Microdosimetry of epthermal neutron field at the Kyoto University Reactor.

Microdosimetric spctra were measured in order to gain the microdosimetric parameters of some epithermal neutron fields.Changes in dose mean lineal energy yd as a function of depth of heaby water showed a trend of softening with heaby water of the beam. The neutron absorbed dose was obtained by using the freqency mean lineal energy.Results show good agreement with measurements with the activation method using gold foil. This study demonstrated how microdosimetric parameters cahnge in radiation quality as a function of heaby water depth

Microdosimetry of KUR epithermal neutron beam.

13th SYmposium on Microdosimetr

低エネルギー陽子の照射による中性子の生物影響のメカニズム研究

研究期間:平成17-19年度 ; 研究種目:基盤研究B ; 課題番号: 1731003

Microdosimetric evaluation of secondary particles in a phantom produced by carbon 290 MeV/nucleon ions at HIMAC

Microdosimetric single event spectra as a function of depth in a phantom for the 290 MeV/nucleon therapeutic carbon beam at HIMAC were measured by using a tissue equivalent proportional counter (TEPC). Two types of geometries were used: one is a fragment particle identification measurement (PID-mode) with time of flight (TOF) method without a backward phantom, and the other is an in-phantom measurement (IPM-mode) with a backward phantom.On the PID-mode geometry, fragments produced by carbon beam in a phantom are identified by the deltaE-TOF distribution between two scintillation counters positioned up- and down-stream relative to the tissue equivalent proportional counter (TEPC). Lineal energy distributions for carbon and five ion fragments (proton, helium, lithium, beryllium and boron) were obtained in the lineal-energy range of 0.1-1000 keV/um at eight depths (7.9-147.9 mm) in an acrylic phantom. In the IPM-mode geometry, the total lineal energy distributions measured at eight depths (61.9-322.9 mm) were compared with the distributions in the PID-mode. Both spectra are consistent with each other. This shows that the PID-mode measurement can be discussed as the equivalent of the phantom measurement. The dose distribution of the carbon beam and fragments were obtained separately. In the depth dose curve, the Bragg peak was observed.Relative biological effectiveness (RBE) for the carbon beam in the acrylic phantom was obtained based on a biological response function as a lineal-energy. The RBE of carbon beam had a maximum of 4.5 at the Bragg peak. Downstream of the Bragg peak, the RBE rapidly decreases. The RBE of fragments is dominated by Boron particles around the Bragg peak region

Characterisation of an ultra-miniature counter for Microdosimetric measurements in a therapeutic 400 MeV/A Carbon beam.

Single event spectra of a clinical carbon beam have been measured by an ultra-miniature tissure-equivalent proportional counter (UMC). In order to cover the energy range of the Bragg peak, the incident energy of the carbon beam was degraded by aluminium plates. Single event spectra for carbon-events incident to the UMC were analysed and selected at several carbon energies using thin scintillation counters. It was found that the dose weighted lineal energy distributions have a doublet peak structure due to incident carbon beam and fragment contributions