A Alshreef*, B Rogers, P Alaei, P Bolan, C Ferreira, University of Minnesota, Minneapolis, MN

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  A Alshreef

PO-GePV-T-43 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: To develop an end-to-end test for GammaTile® brachytherapy brain implants by performing CT and MRI image registration, treatment planning dose calculation, and dose delivery verification.

Methods: A custom-made Solid Water® HE (SW) phantom (30 cm × 30 cm × 2 cm) was cut to hold a single GammaTile (GT Medical Technologies, Inc., Tempe, AZ). A hydrated collagen GammaTile (GT) containing four Cs-131 (3.5 U) seeds located at a nominal distance of 3 mm from the textured side of the tile was placed in the custom-made phantom. Additional SW slabs were used above and below the phantom containing the GT to provide full backscatter conditions. The tile and phantom were scanned using CT and MRI (MP-RAGE) sequences, both with 1 mm slice thickness. The CT and MRI images were registered using Velocity™ software. Distances from the center of each seed to the tile surface were measured from the rigid image registration to estimate the seed positional accuracy within the tile. Planar doses parallel to the tile surface at 0 mm and 5 mm depths in SW were measured using EBT3 Gafchromic film. Measured doses were compared to calculated doses using Eclipse BrachyVision treatment planning system (TPS). Measurements were repeated for 6 tiles from different batches.

Results: Seeds were visible on the CT images and collagen tile was clearly identified on the MRI images. From the image registration, a mean distance of 2.95 mm (range 2.69-3.17 mm) was measured from the center of the seeds to the textured side. Average differences in TPS calculated doses and film measurements were 7.99% and 5.67% for 0 mm and 5 mm depths, respectively.

Conclusion: The proposed End-to-End test considered all the clinical dosimetric steps for a GT implant. Doses calculated from the TPS were verified for a single GT imbedded in a custom-made phantom.

Funding Support, Disclosures, and Conflict of Interest: research supported by GT medical grant

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