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Design and Implementation of a Novel Technique for Verification of TG-43 Dosimetric Parameters for a Directional 103Pd Source

A Damato

A Damato1*, G Cohen1 , K Episcopia1 , S Lim1 , M Rivard2 , T LoSasso1 , (1) Memorial Sloan Kettering Cancer Center, New York, NY, (2) Tufts University School of Medicine, Boston, MA


SU-I-GPD-T-16 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To develop a method to verify TG-43 brachytherapy dosimetric parameters for a directional ¹⁰³Pd source (CivaDot) with gold shield, which must overcome the difficulties compounded by low-energy photons and relatively low dose rates.

Methods: Radiochromic EBT3 film was irradiated at distances of 2.2mm, 5.1mm, 8.0mm, and 11.1mm from the ¹⁰³Pd source along its axis using a custom source/film holder suspended in a water bath. Irradiation times were estimated for source-to-film distances to provide adequate film optical density for analysis. Films were calibrated in air at five orthovoltage x-ray energies ranging from 30-70 kVp at doses from 0-9 Gy and scanned along with the ¹⁰³Pd films five days after the final exposure to minimize temporal response artifacts. Additionally, x-ray and ¹⁰³Pd dose profiles were obtained after removing inverse-square components from depth dose measurements for the x-ray beams (thin window ionization chamber) and Monte Carlo derived depth-dose simulations for ¹⁰³Pd. Comparison of the slopes of these residual profiles determined the optimal x-ray energy for film calibration as a function of distance from the ¹⁰³Pd source.

Results: Slopes analysis determined that optimal calibration x-ray energy was 37kVp for 2.2mm depth, and 50kVp for the 3 higher depths. Film scans were converted to absolute dose using the 37kVp film calibration curve, and corrected for the relative film response of 50kVp when applicable. Distances to agreement for the measured 2D dose distributions and TG-43 calculations were -0.12mm, -0.42mm, 0.26mm and 0.18mm for 2.2mm, 5.1mm, 8.0mm, and 11.1mm depths, respectively.

Conclusion: Absolute dose distributions for the CivaDot ¹⁰³Pd source can be accurately experimentally verified using an orthovoltage x-ray calibration technique.

Funding Support, Disclosures, and Conflict of Interest: One of the co-authors serves as a consultant to CivaTech Oncology, Inc. (Durham, NC).

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