Radiological Physics and Technology最新文献

This study aimed to estimate the effective dose and the risk of exposure-induced cancer death (REID), as well as to establish diagnostic reference levels (DRLs) for common CT examinations conducted in Tabriz, Iran. The investigation included adult patients undergoing abdomen-pelvis, brain, neck, sinus, and chest CT scans. Patient data, exposure parameters, and radiation dose metrics, such as volume CT dose index (CTDI_vol) and dose length product (DLP), were collected and analyzed. The results showed significant variations in radiation dose across different centers for the CT scans. The average effective doses for the different CT scans were 5.65, 1.08, 1.40, 0.46, and 3.68 mSv for abdomen-pelvis, brain, neck, sinus, and chest scans, respectively. The REID values ranged from 14 per million (for sinus scans) to 196 per million (for abdomen-pelvis scans). Additionally, the DRL values for CTDIvol were 11.03 (for abdomen-pelvis), 59.52 (for brain), 8.33 (for neck), 17.05 (for sinus), and 7.83 mGy (for chest). Our results showed that most of the investigated CT scans had lower effective doses compared to the literature and the REIDs were estimated to be low. Minimizing radiation risk can be achieved by reducing CT exams and keeping doses as low as reasonably achievable. The local DRLs from this study were comparable to previous reports and can serve as benchmarks for setting national and international DRLs, helping healthcare facilities optimize radiation practices and improve patient safety in diagnostic imaging.

While layer-stacking irradiation provides a conformal dose distribution, it is vulnerable to respiratory motion. Considering that the motion tolerance has not yet been demonstrated, this study aimed to determine the tolerance level for the amount of target motion. Dose distributions considering motion were simulated for a numerical water phantom using in-house software. Comparisons with measured and simulated physical dose distributions confirmed the validity of the simulation, with gamma analysis showing almost 90% or greater agreement under all conditions with a criterion of 3%/3 mm. The variation in physical dose from static conditions followed a similar trend. Based on the evaluation of the simulated clinical dose uniformity, motion tolerance was derived. The acceptable motion amounts in the lateral direction were 11 mm in respiratory-ungated condition and at least 20 mm with 30% lateral gating at 4 Gy (RBE). In the longitudinal (beam upstream) direction, the acceptable target motion amounts were 3 mm without gating and 6 mm with gating. These results employed worst-case scenarios considering multiple respiratory cycles. In both lateral and longitudinal directions, the motion amounts of 3 mm for non-gating and 5 mm for gating were acceptable. The acceptable target motion amounts improved by 1-9 mm with gating and increased prescribed doses. The dose uniformity and motion tolerance under multiple conditions, although based on a simple system, may be useful for treatment involving target motion in layer-stacking irradiation.

The advancement of irradiation technology has increased the demand for quality control of radiation therapy equipment. Consequently, the number of quality control items and required personnel have also increased. However, differences in the proportion of qualified personnel to irradiation techniques have caused bias in quality control systems among institutions. To standardize the quality across institutions, researchers should conduct mutual quality control by analyzing the quality control data of one institution at another institution and comparing the results with those of their own institutions. This study uses failure mode and effects analysis (FMEA) to identify potential risks in 12 radiation therapy institutions, compares the results before and after implementation of mutual quality control, and examines the utility of mutual quality control in risk reduction. Furthermore, a cost-effectiveness factor is introduced into FMEA to evaluate the utility of mutual quality control.

This study evaluates the dosimetric impact of arc simulation angular resolution in VMAT-based Single Isocentre Multiple Target (SIMT) SRS, focusing on their dependence on target size, isocentre distance, number of arcs, and arc type. A phantom study analysed angular resolution (0.5°, 1°, 2°) effects on dosimetric accuracy for PTVs of 0.5 cm, 1 cm, and 2 cm at distances of 2.5 cm, 5 cm, and 7.5 cm from the isocentre using conformal arc and VMAT plans. Clinical validation involved 32 patients with 2-8 brain metastases, comparing plans recalculated at 1° and 2° resolutions. Dosimetric parameters included: D_near-Min, D_near-Max, D_mean, D_median, TV_PIV, CI_Paddick, GI, and Brain-GTV 12 Gy. For the 0.5 cm diameter target located at 7.5 cm distance from isocentre, phantom results showed TV_PIV, D_mean, and GI deviations of 7.91%, 1.8%, and 0.85 for single-conformal arcs, which decreased to 4.84%, 1.3%, and 0.77 with 4-conformal arcs, and 3.4%, 0.96%, and 0.5 for 4-arc VMAT. Deviations varied based on target size, isocentre distance, number of arcs, and arc type. Clinical results mirrored the phantom study, with maximum TV_PIV and GI deviations of 2.76% and 0.65 for the smallest target (0.6 cm) located at 7.5 cm distance for four-arc VMAT. Other dosimetric parameters showed minimal variations (< 1%). Correlation analysis revealed strong associations between dosimetric differences, target size, and distance (r = 0.6-0.78 for small targets). MANOVA identified TV_PIV as the only significant parameter (p = 0.01). A 1° angular resolution significantly improves dosimetric accuracy for small, distally located targets in SIMT SRS.

Recently, a novel wireless flat-panel detector with auto-exposure control has become available. This study aimed to elucidate the potential advantages of the new detector over conventional detectors through a comprehensive analysis of the physical image quality characteristics. Measurements were conducted on two models: new (720C) and conventional (710C) versions; this assessment was performed by assuming the beam quality for bedside chest radiography, utilizing a portable device for X-ray exposure. The detective quantum efficiency (DQE) was computed based on the presampled modulation transfer function (MTF) and normalized noise power spectrum. The validity of the DQE results was verified through the visualization of the analog blurring components and a detailed analysis of the noise components. The spatial frequency at which the presampled MTF value reached 10% was 5.2 cycles/mm for 720C and 3.9 cycles/mm for 710C. The full width at half-maximum of the spatial spreading of analog components was estimated at 0.09 mm for 720C and 0.14 mm for 710C by the visualization. Regarding the DQE, 720C was superior under low-dose conditions despite no significant differences being observed under high-dose conditions. The new detector demonstrated superior resolution characteristics compared with the conventional detector and an improvement in the DQE under low-dose conditions. However, similar to the conventional detector, a significant dose dependence caused by a structural factor was confirmed for the DQE. These results suggest the existence of an appropriate dose range for maximizing detector performance and provide insights crucial for optimization tasks in the X-ray imaging.

Patient respiration is characterized by respiratory parameters, such as cycle, amplitude, and baseline drift. In treatment planning using four-dimensional computed tomography (4DCT) images, the target dose may be affected by variations in image reconstruction techniques and respiratory parameters. This study aimed to optimize 4DCT image reconstruction techniques for the treatment planning of lung stereotactic body radiotherapy (SBRT) based on respiratory parameters using respiratory motion phantom. We quantified respiratory parameters using 30 respiratory motion datasets. The 4DCT images were acquired, and the phase- and amplitude-based reconstruction images (RI) were created. The target dose was calculated based on these reconstructed images. Statistical analysis was performed using Pearson's correlation coefficient (r) to determine the relationship between respiratory parameters and target dose in each reconstructed technique and respiratory region. In the inhalation region of phase-based RI, r of the target dose and baseline drift was -0.52. In particular, the target dose was significantly reduced for respiratory parameters with a baseline drift of 0.8 mm/s and above. No other respiratory parameters or respiratory regions were significantly correlated with target dose in phase-based RI. In amplitude-based RI, there were no significant differences in the correlation between all respiratory parameters and target dose in the exhalation or inhalation regions. These results showed that the target dose of the amplitude-based RI did not depend on changes in respiratory parameters or respiratory regions, compared to the phase-based RI. However, it is possible to guarantee the target dose by considering respiratory parameters during the inhalation region of the phase-based RI.

Despite the importance of T₂-weighted image in clinical practice, artifacts can significantly degrade image quality and affect diagnosis. This study quantitatively analyzed uterine displacement and surveyed the relationship between the image quality of fast-spin-echo-T₂-weighted image of the female pelvis and quantitative value of uterine displacement. Overall, 147 women (mean age, 46.0 ± 12.8 years; age range, 22-84 years) who had undergone pelvic magnetic resonance imaging examination using a 3 T- magnetic resonance imaging scanner were included. Two radiologists performed a visual assessment of the fast-spin-echo-T₂-weighted image in the sagittal plane in terms of ghosts and motion blur, and classified the image quality into the following three groups: poor, moderate, and excellent. Uterine displacement on half-Fourier acquisition single-shot turbo spin-echo-cine images was calculated, and the maximum amplitude of uterine displacement and summation of uterine displacement were calculated from the displacement map images. The Kruskal-Wallis and Steel-Dwass tests were performed to compare the maximum amplitude of uterine displacement and summation of uterine displacement among the three groups. Poor, moderate, and excellent image qualities were observed in 48, 71, and 28 patients, respectively. The quality of fast-spin-echo-T₂-weighted images degraded statistically significantly with P < 0.01 as the maximum amplitude of uterine displacement increased. The summation of uterine displacement in the poor and moderate groups had greater statistical significance with P < 0.01 than that in the excellent group.

The aim of this study is to evaluate the dynamic accuracy and latency of the surface-guided radiotherapy (SGRT) system using TrueBeam and AlignRT in compliance with SGRT guidelines. Beam characteristics-flatness, symmetry, beam quality, and output-were compared between gated and nongated beams using a two-dimensional ionization chamber array and a Farmer-type chamber. Dynamic accuracy was assessed using a moving platform and breast phantom, with measurements taken for various shift values (5, 10, 30 mm), region-of-interest (ROI) shapes, reference-surface image types (DICOM and capture), surface resolutions, and room illuminations. Latency due to differences in frame rates was evaluated using radiochromic film, calculated from position displacements of profiles at two speeds. Differences in beam characteristics between gated and nongated beams were within 0.1%. Dynamic accuracy showed minimal dependence on settings, with deviations of < 1 mm for a 10-mm shift. A maximum displacement of 1.9 mm was observed with a 30-mm shift at the body ROI. Beam-on latency at 12, 16, 25, and 35 frames per second was 253.2 ± 21.9, 225.7 ± 33.7, 177.1 ± 43.0, and 112.4 ± 29.2 ms, respectively, with similar trends for beam-off latency. This study is the first to evaluate the dynamic accuracy of the TrueBeam and AlignRT system under SGRT-specific settings. While accuracy was generally maintained (< 1 mm), ROI shape significantly impacted results. Latency results indicate that certain frame rates may not meet guideline limits, underscoring the need for careful SGRT system use in clinical applications.

The objective of this study is to verify whether X-ray can be visualized for imaging scattered radiation sources in X-ray radiography using a semiconductor radiation visualization camera with image processing and to evaluate its characteristics. Measurements were performed using a C-arm X-ray fluoroscopy device with a portable radiation visualization camera. The height of the radiation protective board and size of the irradiation field were the conditions that were varied during X-ray radiography. Based on the data obtained from the radiation visualization camera, output images were created displaying the intensity of the scattered radiation in color, which were then superimposed on the images captured with an optical camera. The scattered radiation generated by the phantom and within the X-ray tube were confirmed. These results indicate the feasibility of using this radiation visualization camera for imaging.

One radiation protection measure for medical personnel in X-ray fluoroscopy is using radiation protective plates. A real-time interactive tool visualizing radiation-dose distribution varied with the protective plate position will help greatly to train medical personnel to protect themselves from unnecessary radiation exposure. Monte Carlo simulation can calculate the individual interactions between radiations and objects in the X-ray room, and reproduce the complex dose distribution inside the room. However, Monte Carlo simulation is computationally time-consuming and not suited for real-time feedback. Therefore, we developed a new method to calculate the dose distribution with the presence of protective plates instantly using pre-computed directional vectors, named Directional vector-based Quick evaluation method for Protective plates Effects in X-ray fluoroscopy (DQPEX). DQPEX uses a database of dose distributions and directional vectors precomputed by Monte Carlo code, Particle and Heavy Ion Transport code System (PHITS). Assuming the dose at each position was all contributed from radiations in the direction indicated by the directional vector, the dose reduction by the protective plates at the position was determined whether the backtrace line of the directional vector has a intersect with the protective plate or not. With DQPEX, the whole dose distribution in X-ray room with the presence of a protective plate can be computed about 13 s, which is approximately 1/6000 of the full PHITS simulation. Sufficient accuracy of DQPEX to visualize the effect of a protective plate was confirmed by comparing the obtained dose distribution with those obtained by the full PHITS simulation and measurements.