The influence of Monte Carlo source parameters on detector design and dose perturbation in small field dosimetry

17th International Conference on the Use of Computers in Radiation Therapy

物理学;计算机科学

Charles, P.H.^1 ; Crowe, S.B.^1 ; Kairn, T.^1,2 ; Knight, R.^2 ; Hill, B.^2 ; Kenny, J.^3,4 ; Langton, C.M.^1 ; Trapp, J.V.^1

School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane, GPO Box 2434, Brisbane, QLD 4001, Australia^1

Premion, the Wesley Medical Centre, Suite 1, Auchenflower, QLD 4066, Australia^2

Australian Clinical Dosimetry Service, Australian Radiation Protection and Nuclear Safety Agency, 619 Lower Plenty Road, Yallambie, VIC 3085, Australia^3

Radiation Oncology Queensland, St Andrew's Toowoomba Hospital, Toowoomba, QLD 4350, Australia^4

关键词: Correction factors;    Detector design;    Dose reduction;    Electron energies;    Monte Carlo modelling;    Perturbation correction;    Radiation field;    Source parameters;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/489/1/012006/pdf
DOI  :  10.1088/1742-6596/489/1/012006

学科分类：计算机科学（综合）

来源: IOP

【 摘 要 】

To obtain accurate Monte Carlo simulations of small radiation fields, it is important model the initial source parameters (electron energy and spot size) accurately. However recent studies have shown that small field dosimetry correction factors are insensitive to these parameters. The aim of this work is to extend this concept to test if these parameters affect dose perturbations in general, which is important for detector design and calculating perturbation correction factors. The EGSnrc C++ user code cavity was used for all simulations. Varying amounts of air between 0 and 2 mm were deliberately introduced upstream to a diode and the dose perturbation caused by the air was quantified. These simulations were then repeated using a range of initial electron energies (5.5 to 7.0 MeV) and electron spot sizes (0.7 to 2.2 FWHM). The resultant dose perturbations were large. For example 2 mm of air caused a dose reduction of up to 31% when simulated with a 6 mm field size. However these values did not vary by more than 2 % when simulated across the full range of source parameters tested. If a detector is modified by the introduction of air, one can be confident that the response of the detector will be the same across all similar linear accelerators and the Monte Carlo modelling of each machine is not required.