Comparison of pencil beam and Monte Carlo calculations with ion chamber array measurements for patient-specific quality assurance

Yu Deng; Zhi Chen; Qianxia Wang; Pablo Yepes; Zhuangming Shen; Hongliang Chen; Jie Li; Michael F. Moyers

Radiation Medicine and Protection (Sep 2022)

Comparison of pencil beam and Monte Carlo calculations with ion chamber array measurements for patient-specific quality assurance

Yu Deng,
Zhi Chen,
Qianxia Wang,
Pablo Yepes,
Zhuangming Shen,
Hongliang Chen,
Jie Li,
Michael F. Moyers

Affiliations

Yu Deng: Shanghai Proton and Heavy Ion Center, Shanghai Engineering Research Center of Proton and Heavy Ion Radiation Therapy, Shanghai 201315, China
Zhi Chen: Shanghai Proton and Heavy Ion Center, Shanghai Engineering Research Center of Proton and Heavy Ion Radiation Therapy, Shanghai 201315, China
Qianxia Wang: Rice University, Houston, TX, 77005, USA
Pablo Yepes: Rice University, Houston, TX, 77005, USA
Zhuangming Shen: Shanghai Proton and Heavy Ion Center, Shanghai Engineering Research Center of Proton and Heavy Ion Radiation Therapy, Shanghai 201315, China
Hongliang Chen: Shanghai Proton and Heavy Ion Center, Shanghai Engineering Research Center of Proton and Heavy Ion Radiation Therapy, Shanghai 201315, China
Jie Li: Shanghai Proton and Heavy Ion Center, Shanghai Engineering Research Center of Proton and Heavy Ion Radiation Therapy, Shanghai 201315, China
Michael F. Moyers: Shanghai Proton and Heavy Ion Center, Shanghai Engineering Research Center of Proton and Heavy Ion Radiation Therapy, Shanghai 201315, China; Corresponding author.

Journal volume & issue: Vol. 3, no. 3
pp. 115 – 122

Abstract

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Objective: To determine under what conditions and criteria comparisons between calculations made with the current clinical treatment planning system (Syngo) and an in-house built TPS (TIMPS) would allow skipping of in-beam portal-specific measurements. Methods: Measurements were made with an array of 24 ion chambers in a water phantom for 227 proton and 313 carbon ion portals with and without a range shifter (RS). These measurements were compared with calculations performed with Syngo and TIMPS using metrics of average dose difference and Gamma index. Results: For proton portals without RS, if a Gamma comparison between TIMPS and Syngo passed using criteria of 90% of tested points being within 3% and 3 mm, then 74% of measurements would agree with both TIMPS and Syngo. For proton portals with RS, more than 80% of measurements would agree with both calculations using the same criteria. For carbon ion portals without RS, if a Gamma evaluation between TIMPS and Syngo passed with criteria of 90% of tested points being within 2% and 2 mm, 85% of measurements would agree with both calculations. For carbon ion portals with RS, if a Gamma evaluation between TIMPS and Syngo passed with criteria of 90% of tested points being within 3% and 3 mm, 60% of measurements would agree with both calculations. Conclusions: Both the pencil beam algorithm in Syngo and the FDC algorithm in TIMPS can provide accurate dose calculations in water for most clinical portals. For about 75% of portals, physicists can perform comparisons of calculations instead of phantom measurements to verify Syngo calculations thereby saving a large amount of beam time. There are some portals, however, such as for low-energy protons without RS and high-energy carbon ions, where agreement between the two calculations and measurements are not yet satisfactory to allow the elimination of all measurements.

Published in Radiation Medicine and Protection

ISSN: 2666-5557 (Online)
Publisher: Elsevier
Country of publisher: Netherlands
LCC subjects: Medicine: Medicine (General): Medical physics. Medical radiology. Nuclear medicine
Website: https://www.sciencedirect.com/journal/radiation-medicine-and-protection

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