Document Type : Original Article
Authors
1 Universidade Estadual do Rio de Janeiro, Departamento de Física Aplicada e Termodinâmica (DFAT-UERJ), Rua São Francisco Xavier, 524, Bloco B sala3027, Maracanã, CEP 20550-900, Rio de Janeiro, Brasil
2 Universidade Estadual do Rio de Janeiro, Laboratório de Ciências Radiológicas (LCR-UERJ), Rua São Francisco Xavier, 524, Maracanã, Pavilhão Haroldo Lisboa sala 136 Térreo, CEP 20550-900, Rio de Janeiro, Brasil
Abstract
Background: Radiotherapy is an important technique of cancer treatment using ionizing radiation. The determination of total dose in reference conditions is an important contribution to uncertainty that could achieve 2%. The source of this uncertainty comes from cavity theory that relates the in-air cavity dose and the dose to water. These correction factors are determined from Monte Carlo calculations of ionization chambers. The main problem of this type of calculation is the extremely long computation time to achieve reasonable statistics.
Objective: The main purpose of this work is to present a combination with variance reduction techniques for the case of an ionization chamber in water.
Methods: The egs_chamber code allows for very efficient computation of ionization chamber doses and dose ratios by using various variance reduction techniques, and also permits realistic simulations of the experimental setup due to the use of EGSnrc C++ library. Russian roulette and Photon Cross Section Enhancement were used with egs_chamber code. Tests were performed to obtain the parameters of variance reduction techniques resulting in a maximum efficiency.
Results: It can be seen that the parameters which result in improved Monte Carlo calculation of the efficiency values are XCSE 64 and Russian Roulette (RR) 128.
Conclusion: This study determines the parameters of variance reduction techniques that result in an optimal computational efficiency.
Keywords
- Wulff J. Clinical Dosimetry in Photon Radiotherapy. [Inaugural Dissertation]. Germany: Marburg; 2010.
- Nilsson B, Montelius A, Andreo P, Sorcini B. Perturbation correction factors in ionization chamber dosimetry. Dosimetry in Radiotherapy (IAEA, Vienna). 1988;1:175-85.
- Andreo P, Rodrigues LN, Lindborg L, Kraepelien T. On the calibration of plane-parallel ionization chambers for electron beam dosimetry. Phys Med Biol. 1992;37:1147-65. doi.org/10.1088/0031-9155/37/5/009. PubMed PMID: 1609001.
- Jenkins TM, Nelson WR, Rindi A. Monte Carlo transport of electrons and photons: Springer Science & Business Media; 2012.
- Kawrakow I, Fippel M. Investigation of variance reduction techniques for Monte Carlo photon dose calculation using XVMC. Phys Med Biol. 2000;45:2163-83. doi.org/10.1088/0031-9155/45/8/308. PubMed PMID: 10958187.
- Kawrakow I, Mainegra-Hing E, Rogers D. EGSnrcMP: the multi-platform environment for EGSnrc. National Research Council of Canada, Ottawa. 2006.
- Nelson WR, Hirayama H, Rogers DW. EGS4 code system. Stanford Linear Accelerator Center, Menlo Park: CA (USA); 1985.
- Kawrakow I, Rogers D. The EGSnrc code system: Monte Carlo simulation of electron and photon transport. 2000.
- Kawrakow I. egspp: the EGSnrc C++ class library. National Research Council of Canada Report PIRS. 2005;899.
- Buckley LA, Kawrakow I, Rogers DW. CSnrc: correlated sampling Monte Carlo calculations using EGSnrc. Med Phys. 2004;31:3425-35. doi.org/10.1118/1.1813891. PubMed PMID: 15651625.
- Seco J, Verhaegen F. Monte Carlo techniques in radiation therapy: CRC press; 2013.
- Kawrakow I, Mainegra-Hing E, Rogers DWO, Tessier F, Walters BRB. The EGSnrc Code System: Monte Carlo simulation of electron and photon transport. NRC Technical Report N° PIRS-701; 2013.
- Wulff J, Zink K, Kawrakow I. Efficiency improvements for ion chamber calculations in high energy photon beams. Med Phys. 2008;35:1328-36. doi.org/10.1118/1.2874554. PubMed PMID: 18491527.
- Mora GM, Maio A, Rogers DW. Monte Carlo simulation of a typical 60Co therapy source. Med Phys. 1999;26:2494-502. doi.org/10.1118/1.598770. PubMed PMID: 10587239.
- Almond PR, Biggs PJ, Coursey BM, Hanson WF, Huq MS, Nath R, et al. AAPM’s TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams. Med Phys. 1999;26:1847-70. doi.org/10.1118/1.598691. PubMed PMID: 10505874.
- Absorbed Dose Determination in External Beam Radiotherapy: An International Code of Practice for Dosimetry Based on Standards of Absorbed Dose to Water. International Atomic Energy Agency (IAEA). Volume 398 of Technical Report Series IAEA, Vienna; 2001.
)