Dosimetric characterization of round HDR {sup 192}Ir AccuBoost applicators for breast brachytherapy

Purpose: The AccuBoost brachytherapy system applies HDR {sup 192}Ir beams peripherally to the breast using collimating applicators. The purpose of this study was to benchmark Monte Carlo simulations of the HDR {sup 192}Ir source, to dosimetrically characterize the round applicators using established...

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Bibliographic Details
Published in:Medical physics (Lancaster) 2009-11, Vol.36 (11)
Main Authors: Rivard, Mark J., Melhus, Christopher S., Wazer, David E., Bricault, Raymond J. Jr, Advanced Radiation Therapy, Billerica, Massachusetts 01821
Format: Article
Language:English
Subjects:
BRACHYTHERAPY
COMPUTERIZED SIMULATION
DEPTH DOSE DISTRIBUTIONS
DOSIMETRY
ICRU
INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
IONIZATION CHAMBERS
IRIDIUM 192
MAMMARY GLANDS
MONTE CARLO METHOD
NEOPLASMS
NOMOGRAMS
PHANTOMS
RADIATION PROTECTION AND DOSIMETRY
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Summary:Purpose: The AccuBoost brachytherapy system applies HDR {sup 192}Ir beams peripherally to the breast using collimating applicators. The purpose of this study was to benchmark Monte Carlo simulations of the HDR {sup 192}Ir source, to dosimetrically characterize the round applicators using established Monte Carlo simulation and radiation measurement techniques and to gather data for clinical use. Methods: Dosimetric measurements were performed in a polystyrene phantom, while simulations estimated dose in air, liquid water, polystyrene and ICRU 44 breast tissue. Dose distribution characterization of the 4-8 cm diameter collimators was performed using radiochromic EBT film and air ionization chambers. Results: The central axis dose falloff was steeper for the 4 cm diameter applicator in comparison to the 8 cm diameter applicator, with surface to 3 cm depth-dose ratios of 3.65 and 2.44, respectively. These ratios did not considerably change when varying the phantom composition from breast tissue to polystyrene, phantom thickness from 4 to 8 cm, or phantom radius from 8 to 15 cm. Dose distributions on the central axis were fitted to sixth-order polynomials for clinical use in a hand calculation spreadsheet (i.e., nomogram). Dose uniformity within the useful applicator apertures decreased as depth-dose increased. Conclusions: Monte Carlo benchmarking simulations of the HDR {sup 192}Ir source using the MCNP5 radiation transport code indicated agreement within 1% of the published results over the radial/angular region of interest. Changes in phantom size and radius did not cause noteworthy changes in the central axis depth-dose. Polynomial fit depth-dose curves provide a simple and accurate basis for a nomogram.
ISSN:0094-2405
2473-4209
DOI:10.1118/1.3232001