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Published on: March 11, 2021
Evaluation of a water phantom detector-applicator setup for independent experimental verification of 106Ru ocular
Simon Dahlander1,2, Michael Andrássy3, Daniela Frömberg3
1Department of Oncology Pathology, Karolinska Institute, Stockholm, Sweden.
Background:
106Ru ophthalmic brachytherapy (BT) applicators are used for treating ocular tumors. While manufacturer-provided dosimetry data is commonly used for treatment planning, independent quality assurance (QA) measurements are crucial. However, there is a lack of dedicated equipment and standardized protocols for clinical verification of 106Ru depth-dose distributions.
Purpose:
The BetaCheck-106™ is a prototype compact water phantom detector-applicator setup enabling high precision alignment of 106Ru applicators and detectors. We assess the setup's compatibility with three commercially available detectors (microSilicon, microSilicon X and microDiamond) and its performance in determining full 1D depth-current curves with these detectors. In addition, data from clinical QA-tests of 20 106Ru applicators was used to estimate inhomogeneities in the applicator's 106Ru coating.
Methods:
Measurements were conducted on two 106Ru applicators with different activity levels, one had been in clinical service for one year and one was measured before clinical use. Dose rates were recorded at 1 mm intervals from 2 mm to 10 mm in water using the BetaCheck-106™ setup with the three detectors. Measurement precision and detector response were analyzed. Separately, inter-applicator variability was analyzed using the aforementioned measurements of 20 106Ru applicators.
Results:
The BetaCheck-106™ demonstrated exceptional setup reproducibility (0.23%), enabling precise depth-resolved measurements. Both of the silicon diode detectors examined provided stable and reproducible measurements. The diamond detector performed reproducibly for the high-activity applicator but exhibited depth-dependent signal instability for the low-activity source, likely due to the detector's lower sensitivity. Normalized depth-signal curves for the three detectors all had similar shape. Analysis of measured current per activity of 20 106Ru applicators revealed a depth dependent inhomogeneity effect decreasing with depth.
Conclusions:
The BetaCheck-106™ provides practical high-reproducibility positioning of detector and applicator for 106Ru applicator measurements in water. The silicon detectors successfully characterized both high and low activity applicators up to 10 mm water depth. The diamond detector proved viable for measurements of the applicator with activity 17.8-18.4 MBq, but it lost stability with depth when measuring the one-year old 8.3 MBq activity applicator.
