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Development and Implementation of a Remote Audit Tool for High Dose Rate (HDR) Ir-192 Brachytherapy Using Optically Stimulated Luminescence Dosimetry


K Casey

K Casey1,2*, P Alvarez1, A Lawyer1, S Kry1, R Howell1, S Davidson3, D Followill1, (1) UT MD Anderson Cancer Center, Houston, TX, (2) UT Health Science Center at Houston Graduate School of Biomedical Sciences, Houston, TX (3) The Methodist Hospital, Houston, TX

SU-E-T-81 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose:
Develop and implement a mailable OSLD phantom for 192Ir HDR brachytherapy remote audits.

Methods:
An 8x8x10cm³ polystyrene phantom was designed and built. The phantom has a central channel which accepts a 2mm endobronchial catheter and two slots on each side of the channel that hold one nanoDot dosimeter each. The active Al2O3 dosimeter (0.3mm thick) within each nanoDot is positioned 2cm from the center of the catheter channel. A treatment plan was created with 10 dwell positions spaced 5mm apart in tandem. Dwell times were optimized for a 10 Ci HDR source to deliver 100cGy to a line parallel to and 2cm away laterally from the catheter channel. OSLD correction factors for linearity, fading, dose rate and energy/block were determined. The irradiation uncertainties, introduced by factors such as OSLD orientation, source positioning, and source model were also determined.

Results:
It was determined that OSLD orientation within the phantom slots, dose rate (i.e. source strength), and minor deviations in source positioning introduced <2% deviation in dose measurement. The linearity correction factor was determined to be equal to ((Dose)(-9.490E-5)+1.0095) with an uncertainty of 0.5% (95% CI). Fading correction was determined to be the same as used by the RPC for previous OSLD experiments with an uncertainty of 0.3%. The energy/block correction factor was determined from 41 OSLD irradiations with an 192Ir HDR source with NIST-traceable calibration to be 1.0089 (2.1% std. dev.) for 192Ir energy relative to 60Co and our designed phantom. The overall dose measurement uncertainty is estimated at 5% (2 standard deviations). Four trial audits of three different sources were conducted with an average difference between RPC calculation and institutional dose measurement of 1.5%.

Conclusions:
A simple, accurate, and mailable OSLD phantom for 192Ir HDR brachytherapy remote audits has been developed and characterized with an overall uncertainty of <5%.

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