Plaque-adaptive flexible film dosimetry system for Ru-106 plaque brachytherapy commissioning and quality assurance

Ruthenium-106 (Ru-106) plaque brachytherapy is an established treatment modality for choroidal melanoma that delivers localized beta radiation while sparing surrounding ocular structures. It is widely used in Europe and parts of Asia, whereas COMS Iodine-125 and Palladium-103 plaques remain the standard in the United States. However, its concave geometry presents challenges for accurate dose verification, as conventional flat dosimeters are ill-suited for use during commissioning and quality assurance (QA).

This study aimed to assess the feasibility and dosimetric accuracy of a plaque-adaptive flexible film dosimeter (PFD) for planar and central axis (CAX) dose measurements in Ru-106 plaque brachytherapy.

The PFD consisted of an active layer of lithium salt of pentacosa-10,12-diynoic acid (LiPCDA) enclosed between upper and lower silicone sheets. The flexible film was shaped to conform to the curvature of the Ru-106 plaques and mounted within a dual-layer film holder. A 3D-printed QA tool was used for reproducible positioning. Dose measurements were performed at depths of 1 and 3 mm for CCA, COB, and CIB plaque types using a dual-film configuration. Planar dose distributions were assessed at 33 manufacturer-certified reference points at a 1 mm depth. CAX dose profiles were independently acquired using a microDiamond detector in a water phantom. All measurements were compared with manufacturer-certified reference data. Calibration curves were established based on optical density and dose uncertainties were analyzed.

The dose ratio between 1 and 3 mm depths measured with the PFD differed by -0.2% to 0.4% from the reference data across all plaque types. Planar dose measurements at 33 points yielded a mean difference of 3.0%  ±  2.0% from reference values. In the high-dose central region, the mean differences for CCA, COB, and CIB were 2.1%  ±  0.8%, 2.1%  ±  0.8%, and 2.2%  ±  0.7%, respectively. CAX dose profiles measured with a microDiamond detector differed by 0.89%  ±  0.58%. Total dose uncertainty ranged from 4.43% at 0.3 Gy to 4.19% at 2.4 Gy.

The PFD enabled accurate and high-resolution dose measurements on the curved surfaces of Ru-106 plaques. Both planar and CAX measurements demonstrated strong agreement with manufacturer-certified reference data across all plaque types. This system offers a practical and reproducible solution for commissioning and QA in Ru-106 plaque brachytherapy, supporting its clinical integration for choroidal melanoma treatment.