Author: ChangSeon Kim, Andrew Lukban, Mario Serrano-Sosa, Nadia M. Vassell 👨🔬
Affiliation: Mount Sinai Beth Israel 🌍
Purpose: Commissioning of Flexitron HDR horizontal Leipzig applicators typically includes indirect or direct output verification, using a well chamber specific Revised Correspondence Factor (CFrev) or a suitable detector such as a parallel-plate chamber, respectively. In addition to those methods, we describe a procedure for end-to-end testing of horizontal Leipzig applicators with Ir-192 calibrated OSLDs via PDD measurements.
Methods: OSLDs were calibrated using Ir-192 and a custom designed treatment jig modelled with CAD and 3D-printed. This jig allows for the reproducible and rigid placement of the OSLD detector plane. The design of the 3D printed jig was to reduce partial-volume effects by ensuring that the detector plane can be set parallel to treatment isodose lines at various distances. Similarly, a horizontal Leipzig applicator fixture was modelled and 3D-printed which reproducibly positioned the OSLDs along the Leipzig applicator's central axis. The fixture also allowed for accurate measurements at various depths, when using different thickness of solid water as the exposure medium. For horizontal Leipzig applicators with nominal diameters of 3, 2, and 1 cm, expected doses in water at different depths were calculated from Monte-Carlo based dose tables in the literature and compared to measured doses using Ir-192 calibrated OSLDs.
Results: Measured PDDs for the 3 Leipzig sizes used were within 2.5% of Monte-Carlo values. This is within the same magnitude of percentage error obtained from well chamber CFrev methods and conventional parallel-plate chamber techniques: within 2% and 3%, respectively.
Conclusion: Ir-192 calibrated OSLD end-to-end testing is a complementary method that may be used in the commissioning of Leipzig applicators in HDR.