Quantitative Evaluation of Neurovascular Bundle Doses in Low-Dose-Rate Prostate Brachytherapy Using I-125 Seeds

Abstract

Low dose rate (LDR) prostate brachytherapy is an accepted standard treatment technique for early and intermediate stage prostate cancer. Several studies have reported impotence risk after brachytherapy which may result from dose delivered to neurovascular bundles (NVB). The purpose of this work is to investigate retrospectively the dose delivered to NVB and its potential correlation with erectile dysfunction. Treatment planning and seed implantation techniques that provide optimized doses to NVB are also investigated. The records of ten patients treated with a monotherapy prescription dose of 144 Gy using I-125 implanted seeds were reviewed. Transverse endorectal ultrasound (US) images were obtained and used to contour prostate, urethra and rectum at the start of the procedure with patient in dorsal lithotomy position and under anesthesia using a transrectal US probe. As part of our procedure, NVB were localized using Doppler US imaging on the right and left sides of prostate. An inversely optimized treatment plan was generated using current patient structures. A dose coverage of more than 98% of prostate volume to prescription dose of 144 Gy (V100 = 98-100%) and sparing of 95% of the rectum and urethra volumes as critical structures from 150% dose (V150 < 5%) were achieved in initial plan that is used in the procedure and modified intraoperatively during seed implantation. The mean and standard deviation of the maximum, minimum and mean dose delivered to left and right neurovascular bundles are shown in Table for actual implanted procedures. The dose to NVB correlated strongly with prostate D90 where high D90 implants resulted in high NVB dose, particularly for hot implants in the posterior section of prostate that sided with tumor foci. The mean left NVB dose was 167.96 Gy which is often higher than the prescription dose. Retrospective optimization of the treatment plans of implanted prostates improved substantially the sparing of NVB, for example, the mean of the maximum dose was decreased to half the value compared to non-optimized plans. This study demonstrated that NVB received high mean doses in prostate brachytherapy that was not optimized for NVB doses. The NVB can be spared to lower dose levels if their dose coverage was constrained using dynamic intraoperative inverse planning. Future follow-up study will investigate correlation between the doses delivered to NVB and erectile dysfunction.Poster Viewing Abstract 2481; TableMean and standard deviation of the maximum, minimum and mean dose of the right and left NVBRight NVBLeft NVBMean (Gy)Standard dev. (Gy)Mean (Gy)Standard dev. (Gy)Volume (CC)0.22400.05720.18800.0581Max. dose294.29101.16364.17158.79Min. dose61.7628.0071.0437.69Mean dose128.8725.49167.9651.89 Open table in a new tab