Purpose: To propose an approach for independent determination of the absorbed dose to water (D(water)) depth-dose curves traceable to the external beam primary standards of absorbed dose to water for the dosimetry of ophthalmic ¹⁰⁶Ru plaques used in brachytherapy.
Methods: A microSilicon diode was cross-calibrated against a reference air ionization chamber in terms of the D(water) in a 6 MeV external electron beam. The diode and a high precision setup equipment was used to determine the D(water) depth-dose curves for ¹⁰⁶Ru CCB-type plaques manufactured in 2018 and 2019. Detector blueprints were available and a Monte Carlo (MC) code system PENELOPE-2018 was used to correct for the absorbed-dose energy dependence of the detector between calibration and measurement beam qualities (from 2 to 10 mm distance from the plaque surface). The results were compared with the D(water) depth-dose curves calculated with MC in the absence of the detector and with those determined by the vendor with a plastic scintillator with other traceability. Further analysis was made to determine possible reasons of the discrepancies.
Results: Differences between experimentally determined D(water) depth-dose curves using the microSilicon diode and those provided by the vendor were from -5 % at the reference depth of 2 mm to nearly 20 % at 10 mm depth. The MC-calculated D(water) depth-dose curves in the absence of the detector differed systematically from the vendor values but agreed within their provided uncertainties with the values obtained using the microSilicon detector.
Conclusion: We show that a detector calibration in external beam allows for accurate and independent dosimetry of ¹⁰⁶Ru CCB plaques with lower uncertainties than following an existing method of plaque calibration.