Measurement of microdosimetric spectra with a wall-less tissue-equivalent proportional counter for a 290 MeV/u¹²C beam

Abstract

The frequency distribution of the lineal energy, y, of a 290 MeV/u carbon beam was measured to obtain the dose-weighted mean of y and compare it with the linear energy transfer (LET). In the experiment, a wall-less tissue-equivalent proportional counter (TEPC) in a cylindrical volume with a simulated diameter of 0.72 microm was used. The measured frequency distribution of y as well as its dose-mean value agrees within 10% uncertainty with the corresponding data from microdosimetric calculations using the PHITS code. The ratio of the measured dose-mean lineal energy to the LET of the 290 MeV/u carbon beam is 0.73, which is much smaller than the corresponding data obtained by a wall TEPC. This result demonstrates that a wall-less TEPC is necessary to precisely measure the dose-mean of y for energetic heavy ion beams.

Overview of the PHITS code and its application to medical physics

“…The accuracy of this calculation method was well verified by comparing the results with corresponding data measured using a wall-less tissue-equivalent proportional counter [8]. This tally function was used for calculating the organ dose equivalents based on the Q(y) relationship [9,10] and the RBE-weighted dose estimation, as described in the next section.…”

Overview of particle and heavy ion transport code system PHITS

“…The accuracy of this calculation method was well verified by comparing the results with corresponding data measured using a wall-less tissue-equivalent proportional counter (Tsuda et al, 2010). This tally function was used for calculating the organ dose equivalents based on the Q(y) relationship (Sato et al, , 2009a, which is defined in the ICRU Report 40 (ICRU, 1986).…”

MEASUREMENT OF THE STOCHASTIC RADIAL DOSE DISTRIBUTION FOR A 30-MeV PROTON BEAM USING A WALL-LESS TISSUE-EQUIVALENT PROPORTIONAL COUNTER

“…A distance of 7 mm was kept between the centre of the source and the anode during the calibration, which was performed before and after each beam irradiation. The details of the experimental conditions have been reported elsewhere (36,37) .…”

“…To further investigate the microscopic energy deposition of high-energy protons in the radial direction, a wall-less TEPC (10,36,37) has been used to measure stochastic radial dose distributions due to a narrow proton beam with kinetic energy of 30 MeV because there are little data for protons with energies of .5 MeV. This paper reports the measured values of yf( y) for a 30-MeV proton beam at different radial distances, the radially summed yf( y), a comparison of the authors' experimental yf(y) with that calculated by the particle and heavy ion transport code system, PHITS (38) , and the dependence of y D on radial distance.…”

“…The detection part of the wall-less TEPC (10,36,37) was composed of a thin anode wire and a helical cathode wire, the sizes of each of which were 3 mm in diameter and 3 mm height. The inside of the wall-less TEPC was filled with a propane-based tissue-equivalent gas (22) (TE-gas), the volume percentage of the propane being 54.7 %, the carbon dioxide 39.7 % and the nitrogen 5.6 %.…”