Detailed dosimetric evaluation of intensity-modulated radiation therapy plans created for stage C prostate cancer based on a planning protocol.

BACKGROUND: Intensity-modulated radiation therapy (IMRT) has been employed as a precision radiation therapy with higher conformity to the target. Although clinical outcomes have been reported for many investigations, detailed treatment planning results have not been mentioned to date. The aim of this study was to evaluate the dose specifications of our IMRT treatment plans for locally advanced prostate cancer. METHODS: Seventy-seven clinically applied IMRT plans treated between September 2003 and December 2005, in which patients were irradiated with 78 Gy in the prone position, were retrospectively analyzed. Dosimetric data output from dose volume histograms were evaluated in detail. RESULTS: The mean dose ± standard deviation, homogeneity index, and conformity index to the planning target volume (PTV) were 78.3 ± 0.7 Gy (100.4 ± 0.9%), 13.7 ± 3.0, and 0.83 ± 0.04, respectively. For the clinical target volume, the mean dose was 80.3 ± 0.7 Gy (102.9 ± 0.9%).The V40, V60, and V70 Gy of the rectal wall were 58.3 ± 2.8, 29.6 ± 2.7, and 15.2 ± 3.0%, respectively. Planning difficulties were encountered in patients whose bowels were displaced downward, as constraints imposed by the bowel position altered the dose index of the PTV. In many cases, additional bowel optimization parameters were required to satisfy constraints for organs at risk. However, major deviation could be avoided by inverse planning with computer optimization. CONCLUSION: IMRT allowed the creation of acceptable and practical treatment plans for locally advanced prostate cancer. Reports regarding detailed dosimetric evaluations are mandatory for interpreting clinical outcomes in the future.