Last Modified: August 30, 2008
Dear OncoLink "Ask The Experts,"
If you would please explain the difference in types of radiation machines used specifically for treating anal cancer--the linear accelerator and the IMRT--if there is a difference and whether all cancer treatment centers would utilize the same equipment type.
James M. Metz, MD, Editor-in-Chief of OncoLink and Assistant Professor of Radiation Oncology at the Hospital of the University of Pennsylvania, responds:
Anal cancer is treated primarily with a combination of radiation therapy and chemotherapy. External beam irradiation, otherwise known as x-rays or photons, are generated from a linear accelerator. A linear accelerator can deliver conventional 3-D conformal radiation or Intensity Modulated Radiation Therapy (IMRT). This really comes down to the type of treatment planning being done at the facility that is delivering the treatment and the experience of the radiation oncologist. There are no reported data that IMRT is superior to 3D conformal radiation in terms of cure rates for anal cancer. However, there appear to be significant reductions in side effects with IMRT. This is due to the ability of IMRT to better spare some of the more sensitive normal tissues in the pelvis from exposure to radiation. Better sparing of normal organs appears to make the treatment more tolerable for many patients. In fact, at our institution we have moved to using IMRT for all treatment of anal cancers in combination with chemotherapy. However, as mentioned before, there has never been a prospective randomized trial comparing the two techniques.