Component evaluation of event size spectra for a clinical 14‐MeV neutron beam

Abstract

Microdosimetric investigations were performed in a solid TE phantom at the DT-neutron generator at Hamburg-Eppendorf. Event size spectra were measured at different depths on the axis of a 10 X 10 cm2 field and at different lateral positions at a constant depth. Additionally, the microdosimetric spectrum of a 60Co source was determined. From radiobiological measurements the relative biological effectiveness (RBE) of crypt stem cells of mice was estimated as a function of lineal energy. The measured microdosimetric spectra are folded with this RBE function so that RBE values at different positions in the phantom were obtained. The predicted change of the RBE inside and outside the useful beam of a 10 X 10 cm2 field is shown. Contributions to the RBE dose from the various charged particle components are analyzed separately.

Changes in RBE of 14-MeV (d+T) neutrons for V79 cells irradiated in air and in a phantom: Is RBE enhanced near the surface?

“…Although the number of multiply scattered neutrons may be influenced by the field size -at least for narrow fields [32], the enhancement due to slow recoil protons in event size spectra measured at 0.5 cm depth [34] and the fact that RBE does not change between 1.6 cm and 9.4 cm depth inside the phantom support the notion that RBE may be significantly enhanced in surface layers of a phantom. In the present study using V79 cells, RBE for irradiation free in air was approximately 20% higher than in the phantom.…”

“…Microdosimetric measurements in the 14-MeV (d+T) beam at Hamburg demonstrated a large increase in the contribution of slow-recoil protons to the single-event energy deposition spectrum at 0.5 cm depth [34]. This was attributed to a surface effect in the phantom arising from the interaction of multiply scattered neutrons.…”

A Practical Approach for Continuous In Situ Characterization of Radiation Quality Factors in Space

“…Because microdosimetric energy distributions can be easily and continuously measured in space environments [17][18][19][20] , and assuming that an appropriate biological weighting function is available (the subject of this paper), then radiation quality factors, and thus, corresponding dose equivalents, can be continuously assessed in situ in space environments. This microdosimetric approach, originally suggested by Zaider and Brenner 21 and Bond et al 22 , and endorsed in the International Commission on Radiation Units and Measurements (ICRU) Report 40 9 , has been used extensively in other radiation exposure contexts [22][23][24][25][26][27][28][29][30][31][32][33] .…”