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Objective. Microdosimetry offers a fast tool for radiation quality (RQ) verification to be implemented in treatment planning systems in proton therapy based on variable LET or RBE to move forward from the use of a fixed RBE of 1.1. It is known that the RBE of protons can increase up to 50% higher than that value in the last few millimetres of their range. Microdosimetry can be performed both experimentally and by means of Monte Carlo (MC) simulations. This paper has the aim of comparing the two approaches. Approach. Experimental measurements have been performed using a miniaturized Tissue equivalent proportional counter developed at the Legnaro National Laboratories of the Italian National Institute for Nuclear Physics with the aim of being used as RQ monitors for high intensity beams. MC simulations have been performed using the microdosimetric extension of TOPAS which provides optimized parameters and scorers for this application. Main results. Simulations were compared with experimental microdosimetric spectra in terms of shape of the spectra and their average values. Moreover, the latter have been investigated as possible estimators of LET obtained with the same MC code. The shape of the spectra is in general consistent with the experimental distributions and the average values of the distributions in both cases can predict the RQ increase with depth. Significance. This study aims at the comparison of microdosimetric spectra obtained from both experimental measurements and the microdosimetric extension of TOPAS in the same radiation field. [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 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]

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Ionizing radiation at aircraft and commercial suborbital spaceflight altitudes is driven by space weather and is a health concern for crew and passengers. We compare the response functions of two radiation detectors that were exposed to four different ground‐based laboratory radiation fields as well as flown alongside each other on aircraft. The detectors were a tissue equivalent proportional counter (TEPC) and a Teledyne silicon micro dosimeter chip that was integrated into an Automated Radiation Measurements for Aerospace Safety Flight Module (ARMAS FM). Both detectors were flown onboard commercial and research aircraft. In addition, both detectors were exposed neutrons at the Los Alamos Neutron Science Center, protons at Loma Linda University Medical Center, 56Fe particles at the NASA Space Radiation Laboratory, and also a gamma radiation source at Lawrence Livermore National Laboratory. The response of each of these instruments as well as derived dosimetric quantities are compared for each radiation exposure and the ratio for converting ARMAS absorbed dose in silicon to an estimated absorbed dose in tissue is obtained. This process resulted in the first definitive calibration of the silicon‐based detector like ARMAS to TEPC. In particular, with seven flights of both instruments together, the ARMAS‐derived dose in tissue was then validated with the TEPC‐measured dose in tissue and these results are reported. This work provides a method for significantly improving the accuracy of radiation measurements relevant to human tissue safety using a silicon detector that is easy to deploy and can report data in real time. Key Points: Measurements from a radiation detector based on the Teledyne uDOS001 were cross‐calibrated to measurements from a TEPC microdosimerResults from parallel exposure of these instruments in 4 different radiation fields were utilized to create a new cross‐calibration methodExcellent agreement on seven airline flight measurements was found between the TEPC and the Teledyne uDOS001 using the new method [ABSTRACT FROM AUTHOR]

Tissue equivalent proportional counter (TEPC) is used to measure the micro-dose spectrum of ionizing radiation. Through changing tissue-equivalent gas pressure, TEPC can simulate the case of radiation energy deposition in different sizes of human cells. Various dosimetric quantities can be obtained such as absorbed dose, radiation quality factor and micro-dose equivalent. Because TEPC simulated cell size is less than the range of ionizing radiation particles, TEPC can be used as linear energy transfer spectroscopy, which can identify different linear energy transfer particles in a mixed radiation field and play an important role in mixed neutron–photon radiation field monitoring and protection. A tissue equivalent proportional counter is designed and manufactured in this paper. Through the built of micro-dose detector signal testing platform, and the realization of measurement of micro-dose detector signal debugging and important parameters (stability, energy resolution, etc.) by α source method, micro-dose energy spectrum analysis and experimental measurements of Cf-252 source were ultimately achieved. Results show that the detector has good sealing performance and stability, with 12 h stability better than 2.7%. Based on all the above spectra, micro-dosing spectrum of Cf-252 source was experimentally obtained. [ABSTRACT FROM AUTHOR]