ESTRO 38 Abstract book

S148 ESTRO 38

beam qualities Q and Q0 ) and the ratios fQ/fQ0 were calculated for both beam qualities and air cavities. This ratio fQ/fQ0 is the basis of beam quality correction factors. The particle transport settings and physics lists in each Monte Carlo code were adapted to simulate the radiation transport as accurately as possible. Results In Figure 1 the dose values in the water reference volume and the air cavities for both beam qualities (panel (a) for photons, panel (b) for protons) are shown for the different Monte Carlo codes. In the bottom panel the deviations relative to PENH are shown. For the photon irradiation the results from EGSnrc and PENH agree within two standard deviations or better (largest deviation 0.1%). The dose values obtained with FLUKA and Geant4/TOPAS are up to 1.4% larger compared to PENH. For the proton irradiation the deviations of the three codes capable of transporting protons (PENH, FLUKA and Geant4/TOPAS) are 1% at maximum.

calculated with literature values from [1], whereas the Boutillon theory is fitted to all data points and shown with a solid line. The general recombination parameter m obtained from the fit is in 5% agreement with values in [1], and the initial recombination parameter A in the Boutillon theory is 11 % larger than that predicted by the Jaffe theory.

Conclusion The recombination for dose rates of proton pencil beams below 1 kGy/min in the Roos type ionization chamber is found to be below 1.1 %. The recombination for high energies and dose rates is completely dominated by general recombination where the recombination increases linearly with the dose rate. The recombination for low energies and dose rates below 0.1 kGy/min, on the other hand, is relatively constant. Such a behavior suggests a need to consider initial recombination for low dose-rates which also is indicated by the agreement with the Jaffé theory. OC-0295 Comparison of PENH, FLUKA and Geant4/TOPAS for radiation transport calculations in proton beams K. Baumann 1 , F. Horst 2 , K. Zink 2 , C. Gomà 3 1 University Medical Center Giessen-Marburg, Department of Radiotherapy and Radiooncology, Marburg, Germany ; 2 University of Applied Sciences Giessen, Institute of Medical Physics and Radiation Protection, Giessen, Germany; 3 KU Leuven, Department of Oncology- Laboratory of Experimental Radiotherapy, Leuven, Belgium Purpose or Objective At the time, the IAEA TRS-398 Code of Practice is being updated. Within this framework the RTNORM project is supporting the IAEA working group with experimental as well as Monte Carlo calculated beam quality correction factors for different ionization chambers and beam qualities such as photons and protons. Whereas the use of Monte Carlo codes like EGSnrc and PENELOPE for calculations in high energy photon beams is well established, data for protons are sparce. This works compares the performance of the Monte Carlo codes PENH, FLUKA and Geant4/TOPAS in the calculation of beam quality correction factors in therapeutic proton beams. Material and Methods The absorbed dose to water ( D w) in a reference volume in a water phantom was calculated with each of the Monte Carlo codes PENH, FLUKA and Geant4/TOPAS for the beam qualities Q0 (1.25 MeV mono-energetic photons) and Q (150 MeV protons). Additionally, the absorbed dose ( D air) in two air cavities representing cylindrical and plane- parallel ionization chambers was calculated. EGS was also used to calculate D w and D air in the photon beams. From these absorbed dose values the ratios fQ=(D w /D air ) (for [1] Palmans H et al 2006 PMB 51 903-17 [2] Jaffe G 1913 Ann Phys 42 303-41 [3] TRS-398: IAEA, Vienna 2000.

In Figure 2 the ratios fQ/fQ0 for the two air cavities and each Monte Carlo code are shown. The results agree within two standard deviations or better. The maximum deviation is 0.6%.

Conclusion It was shown that by using appropriate transport settings the results of the fQ/fQ0 – ratios agreed within 0.6%, although the dose values show deviations of up to 1.4%. However, these dose discrepancies tend to cancel out in the fQ/fQ0 –ratios. In other words, PENH, FLUKA and Geant4/TOPAS are suitable to calculate fQ/fQ0 – ratios in proton beams.

Proffered Papers: PH 6: Proffered paper: X-ray guided tumour tracking

OC-0296 Validation of motion-including dose reconstruction on a ground-truth time-resolved moving anatomy J. Bertholet 1 , B. Eiben 2 , M.J. Menten 1 , E.H. Tran 2 , D.J. Hawkes 2 , S. Nill 1 , J.R. McClelland 2 , U. Oelfke 1 1 The Institute of Cancer Research and the Royal Marsden NHS Foundation Trust, Joint Department of Physics,