IJMPCERO  Vol.6 No.1 , February 2017
Direct Measurement of Medical Linear Accelerator Electron Beam Width at Scattering Foil Position
Abstract: Purpose: The aim of this study was to develop a method for the direct measurement of electron beam width and distribution at the scattering foil on the carrousel in a medical linear accelerator gantry head, which differs from an existing indirect method for measuring the focal spot size using a camera or metallic slit located outside the gantry head. Methods: The electron beam emitted by the linear accelerator was used to irradiate radiochromic film mounted on the scattering foil on the carrousel, which was not used for clinical treatment. The electron beam width at the scattering foil position was then evaluated using the full width at half maximum of the Gaussian distribution approximated from each one dimensional distribution of the irradiated radiochromic film. Results: The electron beam width at the scattering foil position was found to be 3.1 to 6.4 mm in the crossline direction and 2.8 to 5.5 mm in the inline direction with electron energy of 4 to 16 MeV. The two-dimensional distribution of the electron beam was therefore elliptical or distorted in shape, not circular. Conclusions: Direct measurement of the electron beam width at the scattering foil in the carrousel of a medical linear accelerator is possible, though the use of lower sensitivity film in addition to indirect methods is expected to bring about better results. However, as this method does not allow for direct measurement of the incident angle of the accelerated electron beam, further improvements and refinements are still needed.
Cite this paper: Shimozato, T. and Aoyama, Y. (2017) Direct Measurement of Medical Linear Accelerator Electron Beam Width at Scattering Foil Position. International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 6, 1-7. doi: 10.4236/ijmpcero.2017.61007.

[1]   Lutz, W.R., Romald, R.D. and Bjarngard, B.E. (1981) Beam Alignment Tests for Therapy Accelerators. International Journal of Radiation Oncology* Biology* Physics, 7, 1727-1731.

[2]   Karzmark, C.J. (1984) Advance in Linear Accelerator Design for Radiotherapy. Medical Physics, 11, 105-128.

[3]   Lutz, W.R., Maleki, N. and Bjarngard, B.E. (1988) Evaluation of a Beam-Spot Camera for Megavoltage X-Rays. Medical Physics, 15, 614-617.

[4]   Jaffray, D.A., Battista, J.J., Fenster, A. and Munro, P. (1993) X-Ray Sources of Medical Linear Accelerators: Focal and Extra-Focal Radiation. Medical Physics, 20, 1417-1427.

[5]   Sham, E., Seuntjens, J., Devic, S. and Podgorsak, E.B. (2008) Influence of Focal Spot on Characteristics of Very Small Diameter Radiosurgical Beams. Medical Physics, 35, 3317-3330.

[6]   Anai, S., Arimura, H., Nakamura, K., Araki, F., Matsuki, T., Yoshikawa, H., Yoshidome, S., Shioyama, Y., Honda, H. and Ikeda, N. (2011) Estimation of Focal and Extra-Focal Radiation Profiles Based on Gaussian Modeling in Medical in Medical Linear Accelerators. Radiological Physics and Technology, 4, 173-179.

[7]   Sawkey, D.L. and Faddegon, B.A. (2009) Determination of Electron Energy, Spectral Width, and Beam Divergence at the Exit Window for Clinical Megavoltage X-Ray Beams. Medical Physics, 36, 698-707.

[8]   Huang, V.W., Senuntjens, J., Devic, S. and Verhaegen, F. (2005) Experimental Determination of Electron Source Parameters for Accurate Monte Carlo Calculation of Large Electron Therapy. Physics in Medicine and Biology, 50, 779-786.

[9]   Varian Medical Systems (2011) Monte Carlo Data Package High Energy Accelerator DWG No. 100040466-02. Rev.2.

[10]   Varian Medical Systems (2010) High Energy Systems (Clinac iX, Trilogy & Clinac Family) Data Book 100021350-02 Section 5.