SU-E-T-285: Revisiting the Nomogram for Intra-Operative Planning Based Pd-103 Brachytherapy

Purpose: The seed implant technique at our institution involves using a published nomogram for seed ordering based on CT based volume studies of the prostate. Ultrasound volume studies are subsequently used in the operating room for planning a modified peripheral loading with urethra sparing seed implant. The purpose of this study is to determine the appropriate modality for prostate volume measurement and creating an updated nomogram for intra-operative planning specific to our technique for pd-103 brachytherapy for efficient seed ordering. Methods: Prostate volumes based on pre-implant CT (Pre-CT), intra-operative ultrasound (TRUS), and post-implant CT (post-CT) studies as well as the total airkerma strength (AKS) of the implants were analyzed for 135 seed implant cases (69 monotherapy, 66 boost). Regression analysis was performed to derive the relationship between the total AKS and pre-CT and TRUS volumes. The correlation between TRUS and pre-CT volumes and TRUS and post-CT volumes were also studied. Results: Ultrasound based prostate volume exhibited a stronger correlation with total AKS than the pre-implant CT volume (R² = 0.97 vs 0.88 for monotherapy and 0.96 vs 0.89 for boost). In general the pre-CT overestimated the prostate volume leading to ordering of a larger number of seeds and thus leading to higher number of unused/wasted seeds. Newly derived TRUS based nomogram was better suited for our technique than the published data. The post-implant CT volume closely followed the ultrasound volume (R² = 0.88) as compared to pre-implant CT volumes (R² = 0.57). Conclusion: In an era of costconscious health care where waste reduction is of utmost importance, an updated technique-specific nomogram is useful for ordering optimal number of seeds resulting in significant cost savings. In addition, our study shows that ultrasound based prostate volume is a better predictor for seed ordering for intra-operative planning than pre-implant CT