Dosimetric Characteristics of 103 Pd (Theragenices, Model 200) Brachytherapy Source
Hadi Rezaee1, Zahra Shakarami1,Mohammad Hosseini2,Mansour Zabihzadeh1,2*, Mostafa Feghhi3

1Department of Medical Physics, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. 2Department of Radiation Oncology, Golestan Hospital, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. 3Department of Ophthalmology, Imam khomeini Hospital, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. *Corresponding author: Email: zabihzadeh@ajums.ac.ir

Abstract: Accurately determination of dosimetric parameters for low-energy 103 Pd source is crucial to use by treatment planning systems. The dosimetric parameters such as the air kerma strength, Sk, dose rate constant, L, radial dose function, g(r) and anisotropy function, F(r, q) for  the low-energy 103 Pd source were investigated. MCNPX (2.6.0) simulation code was used to calculate all dosimetry parameters. Full details of Theragenices-103 Pd source model 200 (dimentiones, materials and energy spectrum) were implementd in MC simulations. The 103 Pd source was centered in infinite water phantom and the radial dose function calculation the dose was scored in concentric rings with different thickness bonded by 88° and 92° conics. Due to symmetry of source geometry and in order to reducing of errors, the 0.5 mm thickness rings were bounded with two oblique cones (with interval angel of 1°) from 0° to 90° in order to calculate Anisotropy function. The air kerma strength, Sk and dose rate constant, L were found equal to 0.646 cGycm2h-1mCi-1 and 0.798 cGyh-1U-1, respectively. For radial dose function, g(r), using an equation as g(r) = a0+a1r+a2r2+a3r2lnr+ a4/r2, Where a0=1.6440, a1=-0.8338, a2=0.1917, a3=-0.0539, a4=-0.0062 with R2=0.9995 have been yielded a better fitting than the fifth-order polynomial equation recommended by AAPM, TG-43U1. The calculated anisotropy values included the distances of clinical interest for this type of low-energy photon source, up to 2 cm, and especially for smaller angles, q<20°, were estimated by different fifth-order polynomial equations with R2>0.9935. The calculated results and extracted equations are in good agreement with the corresponding values reported by AAPM, TG-43U1 and can be used in Monte Carlo based treatment planning system.

Keywords: Brachytherapy; 103 Pd (Theragenics, Model 200) Source; Monte Carlo Simulation; Dosimetry  

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