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Dose Enhancement Measurements at High-Z Dental Materials Using Radiochromic EBT-2 Films


B Poppe

A Schoenfeld1,2, D Poppinga1,2, B Poppe1,2*, N Chofor1,2, (1) University Oldenburg, Oldenburg, Germany (2) Pius Hospital, Oldenburg, Germany

SU-E-T-65 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

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 probe'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 10x10cm² 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 an alignment 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:
Conclusion: 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 with approximately 3mm of water equivalent material.

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