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Standard Fractionation or Hypofractionation…that is the question.

Ryan Perkins, M.D.

December 30, 2020

The other day I was trying to explain to a patient with newly diagnosed prostate cancer about a clinical trial, the Comppare Trial, that randomizes some patients to be treated with proton beam therapy into conventional fractionation (38 treatments) or hypofractionation (20 treatments).  The concepts of conventional fractionation and hypofractionation took some extended explanation.  Last week in a television interview, Dr. Ackerman, extolled the benefits of a hypofractionated course of radiation in breast cancer, both for its cure rate and minimal side effects.  Since this conversation of standard fractionation and hypofractionation are coming up frequently, I thought it reasonable to discuss these concepts.  

I don’t want this to get too difficult.  So here is my simplified explanation of fractionation.  Every radiation treatment is called a fraction.  Forty five treatments is the same as 45 fractions.  Every fraction receives a certain amount of radiation.  The dose of radiation is measured in cGy (centigray).  Just like we measure distance in miles or speed in miles per hour, we give  a certain amount of radiation dose in cGy per fraction.  For example a typical daily treatment for many cancers is 200cGy per fraction.  Thus, after 30 fractions a patient would receive 200cGy x 30 fractions = 6000 cGy.  

Standard fractionation has been developed over many decades trying to maximize cure rates and minimize side effects.  We discovered that for some cancers, like prostate cancer, it takes higher doses (often 45 treatments) to cure the cancer.  For other cancers, like lymphoma, it takes less dose (usually 15 treatments) for cure.  However, these standard fractionation regimens are time consuming and often inconvenient.  

The alternative treatment option is to treat with fewer fractions (treatment days) by giving higher daily doses each day.  So instead of delivering 200cGy per treatment we may give 300cGy per day, decreasing the number of treatment days by one-third!  The key is making these fewer daily treatments of higher dose effective and not increasing toxicity and side effects.  Delivering a higher daily dose and fewer fractions is called hypofractionation.  These combinations of number of daily treatments and dose per treatment are not determined by guesswork.  They are carefully calculated using mathematical models.  

Many clinical trials in the last ten years have been evaluating hypofractionation.  Using hypofractionated radiation therapy, more dose of radiation is delivered per treatment, so patients can complete their course of radiation therapy much faster than conventional treatment.  These clinical trials have been studied in prostate cancer, breast cancer, brain cancer, lung cancer, and brain cancer, and more.  The number of treatments and dose per treatment is carefully determined and then prescribed and studied to determine if it is inferior or equivalent to conventional radiation therapy in its cure rate and toxicity.  

We are still in the early phases of many of these trials but several hypofractionated courses appear to be equivalent to standard fractionation in breast cancer and prostate cancer.  This doesn’t mean that every breast cancer patient or every prostate cancer patient should switch to hypofractionated radiation therapy.  But in certain circumstances and stages of cancer, hypofractionation can often be done safely and will be discussed by your doctor. For example, as Dr. Ackerman stated last week, many early stage breast cancers can be safely and effectively treated in 15 to 20 treatments rather than the standard 34 treatments. The Comppare trial for prostate cancer, as mentioned above, is trying to determine if 20 treatments is just as effective as longer standard courses.

I promise, you will be hearing more and more about hypofractionation in the coming months and years as we try to make radiation therapy more convenient, less costly, with safety as our top priority.  

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