Room: AAPM ePoster Library
Purpose: A novel device (Alpha Tau Medical Ltd.) has been developed to load permanent seeds in FNA needles for EUS-guided diffusive alpha-emitters brachytherapy. This study proposes a replicable calibration geometry to verify the Ra-224 activity of the loading devices.
Methods: A calibration geometry (4 cm separation and 5 mm steel absorber) using the shipping material has been used to determine ?-dose-rate to Ra-224 activity calibration factors for a portable GM counter (Rotem, RAM GENE-1 Mark II). Calibration measurements (n=10) using 1 and 2 cm loading devices (151.2 & 350.8 kBq) were performed with the daughter products in secular equilibrium. The loading devices were removed and placed back between each measurement with a 20s delay. A 3D-printed PLA support was then added. A third geometry without absorber was also considered.
Results: The calibration factors of the 1 cm loading device were found to be 12.97 ± 1.32, 11.65 ± 0.32 and 8.77 ± 0.22 kBq·h/µSv for the absorber-only, absorber & 3D-support and 3D-support-only geometries. An accuracy test was performed by verifying the activity of two additional 1 and 2 cm loading devices (147.5 & 350.1 kBq) using these calibration factors. Relative errors of 13.52% & 1.05%, 0.33% & -0.50% and 0.34% & 8.28% were found for the 1 & 2 cm loading devices using the absorber-only, the absorber & 3D-support and 3D-support-only geometries respectively.
Conclusion: The low activity and self-attenuation from the protective steel capsule makes source verification as recommended by Task Group 53 challenging. This work proposes a replicable calibration geometry for use with a GM counter to allow a fast verification of the loading device activity. A ~70% reduction in measurement uncertainties was obtained with the use of a 3D-printed support. Finally, better accuracy was obtained when using an absorber material to remove low-energy gammas subject to attenuation.
Funding Support, Disclosures, and Conflict of Interest: This work was performed as part of a clinical trial funded by Alpha Tau Medical Ltd. (Tel Aviv, Israel). The author also acknowledges funding from the National Research Council Canada, TransMedTech and Medtech institutes.