AN OPTIMIZED FORWARD-PLANNING TECHNIQUE FOR INTENSITY MODULATED TREATMENT OF PROSTATE CANCER
Ying Xiao, Richard K. Valicenti, James M. Galvin

Department of Radiation Oncology, Kimmel Cancer Center, Jefferson Medical College, Thomas Jefferson University Hospital, Philadelphia, PA

Results:
Applying our technique to five cases where the rectum protrudes into the prostate PTV, the resulting isodose curves have an oval shape for the anterior portion of the gland and show a concavity posteriorly at the position of the rectum. Dose Volume Histograms (DVHs) for the conventional 6-field plan are compared to those obtained by combining the beams using our optimization package with different weighting ((0.1,0.9), (0.5,0.5), (0.7,0.3), (0.9,0.1)) assigned to the rectum and prostate respectively. A total of 60 DVHs were generated and compared. For the optimized plan relative to the standard plan, the percent volume of rectum receiving 95% or more of the prescribed dose decreased by an amount that ranged from 2 to 32%, depending on the PTV shape and the weighting assigned. However, dose homogeneity for the tumor volume when the optimization technique was applied decreased compared to the standard plan. This change was in the range of 0% (no change) to 10%. The table below shows the complete results for one patient, and illustrates the effect of changing the weighting for the rectum. Notice that the 95% isodose line cuts through the rectum for the 10% weighting for the rectum and misses this structure for 70% weighting.