SU-E-T-65: Dose Enhancement Measurements at High-Z Dental Materials Using Radiochromic EBT-2 Films

Abstract

Purpose: The purpose of this work is to investigate the dose enhancement at high-Z interfaces using radiochromic films. In radiation therapy the problem occurs for instance in H&N treatments. The dose enhancement at dental crowns and implants may cause necrosis of tissue or damage to the jawbone. In this study, typical dental materials like dental gold, Wirobond (Co-Cr alloy) zirconium dioxide and titanium were investigated. Methods: Dose enhancement effects were investigated for the following materials: dental gold alloy (73% gold, 16% aurum, 11% other), cobalt-chromium alloy (61%cobalt, 29% chromium, 10% other), zirconium dioxide (stabilized with 5% Y2O3) and titanium. The proximal and distal dose distribution near the robe's interfaces was measured with a slab geometry setup consisting of four EBT-2 films separated by 0.5mm/0.5mm/1mm RW3. This setup was placed between two 6cm stacks of RW3 functioning as build-up material. At a Siemens Primus linac, a 6MV photon beam with a field size of 10×10cm2 and a source to surface distance of 100cm was used. The EBT2 films were digitized at a scanning resolution of 72dpi using an Epson 10000XL flatbed scanner with a transparency unit. Furthermore the films were fixed in analignment frame to prevent Newton rings in the scanned image. The results were verified with Monte Carlo simulations using DOSRZnrc/EGSnrc.Results: The dose enhancement at the proximal surface of the dental gold alloy is 59%, while the other three materials showed enhancements ranging between 20%–25%. The Monte Carlo simulations confirmed these results. In all cases, the dose enhancement decreases to less than 10% at a proximal distance of 3mm. Conclusions: The dose enhancements near dental implant materials should be properly accounted for in treatment plans and, if possible, a safety distance should be created around crowns withapproximately 3mm of water equivalent material.