Impact of urinary catheterization on dosimetry after prostate implant brachytherapy with palladium-103 or iodine-125

PURPOSE: Postoperative dosimetry is integral to quality assurance for prostate brachytherapy. Images on Day 0 are typically obtained with a contrast-filled urinary catheter in place for urethral dose calculations. However, expansion of the urethra and perhaps the prostate by the catheter may affect target coverage. We assessed. the effect of urinary catheterization on target dosimetry after implantation with palladium-103 ((103)Pd) or iodine-125 ((125)I) seeds. METHODS AND MATERIALS: Patients were 29 consecutive men with postimplant dosimetry calculated with and without a urinary catheter after brachytherapy seed implantation; 19 patients received (103)Pd seeds and 10 patients received (125)I seeds. In each case, 14-French caude tip urinary catheters were placed before implantation, and axial CT slices of the pelvis were obtained before and after catheter removal for postimplant dosimetry. Dosimetric parameters were measured and compared with paired Student's t tests. Trends were assessed by linear regression with the Pearson correlation coefficient. RESULTS: Removal of the urinary catheter significantly improved V(100) and D(90) for (103)Pd implants (mean +/- standard deviation (SD), 2.7% +/- 4.2%; range, -0.4% to 15%; p = 0.011 and mean +/- SD, 4.0% +/- 3.4%; range, -0.1% to 13.8%; p < 0.01, respectively). For (125)I implants, catheter removal improved D(90) (mean +/- SD, 1.5% +/- 1.8%; range, -1.3% to 4.2%; p = 0.027). For the (103)Pd group, the magnitude of change in V(100) correlated with prostate size (R(2) = 0.16) and source number (R(2) = 0.15). CONCLUSIONS: Urinary catheterization can artificially reduce target coverage after prostate implant brachytherapy. The patients undergoing (103)Pd implantation with smaller (<30 cm(3)) prostates and fewer (<90) sources are particularly susceptible to reduced D(90) and V(100) when a urinary catheter is present. (C) 2011 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.