Purpose: To investigate the role of intensity-modulated radiation therapy (IMRT) to irradiate the prostate gland and pelvic lymph nodes while sparing critical pelvic organs, and to optimize the number of beams required. Methods and Materials: Target, small bowel, colon, rectum, and bladder were outlined on CT planning scans of 10 men with prostate cancer, Optimized conventional (RT) and 3-dimensional conformal radiotherapy (3D-CRT) plans were created and compared to inverse-planned IMRT dose distributions using dose-volume histograms, Optimization of beam number was undertaken for the IMRT plans. Results: With RT the mean percentage volume of small bowel and colon receiving >45 Gy was 21.4 +/- 5,4%. For 3D-CRT it was 18.3 +/- 7.7% (p = 0.0043) and for 9-field IMRT it was 5.3 +/- 1.8% (p < 0.001 compared to 3D-CRT), For 7, 5, and 3 IMRT fields, it was 6.4 +/- 2,9%, 7.2 +/- 2.8%, and 8.4 +/- 3.8% (all p < 0.001 compared to 3D-CRT), The rectal volume irradiated >45 Gy was reduced from 50.5 +/- 16.3 % (3D-CRT) to 5.8 +/- 2,1% by 9-field IMRT (p < 0.001) and bladder from 52.2 +/- 12.8% to 7 +/- 2.8% (p < 0.001), Similar benefits were maintained for 7, 5, and 3 IMRT fields, Conclusions: The reduction in critical pelvic organ irradiation seen with IMRT may reduce side effects in patients, and allow modest dose escalation within acceptable complication rates. These reductions were maintained with 3-5 IMRT field plans which potentially allow less complex delivery techniques and shorter delivery times. (C) 2000 Elsevier Science Inc.
