Dosimetric Considerations In Clinical Implementation of a 3D Print Material for Patient-Specific Hybrid Intracavitary/Interstitial Gynecologic High-Dose-Rate Brachytherapy Cylinders
Abstract
Purpose
To determine the dosimetric impact of 3D-printed patient-specific cylindrical templates (PSCTs) printed with Formlabs Biomed Clear (BC) resin in gynecologic (GYN) high-dose-rate brachytherapy (HDRBT), and to validate clinical intuition of typical cases that would benefit from PSCTs versus standard vaginal multichannel cylinders (VMCs), for the purpose of clinical implementation.
Methods
Resin Dosimetry: A single channel cylinder was 3D printed with BC resin (1.09 g/cm3) to dimensionally match a clinical 3cm diameter vaginal vault cylinder (Elekta) made of PPSU (1.30g/cm3). Five uniformly weighted dwell positions with 1cm spacing was delivered through the PSCT, the vaginal cylinder, and water. Dose was measured using GafChromic EBT3 film placed in a large water tank at 5mm, 10mm, and 20mm depths. Planned dose was 300cGy to each depth. Planning benefit of PSCTs: PSCT treatment plans in Oncentra (Elekta) were created following the Kelowna method (Kudla 2023. DOI: 10.1016/j.brachy.2023.03.002). A subset of previously treated VMC plans were identified which may benefit from PSCTs due to depth of invasion/lateral extent of the target, and/or organs at risk proximity. Retrospective plans were made by overlaying the PSCT on the VMC in the pre-brachytherapy MRI which mimics the clinical workflow.
Results
Film mean dose and standard deviation was -0.8% ± 1.2% and -3.8% ± 1.2% for BC and PPSU, respectively, relative to water. Three previously VMC-treated vagina primary and endometrial cancer recurrent patients were identified for PSCT re-planning. In all cases the PSCT plans were superior to VMC plans, either through improved target coverage, OAR dose reduction, or both.
Conclusion
It is safe to deliver GYN HDRBT treatments through PSCTs made with Biomed Clear resin since it’s a closer dosimetric equivalent match to water compared to PPSU. PSCTs are more dosimetrically flexible than VMCs because of the addition of optimally placed interstitial needles.