Development and implementation of a remote audit tool for high dose rate (HDR) Ir‐192 brachytherapy using optically stimulated luminescence dosimetry. Issue 11 (22nd October 2013)

• Record Type: Journal Article
• Authors: Casey, Kevin E.; Alvarez, Paola; Kry, Stephen F.; Howell, Rebecca M.; Lawyer, Ann; Followill, David
• Is Part Of: Medical physics. Volume 40:Issue 11(2013)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2013-10-22
• Subjects: Therapeutic applications, including brachytherapy -- Radiation sources -- Dosimetry/exposure assessment; aluminium compounds -- biomedical equipment -- brachytherapy -- dosimetry -- iridium -- luminescence -- measurement uncertainty -- phantoms; HDR -- brachytherapy -- OSL -- audit -- RPC; Radiation therapy -- Scintigraphy; Dosimetry -- Nanodots -- Brachytherapy -- Optically stimulated luminescence -- Infrared sources -- Error analysis -- Ozone -- Medical treatment planning -- Photons -- Electric measurements; Medical physics -- Periodicals; Medical physics; Geneeskunde; Natuurkunde; Toepassingen; Biophysics; Periodicals; Periodicals; Electronic journals; 610.153
• DOI: 10.1118/1.4824915
• Languages: English
• ISSNs: 0094-2405

Abstract

Abstract : Purpose: : The aim of this work was to create a mailable phantom with measurement accuracy suitable for Radiological Physics Center (RPC) audits of high dose‐rate (HDR) brachytherapy sources at institutions participating in National Cancer Institute‐funded cooperative clinical trials. Optically stimulated luminescence dosimeters (OSLDs) were chosen as the dosimeter to be used with the phantom. Methods: : The authors designed and built an 8 × 8 × 10 cm 3 prototype phantom that had two slots capable of holding Al2 O3 :C OSLDs (nanoDots; Landauer, Glenwood, IL) and a single channel capable of accepting all 192 Ir HDR brachytherapy sources in current clinical use in the United States. The authors irradiated the phantom with Nucletron and Varian 192 Ir HDR sources in order to determine correction factors for linearity with dose and the combined effects of irradiation energy and phantom characteristics. The phantom was then sent to eight institutions which volunteered to perform trial remote audits. Results: : The linearity correction factor was k L = (−9.43 × 10 −5 × dose) + 1.009, where dose is in cGy, which differed from that determined by the RPC for the same batch of dosimeters using 60 Co irradiation. Separate block correction factors were determined for current versions of both Nucletron and Varian 192 Ir HDR sources and these vendor‐specific correction factors differed by almost 2.6%. For the Nucletron source, the correction factor was 1.026 [95% confidence interval (CI) = 1.023–1.028], and for the Varian source, it was 1.000 (95% CI = 0.995–1.005). Variations in lateral source positioning up to 0.8 mm and distal/proximal source positioning up to 10 mm had minimal effect on dose measurement accuracy. The overall dose measurement uncertainty of the system was estimated to be 2.4% and 2.5% for the Nucletron and Varian sources, respectively (95% CI). This uncertainty was sufficient to establish a ±5% acceptance criterion for source strength audits under a formal RPC audit program. Trial audits of four Nucletron sources and four Varian sources revealed an average RPC‐to‐institution dose ratio of 1.000 (standard deviation = 0.011). Conclusions: : The authors have created an OSLD‐based 192 Ir HDR brachytherapy source remote audit tool which offers sufficient dose measurement accuracy to allow the RPC to establish a remote audit program with a ±5% acceptance criterion. The feasibility of the system has been demonstrated with eight trial audits to date.