Why not radiate 7 days a week?
Dear OncoLink "Ask The Experts,"
Neha Vapiwala , MD, Radiation Oncologist at the Abramson Cancer Center of the University of Pennsylvania, responds:
Radiation therapy damages both the normal cells and the tumor cells that are located within the radiation field. These cells can heal between radiation treatments. While it is undesirable to allow tumor cells time to heal, it is very necessary to allow some time for normal tissues to repair radiation damage. Studies have taken tissue from various human organs (skin, gut, lung, liver, etc.) and exposed them to radiation to analyze the effects of radiation. These studies have taught us that a regimen of once-daily treatments over a shorter time period (eg: 7 days a week for 4 weeks) can be very damaging to certain normal cells, especially ones that divide rapidly like the skin and lining of the gut. It is also known that extending the overall treatment time, by only treating 5 days a week for 5 and a half weeks, for example, spares these tissues and limits normal tissue toxicity.
Ultimately, in order to treat your tumor you have to deliver all of the intended radiation dose. The total dose is divided into a number of smaller daily doses. In order to deliver all of the necessary daily doses, it is crucial to prevent dose-limiting toxicity (ie: if the skin is too damaged, you can't continue to treat the patient, and have to interrupt the treatment course, which is very bad from a treatment standpoint).
A way to prevent such severe toxicity is to NOT treat continuously every single day, but rather to allow 2 days a week for healing.
Historically, because of U.S. society's convention of weekends as "non-working days", those 2 days for healing were designated to be Saturday and Sunday.