Evaluating the Impact of Spot Position Errors on Dose Distribution: A Comparison between Spot-Scanning Arc Therapy (SPArc) and Intensity-Modulated Proton Therapy (IMPT)

Authors

Peilin Liu, Corewell Health
Lewei Zhao
Gang Liu
Xiaoda Cong, Corewell Health
Xiaoqiang Li, Corewell Health
Xuanfeng Ding, Corewell Health

Document Type

Conference Proceeding

Publication Date

10-2024

Publication Title

Medical Physics

Abstract

Purpose: To quantitatively investigate the impact of spot position error (PE) on the dose distribution in (Spot-scanning arc therapy) SPArc plans versus Intensity-Modulated Proton Therapy (IMPT).

Methods:

Four representative disease sites, including brain, lung, liver, and prostate cancers, were retrospectively selected. Spot position errors were simulated during dynamic SPArc treatment delivery. Two types of errors were generated, including randomized error and systematic error. For each random error scenario, they were further examined across four sub-scenarios (25%, 50%, 75%, and 100% of spots affected) at 1 mm and 2 mm deviations.The randomized errors used two categories with and without Gaussian distribution (PE_ran-GS, PE_ran-UN). Systematic error was simulated by shifting all the spot positions uniformly by 2mm in various directions. The Gamma-index Passing Ratio (GPR) was utilized to evaluate dose perturbations relative to nominal plans.

Results: For PE_ran-GS of 1mm, SPArc and IMPT showed comparable performance, both exceeding a 95% GPR. However, SPArc could provide better GPR in the presence of 2mm PE_ran-GS (figure1). For system error of 1mm, SPArc and IMPT maintained the feasible GPR of over 99%. As the criterion is stricter to 1%/1mm, SPArc provides much better GPR compared to IMPT. As PE of 2mm, SPArc also shows much better GPR. More specifically, SPArc could provide 99.40±0.74%, 93.66±4.75% and 61.53±10.30% of GPR for 3mm/3%, 2mm/2% and 1mm/1% criteria in comparison with IMPT . In the brain case, SPArc could provide smaller dose difference for the rectum (maximum dose: 1.08% vs 17.5%) and bladder (mean dose: 0.61% vs 7.07%) compared to IMPT (table1) with similar differences for other OARs.

Conclusion:

SPArc demonstrates greater resilience to spot position error than IMPT compared to the conventional IMPT. This study offers valuable quantitative data to support future quality assurance investigations in SPArc treatments.

Volume

51

Issue

10

First Page

7785

Recommended Citation

Liu P, Zhao L, Liu G, Cong X, Li X, Ding X. Evaluating the impact of spot position errors on dose distribution: a comparison between spot-scanning arc therapy (SPArc) and intensity-modulated proton therapy (IMPT). Med Phys. 2024 Oct;51(10):7785. doi:10.1002/mp.17457.

Comments

American Association of Physicists in Medicine 66th Annual Meeting & Exhibition, July 21-25 2025, Los Angeles, CA