Technical note Study of the IsoAid ADVANTAGE TM 125 I brachytherapy source dosimetric parameters using Monte Carlo simulation Mahdi Sadeghi Ã , S. Hamed Hosseini Agricultural, Medical and Industrial Research School, Nuclear Science and Technology Research Institute, P.O. Box 31485-498, Gohardasht, Karaj, Iran article info Article history: Received 22 February 2009 Received in revised form 15 August 2009 Accepted 17 August 2009 Keywords: MCNP4C ADVANTAGE TM 125 I Brachytherapy Dosimetry abstract Monte Carlo calculations have been performed using the MCNP4C code for an iodine seed design. As the ADVANTAGE TM I-125, Model IAI-125 source is commercially available for interstitial brachytherapy treatment, dosimetric characteristics (dose rate constant, radial dose function and anisotropy function) of this source were theoretically determined following the updated AAPM task group 43 (TG-43U1) recommendations. The dose distribution around the seed was calculated with Monte Carlo simulation in liquid water. The Monte Carlo calculated dose rate constant of this source in water was found to be 0.986 cGy h 1 U 1 , with an approximate uncertainty of 0.4%. The obtained result has been compared with the previous study. Comparison of the calculated dose rate constant with the value presented by Meigooni et al. shows a very good agreement. Also the anisotropy function and the radial dose function for this source are graphically compared. & 2009 Elsevier Ltd. All rights reserved. 1. Introduction By developing the use of low energy sources in treatment of prostate cancer patient, a variety of sources has been designed and become available for treatment use. The demand for these seeds is increasing as well. For treatment of prostate cancer, 125 I is used because of its low energy emissions, which allow for a rapid decrease in dose with distance (Nath et al., 1995; Rivard et al., 2004). The American Association of Physicists in Medicine (AAPM) has recommended in TG-43U1 that the dosimetric parameters of each seed should be determined before use in treatment (Rivard et al., 2004). In this work, we calculated the dosimetric parameters of the ADVANTAGE TM 125 I, Model IAI-125 source using the MCNP4C code. The calculated dosimetric characteristics of this source have been compared to that of Meigooni et al. (2000), the results of which were calculated using the PTRAN code. 2. Material and methods 2.1. 125 I source description Schematic design of the ADVANTAGE TM 125 I source is shown in Fig. 1 . The source consists of a cylindrical silver core, 3 mm long and 0.5 cm diameter, onto which a thin layer of 0.001 mm thick AgI has been uniformly adsorbed and then encapsulated in a 0.05 mm thick titanium capsule. The external length and the diameter of the capsule are 4.5 and 0.8mm, respectively. This source has an effective active length of 3 mm (Meigooni et al., 2000). 2.2. Monte Carlo evaluation MCNP is a general-purpose, continuous-energy, generalized- geometry, time-dependent, coupled neutron/photon/electron Monte Carlo transport code (Briesmeister, 2000). In this study the Monte Carlo N-particle code (MCNP version 4C) was used for the dose rate simulations around the seed. Monte Carlo simula- tion of the dose distributions around the source was made by assuming a uniform distribution of the 125 I isotope within a 0.001 mm thick layer of silver iodide (AgI) with a density of 6.003 g cm 3 (Meigooni et al., 2000). The AgI was deposited on a 3 mm long and 0.5 mm wide cylindrical silver X-ray marker encapsulated in a 0.05 mm thick wall titanium tube (Fig. 1). The absorbed dose was calculated using the MCNP f6 tally, which reports the energy absorbed per gram of material deﬁned in the detector volume (Sadeghi et al., 2008). The 125 I photon spectrum used in these simulations was from TG-43U1 Table XIII (Rivard et al., 2004). The source was positioned at the center of a 30 cm diameter spherical phantom and an array of detector rings were deﬁned within this spherical phantom for the MCNP simulation. The rings were deﬁned in two cones bisecting the sphere corresponding to ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/apradiso Applied Radiation and Isotopes 0969-8043/$ - see front matter & 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2009.08.007 Ã Corresponding author. Tel.: +98 2614436395; fax: +98 2614464055. E-mail addresses: msadeghi@nrcam.org, mahdisadeghi2003@yahoo.com (M. Sadeghi). Applied Radiation and Isotopes 68 (2010) 211–213