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Are Proton Gantries Needed? An Analysis of 4332 Patient Proton Gantry Treatment Plans From the Past 10 Years

S Yan

S Yan*, H Lu, J Flanz, N Depauw, J Adams, BL Gorissen, Y Wang, J Daartz, T Bortfeld, Massachusetts General Hospital, Boston, MA


SU-E-T-130 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose:To ascertain the necessity of a proton gantry, as compared to the feasibility of using a horizontal fixed proton beam-line for treatment with advanced technology.

Methods:To calculate the percentage of patients that can be treated with a horizontal fixed beam-line instead of a gantry, we analyze the distributions of beam orientations of our proton gantry patients treated over the past 10 years. We identify three horizontal fixed beam geometries (FIXED, BEND and MOVE) with the patient in lying and/or sitting positions. The FIXED geometry includes only table/chair rotations and translations. In BEND, the beam can be bent up/down for up to 20 degrees. MOVE allows for patient head/body angle adjustment. Based on the analysis, we select eight patients whose plan involves beams which are still challenging to achieve with a horizontal fixed beam. These beams are removed in the pencil beam scanning (PBS) plan optimized for the fixed beam-line (PBS-fix). We generate non-coplanar PBS-gantry plans for comparison, and perform a robustness analysis.

Results:The percentage of patients with head-and-neck/brain tumors that can be treated with horizontal fixed beam is 44% in FIXED, 70% in 20-degrees BEND, and 100% in 90-degrees MOVE. For torso regions, 99% of the patients can be treated in 20-degree BEND. The target coverage is more homogeneous with PBS-fix plans compared to the clinical scattering treatment plans. The PBS-fix plans reduce the mean dose to organs-at-risk by a factor of 1.1-28.5. PBS-gantry plans are as good as PBS-fix plans, sometimes marginally better.

Conclusion:The majority of the beam orientations can be realized with a horizontal fixed beam-line. Challenging non-coplanar beams can be eliminated with PBS delivery. Clinical implementation of the proposed fixed beam-line requires use of robotic patient positioning, further developments in immobilization, and image guidance. However, our results suggest that fixed beam-lines can be as effective as gantries.

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