bluuebunny/crossref_metadata_2025_split huggingface dataset:
TU‐H‐207A‐01: Development of Conversion Factors to Account for Different CTDI Phantom Setups On a Wide‐Beam CT Scanner
Authors: Zamora D , Moirano J , Kanal K 
Published: July 2016

Purpose:A fundamental measure performed during an annual physics CT evaluation confirms that system displayed CTDIvol nearly matches the independently measured value in phantom. For wide‐beam (z‐direction) CT scanners, AAPM Report 111 defined an ideal measurement method; however, the method often lacks practicality. The purpose of this preliminary study is to develop a set of conversion factors for a wide‐beam CT scanner, relating the CTDIvol measured with a conventional setup (single CTDI phantom) versus the AAPM Report 111 approach (three abutting CTDI phantoms).Methods:For both the body CTDI and head CTDI, two acquisition setups were used: A) conventional single phantom and B) triple phantom. Of primary concern were the larger nominal beam widths for which a standard CTDI phantom setup would not provide adequate scatter conditions. Nominal beam width (160 or 120 mm) and kVp (100, 120, 140) were modulated based on the underlying clinical protocol. Exposure measurements were taken using a CT pencil ion chamber in the center and 12 o'clock position, and CTDIvol was calculated with ‘nT’ limited to 100 mm. A conversion factor (CF) was calculated as the ratio of CTDIvol measured in setup B versus setup A.Results:For body CTDI, the CF ranged from 1.04 up to 1.10, indicating a 4–10% difference between usage of one and three phantoms. For a nominal beam width of 160 mm, the CF did vary with selected kVp. For head CTDI at nominal beam widths of 120 and 160 mm, the CF was 1.00 and 1.05, respectively, independent of the kVp used (100, 120, and 140).Conclusions:A clear understanding of the manufacturer method of estimating the displayed CTDIvol is important when interpreting annual test results, as the acquisition setup may lead to an error of up to 10%. With appropriately defined CF, single phantom use is feasible.
TU‐H‐207A‐07: Comparison of Performance of Tube‐Current Modulation of Three Commercial MDCT Scanners
Authors: Ohno T , Araki F 
Published: July 2016

Purpose:To compare performance of tube‐current modulation (TCM) of three commercial MDCT scanners (TOSHIBA Aquilion One, SIEMENS SOMATOM Definition AS+, PHILIPS Brilliance iCT) from tube current measurement, image noise measurement, and Monte Carlo (MC) simulation based on time‐resolved air kerma measurement.Methods:CT image acquisitions were performed with and without TCM by means of TCM phantoms with length of 40 cm which consists of three oval phantoms (10×20 cm, 14×28 cm, 18×36 cm) and one cylindrical phantom with diameter of 10 cm. Tube currents for each slice were obtained from the DICOM header information. The image noise was measured as standard deviation of CT numbers in ROI at each CT slice. TCM was tested for two oval phantoms. A time‐resolving ionization chamber was positioned at 0 degree and 270 degree and the time‐resolved air kerma was measured with and without TCM. Three MDCT scanners were modeled using GMctdospp (IMPS, Germany) based on the EGSnrc user code. MC‐calculated dose curves per angle were compared to those measured. MC calculations for TCM were set to maximal tube‐current reduction factors (TCM limit) from 0.3 to 0.8.Results:The tube current changed depending on a phantom size. However, excessive tube current was observed at the boundary of phantoms. This is because the tube current changed gradually in anticipation of thickness change. The variation of image noise was improved by the use of TCM. MC‐calculated dose curves without TCM were in good agreement with the measurement. The variation of dose curves with TCM increased with decreasing TCM limit. The MC‐calculated curve with TCM limit of 0.3 agreed with the measurement in all scanners.Conclusion:TCM is useful to improve the image quality and reduce radiation dose. However, the excessive tube current was observed due to limitation of tube current control.
TU‐H‐206‐04: An Effective Homomorphic Unsharp Mask Filtering Method to Correct Intensity Inhomogeneity in Daily Treatment MR Images
Authors: Yang D , Gach H , Li H , Mutic S 
Published: July 2016

Purpose:The daily treatment MRIs acquired on MR‐IGRT systems, like diagnostic MRIs, suffer from intensity inhomogeneity issue, associated with B1 and B0 inhomogeneities. An improved homomorphic unsharp mask (HUM) filtering method, automatic and robust body segmentation, and imaging field‐of‐view (FOV) detection methods were developed to compute the multiplicative slow‐varying correction field and correct the intensity inhomogeneity. The goal is to improve and normalize the voxel intensity so that the images could be processed more accurately by quantitative methods (e.g., segmentation and registration) that require consistent image voxel intensity values.Methods:HUM methods have been widely used for years. A body mask is required, otherwise the body surface in the corrected image would be incorrectly bright due to the sudden intensity transition at the body surface. In this study, we developed an improved HUM‐based correction method that includes three main components: 1) Robust body segmentation on the normalized image gradient map, 2) Robust FOV detection (needed for body segmentation) using region growing and morphologic filters, and 3) An effective implementation of HUM using repeated Gaussian convolution.Results:The proposed method was successfully tested on patient images of common anatomical sites (H/N, lung, abdomen and pelvis). Initial qualitative comparisons showed that this improved HUM method outperformed three recently published algorithms (FCM, LEMS, MICO) in both computation speed (by 50+ times) and robustness (in intermediate to severe inhomogeneity situations). Currently implemented in MATLAB, it takes 20 to 25 seconds to process a 3D MRI volume.Conclusion:Compared to more sophisticated MRI inhomogeneity correction algorithms, the improved HUM method is simple and effective. The inhomogeneity correction, body mask, and FOV detection methods developed in this study would be useful as preprocessing tools for many MRI‐related research and clinical applications in radiotherapy.Authors have received research grants from ViewRay and Varian.
TU‐H‐206‐08: Quantitative Impact of Biliary Stent Artefacts On MR Images
Authors: Gurney‐Champion O , Bruins Slot T , Lens E , van der Horst A , Klaassen, R , van Laarhoven H , van Hooft J , Nederveen A , Bel A 
Published: July 2016

Purpose:Biliary stents may cause artifacts in MR‐images. These artifacts are caused by differences in susceptibility (artifact‐1), eddy currents during read‐out (artifact‐2) and eddy currents due to the excitation pulse (artifact‐3), which all are MRI sequence‐dependent. In this study, we investigated and quantified the magnitude of these artifacts as a function of the distance from biliary stents, using a sequence‐independent approach where possible.Methods:Eight phantoms were made containing different commercial biliary stents made of nitinol, platinol, stainless steel or polyethylene. To quantify artifact‐1 sequence‐independently, we acquired ΔB0‐maps and T2*‐maps. To maximize artifact‐2, the phantom was placed 130mm off center. We then compared signal ratios from acquisitions with gradients in directions that induced eddy currents and acquisitions with gradients in directions that did not induce eddy currents, to assess the contribution of artifact‐2. We acquired B1‐maps to quantify the effect of artifact‐3.These experiments were performed at 3T. The ΔB0‐maps and T2*‐maps were also acquiered at 1.5T.Finally, we acquired ΔB0‐maps, T2*‐maps and clinical MR‐images in vivo in two pancreatic cancer patients with platinol stents.Results:Artifact‐1 was dominant over the other artifacts. The stainless steel stent showed the largest artifact‐1: decreased T2* and ΔB0>75Hz up to 20mm from the stent's edge which results in signal shifts>3voxels for typical diffusion weighted images with bandwidth BW=25Hz/voxel. The other stents showed a decreased T2* up to 8.5mm/5.1mm (3T/1.5T) from the edge of the stent and had a BW<95Hz/55Hz, resulting in signal shifts <0.2voxels for sequences with BW>500Hz/275Hz at 3T/1.5T. The plastic stent showed no artifacts. In vivo, the changes in B0 and T2* induced by the stent were larger than typical variations in B0 and T2* induced by anatomy.Conclusion:We presented a sequence‐independent measure to quantify susceptibility artifacts. Other artifacts are negligible compared to susceptibility artifacts for biliary stents.
TU‐H‐CAMPUS‐IeP1‐01: Bias and Computational Efficiency of Variance Reduction Methods for the Monte Carlo Simulation of Imaging Detectors
Authors: Sharma D , Sempau J , Badano A 
Published: July 2016

Purpose:Variance reduction techniques (VRTs) are employed in Monte Carlo simulations to obtain estimates with reduced statistical uncertainty for a given simulation time. In this work, we study the bias and efficiency of a VRT for estimating the response of imaging detectors.Methods:We implemented Directed Sampling (DS), preferentially directing a fraction of emitted optical photons directly towards the detector by altering the isotropic model. The weight of each optical photon is appropriately modified to maintain simulation estimates unbiased. We use a Monte Carlo tool called fastDETECT2 (part of the hybridMANTIS open‐source package) for optical transport, modified for VRT. The weight of each photon is calculated as the ratio of original probability (no VRT) and the new probability for a particular direction. For our analysis of bias and efficiency, we use pulse height spectra, point response functions, and Swank factors. We obtain results for a variety of cases including analog (no VRT, isotropic distribution), and DS with 0.2 and 0.8 optical photons directed towards the sensor plane. We used 10,000, 25‐keV primaries.Results:The Swank factor for all cases in our simplified model converged fast (within the first 100 primaries) to a stable value of 0.9. The root mean square error per pixel for DS VRT for the point response function between analog and VRT cases was approximately 5e‐4.Conclusion:Our preliminary results suggest that DS VRT does not affect the estimate of the mean for the Swank factor. Our findings indicate that it may be possible to design VRTs for imaging detector simulations to increase computational efficiency without introducing bias.
TU‐H‐CAMPUS‐IeP1‐03: Comparison of Monte Carlo Simulation and Conversion Factor Based Method On Estimation of Effective Dose in Pediatric Patients Undergoing Interventional Cardiac Procedures
Authors: Leung K , Wong M , Ng Y , Lee S , Ming Chun Chau R , Lee F 
Published: July 2016

Purpose:Interventional cardiac procedures utilize frequent fluoroscopy and cineangiography, which impose considerable radiation risk to patients, especially pediatric patients. Accurate calculation of effective dose is important in order to estimate cancer risk over the rest of their lifetime. This study evaluates the difference in effective dose calculated by Monte Carlo simulation with those estimated by locally‐derived conversion factors (CF‐local) and by commonly quoted conversion factors from Karambatsakidou et al (CF‐K).Methods:Effective dose (E),of 12 pediatric patients, age between 2.5–19 years old, who had undergone interventional cardiac procedures, were calculated using PCXMC‐2.0 software. Tube spectrum, irradiation geometry, exposure parameters and dose‐area product (DAP) of each projection were included in the software calculation. Effective doses for each patient were also estimated by twoMethods:1) CF‐local: conversion factor derived locally by generalizing results of 12 patients, multiplied by DAP of each patient gives E‐local. 2) CF‐K: selected factor from above‐mentioned literature, multiplied by DAP of each patient gives E‐K.Results:Mean of E, E‐local and E‐K were 16.01 mSv, 16.80 mSv and 22.25 mSv respectively. A deviation of −29.35% to +34.85% between E and E‐local, while a greater deviation of −28.96% to +60.86% between E and EK were observed. E‐K overestimated the effective dose for patients at age 7.5–19.Conclusion:Effective dose obtained by conversion factors is simple and quick to estimate radiation risk of pediatric patients. This study showed that estimation by CF‐local may bear an error of 35% when compared with Monte Carlo calculation. If using conversion factors derived by other studies may result in an even greater error, of up to 60%, due to factors that are not catered for in the estimation, including patient size, projection angles, exposure parameters, tube filtration, etc. Users must be aware of these potential inaccuracies when simple conversion method is employed.
TU‐H‐CAMPUS‐JeP1‐05: Dose Deformation Error Associated with Deformable Image Registration Pathways
Authors: Surucu M , Woerner A , Roeske J 
Published: July 2016

Purpose:To evaluate errors associated with using different deformable image registration (DIR) pathways to deform dose from planning CT (pCT) to cone‐beam CT (CBCT).Methods:Deforming dose is controversial because of the lack of quality assurance tools. We previously proposed a novel metric to evaluate dose deformation error (DDE) by warping dose information using two methods, via dose and contour deformation. First, isodose lines of the pCT were converted into structures and then deformed to the CBCT using an image based deformation map (dose/structure/deform). Alternatively, the dose matrix from the pCT was deformed to CBCT using the same deformation map, and then the same isodose lines of the deformed dose were converted into structures (dose/deform/structure). The doses corresponding to each structure were queried from the deformed dose and full‐width‐half‐maximums were used to evaluate the dose dispersion. The difference between the FWHM of each isodose level structure is defined as the DDE. Three head‐and‐neck cancer patients were identified. For each patient, two DIRs were performed between the pCT and CBCT, either deforming pCT‐to‐CBCT or CBCT‐to‐pCT. We evaluated the errors associated by using either of these pathways to deform dose. A commercially available, Demons based DIR was used for this study, and 10 isodose levels (20% to 105%) were used to evaluate the errors in various dose levels.Results:The prescription dose for all patients was 70 Gy. The mean DDE for CT‐to‐CBCT deformation was 1.0 Gy (range: 0.3–2.0 Gy) and this was increased to 4.3 Gy (range: 1.5–6.4 Gy) for CBCT‐to‐CT deformation. The mean increase in DDE between the two deformations was 3.3 Gy (range: 1.0–5.4 Gy).Conclusion:The proposed DDF was used to quantitatively estimate dose deformation errors caused by different pathways to perform DIR. Deforming dose using CBCT‐to‐CT deformation produced greater error than CT‐to‐CBCT deformation.
TU‐H‐CAMPUS‐TeP1‐02: Seated Treatment: Setup Uncertainty Comparable to Supine
Authors: McCarroll R , Beadle B , Fullen D , Balter P , Followill D , Stingo F , Yang J , Court L 
Published: July 2016

Purpose:For some head and neck patients, positioning in the supine position is not well tolerated. For these patients, treatment in a seated position would be preferred. We have evaluated inter‐ and intra‐ fraction uncertainty of patient set‐up in a novel treatment chair which is compatible with modern linac designs.Methods:Five head‐and‐neck cancer patients were positioned in the chair, fitted with immobilization devices, and imaged with orthogonal X‐rays. The couch (with chair attached) was rotated to simulate delivery (without actual treatment), another set of images were acquired, providing a measure of intra‐fraction displacement. The patient then got off of and back onto the chair and the process was repeated, thus providing a measure of inter‐fraction set‐up uncertainty. Six sub‐regions in the head‐and‐neck were rigidly registered to evaluate local intra‐ and interfraction displacement. Image guidance was simulated by first registering one sub‐region; the residual displacement of other sub‐regions was then measured. Additionally, a patient questionnaire was administered to evaluate tolerance of the seated position.Results:The chair design is such that all advantages of couch motions may be utilized. Average inter‐ and intrafraction displacements of all sub‐regions in the seated position were less than 2 and 3 mm, respectively. When image guidance was simulated, interfraction displacements were reduced by an average of 4 mm, providing comparable setup to the supine position. The enrolled patients, who had no indication for a seated treatment position, reported no preference for the seated or the supine position.Conclusion:The novel chair design provides acceptable inter‐ and intra‐fraction displacement, with reproducibility similar to that observed for patients in the supine position. Such a chair will be utilized for patients who cannot tolerate the supine position and use with CBCT images for planning, in a fixed‐beam linac system, and for other treatment sites is under investigation.Funding: Varian Medical Systems
TU‐H‐CAMPUS‐TeP1‐03: Magnetically Focused Proton Irradiation of Small Volume Radiosurgery Targets
Authors: McAuley GA , Slater JM , Wroe AJ 
Published: July 2016

Purpose:To investigate the use of magnetic focusing for small volume proton radiosurgery targets using a triplet combination of quadrupole rare earth permanent magnet Halbach cylinder assembliesMethods:Fourteen quadrupole magnets consisting of 24 segments of radiation hard samarium‐cobalt adhered into k=3 Halbach cylinders with various field gradients (100 to 250 T/m) were designed and manufactured. Triplet combinations of the magnets were placed on a positioning track on our Gantry 1 treatment table. Unmodulated 127 MeV proton beams with initial diameters of 3 to 20 mm were delivered to a water tank using single‐stage scattering. Depth and transverse dose distributions were measured using a PTW PR60020 diode detector and EBT3 film, respectively. This data was compared with unfocused passively collimated beams. Monte Carlo simulations were also performed ‐ both for comparison with experimental data and to further investigate the potential of triplet magnetic focusing.Results:Experimental results using 150 T/m gradient magnets and 15 to 20 mm initial diameter beams show peak to entrance dose ratios that are ∼ 43 to 48 % larger compared with spot size matched 8 mm collimated beams (ie, transverse profile full‐widths at 90% maximum dose match within 0.5 mm of focused beams). In addition, the focusing beams were ∼ 3 to 4.4 times more efficient per MU in dose to target delivery. Additional results using different magnet combinations will also be presented.Conclusion:Our results suggest that triplet magnetic focusing could reduce entrance dose and beam number while delivering dose to small (∼≤ 10 mm diameter) radiosurgery targets in less time compared to unfocused beams. Immediate clinical applications include those associated with proton radiosurgery and functional radiosurgery of the brain and spine, however other treatment sites can be also envisioned.This project was sponsored with funding from the Department of Defense (DOD# W81XWH‐BAA‐10‐1).
TU‐H‐CAMPUS‐TeP1‐04: Novel 3D Printed Plastic Cutouts Filled with Aluminum Oxide for Same Day Electron Radiotherapy
Authors: Mikell J , Lee C , Lam K 
Published: July 2016

Purpose:Clinics that outsource electron cutout manufacturing may be unable to simulate and treat patients on the same day. To enable same day treatment, we investigate the use of 3D printed hollow cutouts filled with 30 grit Al2O3 powder. We verified the dosimetric equivalence of such a cutout relative to an outsourced Copper cutout.Methods:Printing was performed using a Ultibots Kossel 250 V‐Slot 3D printer and polylactic acid filament. Printing files were derived from an in‐house 3D model designed to mate with a Varian 6 cm electron cone. Relative to conventional cutouts (Copper or Cerrobend), the height of the hollow plastic cutout was extended by 1.0 cm to increase attenuation. Measurements were performed for 6 MeV in solid water at dmax (1.4 cm) with Gafchromic™ EBT3 film; the cutout was kidney‐shaped with a long and short axis of approximately 5 and 2 cm, respectively. The Copper cutout was based on an outline of the 3D printed cutout.A calibration film was exposed immediately after the electron irradiations. All films, including an un‐irradiated one, were from the same batch. Films were scanned on an Epson 10000XL flatbed scanner. Film analysis was performed in DoseLab (MOBIUS Medical Systems, Houston, Tx).Results:Visual comparison of the physical cutouts revealed that the Copper cutout had a slightly smaller opening than the printed cutout. Line profiles through the registered films indicated agreement within 5% in the open section. 99.9% of pixels passed gamma analysis with 2% local percent difference, 2 mm DTA, and a 25% threshold.Conclusion:Same day simulation and treatment with electrons is feasible with 3D printing of a hollow cutout filled with Al2O3. Future work will include evaluations of additional cutout shapes at different depths for higher energies. Other printing materials, such as bismuth, are being tested.
TU‐H‐CAMPUS‐TeP2‐01: A Comparison of Noninvasive Techniques to Assess Radiation‐Induced Lung Damage in Mice
Authors: Rubinstein A , Kingsley C , Melancon A , Tailor R , Pollard J , Guindani M , Followill D , Hazle J , Court L 
Published: July 2016

Purpose:To evaluate the use of post‐irradiation changes in respiratory rate and CBCT‐based morphology as predictors of survival in mice.Methods:C57L/J mice underwent whole‐thorax irradiation with a Co‐60 beam to four different doses [0Gy (n=3), 9Gy (n=5), 11Gy (n=7), and 13Gy (n=5)] in order to induce varying levels of pneumonitis. Respiratory rate measurements, breath‐hold CBCTs, and free‐breathing CBCTs were acquired pre‐irradiation and at six time points between two and seven months post‐irradiation. For respiratory rate measurements, we developed a novel computer‐vision‐based technique. We recorded mice sleeping in standard laboratory cages with a 30 fps, 1080p webcam (Logitech C920). We calculated respiratory rate using corner detection and optical flow to track cyclical motion in the fur in the recorded video. Breath‐hold and free‐breathing CBCTs were acquired on the X‐RAD225Cx system. For breathhold imaging, the mice were intubated and their breath was held at full‐inhale for 20 seconds. Healthy lung tissue was delineated in the scans using auto‐threshold contouring (0–0.7 g/cm3). The volume of healthy lung was measured in each of the scans. Next, lung density was measured in a 6‐mm2 ROI in a fixed anatomic location in each of the scans.Results:Day‐to‐day variability in respiratory rate with our technique was 13%. All metrics except for breath‐hold lung volume were correlated with survival: lung density on free‐breathing (r=−0.7482,p<0.01) and breath‐hold images (r=−0.5864,p<0.01), free‐breathing lung volume (r=0.7179,p<0.01), and respiratory rate (r= 0.6953,p<0.01). Lung density on free‐breathing scans was correlated with respiratory rate (r=0.7142,p<0.01) and lung density on breath‐hold scans (r=0.5543,p<0.01). One significant practical hurdle in the CBCT measurements was that at least one lobe of the lung was collapsed in 36% of free‐breathing scans and 45% of breath‐hold scans.Conclusion:Lung density and lung volume on free‐breathing CBCTs and respiratory rate outperform breath‐hold CBCT measurements as indicators for survival from radiation‐induced pneumonitis.This work was partially funded by Elekta.