Abstract
The aim of our work is to provide the up-to-now missing information on the Siemens Artiste FFF 7 MV beam line using a Monte-Carlo model fit to the realistic dosimetric measurements at the linear accelerator in clinical use at our department. The main Siemens Artiste 6MV and FFF 7MV beams were simulated using the Geant4 toolkit. The simulations were compared with the measurements with an ionization chamber in a water phantom to verify the validation of simulation and tuning the primary electron parameters. Hereafter, other parameters such as surface dose, spectrum, electron contamination, symmetry, flatness/unflatness, slope, and characteristic off-axis changes were discussed for both Flat and FFF mode. The mean electron energy for the FFF beam was 8.8 MeV and 7.5 MeV for Flat 6 MV, the spread energy and spot size of the selected Gaussian distribution source were 0.4 MeV and 1mm, respectively. The dose rate of the FFF beam was 2.8 (2.96) times higher than for the flattened beam for a field size of 10×10 (20×20) cm2. The electron contamination has significant contribution to the surface dose especially for the flattened beam. The penumbra, surface dose and the mean energy of photons decrease by removing the flattening filter. Finally, the results show that off-axis changes have no strong effect on the mean energy of FFF beams, while this effect was more considerable for the flattened beam.
Highlights
Over the past years, flattening-filter-free (FFF) beams have gained increasing importance in radiotherapy treatment because of various advantages such as the higher dose rate and reduced treatment times, less head scatter and out-of-field dose, neutron production, and secondary cancer risk
No detailed Monte-Carlo study of the Siemens FFF beam dosimetric properties has been presented in the literature, a few studies have focused on the flat beam properties [13, 14, 15, 16, 17, 18, and 19]
The results of the optimum electron parameters for both depth-dose and beam profiles are illustrated in Fig 2 which shows the Monte Carlo validation in the case of Flat6MV and FFF beam for 10×10 and 20×20 cm2 field sizes
Summary
Over the past years, flattening-filter-free (FFF) beams have gained increasing importance in radiotherapy treatment because of various advantages such as the higher dose rate and reduced treatment times, less head scatter and out-of-field dose, neutron production, and secondary cancer risk. Some properties have been controversely discussed, such as surface dose and spectral effects, which is mainly indebted to the fact that the most often used technical implementation (Varian linacs) applies identical accelerating energy, just leaving out the flattening filter, which results in a softening of the beam. Monte-Carlo simulation of the Siemens Artiste linear accelerator flat 6 MV and FFF 7 MV beam line. Detailed information about the beam softeningeffects, surface dose, the electron contamination, spectral properties and off-axis changes can only be obtained by Monte Carlo modelling. No detailed Monte-Carlo study of the Siemens FFF beam dosimetric properties has been presented in the literature, a few studies have focused on the flat beam properties [13, 14, 15, 16, 17, 18, and 19]. One study has attempted to model the Siemens linac FFF beam [20]; they used literature data [21] to theoretically modify an existing model of a flat-beam Siemens KD accelerator (which does not offer FFF beams in reality) and presented a general analysis of beam quality specifiers rather than a model for the realistic FFF beam
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