Development of a wavelength-separated type scintillator with optical fiber (SOF) dosimeter to compensate for the Cerenkov radiation effect.
Bottom Line: The scintillator of the current SOF dosimeter is a 1-mm diameter hemisphere.A dichroic mirror was used for separating input light signals.Individual signal counting was performed for high- and low-wavelength light signals.
Affiliation: Department of Medical Physics and Engineering, Graduate School of Medicine, Hokkaido University, N-15 W-7 Kita-ku, Sapporo Hokkaido, 060-8638, Japan firstname.lastname@example.org.Show MeSH
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Mentions: Generally, low-energy photons (e.g. under 100 keV) do not generate Cerenkov radiation in the plastic optical fiber. However, generation of a fluorescence from the optical fiber itself might be observed when irradiated with even low-energy photons (10 keV), and thus the optical fiber was shielded with 2-mm-thick lead sheet for this calibration process. A 10-kV X-ray source generated by ECLIPSE III (manufactured by AmpTek Co. Ltd, Ag target) was used to evaluate kSc. The influence of Cerenkov radiation can be ignored by using low-energy photons. Eqs. (6) and (7) can be simplified as follows:(10)Ch1low=aScCsc(11)Ch2low=aSckScCScThen kSc can be calculated by(12)kSc=Ch2lowCh1low.Calibration for the coefficients of kCere was performed by two measurements for which the dose at the scintillator was the same but the amount of Cerenkov radiation was different. Assuming that the calibration geometry of A and B have the same gamma-ray intensity as the scintillators but have different Cerenkov intensities to the optical fiber, each channel count can be expressed as follows: (13)Ch1ACh1BCh2ACh2B=11kSckCereaScCSc,AaScCSc,BaCereCCere,AaCereCCere,B(14)CSc,A=CSc,B.From Eqs. (13) and (14), kCere can be deduced as(15)kCere=Ch2A−Ch2BCh1A−Ch1B.Similarly, the water equivalent dose can be expressed by the following equation:(16)DW=α′Csc=α′aScaScCsc=α′aSckCereCh1−Ch2kCere−kSc.In this study, microSelectron HDR (manufactured by Nucletron Co. Ltd) was used for the 192Ir source. Source calibration details are shown in Table 1. For the probe calibration, the Afterloading calibration phantom (type 9193 manufactured by Nucletron Co. Ltd) was used. As shown in Fig. 4, the phantom is made of 20 cmφ × 12 cm Polymethylmethacrylate (PMMA) with four holes with diameter of 2 cmφ at 8 cm distance from the 192Ir source position (phantom center). At the distance of 8 cm, the absorbed dose rate is adjusted to ∼1 cGy/min when the 37 GBq 192Ir source is used (type 9193 phantom user's manual) . The water-equivalent dose is calculated as follows:Table 1.
Affiliation: Department of Medical Physics and Engineering, Graduate School of Medicine, Hokkaido University, N-15 W-7 Kita-ku, Sapporo Hokkaido, 060-8638, Japan email@example.com.