Radiation therapy dose escalation for prostate cancer: a rationale for IMRT

The response of prostate cancer to radiation was well-documented in the pre-PSA era. Large palpable tumors resolved within months of treatment with relatively modest radiation doses of 64-70 Gy. The use of PSA-based failure as an endpoint, however, has made it clear that cure rates were much lower than appreciated. While doses in this range are still widely used today, data from retrospective, sequential prospective and now randomized studies indicate that for patients with intermediate-to-high risk disease, doses above 70 Gy are associated with a significant reduction in biochemical failure. The use of 3D-conformal radiotherapy to escalate radiation dose has resulted in modest increases in rectal and bladder toxicity. The application of intensity modulated radiotherapy methods allows for greater sparing of the surrounding normal tissues and, hence, the potential to further escalate dose. The results of dose escalation, the ability of IMRT to reduce rectal and bladder exposure to high radiation doses and the use of new imaging methods to more accurately target the prostate are described.