[Evaluation of Stability and Reliability of the Measurement of Absorbed Dose-to-water for an HDR 192Ir Sandwich Setup Phantom].

PURPOSE: In this study, we evaluated the stability and reliability of absorbed dose-to-water for an HDR 192Ir sandwich setup phantom method by comparing measurements with absorbed dose-to-water determination based on the AAPM TG-43 protocol. METHODS: The sandwich setup phantom was designed with a dedicated device for two ion chamber measurements of absorbed dose-to-water for a mHDR-v2r 192Ir brachytherapy source is presented. To test the reliability of sandwich setup phantom of measurements with absorbed dose-to-water, we were compared with values based on AAPM TG-43 protocol and evaluated temporal variations of the measurement, intra-rater reliability. RESULTS: The measured doses at sandwich setup phantom agreed within 1.0% with AAPM TG-43 protocol. In all measurement fractions, the temporal variations of measurement value were less than 1.0%, and the intra-rater reliability were 0.94% or more. CONCLUSIONS: The measurement value obtained by the absorbed dose-towater had good reliability, and sandwich setup phantom is potentially useful and convenient for daily dose management of 192Ir sources in clinics.

Conspicuity of Malignant Liver Tumors on Diffusion-Weighted Imaging With Short tau Inversion Recovery After Gadolinium Ethoxybenzyl Diethylenetriaminepentaacetic Acid Administration.

BACKGROUND: Diffusion-weighted imaging (DWI) has been used for the detection and characterization of liver tumors because it has excellent contrast resolution. DWI using short tau inversion recovery (STIR) can improve tumor-to-liver contrast after gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA) administration that shortens the T1 relaxation of liver parenchyma. PURPOSE: To quantitatively and qualitatively compare the conspicuity of malignant liver tumors on DWI after Gd-EOB-DTPA administration between STIR and chemical shift selective (CHESS) sequences. STUDY TYPE: Single-institution retrospective study. SUBJECTS: Fifty-seven patients with histologically confirmed malignant liver tumors were evaluated. FIELD STRENGTH/SEQUENCE: Low b-value DWIs with STIR and CHESS sequences 18-20 minutes after Gd-EOB-DTPA administration were acquired at 1.5T. ASSESSMENT: Tumor contrast-to-noise ratio (CNR) and visual grade of tumor conspicuity on DWI between STIR and CHESS sequences were compared. STATISTICAL TESTS: Paired Student's t-test and the Wilcoxon signed rank-test were applied. P < 0.05 was considered statistically significant. RESULTS: The mean tumor CNR and visual grade of tumor conspicuity on DWI were significantly higher for STIR than for CHESS (both P < 0.001). Regardless of the presence of chronic liver disease, the mean CNR (normal liver 33.5 ± 19.8 vs. 15.7 ± 12.2, P < 0.001; chronic liver disease 19.6 ± 11.0 vs. 9.2 ± 7.8, P < 0.001) and the visual conspicuity grade (normal liver 3.36 ± 0.64 vs. 2.56 ± 0.77, P < 0.001; chronic liver disease 2.94 ± 0.80 vs. 2.25 ± 0.84, P = 0.001) were significantly higher for STIR than for CHESS. Mean CNR and the visual conspicuity grade were also significantly higher for STIR than for CHESS in patients with hepatocellular carcinomas (CNR 18.1 ± 10.5 vs. 8.8 ± 7.2, P < 0.001; visual grade 2.88 ± 0.83 vs. 2.22 ± 0.87, P = 0.001) or metastases (CNR 35.0 ± 19.3 vs. 16.2 ± 13.1, P < 0.001; visual grade 3.45 ± 0.51 vs. 2.59 ± 0.73, P < 0.001). DATA CONCLUSION: DWI using STIR may be more helpful for depicting malignant liver tumors after Gd-EOB-DTPA administration compared with DWI using CHESS. LEVEL OF EVIDENCE: 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:565-573.

[A Proposal for Evaluating the Positional Accuracy of Add-on Six-degrees-of-freedom Radiotherapy Couch in Couch Rotation for Image-guided Radiotherapy].

PURPOSE: In this study, we proposed and evaluated position correction accuracy assessment method with a phantom for IGRT system with add-on six-degrees-of-freedom radiotherapy (6D) couches in couch rotation. METHODS AND MATERIALS: A phantom was used in a self-build phantom. We were scanned with computed tomography (CT) for radiotherapy planning and planned treatment isocenter to fall in line with CT center by treatment planning system. At first, we examined data of CT slice thickness for digitally reconstructed radiograph of QA phantom. Next, we measured uncertainty for IGRT system. We performed position correction accuracy for IGRT system with QA phantom and digital angle meter. RESULTS: Detection and correction errors for pitch and roll direction were within 0.3 degree in all verifications. CONCLUSIONS: We proposed a quality control method for position correction accuracy of 6D couch. The method was able to evaluate the accuracy of detection and correction of 6D couch and revealed the deviation of the origin of the couch rotation.

[Construction of a Temporary Radiological Image Viewing Network for Large-scale Disasters].

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.

Characteristics of detection accuracy of the patient setup using InBore optical patient positioning system.

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.

Short-time-window Patlak imaging using a population-based arterial input function and optimized Bayesian penalized likelihood reconstruction: a feasibility study.

BACKGROUND: To explore the feasibility of short-time-window Ki imaging using a population-based arterial input function (IF) and optimized Bayesian penalized likelihood (BPL) reconstruction as a practical alternative to long-time-window Ki imaging with an individual patient-based IF. Myocardial Ki images were generated from 73 dynamic 18F-FDG-PET/CT scans of 30 patients with cardiac sarcoidosis. For each dynamic scan, the Ki images were obtained using the IF from each individual patient and a long time window (10-60 min). In addition, Ki images were obtained using the normalized averaged population-based IF and BPL algorithms with different beta values (350, 700, and 1000) with a short time window (40-60 min). The visual quality of each image was visually rated using a 4-point scale (0, not visible; 1, poor; 2, moderate; and 3, good), and the Ki parameters (Ki-max, Ki-mean, Ki-volume) of positive myocardial lesions were measured independently by two readers. Wilcoxon's rank sum test, McNemar's test, or linear regression analysis were performed to assess the differences or relationships between two quantitative variables. RESULTS: Both readers similarly rated 51 scans as positive (scores = 1-3) and 22 scans as negative (score = 0) for all four Ki images. Among the three types of population-based IF Ki images, the proportion of images with scores of 3 was highest with a beta of 1000 (78.4 and 72.5%, respectively) and lowest with a beta of 350 (33.3 and 23.5%) for both readers (all p < 0.001). The coefficients of determination between the Ki parameters obtained with the individual patient-based IF and those obtained with the population-based IF were highest with a beta of 1000 for both readers (Ki-max, 0.91 and 0.92, respectively; Ki-mean, 0.91 and 0.92, respectively; Ki-volume, 0.75 and 0.60, respectively; and all p < 0.001). CONCLUSIONS: Short-time-window Ki images with a population-based IF reconstructed using the BPL algorithm and a high beta value were closely correlated with long-time-window Ki images generated with an individual patient-based IF. Short-time-window Ki images using a population-based IF and BPL reconstruction might represent practical alternatives to long-time-window Ki images generated using an individual patient-based IF.

[Basic Research on Comparative Evaluation of Calculated Dose Distribution Using Monte Carlo Algorithm-equipped Treatment Planning Systems in Volumetric Modulated Arc Therapy].

PURPOSE: The purpose was to study comparative evaluation of calculated dose distribution by X-ray Voxel Monte Carlo (XVMC) for dose calculation in Acuros XB (AXB). The dose commissioning and head and neck volumetric modulated arc therapy (VMAT) clinical cases were compared for AXB in Eclipse and XVMC in Monaco. METHODS: For TrueBeam at 6 MV, we compared the dose commissioning for simple rectangle, heterogeneity correction, and multileaf collimator (MLC) characteristics. 15 clinical cases were compared for computation times, calculation accuracy, dose-volume histogram (DVH), and 3D-γ analysis (γ 3%/2 mm). RESULTS: There was no difference between the calculated values of jaw field, the measurement errors of both were within± 1%, and the dose profiles of water, bone, and lung equivalent slab phantoms were in good agreement. There was no difference in transmission, tongue and groove effect, and there was a difference of less than 10% in leaf-end transmission. In clinical cases, the computation time of XVMC was a half time that of AXB, the average values of the dose difference between the two dose calculations were -1.17±2.14%, and there was no difference in measurement error (AXB: -0.73±0.79%, XVMC: -0.07±1.21%). In DVH, max doses of XVMC were about 3% higher in planning target volume (PTV) and gross tumor volume (GTV), but the pass rate of 3D-γ analysis was overall 95.11±2.59%, which was in good agreement. CONCLUSIONS: Both dose calculation algorithms were equivalent, suggesting that Monaco XVMC is a verification method with a high accuracy for comparative evaluation of calculated dose distribution.

Secondary use of hospital information system data for safe bedside radiography in terms of patient factors.

OBJECTIVE:: The purpose of this study was to use patient data gathered by a hospital information system (HIS) to improve the safe performance of bedside radiography. METHOD:: Hierarchical cluster analysis was used to investigate the factors of hospitalised patients who had undergone radiography in the X-ray room or at the bedside. Logistic regression analysis was then performed to quantify patient factors and calculate the probability of undergoing general radiography or bedside radiography. RESULTS:: Patients were grouped into six clusters by hierarchical cluster analysis on the basis of their factors. We found a remarkable difference between clusters for the ratio of bedside radiography. Results indicated that "types of transportation" and "level of mobility" related to the ratio of bedside radiography. Logistic regression analysis of the associations between the probability of undergoing bedside radiography and patient factors indicated that type of transportation and level of mobility were highly correlated with bedside radiography or general radiography. CONCLUSION:: Our results suggested that the secondary use of HIS data for the quantitative evaluation of patient factors and implementation of those quantitative values in medical records may be useful for the safe performance of bedside radiography as well as providing a method of decision support for doctors to order bedside radiography.

COMPARISON OF THE PERIPHERAL DOSES FROM DIFFERENT IMRT TECHNIQUES FOR PEDIATRIC HEAD AND NECK RADIATION THERAPY.

Intensity-modulated radiation therapy (IMRT) can deliver high and homogeneous doses to the target area while limiting doses to organs at risk. We used a pediatric phantom to simulate the treatment of a head and neck tumor in a child. The peripheral doses were examined for three different IMRT techniques [dynamic multileaf collimator (DMLC), segmental multileaf collimator (SMLC) and volumetric modulated arc therapy (VMAT)]. Peripheral doses were evaluated taking thyroid, breast, ovary and testis as the points of interest. Doses were determined using a radio-photoluminescence glass dosemeter, and the COMPASS system was used for three-dimensional dose evaluation. VMAT achieved the lowest peripheral doses because it had the highest monitor unit efficiency. However, doses in the vicinity of the irradiated field, i.e. the thyroid, could be relatively high, depending on the VMAT collimator angle. DMLC and SMLC had a large area of relatively high peripheral doses in the breast region.

Investigation of whether in-room CT-based adaptive intracavitary brachytherapy for uterine cervical cancer is robust against interfractional location variations of organs and/or applicators.

This study investigates whether in-room computed tomography (CT)-based adaptive treatment planning (ATP) is robust against interfractional location variations, namely, interfractional organ motions and/or applicator displacements, in 3D intracavitary brachytherapy (ICBT) for uterine cervical cancer. In ATP, the radiation treatment plans, which have been designed based on planning CT images (and/or MR images) acquired just before the treatments, are adaptively applied for each fraction, taking into account the interfractional location variations. 2D and 3D plans with ATP for 14 patients were simulated for 56 fractions at a prescribed dose of 600 cGy per fraction. The standard deviations (SDs) of location displacements (interfractional location variations) of the target and organs at risk (OARs) with 3D ATP were significantly smaller than those with 2D ATP (P < 0.05). The homogeneity index (HI), conformity index (CI) and tumor control probability (TCP) in 3D ATP were significantly higher for high-risk clinical target volumes than those in 2D ATP. The SDs of the HI, CI, TCP, bladder and rectum D2cc, and the bladder and rectum normal tissue complication probability (NTCP) in 3D ATP were significantly smaller than those in 2D ATP. The results of this study suggest that the interfractional location variations give smaller impacts on the planning evaluation indices in 3D ATP than in 2D ATP. Therefore, the 3D plans with ATP are expected to be robust against interfractional location variations in each treatment fraction.