Dosimetric Parameters Estimation for I-125 (Model 6711) Brachytherapy Source

Document Type : Original Article

Authors

1 Department of Medical Physics, School of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.

2 Department of Ophthalmology, Emam khomani Hospital, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.

3 Department of Radiation Therapy, Golestan Hospital, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran

Abstract

Background and Objectives: Determination of dose distribution around the applied sources in brachytherapy especially with low-energy is crucial during establishment of treatment planning. In this study dosimetric parameters of a model 6711 I-125 brachytherapy source were calculated using Monte Carlo simulation method.
Subject and Methods:  A homogeneity water phantom with 30 cm3 dimensions was simulated with MCNPX (2.6.0) code. A model 6711 I-125 brachytherapy source with considering of its details (materials, dimensions and its emitted spectrum) was located in the center of phantom. Air Kerma strength, Sk, of source was calculated with locating source inside the vacuum sphere. Recommended dosimetric parameters by AAPM, TG-43 protocol were calculated for the model 6711 I-125 brachytherapy source in this phantom.
Results: The air kerma strength of the model 6711 I-125 source was estimated as equal to 0.557 cGycm2h-1mCi-1. Dose rate constant was 0.885 cGyh-1U-1. The Radial dose function with 5 degree equation and with regression of 0.9989 was estimated by g(r) = -.0001r4+0.0026 r3-0.0178 r2-0.0970 r+1.0995. The 5 degree equations for the anisotropy dose functions were calculated with R2>0.99.
Conclusion: In spite of low-energy emission photons and high dose gradients with radial distance, dosimetric parameters of the model 6711 I-125 source can be calculated by MCNPX Monte Carlo code with acceptable accuracy. Calculated parameters for the model 6711 I-125 brachytherapy source can be used for treatment planning systems in brachytherapy.
 

Keywords


1-Gearheart DM, Drogin A, Sowards K, Meigooni AS, Ibbott GS. Dosimetric characteristics of a new I-125 brachytherapy source. Med Phys 2000;27(10):2278-85. 
2-Rodrıguez EA, Alcon EP, Rodriguez ML, Gutt F, de Almeida CE. Dosimetric parameters estimation using PENELOPE Monte-Carlo simulation code: Model 6711 a 125I brachytherapy seed. Appl Radiat Isot 2005;63(1):41–8.
3-Weaver K. Anisotropy functions for I-125 and Pd-103 sources. Med Phys 1998;25(12):2271-8.
4-Rivard MJ, Coursey BM, DeWerd LA, Hanson WF, Huq MS, Ibbott GS, et al. Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations. Med Phys 2004;31(3):633-74.
5-Awan SB, Dini SA, Hussain M, Soleimani-Meigooni D, Meigooni AS. Cylindrical coordinate based TG-43U1 parameters for dose calculation around elongated brachytherapy sources. J Appl Clin Med Phys 2008;9(2):123-42.
6-Rivard MJ. Monte Carlo radiation dose simulations and dosimetric comparison of the model 6711 and 9011 125I brachytherapy sources. Med Phys 2009;36(2):486-91.
7-Sowards KT, Meigooni AS. A Monte Carlo evaluation of the dosimetric characteristics of the Bests Model 2301 125I brachytherapy source. Appl Radiat Isot 2002;57(3):327–33.
8-Li Z. Monte Carlo calculations of dosimetry parameters of the urocor prostaseed 125I source. Med Phys 2002;29(6):1029-34.
9-Rivard MJ. Comprehensive Monte Carlo calculations of AAPM Task Group Report No. 43 dosimetry parameters for the Model 3500 I-Plant 125I brachytherapy source. Appl Radiat Isot 2002;57(3):381–9.
10-Meigooni AS. Recent developments in brachytherapy source dosimetry. Iran J Radiat Res 2004;2(3):97-105.
11-Hedtjarn H, Carlsson GA, Williamson JF. Monte Carlo-aided dosimetry of the Symmetra model I25.S06 125I, interstitial brachytherapy seed. Med Phys 2000;27(5):1076-85.
12-Mainegra E, Capote R, Lopez E. Dose rate constants for 125I, 103Pd, 192Ir and 169Yb brachytherapy sources: an EGS4 Monte Carlo study. Phys Med Biol 1998;43(6):1557-66.