Development And Implementation Of A Remote Audit Tool For High Dose Rate (Hdr) 192Ir Brachytherapy Using Optically Stimulated Luminescence Dosimetry

Author

Kevin Casey, The University of Texas Graduate School of Biomedical Sciences at HoustonFollow

Date of Graduation

8-2012

Document Type

Thesis (MS)

Program Affiliation

Medical Physics

Degree Name

Masters of Science (MS)

Advisor/Committee Chair

David Followill, Ph.D.

Committee Member

Paola Alvarez, M.S.

Committee Member

Stephen Kry, Ph.D.

Committee Member

Rebecca Howell, Ph.D.

Committee Member

Ann Lawyer, M.S.

Committee Member

Kenneth Hess, Ph.D.

Abstract

This work aimed to create a mailable and OSLD-based phantom with accuracy suitable for RPC audits of HDR brachytherapy sources at institutions participating in NCI-funded cooperative clinical trials. An 8 × 8 × 10 cm³ prototype with two slots capable of holding nanoDot Al₂O₃:C OSL dosimeters (Landauer, Glenwood, IL) was designed and built. The phantom has a single channel capable of accepting all ¹⁹²Ir HDR brachytherapy sources in current clinical use in the United States. Irradiations were performed with an ¹⁹²Ir HDR source to determine correction factors for linearity with dose, dose rate, and the combined effect of irradiation energy and phantom construction. The uncertainties introduced by source positioning in the phantom and timer resolution limitations were also investigated. It was found that the linearity correction factor was where dose is in cGy, which differed from that determined by the RPC for the same batch of dosimeters under ⁶⁰Co irradiation. There was no significant dose rate effect. Separate energy+block correction factors were determined for both models of ¹⁹²Ir sources currently in clinical use and these vendor-specific correction factors differed by almost 2.6%. For Nucletron sources, this correction factor was 1.026±0.004 (99% Confidence Interval) and for Varian sources it was 1.000±0.007 (99% CI). Reasonable deviations in source positioning within the phantom and the limited resolution of the source timer had insignificant effects on the ability to measure dose. Overall measurement uncertainty of the system was estimated to be ±2.5% for both Nucletron and Varian source audits (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 eight participating institutions resulted in an average RPC-to-institution dose ratio of 1.000 with a standard deviation of 0.011.

Keywords

HDR, high dose rate, brachytherapy, dosimetry, OSLD, OSL, RPC, Radological Physics Center, remote audit