Remote auditing of radiotherapy facilities using optically stimulated luminescence dosimeters

Lye, J, Dunn, L, Kenny, J, Lehmann, J, Kron, T, Oliver, C, Butler, D, Alves, A, Johnston, P, Franich, R and Williams, I 2014, 'Remote auditing of radiotherapy facilities using optically stimulated luminescence dosimeters', Medical Physics, vol. 41, no. 3, 032102, pp. 1-10.


Document type: Journal Article
Collection: Journal Articles

Title Remote auditing of radiotherapy facilities using optically stimulated luminescence dosimeters
Author(s) Lye, J
Dunn, L
Kenny, J
Lehmann, J
Kron, T
Oliver, C
Butler, D
Alves, A
Johnston, P
Franich, R
Williams, I
Year 2014
Journal name Medical Physics
Volume number 41
Issue number 3
Article Number 032102
Start page 1
End page 10
Total pages 10
Publisher American Institute of Physics
Abstract Purpose: On 1 July 2012, the Australian Clinical Dosimetry Service (ACDS) released its Optically Stimulated Luminescent Dosimeter (OSLD) Level I audit, replacing the previous TLD based audit. The aim of this work is to present the results from this new service and the complete uncertainty analysis on which the audit tolerances are based. Methods: The audit release was preceded by a rigorous evaluation of the InLight® nanoDot OSLD system from Landauer (Landauer, Inc., Glenwood, IL). Energy dependence, signal fading from multiple irradiations, batch variation, reader variation, and dose response factors were identified and quantified for each individual OSLD. The detectors are mailed to the facility in small PMMA blocks, based on the design of the existing Radiological Physics Centre audit. Modeling and measurement were used to determine a factor that could convert the dose measured in the PMMA block, to dose in water for the facility's reference conditions. This factor is dependent on the beam spectrum. The TPR20,10 was used as the beam quality index to determine the specific block factor for a beam being audited. The audit tolerance was defined using a rigorous uncertainty calculation. The audit outcome is then determined using a scientifically based two tiered action level approach. Audit outcomes within two standard deviations were defined as Pass (Optimal Level), within three standard deviations as Pass (Action Level), and outside of three standard deviations the outcome is Fail (Out of Tolerance). Results: To-date the ACDS has audited 108 photon beams with TLD and 162 photon beams with OSLD. The TLD audit results had an average deviation from ACDS of 0.0% and a standard deviation of 1.8%. The OSLD audit results had an average deviation of −0.2% and a standard deviation of 1.4%. The relative combined standard uncertainty was calculated to be 1.3% (1σ). Pass (Optimal Level) was reduced to ≤2.6% (2σ), and Fail (Out of Tolerance) was reduced to >3.9% (3σ) for the new OSLD audit. Previously with the TLD audit the Pass (Optimal Level) and Fail (Out of Tolerance) were set at ≤4.0% (2σ) and >6.0% (3σ). Conclusions: The calculated standard uncertainty of 1.3% at one standard deviation is consistent with the measured standard deviation of 1.4% from the audits and confirming the suitability of the uncertainty budget derived audit tolerances. The OSLD audit shows greater accuracy than the previous TLD audit, justifying the reduction in audit tolerances. In the TLD audit, all outcomes were Pass (Optimal Level) suggesting that the tolerances were too conservative. In the OSLD audit 94% of the audits have resulted in Pass (Optimal level) and 6% of the audits have resulted in Pass (Action Level). All Pass (Action level) results have been resolved with a repeat OSLD audit, or an on-site ion chamber measurement.
Subject Medical Physics
Keyword(s) OSLD
audit
radiotherapy
Monte Carlo modelling
dosimetry
DOI - identifier 10.1118/1.4865786
Copyright notice © 2014 Am. Assoc. Phys. Med.
ISSN 0094-2405
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Citation counts: TR Web of Science Citation Count  Cited 11 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 11 times in Scopus Article | Citations
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