Using narrow beam profiles to quantify focal spot size, for accurate Monte Carlo simulations of SRS/SRT systems

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

物理学;计算机科学

Kairn, T.^1,2 ; Crowe, S.B.^2 ; Charles, P.H.^2 ; Trapp, J.V.^2

Premion Cancer Care, Brisbane, Australia^1

Science and Engineering Faculty, Queensland University of Technology, Brisbane, Australia^2

关键词: Comparison with measurements;    Focal spot size;    Output factors;    Photon fields;    Photon sources;    Radiochromic film;    Simulated profile;    Varian medical systems;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/489/1/012014/pdf
DOI  :  10.1088/1742-6596/489/1/012014

学科分类：计算机科学（综合）

来源: IOP

【 摘 要 】

This study investigates the variation of photon field penumbra shape with initial electron beam diameter, for very narrow beams. A Varian Millenium MLC (Varian Medical Systems, Palo Alto, USA) and a Brainlab m3 microMLC (Brainlab AB. Feldkirchen, Germany) were used, with one Varian iX linear accelerator, to produce fields that were (nominally) 0.20 cm across. Dose profiles for these fields were measured using radiochromic film and compared with the results of simulations completed using BEAMnrc and DOSXYZnrc, where the initial electron beam was set to FWHM = 0.02, 0.10, 0.12, 0.15, 0.20 and 0.50 cm. Increasing the electron-beam FWHM produced increasing occlusion of the photon source by the closely spaced collimator leaves and resulted in blurring of the simulated profile widths from 0.24 to 0.58 cm, for the MLC, from 0.11 to 0.40 cm, for the microMLC. Comparison with measurement data suggested that the electron spot size in the clinical linear accelerator was between FWHM = 0.10 and 0.15 cm, encompassing the result of our previous output-factor based work, which identified a FWHM of 0.12 cm. Investigation of narrow-beam penumbra variation has been found to be a useful procedure, with results varying noticeably with linear accelerator spot size and allowing FWHM estimates obtained using other methods to be verified.