Advancing Proton Beam Dosimetry in Water: A Particle and Heavy Ion Transport Code System Monte Carlo Simulation of Depth Dose, Range Characteristics, and Linear Energy Transfer Distributions.

Aim: Proton therapy is a cutting-edge radiation oncology technique that uses the Bragg peak to deliver highly localized radiation doses to tumors while minimizing exposure to nearby healthy tissues. For accurate treatment planning, proton depth-dose distributions, range, and linear energy transfer (LET) must be accurately characterized. Materials and Methods: In this study, Monte Carlo (MC) simulations were performed using the Particle and Heavy Ion Transport code System to investigate fundamental dosimetric characteristics of therapeutic proton beams in a water phantom. To investigate depth-dose profiles, proton range, full width at half maximum (FWHM) of the Bragg peak, and peak-to-entrance ratio (PER), monoenergetic proton beams with energies of 50, 100, 150, 200, and 250 MeV were simulated. Additionally, for studying changes in energy deposition along the beam path, dose-averaged LET distributions were examined for specific proton energies of 160 MeV and 250 MeV. Results: The findings show that as proton energy increases, the Bragg peak systematically shifts toward deeper depths while the proton range increases nonlinearly. Changes in dose localization and entrance dose contribution are reflected in the FWHM and PER, which clearly show energy dependence. LET values remain low in the entrance region and increase sharply near the Bragg peak, with high-energy protons exhibiting elevated LET at the distal end of their range. The computed depth-dose ranges and characteristics agree well with published reference data. Conclusion: This study provides a systematic MC-based evaluation of proton beam dosimetric and LET characteristics in water, offering useful insights relevant to proton therapy dose optimization and treatment planning.