Calibration of 90Sr + 90Y planar sources using thermoluminescent dosimeters, radiochromic film, a PMMA phantom and Monte Carlo simulation

Abstract

In some parts of Brazil, 90Sr + 90Y clinical applicators are still in use for dermatological and ophthalmic treatments, even with new technologies worldwide, because they are of lower cost and easier use. Calibration and periodic recalibration of these applicators to verify the absorbed dose rate is essential to ensure accuracy in clinical treatments. This work focused on an alternative calibration method for 90Sr + 90Y sources, utilizing thermoluminescent dosimeters, radiochromic films, and Monte Carlo simulation, following international recommendations. Regarding radiation doses, the thermoluminescent response of μLiF pellets and the response of radiochromic films were evaluated to determine reproducibility, linearity of response, and their dose-response curves. Additionally, radiochromic films were used to determine the dose rate distribution across the areas of the clinical applicators, and the μLiF dosimeters were used as a comparative measure in determining the axial central dose rate of clinical applicators. A PMMA phantom was developed and utilized to perform the calibrations. Monte Carlo simulation was essential for replicating the radioactive properties and correction factors for radiation and deposited doses in two media and at different distances from these sources. This work presents a practical and cost-effective method for calibrating planar 90Sr + 90Y radioactive sources; it was developed to serve locations that lack state-of-the-art technological resources, and was validated for effectiveness and broad applicability. The developed technique allows for long-distance calibration using dosimetric materials, provided they are properly handled and shielded.