Intensity Modulated Radiation Therapy (IMRT) vs. 3D conformal Radiation for prostate cancer

Richard Whittington, MD
Last Modified: March 3, 2002


Dear OncoLink "Ask The Experts,"

I have stage B1 prostate cancer (PSA 7.1, Gleason 6). I am trying to decide whether to undergo IMRT at the considerable inconvenience of traveling to a distant location or to have the standard 3D conformal radiation that is available locally. I would appreciate any information.  


Richard Whittington, MD, Associate Professor of Radiation Oncology at the University of Pennsylvania School of Medicine, responds:

The difference is one of philosophy and not science. IMRT involves using many fields (30 to 60) with each treating part of the tumor so that when they are summed, the dose is similar to the usual 4 to 6 fields most centers use. IMRT will treat some of the tumor to a much higher dose than 3D-CRT, although some, perhaps as much as 20% of the gland may receive 10 to 15% less. IMRT also involves giving much more normal tissue some radiation, but gives less to the rectum and bladder. This may result in fewer side effects initially, but there is potential for more side effects long-term because of the increase amount of normal tissue exposed to low doses of radiation. There are no studies comparing the two methods. There is evidence suggesting that a dose greater than 75 Gy (with either technique) is associated with a higher cure rate, so I would recommend basing the decision on total minimum dose to the gland. However, there is no data specifically showing IMRT improves outcome over 3D conformal radiation.