title: An analytical model to determine interseed attenuation effect in low-dose-rate brachytherapy.
abstract: Brachytherapy treatment planning systems (BTPS) are employing the American Association of Physicists in Medicine (AAPM) Task Group 43 (TG-43)-recommended dosimetric parameters of sources, which are measured in water. The majority of brachytherapy implant volumes are not homogeneous media. Particularly, an implant with multiple seeds significantly changes homogeneity of the implant volume. Heterogeneities, such as attenuation by adjacent seeds or interseed attenuation (ISA), are neglected to this day in all BTPS. The goal of this project is to determine a novel analytical method to evaluate the impact of the dose perturbations (P-value) and/or interseed attenuation effect (ISA-value). This method will be validated for low- and high-energy brachytherapy seeds such as 125I and 192Ir using Monte Carlo (MC) simulation techniques. In this analytical model, determination of dose perturbation and interseed attenuation in a multisource brachytherapy implant is based on MC-simulated 3D kernels of P-values and ISA data for single active and single dummy configurations, arranged at different distances and orientations relative to each other. The accuracy of the final model in multisource implant configurations has been examined by a comparison of the calculated P-values and ISA-values with full Monte Carlo water simulations (FMCWS). This model enabled us to determine the total perturbation and ISA values for any multisource implant, and the results are in excellent agreement with the FMCWS data. The advantage of this model to FMCWS for daily clinical application is the speed of the calculations and ease of the implementation. The new perturbation and ISA formulism have shown a better accuracy for 192Ir than 125I due to Compton scattering and its independence of the atomic number of the chemical composition of the phantom materials. The maximum difference between the ISA model and FMCWS for all cases was less than 5%. This new model can provide inputs for brachytherapy planning software to consider the ISA effect in dose calculations based on TG-43U1 algorithm. This approach is applicable for energy range of 125I to192Ir sources.
authors: Department of Radiation Medical Engineering,1 Science and Research Branch, Islamic Azad University, Tehran, Iran. safigholi@gmail.com
authors: Habib
authors: H
authors: Safigholi
authors: Dariush
authors: D
authors: Sardari
authors: Somaye
authors: S
authors: Karimi Jashni
authors: Seied Rabi
authors: SR
authors: Mahdavi
authors: Ali S
authors: AS
authors: Meigooni
mesh_terms: D000465:Algorithms; D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D007496:Iridium Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008962:Models, Theoretical; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted
chemical_list: D007457:Iodine Radioisotopes; D007496:Iridium Radioisotopes
references: Phys Med Biol. 1998 Jun;43(6):1557-66
references: 9651025
references: Med Phys. 2012 Oct;39(10):6208-36
references: 23039658
references: Med Phys. 2008 Aug;35(8):3671-81
references: 18777927
references: Med Phys. 2006 Dec;33(12):4578-82
references: 17278809
references: Med Phys. 2004 Jul;31(7):2075-81
references: 15305460
references: Med Phys. 1996 Jun;23(6):911-9
references: 8798161
references: Phys Med Biol. 2004 Jul 21;49(14):3171-8
references: 15357190
references: Med Phys. 1992 Mar-Apr;19(2):385-90
references: 1584137
references: Med Phys. 2007 Jun;34(6):2187-205
references: 17654921
references: Med Phys. 2000 May;27(5):1076-85
references: 10841412
references: Med Phys. 1992 Mar-Apr;19(2):401-7
references: 1584139
references: Med Phys. 1995 Feb;22(2):209-34
references: 7565352
references: Med Phys. 2004 Mar;31(3):633-74
references: 15070264
references: Med Phys. 2006 Mar;33(3):595-604
references: 16878563
references: Med Phys. 2005 Aug;32(8):2557-66
references: 16193786
references: Med Phys. 2004 Nov;31(11):3080-6
references: 15587661
references: Med Phys. 2001 Sep;28(9):1875-82
references: 11585218
references: Med Phys. 1998 Dec;25(12):2271-8
references: 9874818
references: Med Phys. 1989 Jul-Aug;16(4):627-31
references: 2770634
references: Med Phys. 1999 Oct;26(10):2054-76
references: 10535622
references: Med Dosim. 2005 Summer;30(2):85-91
references: 15922174