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

Background: 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. Purpose: This study aimed to evaluate the average f_Q using Monte Carlo (MC) code PHITS to assess uncertainties among different MC simulation tools. Additionally, P_Q values for PTW 30013, NACP-02, and PTW 31013 ionization chambers are calculated using PHITS to provide new reference data for P_Q. Furthermore, a new k_Q factor for PTW 31013 chamber is established using MC method, contributing to advancements in proton beam dosimetry protocols. Methods: Monoenergetic proton beams were employed to calculate f_Q, k_Q, and P_Q 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 f_Q values were compared with previous reports, while k_Q and P_Q were benchmarked against literature and Technical Reports Series No. 398 (TRS-398) Rev.1 guideline. Results: Incorporating PHITS‐derived f_Q values reduced the uncertainty of f¯_Q^PHITS compared to previous findings. The k_Q factor for PTW 31013 followed trends observed in cylindrical chambers with varying sensitive volumes; notably, this study represents the first MC estimation of k_Q for this chamber. P_Q values for values deviated by up to 1.7% from unity. Conclusion: The data generated in this study provide important insights for refining proton beam dosimetry, contributing to the improvement of treatment precision.