bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐J‐188: Theoretical Estimation of Margin Necessary for Markerless Motion Tracking
Authors: Patel R , Block A , Harkenrider M , Roeske J 
Published: June 2015

Purpose:To estimate the margin necessary to adequately cover the target using markerless motion tracking (MMT) of lung lesions given the uncertainty in tracking and the size of the target.Methods:Simulations were developed in Matlab to determine the effect of tumor size and tracking uncertainty on the margin necessary to achieve adequate coverage of the target. For simplicity, the lung tumor was approximated by a circle on a 2D radiograph. The tumor was varied in size from a diameter of 0.1 − 30 mm in increments of 0.1 mm. From our previous studies using dual energy markerless motion tracking, we estimated tracking uncertainties in × and y to have a standard deviation of 2 mm. A Gaussian was used to simulate the deviation between the tracked location and true target location. For each size tumor, 100,000 deviations were randomly generated, the margin necessary to achieve at least 95% coverage 95% of the time was recorded. Additional simulations were run for varying uncertainties to demonstrate the effect of the tracking accuracy on the margin size.Results:The simulations showed an inverse relationship between tumor size and margin necessary to achieve 95% coverage 95% of the time using the MMT technique. The margin decreased exponentially with target size. An increase in tracking accuracy expectedly showed a decrease in margin size as well.Conclusion:In our clinic a 5 mm expansion of the internal target volume (ITV) is used to define the planning target volume (PTV). These simulations show that for tracking accuracies in × and y better than 2 mm, the margin required is less than 5 mm. This simple simulation can provide physicians with a guideline estimation for the margin necessary for use of MMT clinically based on the accuracy of their tracking and the size of the tumor.
SU‐E‐J‐189: Determination of Markerless Lung Tumor Position in Real Time: A Feasibility Study Using a Novel Tomo‐Cinegraphy Imaging
Authors: Yi B , Hu E , Yu C , Lee M , Lasio G 
Published: June 2015

Purpose:A Tomo‐Cinegraphy (TC) is a method to generate a series of temporal tomographic images from projection images of the on‐board imager (OBI) while gantry is moving. It is to test if this technique is useful to determine a lung tumor position during treatments.Methods:Tomographic image via background subtraction, TIBS uses a priori anatomical information from a previous CT scan to isolate a SOI from a planar kV image by factoring out the attenuations by tissues outside the SOI (background). This idea was extended to a TC, which enables to generate tomographic images of same geometry from the projection of different gantry angles and different breathing phases. Projection images of a lung patient for CBCT acquisition are used to generate TC images. A region of interest (ROI) is selected around a tumor adding 2cm margins. Center of mass (COM) of the ROI is traced to determine tumor position for every projection images.Results:Tumor is visible in the TC images while the OBI projections are not. The coordinates of the COMs represent the temporal tumor positions. While, it is not possible to trace the tumor motion using the projection images. A source of time delay is the time to acquire projection images, which is always less than a second.Conclusion:TC allows tracking the tumor positions without fiducial markers in real time for some lung patients, if the projection images are acquired during treatments.Partially supported by NIH R01CA133539.
SU‐E‐J‐195: Evaluation of a Camera‐Based External Patient Position Tracking System
Authors: Jeung A , Sloutsky A , Mostafavi H 
Published: June 2015

Purpose:To evaluate the accuracy of a camera‐based patient external position monitoring system optimized for localized patient movements.Methods:A prototype software application implements a template‐based tracking algorithm. The application generates templates located at strategic points on the patient's anatomy as seen in an acquired initial video image frame. For subsequent frames, the template pattern is matched in a userdefined region around those points using cross‐correlation, and the match is used to determine the local motion at those points.A motion stage was used to move a fabric sample (representing patient's clothing) to various positions around a 20 by 20 mm space. An optical camera, at 1.5 m distance, monitored the movement of the sample. At each sample position, the software application evaluated the displacement from initial position based on the camera image; results were compared to the known motion stage displacements.A motorized breathing manikin was set up on a treatment machine couch. The same optical camera was positioned so as to monitor both breathing and random motion of the manikin in simulation of a clinical treatment scenario. Setups for both torso tracking (respiratory) and face tracking (stereotactic head) conditions were simulated and measured for precision and accuracy.Results:On the motion stage, calibrated tracking accuracy and precision were both consistently better than 0.5 mm in both vertical and lateral axes. Similar results were achieved for the manikin motion in the clinical simulations.Conclusion:Localized camera‐based tracking is capable of monitoring external changes in patient position to submillimeter level. While not able to track internal tumor motion directly, such a system would nonetheless be able to detect tiny movements of the body, bumps, and respiratory motion, any of which may signal a need to check the position of the tumor.All work funded by Varian Medical Systems Inc.
SU‐E‐J‐198: Out‐Of‐Field Dose and Surface Dose Measurements of MRI‐Guided Cobalt‐60 Radiotherapy
Authors: Lamb J , Agazaryan N , Cao M , Low D , Thomas D , Yang Y 
Published: June 2015

Purpose:To measure quantities of dosimetric interest in an MRI‐guided cobalt radiotherapy machine that was recently introduced to clinical use.Methods:Out‐of‐field dose due to photon scatter and leakage was measured using an ion chamber and solid water slabs mimicking a human body. Surface dose was measured by irradiating stacks of radiochromic film and extrapolating to zero thickness. Electron out‐of‐field dose was characterized using solid water slabs and radiochromic film.Results:For some phantom geometries, up to 50% of Dmax was observed up to 10 cm laterally from the edge of the beam. The maximum penetration was between 1 and 2 mm in solid water, indicating an electron energy not greater than approximately 0.4 MeV. Out‐of‐field dose from photon scatter measured at 1 cm depth in solid water was found to fall to less than 10% of Dmax at a distance of 1.2 cm from the edge of a 10.5 × 10.5 cm field, and less that 1% of Dmax at a distance of 10 cm from field edge. Surface dose was measured to be 8% of Dmax.Conclusion:Surface dose and out‐of‐field dose from the MRIguided cobalt radiotherapy machine was measured and found to be within acceptable limits. Electron out‐of‐field dose, an effect unique to MRI‐guided radiotherapy and presumed to arise from low‐energy electrons trapped by the Lorentz force, was quantified.Dr. Low is a member of the scientific advisory board of ViewRay, Inc.
SU‐E‐J‐204: Can a Commercial System for MR‐IGRT Be Used to Treat Patients Without Acquiring a CT Scan?
Authors: Wooten H , Yaddanapudi S , Santanam L , Li H , Mutic S 
Published: June 2015

Patients treated using a magnetic‐resonance image guided radiation therapy (MR‐IGRT) system received both CT and MR simulations. During planning, the CT is used to determine relative electron density (RED) using a calibration table. This study aims to investigate the feasibility of MR‐only treatments by comparing CT‐computed dose distributions to those computed with combinations of water (1.0), lung (0.26), tissue (1.02), and bone (1.12) bulk RED overrides, and to identify the effects of the magnetic field on the RED‐overridden doses.Methods:Four patients who received treatment using a commercial MR‐IGRT system were analyzed (1 lung, 2 abdomen, and 1 pelvis). The clinical plans were computed using the first fraction MRI as primary, and the simulation CT as secondary for REDs. Plans were reoptimized using default bulk RED overrides (water/lung and tissue/lung for the lung patient, water/bone, tissue/bone, water only, and tissue only for the abdomen and pelvis patients). Additionally, each plan was re‐optimized to include the static magnetic field. All plans were normalized to the same PTV coverage as the clinical plan. Dose‐difference volumes and DVHs were computed for bulk density override plans, and 3D gamma analyses between each plan and its accompanying magnetic field plan were performed using 3%/3 mm dose difference and distance‐to‐agreement criteria using the PTV and Skin as masking structures.Results:The average differences in PTV and organs‐at‐risk mean dose for all RED combinations tested were −0.19 Gy (−0.62 – 0.06 Gy) and −0.34 Gy (−1.76 – 0.33 Gy), respectively. The average PTV and Skin gamma pass rates for all RED combinations tested were 99.88% (99.5% – 100%) and 98. 35% (96.3% – 99.6%). No systematic differences in DVHs or isodoses were observed.Conclusions:It is likely that that a commercial MR‐IGRT system may produce high quality treatment plans without the need for CT scans.Authors of this abstract are members of the Washington University Radiation Oncology department, which has a research agreement with ViewRay, Inc.
SU‐E‐J‐205: Dose Distribution Differences Caused by System Related Geometric Distortion in MRI‐Guided Radiation Treatment System
Authors: Wang J , Yang J , Marshall S , Wen Z , Court L , Ibbott G 
Published: June 2015

Purpose:MRI has superb soft tissue contrast but is also known for geometric distortions. The concerns and uncertainty about MRI's geometric distortion have contributed to the hesitation of using only MRI for simulation in radiation therapy. There are two major categories of geometric distortion in MRI; system related and patient related. In this presentation, we studied the impact of system‐related geometric distortion on dose distribution in a digital body phantom under an MR‐Linac environment.Methods:Residual geometric distortion (after built‐in geometric correction) was modeled based on phantom measurements of the system‐related geometric distortions of a MRI scanner of a combined MR guided Radiation Therapy (MRgRT) system. A digital oval shaped phantom (40×25 cm) as well as one ellipsoid shaped tumor volume was created to simulate a simplified human body. The simulated tumor volume was positioned at several locations between the isocenter and the body surface. CT numbers in HUs that approximate soft tissue and tumor were assigned to the respective regions in the digital phantom. To study the effect of geometric distortion caused by system imperfections, an IMRT plan was optimized with the distorted image set with the B field. Dose distributions were re‐calculated on the undistorted image set with the B field (as in MR‐Linac).Results:The maximum discrepancies in both body contour and tumor boundary was less than 2 mm, which leads to small dose distribution change. For the target in the center, coverage was reduced from 98.8% (with distortion) to 98.2%; for the other peripheral target coverage was reduced from 98.4% to 95.9%.Conclusion:System related geometric distortions over the 40×25 area were within 2mm and the resulted dosimetric effects were minor for the two tumor locations in the phantom. Patient study will be needed for further investigation.The authors received a corporate research grant from Elekta
SU‐E‐J‐206: Adaptive Radiotherapy for Gynecological Malignancies with MRIGuided Cobolt‐60 Radiotherapy
Authors: Lamb J , Kamrava M , Agazaryan N , Cao M , Low D , Thomas D , Yang Y 
Published: June 2015

Purpose:Even in the IMRT era, bowel toxicity and bone marrow irradiation remain concerns with pelvic irradiation. We examine the potential gain from an adaptive radiotherapy workflow for post‐operative gynecological patients treated to pelvic targets including lymph nodes using MRI‐guided Co‐60 radiation therapy.Methods:An adaptive workflow was developed with the intent of minimizing time overhead of adaptive planning. A pilot study was performed using retrospectively analyzed images from one patient's treatment. The patient's treated plan was created using conventional PTV margins. Adaptive treatment was simulated on the patient's first three fractions. The daily PTV was created by removing non‐target tissue, including bone, muscle and bowel, from the initial PTV based on the daily MRI. The number of beams, beam angles, and optimization parameters were kept constant, and the plan was re‐optimized. Normal tissue contours were not adjusted for the re‐optimization, but were adjusted for evaluation of plan quality. Plan quality was evaluated based on PTV coverage and normal tissue DVH points per treatment protocol. Bowel was contoured as the entire bowel bag per protocol at our institution. Pelvic bone marrow was contoured per RTOG protocol 1203.Results:For the clinically treated plan, the volume of bowel receiving 45 Gy was 380 cc, 53% of the rectum received 30 Gy, 35% of the bladder received 45 Gy, and 28% of the pelvic bone marrow received 40 Gy. For the adaptive plans, the volume of bowel receiving 45 Gy was 175–201 cc, 55–62% of the rectum received 30 Gy, 21– 27% of the bladder received 45 Gy, and 13–17% of the pelvic bone marrow received 40 Gy.Conclusion:Adaptive planning led to a large reduction of bowel and bone marrow dose in this pilot study. Further study of on‐line adaptive techniques for the radiotherapy of pelvic lymph nodes is warranted.Dr. Low is a member of the scientific advisory board of ViewRay, Inc.
SU‐E‐J‐214: MR Protocol Development to Visualize Sirius MRI Markers in Prostate Brachytherapy Patients for MR‐Based Post‐Implant Dosimetry
Authors: Lim T , Wang J , Frank S , Stafford R , Bruno T , Bathala T , Mahmood U , Pugh T , Ibbott G , Kudchadker R 
Published: June 2015

Purpose:The current CT‐based post‐implant dosimetry allows precise seed localization but limited anatomical delineation. Switching to MR‐based post‐implant dosimetry is confounded by imprecise seed localization. One approach is to place positive‐contrast markers (Sirius) adjacent to the negative‐contrast seeds. This patient study aims to assess the utility of a 3D fast spoiled gradient‐recalled echo (FSPGR) sequence to visualize Sirius markers for post‐implant dosimetry.Methods:MRI images were acquired in prostate implant patients (n=10) on Day 0 (day‐of‐implant) and Day 30. The post‐implant MR protocol consisted of 3D T2‐weighted fast‐spin‐echo (FSE), T2‐weighted 2D‐FSE (axial) and T1‐weighted 2D‐FSE (axial/sagittal/coronal). We incorporated a 3D‐FSPGR sequence into the post‐implant MR protocol to visualize the Sirius markers. Patients were scanned with different number‐of‐excitations (6, 8, 10), field‐of‐view (10cm, 14cm, 18cm), slice thickness (1mm, 0.8mm), flip angle (14 degrees, 20 degrees), bandwidth (122.070 Hz/pixel, 325.508 Hz/pixel, 390.625 Hz/pixel), phase encoding steps (160, 192, 224, 256), frequency‐encoding direction (right/left, anterior/posterior), echo‐time type (minimum‐full, out‐of‐phase), field strength (1.5T, 3T), contrast (with, without), scanner vendor (Siemens, GE), coil (endorectal‐coil only, endorectal‐and‐torso‐coil, torsocoil only), endorectal‐coil filling (30cc, 50cc) and endorectal‐coil filling type (air, perfluorocarbon [PFC]). For post‐implant dosimetric evaluation with greater anatomical detail, 3D‐FSE images were fused with 3D‐FSPGR images. For comparison with CT‐based post‐implant dosimetry, CT images were fused with 3D‐FSPGR images.Results:The 3D‐FSPGR sequence facilitated visualization of markers in patients. Marker visualization helped distinguish signal voids as seeds versus needle tracks for more definitive MR‐based post‐implant dosimetry. On the CT‐MR fused images, the distance between the seed on CT to MR images was 3.2±1.6mm in patients with no endorectal coil, 2.3±0.8mm in patients with 30cc‐PFC‐filled endorectal‐coil and 5.0±1.8mm in patients with 50cc‐PFC‐filled endorectal‐coil.Conclusion:An MR protocol to visualize positive‐contrast Sirius markers to assist in the identification of negative‐contrast seeds was demonstrated.S Frank is a co‐founder of C4 Imaging LLC, the manufacturer of the MRI markers.
SU‐E‐J‐215: Towards MR‐Only Image Guided Identification of Calcifications and Brachytherapy Seeds: Application to Prostate and Breast LDR Implant Dosimetry
Authors: Elzibak A , Fatemi‐Ardekani A , Soliman A , Mashouf S , Safigholi H , Han D , Ravi A , Morton G , Song WY 
Published: June 2015

Purpose:To identify and analyze the appearance of calcifications and brachytherapy seeds on magnitude and phase MRI images and to investigate whether they can be distinguished from each other on corrected phase images for application to prostate and breast low dose rate (LDR) implant dosimetry.Methods:An agar‐based gel phantom containing two LDR brachytherapy seeds (Advantage Pd‐103, IsoAid, 0.8mm diameter, 4.5mm length) and two spherical calcifications (large: 7mm diameter and small: 4mm diameter) was constructed and imaged on a 3T Philips MR scanner using a 16‐channel head coil and a susceptibility weighted imaging (SWI) sequence (2mm slices, 320mm FOV, TR/ TE= 26.5/5.3ms, 15 degree flip angle). The phase images were unwrapped and corrected using a 32×32, 2D Hanning high pass filter to remove background phase noise. Appearance of the seeds and calcifications was assessed visually and quantitatively using Osirix (http://www.osirix‐viewer.com/).Results:As expected, calcifications and brachytherapy seeds appeared dark (hypointense) relative to the surrounding gel on the magnitude MRI images. The diameter of each seed without the surrounding artifact was measured to be 0.1 cm on the magnitude image, while diameters of 0.79 and 0.37 cm were measured for the larger and smaller calcifications, respectively. On the corrected phase images, the brachytherapy seeds and the calcifications appeared bright (hyperintense). The diameter of the seeds was larger on the phase images (0.17 cm) likely due to the dipole effect.Conclusion:MRI has the best soft tissue contrast for accurate organ delineation leading to most accurate implant dosimetry. This work demonstrated that phase images can potentially be useful in identifying brachytherapy seeds and calcifications in the prostate and breast due to their bright appearance, which helps in their visualization and quantification for accurate dosimetry using MR‐only. Future work includes optimizing phase filters to best identify and delineate seeds and calcifications.
SU‐E‐J‐217: Multiparametric MR Imaging of Cranial Tumors On a Dedicated 1.0T MR Simulator Prior to Stereotactic Radiosurgery
Authors: Wen N , Glide‐Hurst C , Liu M , Hearshen D , Brown S , Siddiqui S , Chetty I 
Published: June 2015

Purpose:Quantitative magnetic resonance imaging (MRI) of cranial lesions prior to stereotactic radiosurgery (SRS) may improve treatment planning and provide potential prognostic value. The practicality and logistics of acquiring advanced multiparametric MRI sequences to measure vascular and cellular properties of cerebral tumors are explored on a 1.0 Tesla MR Simulator.Methods:MR simulation was performed immediately following routine CT simulation on a 1T MR Simulator. MR sequences used were in the order they were performed: T2‐Weighted Turbo Spin Echo (T2W‐TSE), T2 FLAIR, Diffusion‐weighted (DWI, b = 0, 800 to generate an apparent diffusion coefficient (ADC) map), 3D T1‐Weighted Fast Field Echo (T1W‐FFE), Dynamic Contrast Enhanced (DCE) and Post Gadolinium Contrast Enhanced 3D T1W‐FFE images. T1 pre‐contrast values was generated by acquiring six different flip angles. The arterial input function was derived from arterial pixels in the perfusion images selected manually. The extended Tofts model was used to generate the permeability maps. Routine MRI scans took about 30 minutes to complete; the additional scans added 12 minutes.Results:To date, seven patients with cerebral tumors have been imaged and tumor physiology characterized. For example, on a glioblastoma patient, the volume contoured on T1 Gd images, ADC map and the pharmacokinetic map (Ktrans) were 1.9, 1.4, and 1.5 cc respectively with strong spatial correlation. The mean ADC value of the entire volume was 1141 μm2/s while the value in the white matter was 811 μm2/s. The mean value of Ktrans was 0.02 min‐1 in the tumor volume and 0.00 in the normal white matter.Conclusion:Our initial results suggest that multiparametric MRI sequences may provide a more quantitative evaluation of vascular and tumor properties. Implementing functional imaging during MR‐SIM may be particularly beneficial in assessing tumor extent, differentiating radiation necrosis from tumor recurrence, and establishing reliable bio‐markers for treatment response evaluation.The Department of Radiation Oncology at Henry Ford Health System has research agreement with Varian Medical System and Philips Health Care.
SU‐E‐J‐226: Efficient Use of Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) for Cervical‐Cancer Brachytherapy
Authors: Damato A , Bhagwat M , Buzurovic I , Cormack R , Lee L , Viswanathan A 
Published: June 2015

Purpose:To investigate image modality selection in an environment with limited access to interventional MRI for image‐guided high‐dose‐rate cervical‐cancer brachytherapy.Methods:Records of all cervical‐cancer patients treated with brachytherapy between 1/2013 and 8/2014 were analyzed. Insertions were performed under CT guidance (CT group) or with >1 fraction under 3T MR guidance (MRI group; subMRI includes only patients who also had a CT‐guided insertion). Differences between groups in clinical target volume (CTV), disease stage (I/II or III/IV), number of patients with or without interstitial needles, and CTV D90 were investigated. Statistical significance was evaluated with the Student T test and Fisher test (p <0.05).Results:46 cervical‐cancer patients were included (16 MRI [3 subMRI], 30 CT). CTV: overall, 55±53 cm3; MRI, 81±61 cm3; CT, 42±44 cm3 (p = 0.017). Stage: overall, 24 I/II and 22 III/IV; MRI, 3 I/II and 13 III/IV; CT, 21 I/II and 9 III/IV (p = 0.002). Use of needles: overall, 26 without and 20 with; MRI, 5 without and 11 with; CT, 21 without and 9 with (p = 0.015). CTV D90: overall, 82±5 Gy; MRI, 81±6 Gy; CT, 82±5 Gy (p = 0.78). SubMRI: CTV and D90 (as % of nominal fraction dose) were 23±6 cm3 and 124±3% for MRI‐guided insertions and 21±5 cm3 (p = 0.83) and 106±12% (p = 0.15) for CT‐guided insertions.Conclusion:Statistically significant differences in patient population indicate preferential use of MRI for patients with high‐stage disease and large residual CTVs requiring the use of interstitial needles. CTV D90 was similar between groups, despite the difference in patient selection. For patients who underwent both CT and MRI insertions, a larger MR CTV D90 and similar CTVs between insertions were observed. While MRI is generally preferable to CT, MRI selection can be optimized in environments without a dedicated MRI brachytherapy suite.This work was partially funded by the NIH R21 CA167800 (PI: Viswanathan; aviswanathan@partners.org)