Seed-displacements in the immediate post-implant phase in permanent prostate brachytherapy

Purpose: To investigate differences in seed-displacements between the immediate post-implant phase (day 0-1) and the time to post-plan computed tomography (CT) (day 1-30) in seed prostate brachyther-apy.Materials and methods: Seed positions were identified on the intra-operatively created ultrasound-based treatment plan (day 0) and CT scans of day 1 and 30 for 33 patients. The day 1 (30) seed arrangement was registered onto the day 0 (1) arrangement using a seed-only approach. Based on a 1:1 assignment of seeds via the Kuhn-Munkres algorithm, seed-displacements were analyzed. Displacements were evalu-ated depending on strand-length and anatomical implant location. Resulting dosimetric effects were cal-culated.Results: Seed-displacements in the immediate post-implant phase (median displacements: 3.8 +/- 3.6 mm) were stronger than in the time to post-plan CT (2.1 +/- 2.6 mm) and enhanced along the superior-inferior direction. From day 0 to 1, strands containing one (7.3 +/- 5.4 mm) or two (8.1 +/- 5.8 mm) seeds showed larger displacements than strands of higher lengths (up to 4.2 +/- 7.0 mm), whereas no length -dependency was found to day 30. Seeds implanted in base and apex tended to move towards the prostate midzone during both time periods. D90 (dose that 90% of prostate receives) was with variations of 2 +/- 15 Gy more stable from day 1 to 30 than in the immediate post-implant phase (-18 +/- 11 Gy).Conclusion: Seed-displacements in the immediate post-implant phase was enhanced compared to day 1- 30. This may result from uncertainties in the gold-standard ultrasound-based treatment planning and implantation. Adaptive implantation workflows appear useful for ensuring high implant stability from the beginning.(c) 2023 Elsevier B.V. All rights reserved. Radiotherapy and Oncology xxx (2023) xxx-xxx

Automated summary

The purpose of this study was to investigate differences in seed-displacements between the immediate post-implant phase and the time to post-plan CT in seed prostate brachytherapy. Seed positions were analyzed on treatment plans and CT scans for 33 patients, and the resulting dosimetric effects were calculated. The study found that seed-displacements were greater in the immediate post-implant phase compared to the time to post-plan CT, with enhanced displacements in the superior-inferior direction.