Volume 63 (2018): Edizione 1 (March 2018)

Introduction: Commissioning of the treatment-planning system includes the accuracy of dose calculations in the inhomogeneous absorber. Several results of measurements with regard to inhomogeneity correction factors (CFs) have been published. However, the dependence of CFs on photon-beam energy may preclude such results from being applied to the photon beams of general users. Purpose: The aim of this study was to assess the dependence of CFs on the photon-beam energy. Materials and methods: CFs were calculated by the Batho method for several slab geometries comprised of concentrations of lung tissue and water of 0.25 and 1.00 g/cm³, respectively. The CFs were calculated at 6 MV (TPR²⁰₁₀ = 0.67 ± k * 0.01) and 15 MV (TPR²⁰₁₀ = 0.76 ± k * 0.01) where k = -3, -2, -1, 0, 1, 2, 3. All calculations were performed in the region where a charged-particle equilibrium exists. Results: Changes in CFs of less than 2% were observed across the considered energy ranges. With a change in TPR_20,10 of 0.01, both at 6 and 15 MV at a depth of 5 cm below the lung; and lung thicknesses of 3, 5 and 8 cm over a fi eld surface area of 10 × 10 cm², the change in CF never exceeded 2.4%. The dependences of changes in CFs in terms of TPR_20,10 were 1.74% and 1.20% for field surface areas of 5 × 5 cm2 and 20 × 20 cm2, respectively. A comparison of 42 linear accelerators (LINACs) exhibiting 6 MV and 15 MV of energy installed in Poland showed that the maximum differences in terms of TPR_20,10 at 6 MV and 15 MV were 4.2% and 2.2%, respectively. Conclusion: A linear dependence of CFs on energy was observed. According to observations, the smaller the surface area of the field and deeper the point of interest below the lung, the more dependent CFs are on energy.

The paper discusses the theoretical background in terms of the use of in-phantom recombination chambers in mixed radiation fields, with special attention paid to the question of how the experimentally determined, linear-energy-transfer-dependent (LET) parameters can be applied with regard to the more accurate determination of the chamber response and absorbed dose in mixed radiation fields. Methods of taking the recombination index of radiation quality (RIQ) measurements and theoretical consideration concerning the determination of the absorbed dose are described. Classical Bragg-Gray and Spencer-Attix cavity theories were analysed and their relationship to in-phantom recombination chambers was specifi ed. Methods concerning the estimation of correction factors with regard to RIQ measurements and their importance are highlighted.

Neptunium-237 samples were irradiated in a spallation neutron field produced in accelerator-driven system (ADS) setup QUINTA. Five experiments were carried out on the accelerators at the JINR in Dubna - one in carbon (C6+), three in deuteron, and one in a proton beam. The energy in carbon was 24 GeV, in deuteron 2, 4 and 8 GeV, respectively, and 660 MeV in the proton beam. The incineration study method was based on gamma-ray spectrometry. During the analysis of the spectra several fission products and one actinide were identified. Fission product activities yielded the number of fissions. The actinide (Np-238), a result of neutron capture by Np-237, yielded the number of captures. The main goal of this work was to find out if and how the incineration rate depended on parameters of the accelerator beam.