G Liu^1,2*, L Zhao¹, D Yan¹, G Janssens³, X Li¹, X Ding¹, (1) Beaumont Health System, Royal Oak, MI,USA (2)Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China (3)Ion Beam Applications SA

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  G Liu

PO-GePV-M-229 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: The tolerance window has been playing a critical role in the arc treatment delivery in the photon treatment. However, there is no study has been done on the proton arc delivery module yet. This is the first investigation of Spot-scanning proton arc (SPArc) treatment delivery time and accuracy with various delivery tolerance window settings.

Methods: SPArc plans were generated for four representative disease sites (lung, brain, head neck, liver cancer) with an angle sampling frequency of 2.5 degrees. An in-house dynamic arc controller was used as a simulator mimicking the arc treatment delivery with various tolerance windows (±0.25, ±0.5, ±1, and ±1.25 degrees). The controller generates machine mechanical and irradiation information (logfilesimulation) with one degree of sampling frequency during the arc delivery simulation, such as gantry speed, acceleration and deceleration, spot position, and delivery sequence similar to the actual machine logfiles. The logfilesimulation was then imported to the treatment planning system (TPS) to reconstruct the delivered dose distribution and compared to the initial SPArc plan. A three-dimensional gamma index with criteria 3mm/3% was used to assess delivery accuracy quantitatively. Total treatment delivery time and relative lost time (dynamic arc delivery time –fix beam delivery time)/fix beam delivery time ×100) were reported.

Results: The 3D gamma pass ratio was great than 97% for all the cases. The total delivery time for dynamic arc delivery increased with the decreasing of delivery tolerance windows length. The average delivery time and the relative lost time (%) were 1024±516s(235%±31%),527±262s(73%±13%),375±185s(23%±7%), 322±149s(7%±1%), 311±141s(5%±2%) for tolerance windows as ±0.25, ±0.5, ±1, and ±1.25 degrees respectively.

Conclusion: This is the first investigation of SPArc delivery time and accuracy with different delivery tolerance window settings. The simulated result indicated that the SPArc plan with 2.5degrees sampling frequency can be delivered efficiently and accurately with ±1 or ±1.25degrees tolerance window.

Funding Support, Disclosures, and Conflict of Interest: This study was supported by the research fundings from Ion Beam Application Inc.(IBA) and Beaumont Health Herb and Betty Fisher Research Seed Grant Award. Xuanfeng Ding, Xiaoqiang Li, and Di Yan have a patent related to the Particle Arc Therapy (WO2017156419).The patent has been licensed to Ion Beam Application, Belgium.

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