A study of the effect of setup errors and organ motion on prostate cancer treatment with IMRT.

PURPOSE: To assess the influence of setup errors and organ motion in terms of the probability of tumor control and normal-tissue complications by tumor control probability and normal-tissue complication probability. METHODS AND MATERIALS: Twelve patients were treated for prostate cancer with intensity-modulated radiation therapy. Two orthogonal portal images were taken daily. All patients underwent three computed tomography scans during the 8-week treatment time (i.e., baseline, intermediate, and final). The original treatment plans were re-evaluated, taking into account setup errors and organ motion.
RESULTS: The mean shifts +/- standard deviation of the whole patient population in the lateral, anterior-posterior, and craniocaudal direction were 1.0 +/- 1.5 mm, 0.9 +/- 2.1 mm, and 1.9 +/- 2.1 mm, respectively. In most of the recalculated dose-volume histograms, the coverage of clinical target volume was granted despite organ motion, whereas the rectal wall histograms were often very different from the planned ones.
CONCLUSION: We have studied the impact of prostate and rectum motion, as well as setup errors, on dose-volume histograms. The estimate of these effects may have implications for predictive indications when planning intensity-modulated radiation therapy treatments on prostate.