Asma Sheykhoo1, Sara Abdollahi2, Mohammad Hadi Hadizadeh Yazdi3, Mahdi Ghorbani4, Mohammad Mohammadi5. 1. Physics Department, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran; Medical Physics Department, Reza Radiation Oncology Center, Mashhad, Iran. 2. Medical Physics Department, Reza Radiation Oncology Center, Mashhad, Iran. 3. Physics Department, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran. 4. Medical Physics Research Center, Mashhad University of Medical Sciences, Mashhad, Iran. 5. Department of Medical Physics, Faculty of Medicine, Hamadan University of Medical Sciences, Hamadam, Iran; Department of Medical Physics, Royal Adelaide Hospital, Adelaide, South Australia, Australia.
Abstract
AIM: This study deals with Monte Carlo simulations of the effects which the 550 TXT carbon fiber couch can have on the relevant parameters of a 6 MV clinical photon beam in three field sizes. BACKGROUND: According to the reports issued by the International Commission on Radiation Units and Measurements (ICRU), the calculated dose across a high gradient distribution should be within 2% of the relative dose, or within 0.2 cm of the isodose curve position in the target volume. Nowadays, the use of posterior oblique beam has become a common practice. It is clear that, in radiotherapy, the presence of the couch affects the beam intensity and, as a result, the skin dose. MATERIALS AND METHODS: Firstly, Siemens linear accelerator validation for 6 MV photon beam was performed, and satisfactory agreement between Monte Carlo and experimental data for various field sizes was observed. Secondly, the couch transmission factor for the reference field size and depth was computed, and the skin dose enhancement by the couch was assessed. RESULTS: The largest impact of the carbon fiber couch effect was observed for the 5 × 5 cm2 field size. Such evaluation has not been reported for this couch before. CONCLUSION: Despite providing minimal attenuation for the primary radiation, the assumption that carbon fiber couches are radiotranslucent is not valid, and the effects of couches of this type on the transmission factor, and on the skin dose should be carefully investigated for each field size and depth.
AIM: This study deals with Monte Carlo simulations of the effects which the 550 TXT carbon fiber couch can have on the relevant parameters of a 6 MV clinical photon beam in three field sizes. BACKGROUND: According to the reports issued by the International Commission on Radiation Units and Measurements (ICRU), the calculated dose across a high gradient distribution should be within 2% of the relative dose, or within 0.2 cm of the isodose curve position in the target volume. Nowadays, the use of posterior oblique beam has become a common practice. It is clear that, in radiotherapy, the presence of the couch affects the beam intensity and, as a result, the skin dose. MATERIALS AND METHODS: Firstly, Siemens linear accelerator validation for 6 MV photon beam was performed, and satisfactory agreement between Monte Carlo and experimental data for various field sizes was observed. Secondly, the couch transmission factor for the reference field size and depth was computed, and the skin dose enhancement by the couch was assessed. RESULTS: The largest impact of the carbon fiber couch effect was observed for the 5 × 5 cm2 field size. Such evaluation has not been reported for this couch before. CONCLUSION: Despite providing minimal attenuation for the primary radiation, the assumption that carbon fiber couches are radiotranslucent is not valid, and the effects of couches of this type on the transmission factor, and on the skin dose should be carefully investigated for each field size and depth.
Entities:
Keywords:
550 TXT carbon fiber couch; Beam attenuation; Monte Carlo simulation; Siemens linac; Skin dose
Authors: Indrin J Chetty; Bruce Curran; Joanna E Cygler; John J DeMarco; Gary Ezzell; Bruce A Faddegon; Iwan Kawrakow; Paul J Keall; Helen Liu; C M Charlie Ma; D W O Rogers; Jan Seuntjens; Daryoush Sheikh-Bagheri; Jeffrey V Siebers Journal: Med Phys Date: 2007-12 Impact factor: 4.071