Overview of treatment plan quality in a high dose rate prostate brachytherapy workflow.

Purpose: High dose rate brachytherapy (HDR-BT) has been shown to be an effective treatment for prostate cancer, with treatment plan quality dependent on a number of factors. In this work, we report on the overall performance of our ultrasound (US)-based workflow and the impact of several treatment-specific variables.

Methods and materials: Patients who underwent HDR-BT (boost, monotherapy, and retreatment) using Varian Bravos/US from 2021 to 2023 were sampled for this study. Treatment plan quality was analyzed and plans were categorized with regard to a number of metrics, including: prostate volume, treating physician, planning physicist, number of needles included, estimated planning time, rectum-prostate separation, and bladder-prostate separation. The performance of this program was compared to the performance of our program using previously used modality combinations: Varian Varisource/US, Elekta microSelectron/CT.

Results: Plan quality for our Bravos/US workflow was shown to be consistently above acceptability criteria for all personnel involved; on average: prostate V100%: 98.9% ± 0.1%, rectum V75%: 0.04 ± 0.01 cc, bladder V75%: 0.06 ± 0.01cc, urethra V125%: 0.00 ± 0.00 cc. Prostate coverage was statistically improved with this workflow compared to that using our previous modalities. There was a statistical correlation between organ-at-risk sparing/prostate coverage ratio and prostate volume, number of needles/prostate volume, bladder-prostate separation, and rectum-prostate separation. There was no correlation between plan quality and planning time.

Conclusions: Our US-based HDR-BT program led to target coverage and organ-at-risk sparing that exceeded department thresholds. Results were acceptable regardless of the personnel involved and improved plan quality was obtained using more needles/prostate volume and increased spacing between the prostate and the rectum and bladder.