A: This paper presents the results of the proton irradiation of silicon photomulipliers (SiPMs) by mono-energetic 170 MeV protons with fluence up to 4.6×10 9 particles/cm 2 . In our work, three types of silicon photodetectors from Hamamatsu with areas 3×3 mm 2 and different subpixel sizes of 25×25 µm 2 , 50×50 µm 2 , and 75×75 µm 2 were used. The changes in the SiPM dark count rate (DCR) spectrum before and after irradiation in temperatures in the range of 20 • C to −65 • C are presented. The influence of the DCR changes on the energy resolution of the 662 keV gamma line from the 137 Cs for a non-irradiated GAGG:Ce (1%) scintillator is investigated. The time period of usability of the SiPM detector irradiated by protons in cosmic space was estimated.
Few studies have directly compared passive scattering (PS) to intensity-modulated proton therapy (IMPT) in the delivery of ultra-hypofractionated proton beams to the localized prostate cancer (PCa). In this preliminary study involving five patients previously treated with CyberKnife, treatment plans were created for PS and IMPT (36.25 CGE in five fractions with two opposing fields) to compare the dosimetric parameters to the planning target volume (PTV) and organs-at-risk (OAR: rectum, bladder, femoral heads). Both plans met the acceptance criteria. Significant differences were observed in the minimum and maximum doses to the PTV. The mean dose to the PTV was lower for PS (35.62 ± 0.26 vs. 37.18 ± 0.14; p = 0.002). Target coverage (D98%) was better for IMPT (96.79% vs. 99.10%; p = 0.004). IMPT resulted in significantly lower mean doses to the rectum (16.75 CGE vs. 6.88 CGE; p = 0.004) and bladder (17.69 CGE vs. 5.98 CGE p = 0.002). High dose to the rectum (V36.25 CGE) were lower with PS, but not significantly opposite to high dose to the bladder. No significant differences were observed in mean conformity index values, with a non-significant trend towards higher mean homogeneity index values for PS. Non-significant differences in the gamma index for both fields were observed. These findings suggest that both PS and IMPT ultra-hypofractionated proton therapy for PCa are highly precise, offering good target coverage and sparing of normal tissues and OARs.
The aim of this study was to investigate the absorbed dose and the linear energy transfer (LET) of a scanning proton pencil beam at the Proton Therapy Center Czech, applied to phantoms containing metal implants.
We investigated two different phantoms composed of commonly used metals with a known chemical composition. Two rectangular phantoms consisted of water-equivalent environment material with a 65 mm thickness surrounding the 2, 5, 10 and 15 mm inserts of grade-2 and grade-5 Titanium. Track-etched detectors (TEDs) were placed behind the phantoms to gather the data. The measured LET spectra behind the implants were compared with Monte Carlo simulations using the Geant4 toolkit, version 10.03.p01. The simulations were used to provide additional information regarding the contribution of each type of particles to the LET spectra (protons, alpha particles, deuteron, neutrons, photons, and electrons) and to estimate the LET spectra above the TED’s detection threshold. We used two different beam energies to study the most pertinent irradiation scenarios, one in the Bragg curve plateau and one at the maximum.
The measurement of the LET spectra behind phantoms irradiated with a proton beam in the plateau region of the Bragg curve led to the detection of numerous particles with a very high LET. Lateral dose enhancement at the border between implants and the plastic material was detected when the phantoms were exposed to a proton beam and the data were recorded in the Bragg peak maximum. In this area, the dose increased 13 times for grade-2 Ti and 12 times for grade-5 Ti.
The performed experimental study highlights the effect of dental implants on the LET spectra and absorbed dose when a proton pencil beam is crossing high-density titanium.
EBT film yielded the best visual matching. Both EBT and RTQA films confirmed good conformity between calculated and measured doses, thus confirming that wax boluses used to modify the proton beam resulted in good dose distributions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.