[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.

[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.

Multi-institutional questionnaire-based survey on online adaptive radiotherapy performed using commercial systems in Japan in 2023.

In this study, we aimed to conduct a survey on the current clinical practice of, staffing for, commissioning of, and staff training for online adaptive radiotherapy (oART) in the institutions that installed commercial oART systems in Japan, and to share the information with institutions that will implement oART systems in future. A web-based questionnaire, containing 107 questions, was distributed to nine institutions in Japan. Data were collected from November to December 2023. Three institutions each with the MRIdian (ViewRay, Oakwood Village, OH, USA), Unity (Elekta AB, Stockholm, Sweden), and Ethos (Varian Medical Systems, Palo Alto, CA, USA) systems completed the questionnaire. One institution (MRIdian) had not performed oART by the response deadline. Each institution had installed only one oART system. Hypofractionation, and moderate hypofractionation or conventional fractionation were employed in the MRIdian/Unity and Ethos systems, respectively. The elapsed time for the oART process was faster with the Ethos than with the other systems. All institutions added additional staff for oART. Commissioning periods differed among the oART systems owing to provision of beam data from the vendors. Chambers used during commissioning measurements differed among the institutions. Institutional training was provided by all nine institutions. To the best of our knowledge, this was the first survey about oART performed using commercial systems in Japan. We believe that this study will provide useful information to institutions that installed, are installing, or are planning to install oART systems.

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.

[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.

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.

Nationwide survey on pediatric CT among children of public health and school nurses to examine a possibility for a follow-up study on radiation effects.

A nationwide survey was conducted in Japan on paediatric CT among children of public health and school nurses to examine a possibility for a follow-up study on radiation effects. A survey questionnaire was sent out to 3173 public primary and junior high schools and 317 public health centres during October to December in 2009. According to the collected responses, 410 (16.2 %) children received the CT scans and the total number of CT scans was 585. Most of respondents expressed a high interest in radiation health effects and an intent to participate in the epidemiological study that will follow-up the health conditions of children. This study provides information to discuss the feasibility of the epidemiological study on health effects in children who received CT scans.