Update of the CLRP eye plaque brachytherapy database for photon-emitting sources

Abstract

To update and extend the Carleton Laboratory for Radiotherapy Physics (CLRP) Eye Plaque (EP) dosimetry database for low-energy photon-emitting brachytherapy sources using egs brachy, an open-source EGSnrc application. The previous database, CLRP EPv1, contained datasets for the Collaborative Ocular Melanoma Study (COMS) plaques (10-22 mm diameter) with 103 Pd or 125 I seeds (BrachyDose-computed, 2008). The new database, CLRP EPv2, consists of newlycalculated 3D dose distributions for 17 plaques [8 COMS, 5 Eckert & Ziegler BEBIG, and 4 others representative of models used worldwide] for 103 Pd, 125 I, and 131 Cs seeds. Acquisition and Validation Methods: Plaque models are developed with egs brachy, based on published/manufacturer dimensions and material data. The BEBIG plaques (modelled for the first time) are identical in dimensions to COMS plaques but differ in elemental composition and/or density. Previously-benchmarked seed models are used. Eye plaques and seeds are simulated at the centre of fullscatter water phantoms, scoring in (0.05 cm) 3 voxels spanning the eye for scenarios: (i) 'HOMO': simulated TG43 conditions; (ii) 'HETERO': eye plaques and seeds fully modelled; (iii) 'HETsi' (BEBIG only): one seed is active at a time with other seed geometries present but not emitting photons (inactive); summation over all i seeds in a plaque then yields 'HETsum' (includes interseed effects). For validation, doses are compared to those from CLRP EPv1 and published data.