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Dose Measurements and Monte Carlo Simulations of a Directional LDR Brachytherapy Source Array

M Aima*, L DeWerd, J Micka, C Hammer, J Hull, W Culberson, Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI


(Wednesday, 8/1/2018) 7:30 AM - 9:30 AM

Room: Davidson Ballroom A

Purpose: The primary aim of this work is to perform dose measurements of a new directional ¹�³Pd low-dose rate brachytherapy source array called the CivaSheet.™ The measured dose distribution was compared to Monte Carlo (MC) simulations, and the validity of dose distribution superposition of individual array elements (CivaDots) was assessed.

Methods: A PMMA phantom was constructed to perform CivaSheet dose-to-water measurements using a stacked-film dosimeter. A CivaSheet (5×5 cm²) consisting of 36 CivaDots was placed in the center of the phantom, and 7 Gy was the target prescription dose at 0.5 cm depth (hot-side) on the source central axis. Six Gafchromic EBT3 films were placed at various depths on the hot-side of the source (0.5―5 cm) and one film was placed on the cold-side (1 cm). A flatbed scanner (10000XL) was used for readout. The source and measurement setup geometry were simulated using MCNP6 code for dose distribution comparison, and determination of associated correction factors. Additional well chamber measurements were performed to assess the air-kerma strength constancy of cropped CivaDots.

Results: A pixel-by-pixel subtraction map of the measured and MC-predicted CivaSheet dose-to-water distributions resulted in a maximum difference of 0.38 Gy with 90% of the pixels within ±0.21 Gy of the MC-calculated dose at 0.5 cm depth (7 Gy prescription). Dose differences were within ±0.14 Gy and ±0.07 Gy of MC-calculated dose distributions at 1 cm and all other depths respectively. CivaDot dose distribution superposition resulted in maximum differences of 0.42 Gy with 90% of pixels within ±0.24 Gy of MC-calculated dose. Well chamber measurements of cropped CivaDots resulted in maximum differences of ±4.3% from batch-average air-kerma strength, with most sources within ±2.0%.

Conclusion: Dose measurements of the directional CivaSheet source were performed successfully using a stacked-film dosimeter, and subsequent comparisons to MC dose distributions resulted in agreement within uncertainties.

Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by NCI contract (HHSN261201200052C) through CivaTech Oncology Inc.


Absolute Dosimetry, Monte Carlo, Brachytherapy


TH- Brachytherapy: Dose measurement

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