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Publications (3)5.82 Total impact

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    ABSTRACT: Purpose: To investigate the use of optically stimulated luminescent dosimeters (OSLDs) for high dose rate (HDR) Ir-192 brachytherapy. While common in megavoltage radiotherapy applications, the performance of OSLDs using kilovoltage energies, high dose gradient and high dose rate regions ubiquitous to HDR has not been demonstrated. Methods: Commercially available nanoDotTM (Landauer, Glenwood, IL) OSLDs - 5mm diameter and 0.2mm thickness - were irradiated using an Ir-192 source in various geometries to determine dose rate dependence. Angular geometries were created using a circular applicator designed for accelerated partial breast irradiation by Accuboost®. Results: Response remained linear for high doses and was independent of dose rate. Specifically, the OSLDs were shown to be linear with dose up to 200 cGy then became slightly supra-linear up to 600 cGy. There was a slight angular dependence for OSLDs which becomes significant in 'edge-on' scenarios. An asymmetry in this angular dependence was discovered, but was attributed to cable curvature, point source approximation, and positioning within its plastic casing. Conclusions: Clinical HDR doses of 300 cGy fall within the linear, dose-rate-independent region. Angular independence can be maintained by avoiding extreme 'edge-on' measurement geometries. Because of re- readability, OSLDs can serve as a permanent record or alternatively be annealed within a few hours using conventional fluorescent light. Lastly, OSLDs are produced for only $5 each. Due to these features, in conjunction with the dosimetric performance, OSLDs should be considered a reliable tool for in vivo HDR brachytherapy measurements.
    Medical Physics 06/2012; 39(6):3775. · 2.91 Impact Factor
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    ABSTRACT: Purpose: The Monte Carlo calculation algorithm in the MultiPlan (Accuray, Palo Alto, CA) treatment planning system used for CyberKnife (Accuray) robotic radiosurgery requires in-air measurements. In this study, results were compared for the impact of build-up caps using a diode detector for small field in-air measurements. Methods: Two acrylic caps custom-made for the SFD diode detector (IBA, Germany) of two thicknesses were compared against free-in-air measurements. The 1.5 and 5 cm thicknesses correspond to Dmax and a depth beyond the range of electron contamination, respectively. A Blue Phantom (IBA) was used to position the diode 80 cm SAD. Measurements were made for all 12 fixed cones ranging from 5 to 60 mm. Results: For the 5 mm cone, there is a 15.6% and 20.0% difference in the Sc factor between the 1.5 cm and 5 cm buildup caps, respectively, versus the free-in-air measurement. For the 7.5 mm cone, the difference is 6.3% and 10.4% for the 1.5 cm and 5 cm buildup caps, respectively, versus the free-in-air measurement. While generally decreasing, the Sc factor for either buildup cap does not agree within 2% to free-in-air measurements until the cone used is larger than 40 mm. Overall, the two buildup caps yield similar Sc factors and the differences observed are attributed to electron contamination. Conclusions: The Monte Carlo calculation algorithm used by the CyberKnife planning manual does not refer to any build-up caps. This study has shown that, particularly for small fields, there are large differences in Sc factors measured with and without buildup caps. In general, for fields smaller than 10 mm, build-up caps should be carefully chosen, especially in commissioning data.
    Medical Physics 06/2012; 39(6):3743. · 2.91 Impact Factor
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    ABSTRACT: Purpose: The objective was to determine whether optically stimulated luminescent dosimeters (OSLDs) were appropriate for in vivo measurements in high dose rate brachytherapy. In order to make this distinction, three dosimetric characteristics were tested: dose linearity, dose rate dependence, and angular dependence. The Landauer nanoDot™ OSLDs were chosen due to their popularity and their availability commercially. Methods: To test the dose linearity, each OSLD was placed at a constant location and the dwell time was varied. Next, in order to test the dose rate dependence, each OSLD was placed at different OLSD-to-source distances and the dwell time was held constant. A curved geometry was created using a circular Accuboost(®) applicator in order to test angular dependence. Results: The OSLD response remained linear for high doses and was independent of dose rate. For doses up to 600 cGy, the linear coefficient of determination was 0.9988 with a response of 725 counts per cGy. The angular dependence was significant only in "edge-on" scenarios. Conclusion: OSLDs are conveniently read out using commercially available readers. OSLDs can be re-read and serve as a permanent record for clinical records or be annealed using conventional fluorescent light. Lastly, OSLDs are produced commercially for $5 each. Due to these convenient features, in conjunction with the dosimetric performance, OSLDs should be considered a clinically feasible and attractive tool for in vivo HDR brachytherapy measurements.
    Frontiers in Oncology 01/2012; 2:91.