The goal of this research was to create the most appropriate index dose for the optimization of protection in medical exposure in general radiography in Kanagawa prefecture. We distributed questionnaires to 272 medical institutions in Kanagawa prefecture. The investigation period was from October 2015 to February 2016. Entrance surface dose (ESD) was used as the index dose. Investigated regions in general radiography were the adult chest, adult abdomen, and infant chest (anterior-posterior projections for all regions). The effective response rate was 35%. ESD was significantly lower with a flat panel detector (FPD) than with computed radiography (CR) in all regions (adult chest and abdomen: p<0.001; infant chest: p<0.05) [e.g., mean (±standard deviation) ESD in the adult chest was 0.16±0.06 mGy with FPD and 0.24±0.10 mGy with CR]. In the infant chest with CR, ESD was significantly higher using a grid (0.15±0.07 mGy) compared to not using a grid (0.10±0.05 mGy; p<0.05). Based on these results, we propose the benchmark dose of each medical equipment, such as adult chest: FPD, 0.2 mGy; CR, 0.3 mGy.

Purpose: The aim of this study was to evaluate the effect of misregistration between single-photon emission computed tomography (SPECT) and computed tomography (CT) images on bone SPECT. Methods: We acquired SPECT and CT images of a body phantom filled with bone-equivalent solution and ^99mTc for evaluation of bone SPECT. SPECT images were reconstructed using attenuation correction maps obtained by shifting the attenuation coefficients from non-shifted values (reference). Activity concentrations, SPECT standardized uptake values (SPECT-SUVs), and tumor background ratios (TBRs) were evaluated. Results: Activity concentrations and SPECT-SUVs decreased with decreasing attenuation coefficient. The difference in attenuation coefficient was especially large between the shifted-to-lung (0.085 cm⁻¹) and reference (0.249 cm⁻¹) values. Non-shifted and shifted-to-lung SPECT-SUVs were 11.5±1.0 and 2.3±0.2, respectively. TBR also decreased with decreasing attenuation coefficient. The maximum percentage change in TBR was 86% in the shifted-to-lung value. Conclusions: Our results indicate that the accuracy of activity concentration and lesion detectability was commonly affected by misalignment between SPECT and CT images. Although the impact of SPECT/CT misregistration on bone SPECT is case-specific and difficult to predict, it is important to reduce the incidence of misregistration errors for quantitative bone SPECT imaging.

Purpose and Methods: External radiotherapy of target regions using high-energy beams leads to excessive exposure along with individual variation in therapeutic and adverse effects. However, high-precision radiotherapy utilizes 3D-multi detector computed tomography to confirm both target position and administer radiation dose. To install the individual bioinformation in the radiotherapy plan (particularly, radiosensitivity into the target region and/or the around normal tissue), the investigation of biomarkers, which are able to estimate their radiosensitivity was performed. The aim of this investigation is to screen for suitable radiosensitivity biomarkers using the human colorectal cancer-derived HCT 116 cell line. Results: We found that cell damage and micronucleus frequency significantly increased dose dependently after exposure to 6 Gy X-irradiation (1 Gy/min). In contrast, total RNA concentration (69.8–85.2 ng/ml) remained stable in the cell culture supernatant despite radiation dose variation. Additionally, 52 specific micro RNAs were detected after exposure to 6 Gy X-irradiation. Conclusion: These results suggest that radiosensitivity, including extent of cellular damage in target or normal tissue, can be indirectly estimated by monitoring the expression of micro RNAs.

It is a useful method for the adaptive radiotherapy (ART) to calculate absorbed dose accurately on the image set taken by on-board cone beam computed tomography (CBCT) attached to linac for image-guided radiation therapy (IGRT). For this purpose, a simple and accurate calculation method is necessary. Several papers report that it is possible to calculate easily and accurately by using several methods of researches in the neck and prostate, but the lung density varies greatly depending on patient thorax condition. In this study, we propose a new dose recalculation method, which is a simple procedure and can achieve accurate dose calculation considered different lung densities in each patient. By using this method, it is possible to calculate exclusive of artifacts in CBCT because of overriding the lung density. The dose error between dose recalculation of the CBCT image and treatment plan agreed within±1%. Therefore, this method is expected to be a useful method for accurate dose calculation with CBCT image for ART.

Recently, a medical linear accelerator with a flattening filter free (FFF) mode has led to the use of FFF X-ray beams at clinical sites. The usefulness of FFF X-ray beams in high-precision radiation therapy has been reported. Therefore, the quality assurance and quality control for FFF X-ray beams have become necessary. In this study, the characteristics of the detectors of a newly developed 2-D diode array (MapCHECK2, Sun Nuclear Corporation) for FFF X-ray beams, i.e., dose reproducibility, dose rate dependence, dose linearity, and output factor, were evaluated. For the measurements, 6 and 10 MV FFF beams were used. The results showed that the coefficient of variation for dose reproducibility was within 0.08%, the dose rate dependence was less than 1.0%, the coefficient of determination of dose linearity was found to be R²=1.0, which was high, and the output factor agreed within 2.5% as compared with the farmer ion chamber, diode E, and pinpoint ion chamber for field sizes greater than 2×2 cm². The results suggested that MapCHECK2 could be a useful tool for quality assurance and quality control for FFF X-ray beams.