In April 2011, the International Radiological Protection Committee recommended that “The equivalent dose of the crystalline lens should not exceed 20 mSv/year, averaged over defined periods of 5 years, with no single year exceeding 50 mSv”. Based on this recommendation, it is predicted that the equivalent dose limit of our crystalline lens can be lowered in the near future. Therefore, it is important to grasp the current situation of radiation exposure. The purpose of this study is to measure the crystalline lens of surgeons by focusing on the CT-fluoroscopy guided interventional radiology’s (IVRs). We also examined whether the exposure dose of the crystalline lens can be correctly evaluated by measuring the unequal exposure dose of the neck, which is usually used for the unequal exposure measurement. Results of the analysis of 200 CT-fluoroscopy guided IVR procedures showed that the unequal exposure dose of the neck was significantly correlated with the exposure dose of the crystalline lens which was measured near the left eye ball (R=0.83). However, the exposure dose of the crystalline was 33% lower than those of the neck. Therefore, although the individual dosimeter worn on the neck can be used as the useful index of the exposure dose of the crystalline lens, the results can be overestimated.
Recently, many methods are suggested to evaluate spatial resolution in MRI. However, those techniques are not simple and easy. The International Electrotechnical Commission (IEC) recommends a method to evaluate spatial resolution using a periodic pattern image as IEC 62464-1. IEC 62464-1 prescribes specifications and placement of phantom, and a method of analysis, but these details grounds are not clear. A purpose of this study is to examine the effect in each factor of IEC 62464-1 method and define the characteristics of this method. Nine phantoms with different plate thickness were made including prescribed specifications of IEC 62464-1. Imaging was conducted with changing the placement angle of these phantoms. Also, analysis was carried out in region of interest (ROI) of three different size. As a result, the placement angle of the phantom, measurement error was <1% on a condition prescribed by a method of IEC 62464-1. There was not the effect if the transverse diameter for the longitudinal diameter exceeded 100% fort the size of ROI. In specifications of the phantom, there was not the dependence for the thickness of the plate of the phantom in IEC 62464-1 prescribes.
This study was to reveal the characteristics for each correction effect of specific binding ratio (SBR) and standardized uptake value (SUV) in the dopamine transporter (DAT) single photon emission computed tomography (SPECT). We created the 123I solution of five radioactive concentrations, which was filled with two types of striatum phantom such as separated or integrated caudate and putamen. We created 10 striatum accumulation models by combining the 123I solution. Images were reconstructed using ordered subset expectation maximization (OSEM) incorporating attenuation correction (AC), scatter correction (SC) or resolution recovery (RR) for the collected data of 10 striatum accumulation models and 66 patients. Correction combinations were AC, ACSC, ACRR and ACSCRR. The SBR, SUVmean and SUVmax were evaluated correlation and relative error between SBR, SUVmean and SUVmax by each correction method. The SBR and SUV had a significant positive correlation with all correction methods. The minimum values of relative error for SBR, SUVmean and SUVmax were 39.7% with ACSCRR, 18.4% with AC and 16.5% with ACSC, respectively. In addition, the ACSC of SBR and SUVmean was almost same value. The SBR showed significantly higher values by incorporating SC, while the SUV was significantly higher values by incorporating RR. It was suggested that SUV could be used for the quantitative index of DAT SPECT. Furthermore, we demonstrated the characteristic among each correction for SBR and SUV.
Purpose: We conducted a multicenter study to investigate the current status of difference between the actual values at the patient entrance reference point (PERP) and display air kerma. Methods: We exposure dose and fluoroscopy dose were measured by 32 apparatuses at 32 member institutions of the Japanese Society of Circulation Imaging Technology (CITEC) under unified conditions, and the actual measured values and display air kerma were compared. We entrance doses during fluoroscopy and imaging were measured at the PERP, with focus detector distance (FDD) 110 cm, a copper plate of 3.5 mm in thickness adhered to the front face of flat panel detector (FPD) as absorber, field-of-view (FOV) 18 cm, and the frame rate of 15 f/s, excluding the bed. Display air kerma were recorded at the same time. JIS (Z 4751-2-43: 2012) specify “The reference air kerma rate and the cumulative reference air kerma shall not deviate from their respective display air kerma by more than ±35% over the range of 6 mGy/min and 100 mGy to the maximum value.” The number of apparatuses display air kerma deviated from this condition and its percentage were obtained. Results: The mean difference percentage between actual measured values and display air kerma in 32 apparatuses was approximately 15.6%, with some apparatuses showing substantially different display air kerma. Conclusion: In order to estimate patients’ skin exposure dose from display air kerma more accurately, it is necessary to perform calibration of the apparatus by regular dose measurement or convert values.
Some radiation detectors are used for quality assurance and measured to radiation dose for high precision external beam radiotherapy. Recently, plastic scintillation detectors for MeV X-ray measurement are commercially released. The purpose of this study was to evaluate the performance of a commercial plastic scintillation detector with respect to the dose linearity, dose rate dependence, and the output coefficient compared the ionization chamber and the semiconductor detector using each different X-ray energy with or without flattening filter. The result that the dose linearity of each detector showed a linear response in any detectors. Dose rate dependence of plastic scintillation detector was increased when setting dose rate was changed, especially setting to low dose rate. The output coefficient of plastic scintillation detector was equivalent as that of the semiconductor detector even in smallest irradiation field. In conclusion, it was suggested that the plastic scintillation detector is a suitable detector in dose verification measurements for high precision external beam radiotherapy, although we must be with care to low dose rate measurements.