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Session: Multi-Disciplinary General ePoster Viewing [Return to Session]

Initial Experience with Online CT-Based Adaptive Radiotherapy in the Abdomen

A Price1*, E Laugeman1, B Cai2, T Kim1, Y Hao1, O Green1, H Gay1, P Samson1, H Kim1, M Spraker1, G Hugo1, L Henke1, (1) Washington University in St. Louis, St. Louis, MO, (2) UT Southwestern Medical Center, Dallas, TX


PO-GePV-M-76 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: CT-Based online adaptive radiotherapy using an integrated ring-gantry platform recently gained FDA clearance. This study describes our institution’s early experience with abdominal CT-guided stereotactic adaptive radiotherapy (CT-STAR) to help guide other CT-based adopters.

Methods: Our institution specifically targeted abdominal treatment sites with minimal tumor motion. We analyzed anatomical movement for both the target and OAR from the initial planning scans, determining the need for planning ITVs or motion planning risk volumes (mPRV). Patients were either treated at end-exhale breath hold or free breathing, which was determined by both patient compliance and tumor motion needs. Dosimetric indices from planning images, anatomy-of-the-day, and adapted anatomy were collected. Treatment times for each disease site were also collected.

Results: Our institution treated two para-aortic lymph node (PA-LN) and one anterior retroperitoneal lymph node (R-LN). Both PA-LN patients were scanned at end-exhale breath hold for adaptive contouring but treated at shallow free-breathing. The average tumor motion was 0.2cm and the average adjacent OAR motion was 0.4cm. In the R-LN patient, the patient was scanned and treated at end-exhale breath-hold. For the R-LN patient, the bowel dose was exceeded in all predicted plans. For the first PA-LN patient, the predicted plan exceeded small bowel constraints in all five fractions and exceeded the duodenum constraint in two of the five fractions. In the second PA-LN patient, the predicted plan exceeded small bowel constraints in all five fractions. For all three patients, adaptive treatment plans were within bowel tolerance. The average treatment times were 61.6min ± 23.6min (mini: 31min. max: 114min).

Conclusion: Abdominal adaptive treatments with minimal motion were successfully treated in an acceptable time period. mPRVs can additionally account for predictable intra-fraction OAR motion in the absence of respiratory gating.

Funding Support, Disclosures, and Conflict of Interest: Geoff Hugo, Bin Cai, Matt Spraker, Lauren Henke, Hyun Kim have grant funding from Varian outside this work. Olga Green, Alex Price, and Lauren Henke have speaker fees from ViewRay



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