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Inter-Laboratory Comparison for Surface Dose Rate From a Ru-106 Episcleral Plaque Measured with a Convex Windowless Extrapolation Chamber, EBT3 Film, a Scintillation Detector, and Alanine Pellets

J Hansen*, W Culberson , L DeWerd , university of Wisconsin-Madison, Madison, WI


(Sunday, 7/29/2018) 5:05 PM - 6:00 PM

Room: Karl Dean Ballroom A2

Purpose: Surface dose rate was measured from a curved ¹��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 ¹��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 Water™ 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 ±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 ¹��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.


Eye Plaques, Extrapolation Chamber, Surface Dose


TH- Brachytherapy: Dose measurement

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