Simulation Free Direct-to-Unit Large-Animal SBRT Workflow
Abstract
Purpose
Large-animal studies of stereotactic arrhythmia radiotherapy (STAR) are faced with financial and logistical difficulties that limit widespread implementation. We developed a single-platform STAR porcine workflow on an O-ring linac utilizing manual end-exhalation gating and contrast-enhanced CBCT. We evaluated this workflow’s ability to achieve adequate target coverage, OAR sparing, and QA requirements.
Methods
A veterinary team, certified medical physicist and radiation oncologist were present for all treatment sessions. An initial control animal underwent manually gated, contrast-enhanced CBCT imaging to create a template treatment plan. CTVs included transmural scar with 5-mm expanded PTVs. Two VMAT template workflows utilizing 6FFF were developed: one for domestic pigs with a single-fraction 25 Gy prescription to the PTV with intentional CTV hotspots >35 Gy, and one for mini pigs with 15 Gy to the PTV with intentional CTV hotspots >25 Gy. Subsequent animals were treated by aligning daily contrast-enhanced CBCT imaging to the template and treated with manual end-exhalation gating. Delivered dose-distribution for each animal was calculated by transferring the template plan to treatment-day imaging and recalculating dose. QA was performed with EPID gamma analysis and an IROC Houston phantom for end-to-testing.
Results
Across 3 mini pigs (template CTV/PTV=17.0/62.8 cc) and 3 domestic pigs (template CTV/PTV=35.2/98.7 cc), plans achieved adequate target coverage. For mini-pigs, CTV D95=25.22 Gy (template) vs 25.26 Gy (treated median); PTV D95=16.27 vs 16.34 Gy. For domestics, CTV D95=35.52 vs 35.13 Gy; PTV D95=26.17 vs 25.88 Gy. OAR doses remained within conservative porcine SBRT constraints. QA passed with EPID gamma of 95.7% (2%/2 mm) for domestics and 99.7% (2%/2mm) for minis. IROC end-to-end testing passed (TLD: within 2%, film: 100% gamma at 7%/5 mm).
Conclusion
This study designed and validated a large animal STAR workflow adapted for porcine studies, with acceptable coverage and OAR sparing, potentially lowering barriers that inhibit this research.