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Contrast effects on dosimetry of a partial breast irradiation system
Author(s) -
Kassas Bassel,
Mourtada Firas,
Horton John L.,
Lane Richard G.
Publication year - 2004
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1763006
Subject(s) - balloon , dosimetry , brachytherapy , kerma , nuclear medicine , imaging phantom , materials science , balloon catheter , medicine , biomedical engineering , radiology , radiation therapy , surgery
MammoSite ® is a high‐dose rate brachytherapy procedure for partial breast irradiation, which uses a balloon filled with radiopaque iodine‐based contrast solution and catheter for insertion of192 Ir high‐dose‐rate source. The radiopaque material helps visualizing the balloon contour, catheter, and source position within the balloon, which is essential for computerized tomography‐based treatment planning and for daily QA using x‐ray radiographs. Because of the high content of iodine in contrast media, increased absorption and attenuation of photons may take place within the balloon, which would affect the resultant dose rates outside the balloon. The impact of the concentration of the radiopaque solution on the physical dosimetry of this brachytherapy procedure is investigated in this study using MCNPX (version 2.4) Monte Carlo simulation. Calculations were based on a 30 cm diameter water sphere phantom. The source geometry was that of the Nucletron microSelectron HDR v2192 Ir source. Concentration of the iodine‐based radiopaque solution was varied from 5% to 25% by volume, a range recommended by the balloon's manufacturer. Balloon diameters of 4, 5, and 6 cm were simulated. Dose rate per unit air‐kerma strength was calculated in 1 mm scoring bin steps. The dose rate reduction at the typical prescription line of 1 cm away from the balloon surface ranged from − 0.8 % for the smallest balloon diameter and contrast concentration to a maximum of − 5.7 % for the largest balloon diameter and contrast concentration, relative to a water‐filled balloon. Limiting the contrast concentration to 10% would insure less than 3% reduction in the prescription dose, regardless of balloon diameter.