Room: Karl Dean Ballroom A2
Purpose: Surface dose rate was measured from a curved Â¹â?°â?¶Ru episcleral plaque using a convex windowless extrapolation chamber. Results were compared with measurements made using un-laminated EBT3 film, a scintillation detector at Eckert & Ziegler BEBIG, and alanine pellets at the National Physical Laboratory (NPL).
Methods: A CCB model Â¹â?°â?¶Ru source was acquired as part of an inter-laboratory comparison with the manufacturer and NPL. Surface dose rate measurements were performed with a convex windowless extrapolation chamber developed for this work, and results were compared with on-contact measurements made with un-laminated EBT3 film pieces curved over a spherical Virtual Waterâ„¢ phantom. A Monte Carlo correction for film measurements was generated to account for volume-averaging in the active film layer and backscatter conditions for the phantom versus water. To compare extrapolation chamber measurements with the dose rate result from NPL using alanine pellets in a Perspex phantom, an additional Monte Carlo correction was simulated accounting for differences in surface geometry and phantom backscatter.
Results: Based on five trials, surface dose rate from the convex extrapolation chamber was 2.69 mGy/s with a standard deviation of Â±0.4%. This value was 2.8% higher than the corrected film result for surface dose rate, which was within the combined measurement uncertainties. Furthermore, the convex extrapolation chamber result was 4.2% lower than the surface dose rate determined at BEBIG and 4.2% higher than the corresponding value from NPL for the same source.
Conclusion: A convex windowless extrapolation chamber was developed as a primary measurement device to determine surface dose rate from curved Â¹â?°â?¶Ru eye plaques. Through an inter-laboratory comparison, the accuracy of surface dose rate results from current dosimetry methods was verified within 4.2% for measurements made with radiochromic film, a scintillation detector, and alanine.