Monte Carlo investigation of Ge-doped silica fiber detectors for precision small field dosimetry

Accurate dosimetry in small radiation fields remains a critical challenge in modern radiotherapy due to high dose gradients and limited detector spatial resolution. This study investigates the dosimetric performance of Ge-doped silica fiber radioluminescence (RL) detectors for small field measurements through Monte Carlo simulations using the TOPAS tool. Reference data from IAEA database were utilized for implementation of small radiation fields and validation, by comparing experimental beam profile and depth dose measurements for various field sizes. Quality dependence factors (QDFs) were calculated based on the formalism of the IAEA-AAPM working group, considering a Varian Clinac iX linear accelerator with a 10×10 cm 2 reference field and various small fields of 0.5×0.5 cm 2 , 1×1 cm 2 , 2×2 cm 2 and 4×4 cm 2 . The study explored different fiber detector diameters from 125 μm to 2 mm to optimize spatial resolution for small field dosimetry. Simulated electron spectra in various situations were analyzed in both water and fiber volumes to understand reasons behind detector response variations. Notably, the detector diameter significantly influenced quality dependence, with competing effects between energy dependence and a field size dependent spectral discrepancy leading to an optimal balance at a 0.5 mm fiber diameter. Calculated QDFs aligned well within the range reported for other detector types, supporting the applicability of Ge-doped silica fiber RL detectors for precise dose measurements in small radiation fields, offering a potential alternative for advanced radiotherapy applications. • Monte Carlo simulations assess QDF in Ge-doped silica fiber dosimeters • Spectral differences in fiber volume and water affect dose measurement • Smaller fiber diameters show higher low-energy electron contribution • 0.5 mm diameter identified as optimal with minimum QDF correction needed • Results support fiber dosimeter customization for small-field applications