HDR) forms of brachytherapy for the treatment of gynecological cancers specifically cervical and endometrial cancer. 

Systemic radiotherapy involves injection of either a radioactive or a radiolabeled product into the bloodstream so that radiation would potentially reach all areas involved by cancer. The most common form of using a radioactive product is in the  treatment of thyroid cancer by using radioactive Iodine (I-131). Examples for radiolabled products are radioactive monoclonal antibodies such as Rituxan, Zevelin and Bexxar. These products are often used in the treatment of non-Hodgkin lymphomas.

What form of radiation a radiation oncologist would recommend depends on many factors but mainly the type of cancer, the stage of cancer and its location.  What equips a radiation oncologist is not only four years of specialty training including radiation physics and biology but the evidence supporting these forms of treatments based on decades of research in the field. For each type of cancer there is a standard of care basically dictating what the appropriate radiation should consist of. For example for cervical cancer a combination of external radiation and brachytherapy is used. For prostate cancer one can use either external radiation or seed implant of a combination of both.

The duration of radiation treatments are also determined by the type and stage of the courses. Before prescribing any dose of radiation, a radiation oncologist has to first determine what the intention of the treatment would be. Treatment intent is either palliative or definitive.

Palliative treatment are usually given either to palliate pain, remove compression of tumor on a vital organ such as spinal cord, preventing fracture if the cancer has spread to a weigh-bearing bone, or in the case of brain metastasis to relieve the life-threatening pressure inside the brain. Palliative treatments are often given in short courses of 2-3 weeks not only because the radiation dose per individual treatments (aka fractions) is usually higher but also because the total dose of radiation is lower. Palliative radiation is often used stage IV. That is when the cancer has spread to other organs and even though it might be treatable, it is not curable.

Definitive treatment is given when, based on the stage of the cancer, statistically there is a chance for its cure (i.e. stage I-III). Depending on the type of cancer, definitive radiation can take up to 9 weeks not only because the radiation dose per individual treatments (aka fractions) is usually lower but also because the total dose of radiation is higher. Definitive treatments are given to the primary site of cancer (i.e. original site where the cancer started).

Radiation is normally given five days a week Monday through Friday. In some instances twice a day radiation may be recommended. In this case the two treatments are at least six hours apart. How long each individual treatment would take depends on many factors including the dose per fraction, the number of fields used to treat a target, the technology used and the energy and form of radiation.

Brachytherapy (aka “internal radiation”) is usually given in much fewer number of treatments. For example prostate seed implant requires one procedure to place the seeds in the prostate. In treatment of gynecological cancers depending on whether Low Dose Radiation (LDR) or High Dose Rate (HDR) radiation is used anywhere between 2 to 6 treatments often one to two weeks apart is given. In a similar manner systemic radiation, in the form of an injection or oral intake, would require much fewer number of treatments. For example treatment of thyroid cancer using I-131 often requires only one treatment.

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