Energy spectra in water for the 6 MV X-ray therapeutic beam generated by Clinac-2300 linac

• Energy spectra in water were obtained by the use of Monte Carlo calculations (GEANT4).
• The studies were performed for the 6 MV X-ray beam from a medical Clinac-2300 linac.
• The spectra depend on a depth in water and on a distance from the beam central-axis.
• Shapes of the spectra and the beam mean energy depend also on a radiation field size.
• Shapes of the spectra and the beam mean energy does not depend on a bin size.

There is a lack of extensive data comprising energy spectra of therapeutic beams used in teleradiotherapy, generated by medical linear accelerators. In particular there is a lack of the data for energy spectra in water. However, the spectra in water differ from those in air significantly because of strong photon scattering processes. The aim of this paper was the presentation of the wide range of detailed data for the 6 MV X-ray therapeutic beams from a medical linear accelerator Clinac-2300 by Varian. The presented data were derived by the use of Monte Carlo computer simulations (GEANT4 code). The performed investigations indicate that shapes of the spectra, total number of photon registered in a bin as well as mean energy of the considered beam depend on a depth in water, on a distance from the central-axis of the beam and on a radiation field size. However, shapes of the spectra as well as the beam mean energy does not depend on a bin size, independently of a depth in water and a radiation field whereas total number of photon registered in a bin is related to a bin size. Majority of the presented results were obtained for a cylindrical 1.41 cm3 bin with the radius of 1.5 cm. The obtained data are very useful for the accurate absorbed depth-dose determination particularly outside the reference conditions, for advanced treatment planning systems, for constructors of medical accelerators etc.