bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐J‐199: A Software Tool for Quality Assurance of Online Replanning with MR‐Linac
Authors: Chen G , Ahunbay E , Li X 
Published: June 2015

Purpose:To develop a quality assurance software tool, ArtQA, capable of automatically checking radiation treatment plan parameters, verifying plan data transfer from treatment planning system (TPS) to record and verify (R&V) system, performing a secondary MU calculation considering the effect of magnetic field from MR‐Linac, and verifying the delivery and plan consistency, for online replanning.Methods:ArtQA was developed by creating interfaces to TPS (e.g., Monaco, Elekta), R&V system (Mosaiq, Elekta), and secondary MU calculation system. The tool obtains plan parameters from the TPS via direct file reading, and retrieves plan data both transferred from TPS and recorded during the actual delivery in the R&V system database via open database connectivity and structured query language. By comparing beam/plan datasets in different systems, ArtQA detects and outputs discrepancies between TPS, R&V system and secondary MU calculation system, and delivery. To consider the effect of 1.5T transverse magnetic field from MR‐Linac in the secondary MU calculation, a method based on modified Clarkson integration algorithm was developed and tested for a series of clinical situations.Results:ArtQA is capable of automatically checking plan integrity and logic consistency, detecting plan data transfer errors, performing secondary MU calculations with or without a transverse magnetic field, and verifying treatment delivery. The tool is efficient and effective for pre‐ and post‐treatment QA checks of all available treatment parameters that may be impractical with the commonly‐used visual inspection.Conclusion:The software tool ArtQA can be used for quick and automatic pre‐ and post‐treatment QA check, eliminating human error associated with visual inspection. While this tool is developed for online replanning to be used on MR‐Linac, where the QA needs to be performed rapidly as the patient is lying on the table waiting for the treatment, ArtQA can be used as a general QA tool in radiation oncology practice.This work is partially supported by Elekta Inc.
SU‐E‐J‐202: Performance of the Patient QA Systems in a Hybrid MRI‐Linac
Authors: Houweling A , Vries W de , Wolthaus J , Woodings S , van Asselen B , Kok J , Lagendijk J , Raaymakers B 
Published: June 2015

Purpose:The first clinical MR‐linac will soon become operational, therefore patient plan QA procedures and equipment have to become MRcompatible. Reference dosimetry is affected by the magnetic field, however, relative dosimetry using patient QA systems haven't been investigated extensively. The purpose of this study was to examine the performance characteristics of the MR‐compatible ArcCHECK and Delta4 systems in a transverse 1.5 T magnetic field.Methods:Recently MR‐compatible versions of both ArcCheck (Sun Nuclear) and Delta4 (Scandidos) have been developed. To examine the performance characteristics within the magnetic field, the reproducibility, dose linearity, dose rate dependence, field size and angular dependence were evaluated on the MR‐linac (8 MV FFF beam, SAD of 142 cm) and a conventional linac (Elekta, 6MV). To allow comparison of the measurements with and without magnetic field, the measurement setup for the conventional linac is adapted to mimic the setup at the MR‐linac if possible (e.g. SAD, dose rate). The results from the MR‐linac were benchmarked to the results from the conventional linac as being the clinical reference.Results:At the moment of writing, measurements for the Delta4 are still running. Therefore, only the results of the ArcCheck are presented in this abstract. No significant difference was observed in the reproducibility of the ArcCheck (<0.06%) between both linacs. The maximum dose response difference when measuring the dose linearity was less than 0.4% and the varying dose rate resulted in maximal dose differences of 1.0% for both linacs. Response variation for varying field sizes was <2.6% at the conventional linac, and <1.0% at the MR‐linac. Angular response was similar for both linacs.Conclusion:The reproducibility, dose linearity, dose rate dependence, field size and angular dependence of the MR compatible ArcCheck were not influenced by the presence of a transverse 1.5 T magnetic field. The results for the Delta4 are about to follow.Equipment is generously provided by Sun Nuclear Corporation (Melbourne, USA) and Scandidos (Uppsala, Sweden)
SU‐E‐J‐207: Effect of Pulse Sequence Parameters On Geometric Distortions Induced by a Titanium Brachytherapy Applicator
Authors: Shea S , Diak A , Surucu M , Harkenrider M , Yacoub J , Roeske J , Small W 
Published: June 2015

Purpose:To investigate the effect of readout bandwidth and voxel size on the appearance of distortion artifacts caused by a titanium brachytherapy applicator.Methods:An acrylic phantom was constructed to rigidly hold a MR conditional, titanium Fletcher‐Suit‐Delclos‐style applicator set (Varian Medical Systems) for imaging on CT (Philips Brilliance) and 1.5T MRI (Siemens Magnetom Aera). Several variants of MRI parameters were tried for 2D T2‐weighted turbo spin echo imaging in comparison against the standard clinical protocol with the criteria to keep relative SNR loss less than 20% and imaging time as short as possible. Two 3D sequences were also used for comparison with similar parameters. The applicator tandem was segmented on axial CT images (0.4×0.4×1.5mm 3 resolution) and the CT images were registered to the 3D MR images in Eclipse (Varian). The applicator volume was then overlaid on all MRI sets in 3D‐Slicer and distances were measured from the tandem tip to the MRI artifact edge in right/left/superior and anterior/posterior/superior directions from coronal and sagittal 2D acquisitions, respectively, or 3D data reformats. Artifact regions were also manually contoured in coronal/sagittal orientations for area measurements.Results:As would be expected, reductions in voxel size and increases in readout bandwidth reduced artifact size (average max artifact length decreased by 0.95 mm and average max area decrease by 0.27 cm2). Interestingly, bandwidth increases yielded reductions in area (0.19 cm2) and in distance measurements (1 mm) even with voxel increases, as compared to a standard protocol. This could be useful when high performance protocols are not feasible due to long imaging times.Conclusion:We have characterized artifacts caused by cervical brachytherapy applicator across multiple sequence parameters at 1.5T. Future work will focus on finalizing an optimal protocol that balances artifact reduction with imaging time and then testing this new protocol in patients.
SU‐E‐J‐211: Assessing the Consistency of the ViewRay 0.35 T MRI System
Authors: Yan Y , Saenz D , Bayouth J , Paliwal B 
Published: June 2015

Purpose:ViewRay is a novel image‐guided radiotherapy approach with an integrated 0.35 T MR unit and three Cobalt‐60 heads. In order to continuously ensure the high resolution and high soft tissue contrast available in MR images, we quantified a multitude of relevant imaging parameters over a period of six months to establish its stability and imaging quality. In the assessment process, consideration is also given to the need to establish the number of tests required to have confidence in the performance of the system for radiation therapy planning applications.Methods:Daily, weekly, monthly and annual imaging tests were performed over a period of six months using standardized phantoms (a 24 cm diameter sphere and the ACR phantom) to quantify the performance of the system. In addition to the ACR and NEMA recommended tests, we also included element testing, spatial integrity, Eddy current and magnetic field inhomogeneity measurements. The ACR test is used for assessing the following parameters for T1 and T2: geometric accuracy, high contrast spatial resolution, slice thickness accuracy, slice position accuracy, percent signal ghosting, low contrast object detectability. It also includes percent image uniformity (PIU) for T1. The NEMA test is primarily designed to check SNR and PIU.Results:Over the period of six months, all the parameters were maintained within the recommendations provided in the ACR and NEMA standards. PIU and SNR were found to be sensitive to malfunctions in the components of the multileaf collimators. Details of the findings will be presented.Conclusion:The data suggests that ViewRay imaging system has functioned in a consistent and reliable manner. MR imaging from ViewRay 0.35T system complies with the ACR and NEMA recommended acceptance standards.
SU‐E‐J‐213: Visualization of Scans and Metrics for Longitudinal Informatics
Authors: Apte A , Veeraraghavan H , Tyagi N , Kijewski P , Deasy J 
Published: June 2015

Purpose:To present new tools for visualizing scans across multiple timepoints alongwith changes in critical metrics.Method:MR scans for a Lung cancer patient were acquired at four different timepoints. A display consisting of 2×2 panels was developed to show the four scans in Transverse, Sagittal or Coronal cut‐planes. In order to make sure the user is looking at the same scan‐section at different timepoints, two kinds of registration modes were built in: (1) Anatomical registration: Scans at different time points are rigidly registered to the first timepoint. Here, regular anatomical structures like bones are used to drive the registration. (2) Matching tumor mid‐plane plane: In this mode the mid‐planes of the tumors are matched to register the scans. This mode is useful to users who are interested in looking at the tumor shrinkage/growth longitudinally. Once image registration is performed according to the selected mode, the user can scroll across scan slices together at different timepoints. It is possible to make fine adjustments to the image registration by nudging a particular timepoint by few slices. It is also possible to evaluate the accuracy of registration by using the spotlight tool that highlights the region selected on one of the timepoints, on all the timepoints. Linear interpolation from the neighboring scan slices is used to display a cut‐plane located in between slices. The visualization is further improved using the sinc upsampling filter. Once the scans at different timepoints are registered, it is possible to extract metrics for the structures of interest. Currently, statistical features and the first and second order texture features could be extracted at different timepoints.Results:The new features and updates are built into CERR.Conclusion:The tool developed would help visualize scans taken longitudinally along with providing insight into how the critical metrics change over time.
SU‐E‐J‐219: A Dixon Based Pseudo‐CT Generation Method for MR‐Only Radiotherapy Treatment Planning of the Pelvis and Head and Neck
Authors: Maspero M. , Seevinck P.R. , Meijer G.J. , Lagendijk J.J.W. , Viergever M.A. , van den Berg C.A.T. 
Published: June 2015

Purpose:To develop an image processing method for MRI‐based generation of electron density maps, known as pseudo‐CT (pCT), without usage of model‐ or atlas‐based segmentation, and to evaluate the method in the pelvic and head‐neck region against CT.Methods:CT and MRI scans were obtained from the pelvic region of four patients in supine position using a flat table top only for CT. Stratified CT maps were generated by classifying each voxel based on HU ranges into one of four classes: air, adipose tissue, soft tissue or bone.A hierarchical region‐selective algorithm, based on automatic thresholding and clustering, was used to classify tissues from MR Dixon reconstructed fat, In‐Phase (IP) and Opposed‐Phase (OP) images. First, a body mask was obtained by thresholding the IP image. Subsequently, an automatic threshold on the Dixon fat image differentiated soft and adipose tissue. K‐means clustering on IP and OP images resulted in a mask that, via a connected neighborhood analysis, allowing the user to select the components corresponding to bone structures.The pCT was estimated through assignment of bulk HU to the tissue classes. Bone‐only Digital Reconstructed Radiographs (DRR) were generated as well. The pCT images were rigidly registered to the stratified CT to allow a volumetric and voxelwise comparison. Moreover, pCTs were also calculated within the head‐neck region in two volunteers using the same pipeline.Results:The volumetric comparison resulted in differences <1% for each tissue class. A voxelwise comparison showed a good classification, ranging from 64% to 98%. The primary misclassified classes were adipose/soft tissue and bone/soft tissue. As the patients have been imaged on different table tops, part of the misclassification error can be explained by misregistration.Conclusion:The proposed approach does not rely on an anatomy model providing the flexibility to successfully generate the pCT in two different body sites.This research is founded by ZonMw IMDI Programme, project name: “RASOR sharp: MRI based radiotherapy planning using a single MRI sequence”, project number: 10‐104003010
SU‐E‐J‐229: Magnetic Resonance Imaging of Small Fiducial Markers for Proton Beam Therapy
Authors: Hu Y , James J , Panda A , Vargas C , Silva A , Liu W , Shen J , Ding X , Paden R , Hanson J , Wong W , Schild S , Bues M 
Published: June 2015

Purpose:For proton beam therapy, small fiducial markers are preferred for patient alignment due to less interference with the proton beam. Visualizing small fiducial markers can be challenging in MRI. This study intends to investigate MRI imaging protocols for better visualization of small fiducial markers.Methods:Two carbon and two coil‐shaped gold markers were placed into a gel phantom. Both carbon markers had a diameter of 1mm and a length of 3mm. Both gold markers had a length of 5mm. One gold marker had a diameter of 0.5mm and the other had a diameter of 0.75mm. T1 VIBE, T2 SPACE, TrueFISP and susceptibility weighted (SW) images were acquired. To improve marker contrast, high spatial resolution was used to reduce partial volume effect. Slice thickness was 1.5mm for all four sequences and in‐plane resolution was 0.6mm for TrueFISP, 0.7mm for T1 VIBE, and 0.8mm for T2 SPACE and SW. For comparison purpose, a 3D T1 VIBE image set at 3mm slice thickness and 1.2mm in‐plane resolution was also acquired.Results:All markers were visible in all high‐resolution image sets. In each image set, marker‐induced signal void was the smallest (in diameter) for carbon markers, followed by the 0.5mm gold marker and the largest for the 0.75mm gold marker. The SW images had the largest marker‐induced signal void. However, those might be confused by susceptibility‐gradient‐induced signal voids. T1 VIBE had good visualization of markers with nicely defined edges. T2 SPACE had reasonable visualization of markers but edges were slightly blurred. TrueFISP had good visualization of markers only if they were not masked by banding artifacts. As a comparison, all markers were hardly visible in the standard resolution T1 VIBE images.Conclusion:3D high‐resolution T1 VIBE and SW have great potential in providing good visualization of small fiducial markers for proton beam therapy.
SU‐E‐J‐230: Evaluation of ViewRay 0.35 T MRI Normal Structure Segmentation
Authors: Paliwal B , Asprey W , Yan Y , Saenz D , Bayouth J 
Published: June 2015

Purpose:In order to take advantage of the high resolution soft tissue imaging available in MR images, we investigated 3D images obtained with the low field 0.35 T MR in ViewRay to serve as an alternative to CT scans for radiotherapy treatment planning. In these images, normal and target structure delineation can be visualized. Assessment is based upon comparison with the CT images and the ability to produce comparable contours.Methods:Routine radiation oncology CT scans were acquired on five patients. Contours of brain, brainstem, esophagus, heart, lungs, spinal cord, and the external body were drawn. The same five patients were then scanned on the ViewRay TrueFISP‐based imaging pulse sequence. The same organs were selected on the MR images and compared to those from the CT scan. Physical volume and the Dice Similarity Coefficient (DSC) were used to assess the contours from the two systems. Image quality stability was quantitatively ensured throughout the study following the recommendations of the ACR MR accreditation procedure.Results:The highest DSC of 0.985, 0.863, and 0.843 were observed for brain, lungs, and heart respectively. On the other hand, the brainstem, spinal cord, and esophagus had the lowest DSC. Volume agreement was most satisfied for the heart (within 5%) and the brain (within 2%). Contour volume for the brainstem and lung (a widely dynamic organ) varied the most (27% and 19%).Conclusion:The DSC and volume measurements suggest that the results obtained from ViewRay images are quantitatively consistent and comparable to those obtained from CT scans for the brain, heart, and lungs. MR images from ViewRay are well‐suited for treatment planning and for adaptive MRI‐guided radiotherapy. The physical data from 0.35 T MR imaging is consistent with our geometrical understanding of normal structures.
SU‐E‐J‐233: Effect of Brachytherapy Seed Artifacts in T2 and Proton Density Maps in MR Images
Authors: Mashouf S , Fatemi‐Ardekani A , Song W 
Published: June 2015

Purpose:This study aims at investigating the influence of brachytherapy seeds on T2 and proton density (PD) maps generated from MR images. Proton density maps can be used to extract water content. Since dose absorbed in tissue surrounding low energy brachytherapy seeds are highly influenced by tissue composition, knowing the water content is a first step towards implementing a heterogeneity correction algorithm using MR images.Methods:An LDR brachytherapy (IsoAid Advantage Pd‐103) seed was placed in the middle of an agar‐based gel phantom and imaged using a 3T Philips MR scanner with a 168‐channel head coil. A multiple echo sequence with TE=20, 40, 60, 80, 100 (ms) with large repetition time (TR=6259ms) was used to extract T2 and PD maps.Results:Seed artifacts were considerably reduced on T2 maps compared to PD maps. The variation of PD around the mean was obtained as −97% to 125% (±1%) while for T2 it was recorded as −71% to 24% (±1%).Conclusion:PD maps which are required for heterogeneity corrections are susceptible to artifacts from seeds. Seed artifacts on T2 maps, however, are significantly reduced due to not being sensitive to B0 field variation.
SU‐E‐J‐235: Audiovisual Biofeedback Improves the Correlation Between Internal and External Respiratory Motion
Authors: Lee D , Greer P , Ludbrook J , Paganelli C , Pollock S , Kim T , Keall P 
Published: June 2015

Purpose:External respiratory surrogates are often used to predict internal lung tumor motion for beam gating but the assumption of correlation between external and internal surrogates is not always verified resulting in amplitude mismatch and time shift. To test the hypothesis that audiovisual (AV) biofeedback improves the correlation between internal and external respiratory motion, in order to improve the accuracy of respiratory‐gated treatments for lung cancer radiotherapy.Methods:In nine lung cancer patients, 2D coronal and sagittal cine‐MR images were acquired across two MRI sessions (pre‐ and mid‐treatment) with (1) free breathing (FB) and (2) AV biofeedback. External anterior‐posterior (AP) respiratory motions of (a) chest and (b) abdomen were simultaneously acquired with physiological measurement unit (PMU, 3T Skyra, Siemens Healthcare Erlangen, Germany) and real‐time position management (RPM) system (Varian, Palo Alto, USA), respectively. Internal superior‐inferior (SI) respiratory motions of (c) lung tumor (i.e. centroid of auto‐segmented lung tumor) and (d) diaphragm (i.e. upper liver dome) were measured from individual cine‐MR images across 32 dataset. The four respiratory motions were then synchronized with the cine‐MR image acquisition time. Correlation coefficients were calculated in the time variation of two nominated respiratory motions: (1) chest‐abdomen, (2) abdomen‐diaphragm and (3) diaphragm‐lung tumor. The three combinations were compared between FB and AV biofeedback.Results:Compared to FB, AV biofeedback improved chest‐abdomen correlation by 17% (p=0.005) from 0.75±0.23 to 0.90±0.05 and abdomen‐diaphragm correlation by 4% (p=0.058) from 0.91±0.11 to 0.95±0.05. Compared to FB, AV biofeedback improved diaphragm‐lung tumor correlation by 12% (p=0.023) from 0.65±0.21 to 0.74±0.16.Conclusions:Our results demonstrated that AV biofeedback significantly improved the correlation of internal and external respiratory motion, thus suggesting the need of AV biofeedback in respiratory‐gated treatments.
SU‐E‐J‐239: Influence of RF Coil Materials On Surface and Buildup Dose From a 6MV Photon Beam
Authors: Ghila A , Fallone B , Rathee S 
Published: June 2015

Purpose:In order to perform real time tumour tracking using an integrated Linac‐MR, images have to be acquired during irradiation. MRI uses RF coils in close proximity to the imaged volume. Given current RF coil designs this means that the high energy photons will be passing through the coil before reaching the patient. This study experimentally investigates the dose modifications that occur due to the presence of various RF coil materials in the treatment beam.Methods:Polycarbonate, copper or aluminum tape, and Teflon were used to emulate the base, conductor and cover respectively of a surface RF coil. These materials were placed at various distances from the surface of polystyrene or solid water phantoms which were irradiated in the presence of no magnetic field, a transverse 0.2T magnetic field, and a parallel 0.2T magnetic field. Percent depth doses were measured using ion chambers.Results:A significant increase in surface and buildup dose is observed. The surface dose is seen to decrease with an increasing separation between the emulated coil and the phantom surface, when no magnetic field is present. When a transverse magnetic field is applied the surface dose decreases faster with increasing separation, as some of the electrons created in the coil are curved away from the phantom's surface. When a parallel field is present the surface dose stays approximately constant for small separations, only slightly decreasing for separations greater than 5cm, since the magnetic field focuses the electrons produced in the coil materials not allowing them to scatter.Conclusion:Irradiating a patient through an RF coil leads to an increase in the surface and buildup doses. Mitigating this increase is important for the successful clinical use of either a transverse or a parallel configuration Linac‐MR unit.This project is partially supported by an operating grant from the Canadian Institute of Health Research (CIHR MOP 93752)