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Measurements in the stray radiation field from a proton therapy pencil beam at energies 70 and 146 MeV were performed using microdosimetric tissueequivalent proportional counters (TEPCs). The detector volumes were filled with a propane-based tissue-equivalent gas at low pressure simulating a mean chord length of 2 mmin tissue. Investigations were performed with and without a beam range shifter, and with different air gaps between the range shifter and a solid water phantom. The absorbed dose, the dose-mean lineal energy, and the dose equivalent were determined for different detector positions using the variance-covariance method. The influence from beam energy, detector- and range-shifter positions on absorbed dose, LET, and dose equivalent were investigated. Monte Carlo simulations of the fluence, detector response, and absorbed dose contribution from different particles were performed with MCNP 6.2. The simulated dose response for protons, neutrons, and photons were compared with, and showed good agreement with, previously published experimental data. The simulations also showed that the TEPC absorbed dose agrees well with the ambient absorbed dose for neutron energies above 20 MeV. The results illustrate that changes in both dose and LET variations in the stray radiation field can be identified from TEPC measurements using the variance-covariance method. The results are in line with the changes seen in the simulated relative dose contributions from different particles associated with different proton energies and range-shifter settings. It is shown that the proton contribution scattered directly from the range shifter dominates in some situations, and although the LET of the radiation is decreased, the ambient dose equivalent is increased up to a factor of 3. [ABSTRACT FROM AUTHOR]

Measurements in the stray radiation field from a proton therapy pencil beam at energies 70 and 146 MeV were performed using microdosimetric tissue-equivalent proportional counters (TEPCs). The detector volumes were filled with a propane-based tissue-equivalent gas at low pressure simulating a mean chord length of 2 μm in tissue. Investigations were performed with and without a beam range shifter, and with different air gaps between the range shifter and a solid water phantom. The absorbed dose, the dose-mean lineal energy, and the dose equivalent were determined for different detector positions using the variance–covariance method. The influence from beam energy, detector- and range-shifter positions on absorbed dose, LET, and dose equivalent were investigated. Monte Carlo simulations of the fluence, detector response, and absorbed dose contribution from different particles were performed with MCNP 6.2. The simulated dose response for protons, neutrons, and photons were compared with, and showed good agreement with, previously published experimental data. The simulations also showed that the TEPC absorbed dose agrees well with the ambient absorbed dose for neutron energies above 20 MeV. The results illustrate that changes in both dose and LET variations in the stray radiation field can be identified from TEPC measurements using the variance–covariance method. The results are in line with the changes seen in the simulated relative dose contributions from different particles associated with different proton energies and range-shifter settings. It is shown that the proton contribution scattered directly from the range shifter dominates in some situations, and although the LET of the radiation is decreased, the ambient dose equivalent is increased up to a factor of 3.

Abstract: Beam tests were performed for a Micro Pixel Chamber (-PIC) with a detection volume of to investigate the response to heavy ions. The three-dimensional tracks of carbon, silicon, and iron beams were successfully observed and their track lengths were measured. Additionally, Linear Energy Transfer (LET) distributions of each ion were obtained, and the mean LET values were consistent with the theoretical calculation of mass stopping power within an error of . This detector is a candidate for an ideal dosimeter in space. [Copyright &y& Elsevier]

Microdosimetric parameters measured by a TEPC have been studied in the mixed radiation fields generated by the two D-T neutron generators developed at BARC and IGCAR facilities of DAE, India. These two generators differ in their sizes and designs. The present study reveals that the radiation fields by these two generators are significantly different. In the case of compact design (IGCAR generator) due to the significant contribution of bremsstrahlung photons in the total radiation field, the frequency and dose mean lineal energy, average quality factors are considerably less (factors of 3 to 6) than the BARC D-T generator. The study also reveals that the photon contribution to the total dose equivalent can be as high as 30% for compact D-T generator. • Measurement of microdosimetric parameters of neutrons produced by D-T generator using TEPC. • Average quality factor of the mixed radiation field of the D-T generator. • Microdosimetric spectra of high energy neutrons. [ABSTRACT FROM AUTHOR]