Purpose: When performing single-point dose verification in VMAT, it is necessary to avoid the regions with steep dose gradient. We propose a method to obtain the estimated value ( U_plan) of uncertainty of the absolute dose measurement due to the phantom setup error by using dose gradient calculated from treatment planning system (TPS), for evaluating the appropriate measurement points. Methods: The dose gradient was calculated from the planned dose values in the vicinity of the isocenter point using TPS. The phantom setup error was estimated. The U_plan was calculated using the proposed formula after estimating the phantom setup error. Then, the dose gradient was calculated from the measured dose values in the vicinity of the isocenter point specified by TPS using the Tough water phantom with ionization chamber (IC), and U_meas was calculated as in U_plan. Results: The correlation coefficient between U_plan and U_meas was 0.984, which indicates a high correlation. The average of the difference between U_meas and U_plan was −0.24%. We considered that this result was caused by the influence of volume averaging effect of IC. Conclusion: The U_plan obtained from this proposed method reflects the uncertainty of the absolute dose measurement due to the phantom setup error and is useful for evaluating the appropriate measurement points for absolute dose measurement.

Purpose: Radiography training for students in colleges of radiology should be based on real clinical situations. The purpose of this study was to verify the clinical validity of our originally developed scenarios for chest X-ray training and the instructional contents using gaze information of experienced radiology technologists (RTs). Methods: We divided 8 RTs with different experiences into an evaluator group (3 RTs) and a subject group (5 RTs). The evaluator group created a validation model consisting of 31 items, a chest X-ray scenario, instructional contents, and gaze attention objects during the scenario. The subject group simulated chest X-ray wearing an eye tracker. The evaluator group evaluated fit rates of the validation model to subjects’ procedures based on gaze information to verify the clinical validity of the validation model. Results: The subject group procedures did not deviate from the scenario. We obtained a fit rate of 91.6±6.70%. Conclusion: Our validation model showed more than 90% fitting with the chest X-ray techniques of five RTs with different backgrounds. This result suggested that the scenario and instructional contents in this study had clinical validity.

Purpose: To verify the effectiveness of optimizing the number of mask images in DSA for radiation dose reduction during cerebral angiography. Methods: A total of 60 angiography sessions in 2 times for 30 patients performed by the same operator were included in this study. In order to compare the effects of optimization to change the injection delay time of DSA from 1 s to the shortest possible time, the number of mask images, the number of imaging frames, and radiation doses between sessions were compared and analyzed retrospectively. Results: In one DSA run, the number of mask images was decreased from 6 (5–7) to 3 (2–3) frames (p<0.01)/57.1% (median [IQR]/reduction rate), the number of imaging frames was decreased from 34 (32–36) to 32 (29–34) frames (p<0.01)/7.9%, and the radiation dose was decreased from 33 (23–47) to 30 (21–40) mGy (p<0.01)/8.3%. In magnification angiography, the reductions rate was significantly increased. In one angiography session, the number of mask images was decreased from 45 (35–72) to 19 (16–34) frames (p<0.01)/54.6%, the number of imaging frames was decreased from 242 (199–385) to 211 (181–346) frames (p<0.01)/8.3%, the radiation dose of DSA was decreased from 295 (190–341) to 242 (167–305) mGy (p<0.01)/11.6%, and the total radiation dose was decreased from 369 (259–418) to 328 (248–394) mGy (p<0.01)/7.5%. Conclusion: Using the shortest possible injection delay time for the number of mask image optimization was an effective radiation dose reduction method.

Purpose: This study aimed to compare the dose evaluation methods by constructing simulation models using the Monte Carlo calculation code and propose an evaluation method for cone beam CT (CBCT) that ensures accuracy and practicality. Methods: The Particle and Heavy Ion Transport code System (PHITS) ver. 3.26 was used as the Monte Carlo calculation code. CBCT doses were measured by CB dose index (CBDI) and American Association of Physicists in Medicine task group 111 (TG111) methods. The CBDI was compared with the equilibrium doses obtained by the TG111 method. Results: Although CBDI was lower than equilibrium doses obtained by the TG111 method, its practicality was ensured because it can be measured using the dosimeter and phantom that are commonly used. In contrast, the TG111 method guarantees accuracy, but it is difficult to prepare a long phantom to obtain the equilibrium dose. The TG111 method with a phantom length of 15 cm underestimated the equilibrium dose by 20% compared to that with a phantom length of 45 cm that satisfies the dose equilibrium. Therefore, the equilibrium dose obtained by the TG111 method with a phantom length of 15 cm is multiplied by 1.20 to obtain the equilibrium dose equivalent to that with a phantom length of 45 cm. Conclusion: This study has proposed the dose evaluation method that combines guarantees accuracy and practicality in CBCT.

The Ministry of Health, Labor and Welfare mandated the creation of the business continuity plan (BCP) for disaster key hospitals on March 31, 2017. Supposing the hospital information system (HIS) failure occurred, the picture archiving and communication system (PACS) also suffers obstacles, we assumed building a new network was necessary for radiological examination images. The purpose of this study was to investigate whether building a new network for radiological examination images is necessary in an emergency. Using wireless fidelity (Wi-Fi), the new network consisting of one image server and two tablet terminals A and B was constructed. The study measured the portable image transfer time for various stages of the network. The results were as follows: Transfer time from the mobile X-ray unit to the image server was 4.12±0.86 s, that from the image server to the tablet device A was 5.14±0.71 s, and that from the image server to the tablet device B was 7.32±1.66 s. Therefore, the new network configuration can provide a reliable means of accessing radiological images during emergency situations when the HIS and PACS may experience obstacles or failures.

Purpose: Several studies present the unsuitability of the tilted-wire method for slice sensitivity profile (SSP) in helical scan. We compared the accuracy for SSP by the tilted-wire averaging method using multiple wire profiles and by the conventional micro-coin method. Methods: A micro-coin phantom positioned at the center or the off-center was scanned using a 64-detector row CT scanner in different positions where an X-ray tube starts scanning. In the same way, tilted-wire averaging phantoms, approximately 70 mm in diameter, in the shape of a donut, 8 wires tilted from the circumference toward the center, were scanned. Images were reconstructed with a slice thickness of 0.5 mm. Results: The relative errors of full width at half maximum (FWHM) by the tilted-wire averaging method were −0.015 mm to −0.004 mm (−1.98% to −0.56%) at the center compared to those by the micro-coin method, and it is almost the same value regardless of the number of wires. Relative errors were 0.001 mm to 0.029 mm (0.11% to 3.74%) at the upper 8 cm from the center, and 0.014 mm to 0.078 mm (1.86% to 10.25%) at the upper 16 cm, and the value of relative errors increased as it got farther from the center and as the number of wires went fewer. Conclusion: This study indicated that accurate measurement of SSP may be achieved by using 4 (arranged every 90 degrees) or more averaging wires.