Postoperative radiotherapy for prostate cancer : evaluation of target motion and treatment techniques (intensity-modulated versus conformal radiotherapy).

PURPOSE: To determine the extent of target motion in postprostatectomy radiotherapy (RT) and the value of intensity-modulated radiotherapy (IMRT) compared to three-dimensional conformal radiotherapy (3D-CRT). PATIENTS AND METHODS: 20 patients underwent CT scans in supine position with both a full bladder (FB) and an empty bladder (EB) before RT and at three dates during the RT series. Displacements of the CTV (clinical target volume) center of mass and the posterior border were determined. 3D-CRT and IMRT treatment plans were compared regarding homogeneity, conformity, and dose to organs at risk.
RESULTS: In the superior-inferior direction, larger displacements were found for EB compared to FB scans; anterior-posterior and right-left displacements were similar. With an initial rectum volume of < 115 cm(3), 90% of displacements at the posterior border were within a margin of 6 mm. The non-target volume irradiated in the high-dose area doubled in 3D-CRT versus IMRT plans (80 cm(3) vs. 38 cm(3) encompassed by the 95% isodose). Bladder dose was significantly lower with IMRT, but no advantage was found for the integral rectal dose. An adequate bladder filling was paramount to reduce the dose to the bladder.
CONCLUSION: Postprostatectomy RT can be recommended with FB due to an improved CTV position consistency and a lower dose to the bladder. With improved non-target tissue and bladder volume sparing, IMRT is an option for dose escalation. However, this analysis did not find an advantage concerning the integral rectal dose with IMRT versus 3D-CRT.