Radiological Physics and Technology最新文献

Clinical studies of ion beam therapy have been performed at the Lawrence Berkeley Laboratory (LBL), National Institute of Radiological Sciences (NIRS), Gesellschaft für Schwerionenforschung (GSI), and Deutsches Krebsforschungszentrum (DKFZ), in addition to the development of equipment, biophysical models, and treatment planning systems. Although cancers, including brain tumors and pancreatic cancer, have been treated with the Bevalac's neon-ion beam at the LBL (where the first clinical research was conducted), insufficient results were obtained owing to the limited availability of neon-ion beams and immaturity of related technologies. However, the 184-Inch Cyclotron's helium-ion beam yielded promising results for chordomas and chondrosarcomas at the base of the skull. Using carbon-ion beams, NIRS has conducted clinical trials for the treatment of common cancers for which radiotherapy is indicated. Because better results than X-ray therapy results have been obtained for lung, liver, pancreas, and prostate cancers, as well as pelvic recurrences of rectal cancer, the Japanese government recently approved the use of public medical insurance for carbon-ion radiotherapy, except for lung cancer. GSI obtained better results than LBL for bone and soft tissue tumors, owing to dose enhancement enabled by scanning irradiation. In addition, DKFZ compared treatment results of proton and carbon-ion radiotherapy for these tumors. This article summarizes a series of articles (Parts 1-3) and describes future issues of immune ion beam therapy and linear energy transfer optimization.

The purpose was to investigate air-kerma area product (P_KA) and entrance surface air-kerma rate ([Formula: see text]_a,e) on the effect of the shape of automatic dose rate control (ADRC) in the presence of a wedge compensation filter. We compared and evaluated the variability of the X-ray output using a combination of wedge compensation filters and the ADRC. Two ADRC shapes (round and square) and three poly-methyl-methacrylate thicknesses (15, 20, and 25 cm) were used. A wedge compensation filter was inserted 2 cm at a time, up to 6 cm. When the wedge compensation filter was inserted to 6 cm for 20 cm of poly-methyl-methacrylate, the X-ray output fluctuated significantly. The P_KA was reduced by 39% when the wedge compensation filter was inserted to 6 cm and by 59% when it was inserted to 4 cm under round-type for 20 cm poly-methyl-methacrylate. The shape of the ADRC affects [Formula: see text]_a,e and P_KA.

This study aimed to investigate the educational environment of radiotherapy technology and medical physics specialists (RTMP) in Japan. We conducted a nationwide questionnaire survey in radiotherapy institutions between June and August 2022. Participants were asked questions regarding the educational system, perspectives on updating RTMP's skills and qualifications, and perspectives on higher education for RTMP at radiotherapy institutions. The results were then analyzed in detail according to three factors: whether the hospital was designed for cancer care, whether it was a Japanese Society for Radiation Oncology (JASTRO)-accredited hospital, and whether it was an intensity-modulated radiation therapy charged hospital. Responses were obtained from 579 (69%) nationwide radiation therapy institutions. For non-qualified RTMP, 10% of the institutions had their own educational systems, only 17% of institutions provided on-the-job training, and 84% of institutions encouraged participation in educational lectures and workshops in academic societies. However, for qualified RTMP, 3.0% of institutions had their own educational systems, only 8.9% of the institutions provided on-the-job training, and 83% encouraged participation in academic conferences and workshops. Less than 1% of the facilities offered salary increases for certification, whereas 8.2% offered consideration for occupational promotion. Regarding the educational environment, JASTRO-accredited hospitals were better than general hospitals. Few institutions have their own educational systems for qualified and non-qualified RTMP, but they encourage them to attend educational seminars and conferences. It is desirable to provide systematic education and training by academic and professional organizations to maintain the skills of individuals.

Attenuation correction (AC) is essential for quantitative positron emission tomography (PET) images. Attenuation coefficient maps (μ-maps) are usually generated from computed tomography (CT) images when PET-CT combined systems are used. If CT has been performed prior to PET imaging, pre-acquired CT can be used for brain PET AC, because the human head is almost rigid. This pre-acquired CT-based AC approach is suitable for stand-alone brain-dedicated PET, such as VRAIN (ATOX Co. Ltd., Tokyo, Japan). However, the headrest of PET is different from the headrest in pre-acquired CT images, which may degrade the PET image quality. In this study, we prepared three different types of μ-maps: (1) based on the pre-acquired CT, where namely the headrest is different from the PET system (μ-map-diffHr); (2) manually removing the headrest from the pre-acquired CT (μ-map-noHr); and (3) artificially replacing the headrest region with the headrest of the PET system (μ-map-sameHr). Phantom images by VRAIN using each μ-map were investigated for uniformity, noise, and quantitative accuracy. Consequently, only the uniformity of the images using μ-map-diffHr was out of the acceptance criteria. We then proposed an automated method for removing the headrest from pre-acquired CT images. In comparisons of standardized uptake values in nine major brain regions from the ¹⁸F-fluoro-2-deoxy-D-glucose-PET of 10 healthy volunteers, no significant differences were found between the μ-map-noHr and the μ-map-sameHr. In conclusion, pre-acquired CT-based AC with automated headrest removal is useful for brain-dedicated PET such as VRAIN.

Skin marks are widely used in external radiation therapy to ensure the accuracy of the irradiation position. However, conventional skin markers contain harmful substance, so we developed an alternative skin marker. The purpose of this study was to investigate the feasibility of using a novel water-based pigment marker comprising safe materials commonly used in cosmetics for clinical radiation therapy. We investigated various properties of the marker, namely marker longevity, color variety, line visibility, ink bleeding, and line durability, and improved the marker in response to the feel when drawing or being drawn on. The durability of the ink was evaluated by simultaneously applying the new marker and oil-based pen and comparing the period until the marks faded and became invisible. In clinical trial, we applied marks on the skin of 56 patients over three months to observe symptoms and visible changes in the skin. There were no complications of discomfort or pain, owing to the improvements in the marker tip. The marks drawn on the arms of volunteers with the new marker and the oil-based pen remained visible for a mean of 7.2 days and 3.6 days, respectively (P value < 0.001). The percentages of participants with no symptoms and no visible changes were 100%, respectively. We developed an alternative skin marker that complies with current regulatory standards by excluding crystal violet. The newly developed marker has features suitable for clinical use, such as resistance to smudging and water, marker tip shape and texture, and color variations.

We propose a novel method for calculating the effective dose that closely reflects the individual attenuation, utilizing two conversion coefficients. A total of 180 adult patients who underwent abdomen-pelvis computed tomography were categorized into six groups based on sex and body type. The effective dose was calculated by multiplying the dose-length product with the effective dose conversion coefficient and the size-specific dose estimate conversion factor. The effective dose calculated using a simulation-based dose calculator (WAZA-ARI) was employed as the reference value. The following values, obtained through both methods, were compared within each category: distribution of the effective dose, median effective dose, and relative difference in median effective dose across additional body mass index (BMI) categories. For male patients, no significant disparity was observed in the median effective doses calculated using the two methods. The relative differences in median effective doses across additional BMI categories ranged from - 5 to 6%. Conversely, among female patients, the median effective dose calculated using our method slightly undercut that calculated using WAZA-ARI, with relative differences ranging from - 16 to - 9%. Additionally, relative differences in median effective dose across additional BMI categories ranged from - 18 to - 7%. The median effective dose differed slightly depending on the calculation method because of the different reference phantoms applied in dose calculations. Our proposed method is sensitive to individual size and helps compute a size-specific effective dose.

Inter-crystal scattering (ICS) events cause degradation of the contrast in PET images. We developed the X'tal cube PET detector with submillimeter spatial resolution, which consisted of a segmented LYSO scintillator and 96 MPPCs. For this high spatial resolution PET detector, the ICS event was not negligible. In this study, we proposed a method to discriminate the ICS events and showed its feasibility by the following method. For each 96 MPPC, we measured the mean and standard deviation of the peak in the pulse height distribution obtained by the photoabsorption events in a scintillator pixel. Every time a newly detected event was identified as the segment, we monitored the reduced chi-square value that was calculated with the pulse height and the prepared mean and the standard deviation for each 96 MPPC. Since the pulse height caused by the photoabsorption event resulted in a small reduced chi-square value, we could eliminate the ICS events by setting a threshold on the reduced chi-square value. We carried out both a Monte Carlo simulation and a scanning experiment. By the simulation, we confirmed that the threshold of the reduced chi square significantly discriminated the ICS event. We obtained the response function by a scanning experiment with a 0.2 mm slit beam of 511 keV gamma-ray. The standard deviation of the response function was improved from 1.6 to 1.06 mm by eliminating the ICS events. The proposed method could significantly eliminate the ICS events and retain the true events.

This study aimed to evaluate the impact of region of interest (ROI) size on noise-power spectrum (NPS) measurement in computed tomography (CT) images and to propose a novel method for measuring NPS independent of ROI size. The NPS was measured using the conventional method with an ROI of size P × P pixels in a uniform region in the CT image; the NPS is referred to as NPS_R=P. NPSs_{R=256, 128, 64, 32, 16, and 8} were obtained and compared to assess their dependency on ROI size. In the proposed method, the true NPS was numerically modeled as an NPS_model, with adjustable parameters, and a noise image with the property of the NPS_model was generated. From the generated noise image, the NPS was measured using the conventional method with a P × P pixel ROI size; the obtained NPS was referred to as NPS'_R=P. The adjustable parameters of the NPS_model were optimized such that NPS'_R=P was most similar to NPS_R=P. When NPS'_R=P was almost equivalent to NPS_R=P, the NPS_model was considered the true NPS. NPSs_{R=256, 128, 64, 32, 16, and 8} obtained using the conventional method were dependent on the ROI size. Conversely, the NPSs (optimized NPSs_model) measured using the proposed method were not dependent on the ROI size, even when a much smaller ROI (P = 16 or 8) was used. The proposed method for NPS measurement was confirmed to be precise, independent of the ROI size, and useful for measuring local NPSs using a small ROI.

This study aimed to evaluate the detection accuracy of the AlignRT-InBore system in surface-guided radiation therapy using a phantom and to determine the feasibility of the system by conducting a comparative analysis with cone-beam computed tomography (CBCT) registration. The AlignRT-InBore system integrated with the ETHOS Therapy was used. A phantom and a QUASAR phantom were employed to examine the specific areas of interest relevant to clinical cases. The evaluation involved monitoring translations for approximately 30 min and assessing the position detection accuracy for static and moving objects. Fifty clinical cases were used to evaluate the position detection accuracy and its relationship with the localization accuracy of CBCT before treatment. The detection accuracy of static and moving objects was within 1.0 mm using the phantom. However, the longitudinal direction tended to be larger than the other directions. Regarding the accuracy of localization in clinical cases, a strong and statistically significant (p < 0.01) correlation was observed in each direction. A detection accuracy within 1.0 mm is possible for static and moving objects. The detection accuracy of the patient setup using the InBore optical patient positioning system was extremely high, and the patient could be detected with high precision, suggesting its usefulness.

This study investigated the influence of iterative reconstruction (IR) methods on computed tomography (CT) images when training convolutional neural network (CNN) models to diagnose pulmonary emphysema. To evaluate the influence of the IR algorithm on CNN, the present study comprised two steps: the comparison of noise reduction by IR algorithms using phantom examinations and the change in performance of CNN with IR algorithms using patient data. We retrospectively analyzed 97 patients. Raw CT data were reconstructed using the filtered back-projection (FBP) and adaptive statistical iterative reconstruction V (ASIR-V) algorithms with blending levels of 30%, 50%, and 70%. The models were trained using reconstructed CT images and were named the FBP, ASIR-V30, ASIR-V50, and ASIR-V70 models. The mean and the standard deviation of the CT values were 11.3 ± 21.2 at FBP, 11.0 ± 17.3 at ASIR-V30, 11.0 ± 14.4 at ASIR-V50, and 11.0 ± 11.8 at ASIR-V70. For all the evaluation metrics, the best values were obtained with the FBP model applied to the ASIR-V70 test images. The worst values were obtained with the ASIR-V70 model applied to the FBP test images. The model trained with FBP images exhibited significantly better performance than the models trained using IR images. The reduction in image noise with the IR algorithm on the test images contributed to improving the accuracy of the classification of emphysema subtypes using CNN.