Technological advances in external-beam radiation therapy for the treatment of localized prostate cancer.

The relative inability of conventional radiotherapy to control localized prostate cancer results from resistance of subpopulations of tumor clonogens to dose levels of 65 to 70 Gy, the maximum feasible with traditional two-dimensional (2D) treatment planning and delivery techniques. Several technological advances have enhanced the precision and improved the outcome of external-beam radiotherapy. The three-dimensional conformal radiotherapy (3D-CRT) approach has permitted significant increases in the tumor dose to levels beyond those feasible with conventional techniques. Intensity-modulated radiotherapy (IMRT), an advanced form of conformal radiotherapy, has resulted in reduced rectal toxicity, permitting tumor dose escalation to previously unattainable levels with a concomitant improvement in local tumor control and disease-free survival. The combination of androgen deprivation and conventional-dose radiotherapy, tested mainly in patients with locally advanced disease, has also produced significant outcome improvements. Whether androgen deprivation will preclude the need for dose escalation or whether high-dose radiotherapy will obviate the need for androgen deprivation remains unknown. In some patients, both approaches may be necessary to maximize the probability of cure. In view of the favorable benefit-risk ratio of high-dose IMRT, the design of clinical trials to resolve these critical questions is essential.