Dosimetry and microdosimetry of 10–220 MeV proton beams with CR-39 and their verifications by calculation of reaction cross sections using ALICE, TALYS and GEANT4 codes

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Abstract

High- and intermediate-energy protons are not able to directly form a track in a CR-39 etch detector (TED). Such detectors, however, can be used for the detection and dosimetry of the beams of these particles through the registration of secondary charged particles with sufficiently high values of linear energy transfer (LET). High-energy protons (72–220 MeV) and Intermediate-energy protons (10–30 MeV) with low LET values ranging from 1.1 down to 0.4 keV/μm and 5.87 down to 2.40 keV/μm, respectively are considered in this study. It seems to be sufficient to create secondary particles, although the LET values are low. This phenomenon can modify the characteristics of the energy transfer process due to these particles, which should be taken into account when such particles are used for radiobiology studies or for radiotherapy. The importance of these secondary particles was investigated experimentally by means of an LET spectrometer based on a chemically etched track detector in which the tracks of the primary protons are not revealed. Experiments were performed with proton beams available at the Nuclear Research Center for Agriculture and Medicine (NRCAM) in Karaj, Iran and at the National Cancer Center (NCC) in Seoul, Korea with protons of primary energies of about 10–30 MeV and 72–220 MeV respectively. The contribution of the secondary particle dose increases as the proton energy decreases. The origin of the secondary particles in interactions with protons having high and intermediate energies due to various nuclear reactions was calculated by the both ALICE and TALYS computer codes. The secondary microdosimetry doses were also calculated by GEANT4 code. There is large discrepancy between experimental and calculated results in low proton energies. It has been verified that there is a good correlation between the experimentally obtained results and the reaction cross sections predicted by ALICE and TALYS codes.

Introduction

In order to create particle tracks, a solid state nuclear track detector (SSNTD) is exposed to nuclear radiation (neutrons or charged particles), etched, and later examined microscopically (Ghergherehchi et al., 2008). High-energy proton radiotherapy beams give growth to secondary heavy charged particles with raised linear energy transfer (LET) that contribute to the dose in a patient. This contribution to the characteristics of radiotherapy proton beams was experimentally considered by means of an LET spectrometer based on a track detector (Molokanov et al., 2002). Ionizing radiation damage depends both on the radiation quality (space and time distributions of dose and energy deposition distributions on the microscopic level) and on the radiation quantity (absorbed dose). There are some advantages of track detectors in comparison to other microdosimetry methods, but high-LET particles have to be considered in low LET intense radiation beams and fields, or long irradiate time is expected (Spurný et al., 2001). In this study, a spectrometer of LET based on the track detectors etched with a chemical etched poly allyl diglycol carbonate (commercially known as CR-39) was employed to determine the dosimetric and microdosimetric characteristics pertinent to the secondary high-LET particles born in the detectors irradiated in the proton beams with primary energies of 72–220 MeV. The goal of the experiments was to study qualitative and quantitative changes in the secondary particle characteristics with the mentioned proton energy.

Section snippets

Material and methods

Irradiation was performed at both NRCAM in Iran (Ghergherehchi et al., 2011) and the National Cancer Center (NCC), in Korea. The CR-39 detectors were positioned on a controlled revolving-substrate step-motor orthogonal to the beam direction inside the vacuum chamber. Our samples were irradiated by different energy cyclotron with a beam current of 5 nA over time periods ranging between 1 and 3 min. The CR-39 track detectors (available from Intercast Europe SpA via Natta 10/a 43100, Parma, Italy)

Result and discussion

The LET spectrometer has the potential to study both the dose D (L) and the dose equivalent H (L) distributions in terms of the LET. In order to determine H (L), we used the recommendations of the International Commission on Radiological Protection (ICRP) from both 1990 and 2004 for the quality factors (ICRP, 1990, 2004). To determine the LET values in the range of 17 < LET < 710 keV/μm in tissue, only the spectra for V-values ranging from V > 0.7 up to V < 1.7 were collected. The number of

Conclusion

The spectrometer of LET was used to determine the dosimetric characteristics and the LET spectra in the high-energy proton beams. The contribution of secondary neutron and δ-rays doses were found to be significant and not be able to determinate by CR-39 or other SSNTD's. Therefore for obtaining neutrons contributions it is necessary to use real time neutron spectrometers systems such as Neutron Time of Flight measurement or Neutron Unfolding techniques using NE-213 scintillator detector along

Acknowledgments

This research was supported by WCU (World Class University) program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (R31-2008-10029) and Nuclear R&D program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (2011-0020790).

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