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Dosimetry Parameters Revisited for the IsoAid Model IAI-125A Brachytherapy Seed

P Aryal

P Aryal1*, J Molloy2, M Rivard3, (1) Univ Kentucky - Chandler Medical Ctr, Lexington, KY, (2) Univ Kentucky, Lexington, KY, (3) Tufts Medical Center, Boston, MA

SU-E-T-354 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Investigate and analyze TG43 dosimetry parameters for the IsoAid I¹²⁵ model IAI 125A seed

Methods: We revisited dosimetry for the IsoAid advantage I¹²⁵ model IAI 125A seed to verify the published TG43 parameters. The IsoAid seed was examined based on manufacturer data and detailed information published in literature. The MCNP5 Monte Carlo radiation transport code was used. Sensitivity of these dosimetry parameters was assessed by changing a total of 10 geometric and computational variables, including source coating thickness, capsule design, photon emission spectrum, and cross section library. The calculated dose rate constants and radial dose functions were then compared with published literature values.

Results: Compared to the reference simulation conditions of a 0.5 um source coating, recent capsule design data, the NNDC photon spectrum, and the ZAID.04p MCNP5 cross section libraries, the highest dose rate constant variation was +3.1% and the lowest was â‚‹4.0% compared to our value of 0.922 cGy/h/U. Calculated values by Solberg et al. (2002) and Meigooni et al. (2002) were 0.962 and 0.98 cGy/h/U respectively. There were significant differences (>10%) between the published values for the radial dose function and those calculated herein, becoming increasingly disparate as radial distance increased. These differences could be explained within a few percent by performing simulations with their photon emission spectrum and using older cross section libraries. For the similarly designed model 6711 seed, our dose rate constant results agreed within 0.2% and within 0.5% for gL(0.5
Conclusion: A modern investigation of the TG43 dosimetry parameters for the I¹²⁵ IsoAid seed indicates clinically-significant differences with published results used for the AAPM consensus values. We suggest that the AAPM revisit dosimetry for this and other seeds included in the 2004 and 2007 reports.

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