Experimental and computational dosimetry in an integrated workflow for remote audits in Ir-192 interstitial brachytherapy: Development and pilot implementation

Abstract

Purpose: This work describes the development and pilot implementation of a comprehensive remote dosimetry audit for Ir-192 high-dose-rate interstitial brachytherapy, integrating independent experimental and computational dosimetry within a unified workflow.Methods: A compact water-equivalent phantom accommodating two plastic catheters, ten optically stimulated luminescent dosimeters (OSLDs), and two radiochromic films was designed to enable independent point-approximating and 2D dose measurements. A user-selected treatment plan with 36 source dwell positions was generated in a clinical treatment planning system (TPS), accounting for dosimeter dose ranges. Computational audit testing was performed by analyzing DICOM-RT files and conducting Monte Carlo (MC) simulations to obtain independent 3D dose calculations for the same plan and phantom geometry. Dosimetry results were compared to TPS calculations (TG43 and a Model Based Dose Calculation Algorithm, MBDCA) using the 3D Gamma Index (GI) test, dose difference maps, and dose-volume histogram comparisons, wherever applicable. Procedures were optimized to minimize clinical workload.Results:The pilot study was completed within ten days of phantom delivery. Measurement corrections were applied when necessary using correction factors from side studies. GI criteria were adapted to the uncertainty of each dosimetry system. Excellent agreement between MBDCA and experimental or MC results was observed. Within the volume of interest, TG-43 systematically overestimated dose relative to MC results (median difference: +2.16%), attributed to missing scatter conditions and phantom material.Conclusion:Despite the labor-intensive workflow, the protocol is suitable for remote Ir-192 audits with acceptable uncertainties. Combining experimental and computational dosimetry enhances audit robustness and supports comprehensive brachytherapy auditing programs.