Sci-Sat AM(2): Brachy-09: Investigation of catheter displacement in HDR prostate brachytherapy

During prostate cancer treatment with HDR brachytherapy, catheters are inserted into the prostate. Between planning and treatment, catheters may move inferiorly due to edema. If undetected, treatment proceeds without correcting the catheter displacement, and an incorrect treatment is delivered. The purpose of this study was to investigate the consequences of catheter displacement on prostate coverage and critical structure avoidance. Ten patient plans were selected in which movement of the catheters had been observed. The original treatment plan, generated using Nucletron PLATO (ver. 14.3.2), was adjusted introducing inferior catheter offsets of 5, 10, 20, and 30 mm. The original treatment dwell times were re-entered into the offset plans to determine the consequences of the displacement. DVH data was calculated for the prostate, rectum, urethra, and bladder. Prostate V100 decreased from 99% to 36% over the ten patients studied. For the urethra, the D10 increased (114.1% to 128.2%), as did the V125 (2.7% to 12.8%). In the rectum the V75 initially increased as the catheters shifted inferiorly, but dropped as the shift increased beyond 10 mm. In the penile bulb the V75 increased as a function of shift (from 2.1% to 44.8%). Every effort should be made to ensure that the catheters do not move during prostate treatment. A small shift, 5 mm, would result in a small deviation of the dose distribution. In this case a re-optimization of the plan is unnecessary. Larger shifts will have a serious impact on the dose delivered to the prostate and to sensitive normal structures.