Investigate gantry position error effect on dynamic spot-scanning proton arc (SPArc) therapy

Area of Science:

• Radiation Oncology
• Medical Physics
• Proton Therapy

Background:

• Spot-scanning proton arc therapy (SPArc) offers improved dose conformity for complex targets through dynamic delivery.
• Dynamic delivery techniques are susceptible to gantry position errors (GPEs), potentially compromising treatment accuracy.
• Quantitative assessment of GPEs' dosimetric impact on SPArc is needed for clinical implementation.

Purpose of the Study:

• To quantitatively evaluate the dosimetric impact of systematic and random GPEs during dynamic SPArc delivery.
• To assess the sensitivity of different treatment sites (brain SRS, lung, liver, prostate) to GPEs.

Main Methods:

• Twelve clinical cases across various cancer sites were analyzed under simulated systematic and random GPEs (±0.5° to ±2°).
• SPArc plans were generated using RayStation and simulated treatment delivery using a validated IBA DynamicARC® system model.
• Dosimetric impact was assessed by analyzing target coverage (D98) and gamma passing ratios (GPR) under 3%/3 mm and 2%/2 mm criteria.

Main Results:

• Under the 3%/3 mm criterion, GPR remained >98% for all sites, with lung, liver, and prostate exceeding 99.4% even at 2° systematic GPE.
• Brain SRS cases were most sensitive; GPR dropped to 89.52% under 2%/2 mm and 2° systematic GPE, while other sites maintained >93%.
• Random GPEs had minimal impact, with all plans achieving >96% GPR even under the strictest 2%/2 mm criterion.

Conclusions:

• Systematic GPEs pose a greater dosimetric risk than random GPEs in SPArc, with varying impact based on disease site and error magnitude.
• Brain SRS is particularly sensitive to systematic GPEs, necessitating stringent quality assurance.
• Findings can inform machine quality assurance protocols and error tolerance thresholds for clinical SPArc implementation.