Monte Carlo-calculated perturbation correction factors in clinical proton beams using PHITS

TL;DR

This paper uses PHITS simulations to calculate correction factors for proton therapy dosimetry, aiming to reduce uncertainties and improve treatment accuracy.

Contribution

The study provides new reference data for PQ and a novel kQ factor for the PTW 31013 chamber using Monte Carlo simulations.

Findings

Using PHITS reduced the uncertainty in fQ values compared to previous studies.

The kQ factor for PTW 31013 follows trends in cylindrical chambers and is the first Monte Carlo estimation for this chamber.

PQ values deviated by up to 1.7% from unity, indicating variability in chamber response.

Abstract

•The number of proton therapy facilities is currently increasing.•Incorporating fQ values computed using PHITS reduced the uncertainty of f¯QPHITS.•Variation in fQ and PQ was observed depending on the Monte Carlo code employed.

The number of proton therapy facilities is currently increasing.

Incorporating fQ values computed using PHITS reduced the uncertainty of f¯QPHITS.

Variation in fQ and PQ was observed depending on the Monte Carlo code employed.

Accurate absolute dosimetry is essential for achieving high-precision proton beam therapy. Consequently, a comprehensive characterization of the ionization chamber’s response properties is necessary.

This study aimed to evaluate the average fQ using Monte Carlo (MC) code PHITS to assess uncertainties among different MC simulation tools. Additionally, PQ values for PTW 30013, NACP-02, and PTW 31013 ionization chambers are calculated using PHITS to provide new reference data for PQ. Furthermore, a new kQ factor for PTW 31013 chamber is established using MC method, contributing to advancements in proton beam dosimetry protocols.

Monoenergetic proton beams were employed to calculate fQ, kQ, and PQ for Farmer, Semiflex, and plane‐parallel chambers. The absorbed dose deposited within the sensitive volume of each chamber was determined via simulations employing PHITS, thereby providing the basis for the estimation of these factors. Computed fQ values were compared with previous reports, while kQ and PQ were benchmarked against literature and Technical Reports Series No. 398 (TRS-398) Rev.1 guideline.

Incorporating PHITS‐derived fQ values reduced the uncertainty of f¯QPHITS compared to previous findings. The kQ factor for PTW 31013 followed trends observed in cylindrical chambers with varying sensitive volumes; notably, this study represents the first MC estimation of kQ for this chamber. PQ values for values deviated by up to 1.7% from unity.

The data generated in this study provide important insights for refining proton beam dosimetry, contributing to the improvement of treatment precision.

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