(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: To evaluate dosimetric changes from source migration and decay for three different seed radioisotopes when imbedded in a collagen carrier/spacer in brain brachytherapy.
Methods: Seven patients undergoing Cs-131 implantation and subsequent IGRT on an IRB-approved trial were identified. Seed positions (avg.18/implant) were manually defined on 47 image sets acquired 7-57 days post-implant and for 3 additional image sets acquired at 82-289 days. In addition to the clinical post-implant Cs-131 plans, hypothetical post-implant plans were generated for I-125 and Pd-103 utilizing the same seed positions as Cs-131 plans while modifying seed strength to match the Cs-131 60Gy brachytherapy volume. To model the impact of seed migration and decay, plans were recalculated for 2 scenarios: 1) assuming seed positions on a given image set were unchanged until acquisition of the subsequent set, and 2) assuming seed positions had changed on the day after the prior image set was acquired.
Results: For scenarios 1 and 2, respectively, the average mean dose difference to the 60Gy volume compared to the post-implant plans, was 0.4Gy (0.6%, range 0.1-1.0Gy) and 0.9Gy (1.5%, range 0.2-1.7Gy) for Cs-131, 1.2Gy (2.0%, range 0.1-2.1Gy) and 1.6Gy (2.6%, range 1.2-2.6Gy) for I-125, and 0.8Gy (1.3%, range 0.2-1.5Gy) and 1.4Gy (2.3%, range 0.3-1.9Gy) for Pd-103. Differences in V100, V150 and V200 on average were <0.3cc for all 3 radioisotopes. Differences in V30 and V15 were <0.3cc and <0.4cc for Cs-131, <0.4cc and <0.6cc for Pd-103, and <0.7cc and <1.2cc for I-125. Inclusion of extended time points for I-125 plans did not result in significant changes from the above values.
Conclusion: The largest dosimetric impact from seed migration was for I-125 and the least for Cs-131. Observed dose differences from seed migration are relatively small across all three radioisotopes and may not be clinically significant, implying the robustness of the implantation technique.
Keywords
Brain, Brachytherapy, Seed Localization
Taxonomy
TH- Brachytherapy: Intraoperative planning
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