2090 - A Clinical Evaluation of In-Room Surgical Computed Tomography System for Intensity Modulated Proton Therapy

Purpose/Objective(s): Intensity-modulated proton therapy offers superior target coverage and normal tissue sparing compared to the double-scatter system. The in-room computed tomography (CT) system generates planning-CT-level image quality, enabling daily proton dose evaluation and providing opportunities for both offline and online plan adaptation. This study evaluates the daily proton plan dosimetry of two in-room CT systems: a surgical CT and a diagnostic CT.

Materials/Methods: Two in-room CT systems were installed in separate proton vaults to enable three-dimensional image-guided radiotherapy. The two proton systems are beam-matched, allowing patient transfers between vaults. This study included ten clinical proton therapy patients with minimal anatomical changes, who were scanned on both in-room CT scanners throughout their treatment course. Treatment plans were created based on simulation CT and evaluated using daily CT scans from each in-room CT scanner. Disease sites were limited to the brain and head&neck which have tight immobilization. The dosimetric parameters analyzed included mean dose, D99, D95, D2cc, and D1cc of the planning targets. Dosimetric variations were calculated using the treatment plans as a reference.

Results: Minimal variation from treatment plan was observed in evaluation plans on both CT scans. Table shows the range of dosimetric variations in percentage differences from the treatment plan for evaluation plans on both CT systems. The values represent the minimum, maximum, and standard deviation of the percentage differences for all ten patients, respectively.

Conclusion: Clinical evaluations on both the surgical CT and diagnostic CT showed no substantial variation from the original plan. The surgical CT demonstrated potential for offline or online plan adaptation.