Influence of initial electron beam parameters on Monte Carlo calculated absorbed dose distributions for radiotherapy photon beams

• Published in: Medical physics (Lancaster) 2004-04, Vol.31 (4), p.907-913
• Main Authors: Tzedakis, Antonis, Damilakis, John E., Mazonakis, Michael, Stratakis, John, Varveris, Haralambos, Gourtsoyiannis, Nicholas
• Format: Article
• Language: English
• Subjects: absorbed dose; Algorithms; BEAM code; biological effects of ionising particles; Body Burden; Computer Simulation; dosimetry; Dosimetry/exposure assessment; electron beam effects; Electron beams; Electrons - therapeutic use; Field size; initial electron beam; linear accelerators; Linear Energy Transfer; Models, Biological; Models, Statistical; Monte Carlo; Monte Carlo Method; Monte Carlo methods; Particle Accelerators; Photons; Photons - therapeutic use; Physicists; radiation therapy; Radiometry - methods; Radiotherapy - methods; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods; Radiotherapy sources; Reproducibility of Results; Scattering, Radiation; Sensitivity and Specificity; Statistical properties
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.1668551

Our aim in the present study was to investigate the effects of initial electron beam characteristics on Monte Carlo calculated absorbed dose distribution for a linac 6 MV photon beam. Moreover, the range of values of these parameters was derived, so that the resulted differences between measured and calculated doses were less than 1%. Mean energy, radial intensity distribution and energy spread of the initial electron beam, were studied. The method is based on absorbed dose comparisons of measured and calculated depth-dose and dose-profile curves. All comparisons were performed at 10.0 cm depth, in the umbral region for dose-profile and for depths past maximum for depth-dose curves. Depth-dose and dose-profile curves were considerably affected by the mean energy of electron beam, with dose profiles to be more sensitive on that parameter. The depth-dose curves were unaffected by the radial intensity of electron beam. In contrast, dose-profile curves were affected by the radial intensity of initial electron beam for a large field size. No influence was observed in dose-profile or depth-dose curves with respect to energy spread variations of electron beam. Conclusively, simulating the radiation source of a photon beam, two of the examined parameters (mean energy and radial intensity) of the electron beam should be tuned accurately, so that the resulting absorbed doses are within acceptable precision. The suggested method of evaluating these crucial but often poorly specified parameters may be of value in the Monte Carlo simulation of linear accelerator photon beams.