Author: Xiaoda Cong, Xuanfeng Ding, Gang Liu, Peilin Liu, Lewei Zhao 👨🔬
Affiliation: Department of Radiation Oncology, Stanford University, Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Corewellhealth William Beaumont University Hospital 🌍
Purpose:
This study investigates the dosimetric impact of systematic and random gantry position errors (GPE) during dynamic Spot-Scanning Proton Arc Therapy (SPArc) delivery.
Methods:
Four cases (brain SRS, lung, liver, prostate) were selected to simulate dose perturbations caused by GPE. Treatment plans were generated using an in-home script in RayStation. Dynamic delivery was simulated using a validated model and controller based on the IBA DynamicARC® prototype, with virtual machine logfiles reconstructing delivery details. Systematic (±0.5° to ±2°) and random (0–0.5° to 0–2°) rotational errors per 180° arc were introduced by adjusting gantry rotational velocity. Dosimetric effects were evaluated using target coverage (D98) and gamma-index pass rates (GPR) under 3%/3mm and 2%/2mm criteria with a 10% dose threshold.
Results:
Under the 3%/3mm criterion, all cases achieved GPR >95%. Liver, lung, and prostate plans showed high “robustness” (GPR >99%), while brain SRS was more sensitive to systematic GPE, with GPR dropping to 95.43% at 2° due to smaller targets and steep gradients. Under the stricter 2%/2mm criterion, brain SRS shows the largest decline, with GPR falling to 79.84% (systematic) and 90.63% (random) at 2°. The liver case remained resilient (GPR >97%), while lung and prostate cases achieved GPR >91% (Table 1, Figure 1 in the supporting document).
Conclusion:
This study provides the first quantitative analysis of GPE effects in dynamic SPArc delivery. Systematic GPE has a greater impact than random GPE, with dose perturbations influenced by target size, anatomical complexity, and error magnitude.