Author: ChangSeon Kim, Andrew Lukban, Mario Serrano-Sosa, Nadia M. Vassell 👨🔬
Affiliation: Mount Sinai Beth Israel 🌍
Purpose: Ocular HDR brachytherapy is used as an alternative treatment for eye cancer, especially with extrascleral extension in the orbit. This complex procedure inserts catheters into the orbit affixed to the skin with sutured buttons and medical epoxy. In this work we provide an end-to-end comprehensive dose verification for ocular HDR brachytherapy using iridium-192 calibrated OSLDs and a 3M phantom skull.
Methods: One orbital cavity of a 3M phantom skull was drilled out. A custom OSLD holder was 3D printed and placed into the orbital cavity. Ballistic gelatin comprising of a 1:8 ratio of gelatin powder and water was then poured to mold into the orbital cavity around the OSLD holder. Five plastic catheters were inserted into the orbit to simulate an ocular HDR treatment. Marker wire was placed into each needle to guide digitization. Planning CT was acquired using 1mm slices thickness. A treatment plan was created and dose to the OSLD was determined from TPS. On the same day of irradiation, an OSLD dose calibration was performed using an “in water” custom-made in-house jig with a calibrated Ir-192 source and TG43 dose formalism. The phantom skull was irradiated and OSLD dose was calculated using the Landauer MicroStar system and same day dose calibration factor.
Results: The ballistic gelatin mold held strongly during CT showing minimal air gaps around OSLD holder. Weak and strong readings both showed less than 4% difference between planned and delivered OSLD dose. This is consistent with similar testing previously performed by this institution using this method.
Conclusion: End-to-end testing is an important process in evaluating multiple steps of a lengthy treatment procedure. In this work, we utilized a phantom and Ir-192 calibrated OSLDs to enable us to follow a typical ocular HDR procedure and verify our delivered dose is both accurate and consistent.