Intensity modulated radiation therapy (IMRT) following prostatectomy: Morefavorable acute genitourinary toxicity profile compared to primary IMRT for prostate cancer

Purpose: To report our initial experience on postprostatectomy IMRT (PPI), addressing acute genitourinary cem toxicity in comparison to primary IMRT ( PI) for prostate cancer. Methods and Materials: From April 1998 to December 1999, 40 postprostatecto my patients were treated with intensity modulated radiation therapy (IMRT) to a median prescribed dose of 64 Gy (mean dose of 69 Gy). The Radiation Th erapy Oncology Group (RTOG) scoring system was used to assess acute GU toxi city. Target volume and maximum and mean doses were evaluated. The mean dos es to the bladder and irradiated bladder volume receiving >65 Gy were asses sed. These were compared to those of 125 patients treated with PI to a pres cribed dose of 70 Gy (mean dose of 76 Gy). Results: The acute GU toxicity profile is more favorable in the PPI group w ith 82.5% of Grade 0-1 and 17.5% of Grade 2 toxicity compared to 59.2% and 40.8%, respectively, in the PI group (p < 0.001). There was no Grade 3 or h igher toxicity in either group. The target volume was larger in the PPI gro up, while the maximum and mean doses to the target were higher in the PI gr oup. The mean dose delivered to the bladder was higher in the PPI group. Th e irradiated bladder volume receiving >65 Gy was significantly larger in th e PI group (p < 0.001). Conclusions: PPI can be delivered with acceptable acute GU toxicity. The la rger PPI target volume may be related to the difficulty in delineating pros tatic fossa. Despite a larger target volume and a higher mean dose to the b ladder, PPI produced a more favorable acute GU toxicity profile. This may b e related to a combination of lower mean and maximum doses and smaller blad der volumes receiving >65 Gy in the PPI group, as well. as urethral rather than bladder irradiation. The findings have implications in the evaluation of IMRT treatment plan for prostate cancer, whereby the irradiated bladder volumes above 65 Gy may be more meaningful than the mean dose to the bladde r. Longer term toxicity results are awaited. (C) 2001 Elsevier Science Inc.