Correction factors and uncertainties in in-vivo point dose measurements

In-vivo dosimetry is associated with high measurement uncertainties, partly due to deviations in detector response under clinical compared to calibration conditions, especially for IMRT/VMAT, stereotactic radiosurgery, and total body irradiation. This study proposes a procedure for detector calibration and correction, evaluates its feasibility, quantifies uncertainties, and provides guidance for determining correction factors. Correction factors for in-vivo ionization chambers (ICs), Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), and Optically Stimulated Luminescence Detectors (OSLDs) were obtained. Correction factors for field size, dose rate, angular, temperature dependence and response variation were derived experimentally. Correction factors were applied to measurements of irradiation plans simulating clinical treatments, including static fields, stereotactic, and total body irradiation using an anthropomorphic phantom. Measured data with and without applied correction factors were compared to doses calculated by treatment planning systems (TPS). Application of correction factors improved agreement between calculated and measured doses by up to 7.5% for MOSFETs, 3.1% for ICs, and 0.9% for OSLDs. Deviations between detectors were reduced by up to 0.6%. Maximum relative dose errors without correction factors compared to the uncertainties of the correction factors highlighted the benefit of corrections, particularly for MOSFETs (11.5% error vs. 4.4% uncertainty) and ICs (8.6% vs. 0.7%). For OSLDs, maximum uncertainties (6.5%) were slightly higher than the observed dose errors (4.5%). The results indicate, despite the uncertainties, both the necessity and benefit of applying the described correction factors.