bluuebunny/crossref_metadata_2025 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 two

Methods:

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 assemblies

Methods:

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.
TU‐H‐CAMPUS‐TeP2‐05: Selective Protection of Normal Tissue by Cerium Oxide Nanoparticles During Radiation Therapy
Authors: Ouyang Z , Yasmin‐Karim S , Strack G , Sajo E , Ngwa W
Published: July 2016

Purpose:

Cerium oxide nanoparticles (CONPs) have unique pH dependent properties such that they act as a radical modulator. These properties may be used in radiation therapy (RT) to protect normal tissue. This work investigates the selective radioprotection of CONPs in‐vitro and potential for in‐situ delivery of CONPs in prostate cancer RT.

Methods:

i) Normal human umbilical vein endothelial cells (HUVEC) and human prostate cancer cells (PC‐3) were treated with 0 or 2 ng/mL CONPs (NP size: 5 nm). 2 Gy of 100 kVp radiation was delivered to the cells 4 hours after the CONP treatment. Cell viability was checked 48 hours later using MTS assays. ii) A prostate tumor was modeled as a 2‐cm diameter sphere. CONPs were proposed to be loaded in a hollow radiotherapy fiducial marker. The concentration profile for the CONPs within the tumor was modeled with a previously validated diffusion equation employed in other studies for nanoparticles 10 nm or less.

Results:

i) Without radiation, cell viability was above 90% when treated with 2 ng/mL CONPs for both HUVEC and PC‐3. After irradiation, a slightly higher viability was observed in HUVEC with CONPs than the ones without CONPs, and this effect was not observed in PC‐3. ii) Based on the calculations, 2 ng/mL of CONPs could be delivered to normal cells by diffusion with a 1 µg/mL initial concentration within two weeks.

Conclusion:

We conclude that CONPs can provide selective radioprotection. The delivery of needed concentrations of CONPs is feasible via in‐situ release from radiotherapy biomaterials (e.g. fiducials) loaded with the CONPs.
TU‐H‐CAMPUS‐IeP3‐01: Simultaneous PET Restoration and PET/CT Co‐Segmentation Using a Variational Method
Authors: Li L , Lu W , Tan S
Published: July 2016

Purpose:

PET images are usually blurred due to the finite spatial resolution, while CT images suffer from low contrast. Segment a tumor from either a single PET or CT image is thus challenging. To make full use of the complementary information between PET and CT, we propose a novel variational method for simultaneous PET image restoration and PET/CT images co‐segmentation.

Methods:

The proposed model was constructed based on the Γ‐convergence approximation of Mumford‐Shah (MS) segmentation model for PET/CT co‐segmentation. Moreover, a PET de‐blur process was integrated into the MS model to improve the segmentation accuracy. An interaction edge constraint term over the two modalities were specially designed to share the complementary information. The energy functional was iteratively optimized using an alternate minimization (AM) algorithm. The performance of the proposed method was validated on ten lung cancer cases and five esophageal cancer cases. The ground truth were manually delineated by an experienced radiation oncologist using the complementary visual features of PET and CT. The segmentation accuracy was evaluated by Dice similarity index (DSI) and volume error (VE).

Results:

The proposed method achieved an expected restoration result for PET image and satisfactory segmentation results for both PET and CT images. For lung cancer dataset, the average DSI (0.72) increased by 0.17 and 0.40 than single PET and CT segmentation. For esophageal cancer dataset, the average DSI (0.85) increased by 0.07 and 0.43 than single PET and CT segmentation.

Conclusion:

The proposed method took full advantage of the complementary information from PET and CT images.

This work was supported in part by the National Cancer Institute Grants R01CA172638. Shan Tan and Laquan Li were supported in part by the National Natural Science Foundation of China, under Grant Nos. 60971112 and 61375018.
TU‐H‐CAMPUS‐IeP3‐03: Validation of Image Registration Methods for Brain Magnetic Resonance Imaging
Authors: Lin J , Fuentes D , Chandler A , Hazle J , Schellingerhout D , MacLellan C
Published: July 2016

Purpose:

To assess the performance of both commercial and open‐source co‐registration solutions as applied to intra‐subject, multi‐sequence, magnetic resonance (MR) images of the brain.

Methods:

Twenty (20) patients were imaged on clinical 3.0T MR scanners to obtain T2‐weighted (T2W), fluid attenuation inversion recovery (FLAIR), susceptibility weighted angiography (SWAN), and T1 post‐contrast (T1C) image sequences. Fiducial landmark sites (n=15 per sequence, 4 sequences per patient, 1200 total planned for 4 sequences and 20 patients, 1175 total realized) were specified throughout these image volumes to define identical locations across sequences. Both commercial (General Electric [GE] VolumeViewer) and open‐source software (Advanced Normalization Tools [ANTs]) registration solutions were applied using the T2W sequence as the fixed reference. Landmark and image similarity (cross‐correlation [CC], mutual information [MI]) based registrations were performed for all image pairs. Rigid (6DOF) and affine (12DOF) transformations were considered. The Euclidean Target‐to‐Registration Error (TRE) was calculated at all landmarks of each image pair.

Results:

Prior to registration, TRE values for FLAIR, SWAN, and T1C were 2.07 ± 0.55 mm, 2.63 ± 0.62 mm and 3.65 ± 2.00 mm, respectively. Post‐registration, the best (smallest) average TRE values for FLAIR, SWAN, and T1C were 1.55 ± 0.46 mm (rigid MI), 1.34 ± 0.23 mm (affine MI) and 1.06 ± 0.16 mm (GE), respectively.

Conclusion:

This study presents a methodology to quantify the registration accuracy of commercial algorithms (whose figures of merit are often not publically available, despite clinical use), and compares that accuracy to open‐source alternatives. All sequences, on average, were improved by spatial registrations that corrected for patient motion, and such motion itself was found to increase with time spent in the MR scanner. The neuroanatomical information encoded in these landmarks, as placed on images with different contrast mechanisms, collectively represents a comprehensive dataset for quantitative evaluation of clinically‐used registration software.

A.C. is an employee of GE Healthcare. This research was supported in part by the National Cancer Institute (Cancer Center Support Grant CA016672 and Training Grant 5T32CA119930). J.S.L. acknowledges support from the Baylor College of Medicine Medical Scientist Training Program and the Cullen Trust for Higher Education Physician/Scientist Fellowship Program.
TU‐H‐CAMPUS‐JeP3‐03: Clinical Implementation of An Online Replanning Process
Authors: Ates O , Ahunbay E , Chen G , Lawton C , Li X
Published: July 2016

Purpose:

The purpose of this study is to report the clinical implementation of an online replanning process with CT‐on‐Rails to address daily interfractional variations.

Methods:

A treatment planning package (MONACO/ADMIRE/MOSAIQ, Elekta) is used to perform online adaptive replanning, using segment aperture morphing (SAM) algorithm implemented in MONACO, based on daily CTs acquired from a CT‐on‐Rails (ARTISTE, Siemens). The online replanning is implemented in prostate RT in the following workflow:(1) Generating a target contour based on the image of the day, using ADMIRE deformable image registration software with manual editing if necessary; (2) Automatically modifying segment apertures from the original plan using the SAM algorithm to account for the changes in the target from planning to daily CTs including deformation; (3) Calculating the dose distribution for the new apertures with the same MUs as in the original plan;(4) Transferring the new plan into MOSAIQ Record & Verify system;(5) Performing a pre‐delivery QA using both our home‐grown and RADCALC software (LifeLine);(6) Delivering the adaptive plan for the fraction.The entire workflow takes <10 min. using a 16‐CPU hardware.

Results:

The online adaptive replanning process was successfully applied during RT for prostate cancers. The adaptive plan significantly improved the plan quality in both target coverage and organs‐at‐risk (OAR) sparing when compared to the current standard of practice; IGRT repositioning plan. For the average of 10 prostate cases, PTV‐V100, Rectum‐V70, and Bladder‐V45 (%) coverages were (92.84 ± 1.61/97.61 ± 1.45/98.85 ± 1.13), (6.76 ± 2.37/5.40 ± 2.61/3.52 ± 0.94) and (8.20 ± 3.55/5.72 ± 2.61/6.68 ± 3.21) for the IGRT, online SAM, and reoptimization plans, respectively.

Conclusion:

The online adaptive replanning workflow is clinically practical for prostate RT and can quickly generate adaptive plans with superior plan qualities when compared to the repositioning plans, improving the management of interfractional variations.

This study was partially supported by Elekta Inc.
TU‐H‐CAMPUS‐TeP3‐04: Probing the Dose Enhancement Due to a Clinically‐Relevant Concentration of Gold Nanoparticles and Yb‐169 Gamma Rays Using PRESAGE Dosimeters
Authors: Cho J , Alqathami M , Reynoso F , Cho S
Published: July 2016

Purpose:

To probe physical evidences of the dose enhancement due to a low/clinically‐relevant concentration of gold nanoparticles (GNPs) and Yb‐169 gamma rays using PRESAGE dosimeters.

Methods:

A PRESAGE cuvette was placed at approximately 2 mm above the plane containing three novel Yb‐169 brachytherapy seeds (3.2, 3.2, and 5.3 mCi each). Two types of PRESAGE dosimeters were used – plain PRESAGEs (controls) and PRESAGEs loaded with 0.02 wt. % of GNPs (GNP‐PRESAGEs). Each PRESAGE dosimeter was irradiated with different time durations (0 to 24 hours) to deliver 0, 4, 8, 16 and 24 Gy of dose. For a reference/comparison, both types of PRESAGEs were also irradiated using 250 kVp x‐rays with/without Er‐filter to deliver 0, 3, 10, and 30 Gy of dose. Er‐filter was used to emulate Yb‐169 spectrum using 250 kVp x‐rays. The absorption spectra of PRESAGEs were measured using a UV spectrophotometer and used to determine the corresponding optical densities (ODs).

Results:

GNP‐PRESAGEs exposed to Yb‐169 sources showed ∼65% increase in ODs compared with controls. When exposed to Er‐filtered and unfiltered 250 kVp x‐rays, they produced smaller increases in ODs, ∼41% and ∼37%, respectively. There was a linear relationship between ODs and delivered doses with a goodness‐of‐fit (R2) greater than 0.99.

Conclusion:

A notable increase in the ODs (∼65%) was observed for GNP‐PRESAGEs irradiated by Yb‐169 gamma rays. Considering the observed OD increases, it was highly likely that Yb‐169 gamma rays were more effective than both Er‐filtered and unfiltered 250 kVp x‐rays, in terms of producing the dose enhancement. Due to several unknown factors (e.g., possible difference in the dose response of GNP‐PRESAGEs vs. PRESAGEs), however, a further investigations is necessary to establish the feasibility of quantifying the exact amount of macroscopic or microscopic/local GNP‐mediated dose enhancement using PRESAGE or similar volumetric dosimeters. Supported by DOD/PCRP grant W81XWH‐12‐1‐0198

This investigation was supported by DOD/PCRP grant W81XWH‐12‐1‐0198.
WE‐AB‐204‐00: Diversity and Inclusion in Medical Physics
Authors: Avery Stephen
Published: July 2016

Many efforts have been made to increase diversity in the science workforce. In order for us to be competitive in innovation and ingenuity we need to reach out to any source of intellectual talent. Having greater diversity can only increase the creativity in medical physics. In order for students to succeed academically they need role models and mentors with whom they can identify. Literature has shown that racial and ethnic diversity has both direct and indirect positive effects on the educational outcomes, career advancement and motivation of students. Diversity not only focuses on race, ethnicity and gender, but it can also include socioeconomic status, sexual orientation and more. Underrepresented populations have had low numbers over the years not only in medical physics but also in the sciences in general. With the rapidly changing face of our country we need to address how we attract and train the next generation of scientists to stay competitive. It is necessary to examine the role that diversity and inclusion play in the long term goals of institutions, workplaces and classrooms. To increase innovation we must engage people from all walks of life with different perspectives and life experiences to solve the problems that we will face. Diversity should be viewed as a strategy to achieve our goals instead of acts of good citizenship. Many of today's businesses and corporations have discovered that embracing diversity prepares future leaders in today's global market.

This lecture will provide insight to how differences within our society can drive innovation. We will provide an overview of the role diversity and inclusion plays in the clinic, education and research to develop the future workforce in medical physics.

Learning Objectives:

Understanding the role diversity and inclusion plays in medical physics.

The importance of developing education and research strategies for a global workforce.

How to develop a roadmap to diversity excellence within AAPM.
WE‐AB‐204‐03: Increasing Access to Medical Physics Education and Research Excellence (AMPERE)
Authors: Ngwa W.
Published: July 2016

Many efforts have been made to increase diversity in the science workforce. In order for us to be competitive in innovation and ingenuity we need to reach out to any source of intellectual talent. Having greater diversity can only increase the creativity in medical physics. In order for students to succeed academically they need role models and mentors with whom they can identify. Literature has shown that racial and ethnic diversity has both direct and indirect positive effects on the educational outcomes, career advancement and motivation of students. Diversity not only focuses on race, ethnicity and gender, but it can also include socioeconomic status, sexual orientation and more. Underrepresented populations have had low numbers over the years not only in medical physics but also in the sciences in general. With the rapidly changing face of our country we need to address how we attract and train the next generation of scientists to stay competitive. It is necessary to examine the role that diversity and inclusion play in the long term goals of institutions, workplaces and classrooms. To increase innovation we must engage people from all walks of life with different perspectives and life experiences to solve the problems that we will face. Diversity should be viewed as a strategy to achieve our goals instead of acts of good citizenship. Many of today's businesses and corporations have discovered that embracing diversity prepares future leaders in today's global market.

This lecture will provide insight to how differences within our society can drive innovation. We will provide an overview of the role diversity and inclusion plays in the clinic, education and research to develop the future workforce in medical physics.

Learning Objectives:

Understanding the role diversity and inclusion plays in medical physics.

The importance of developing education and research strategies for a global workforce.

How to develop a roadmap to diversity excellence within AAPM.
WE‐A‐BRC‐02: Lessons Learned: Clinical Trials and Operations
Authors: Evans S.
Published: July 2016

Quality and safety in healthcare are inextricably linked. There are compelling data that link poor quality radiation therapy to inferior patient survival. Radiation Oncology clinical trial protocol deviations often involve incorrect target volume delineation or dosing, akin to radiotherapy incidents which also often involve partial geometric miss or improper radiation dosing. When patients with radiation protocol variations are compared to those without significant protocol variations, clinical outcome is negatively impacted. Traditionally, quality assurance in radiation oncology has been driven largely by new technological advances, and safety improvement has been driven by reactive responses to past system failures and prescriptive mandates recommended by professional organizations and promulgated by regulators. Prescriptive approaches to quality and safety alone often do not address the huge variety of process and technique used in radiation oncology. Risk‐based assessments of radiotherapy processes provide a mechanism to enhance quality and safety, both for new and for established techniques. It is imperative that we explore such a paradigm shift at this time, when expectations from patients as well as providers are rising while available resources are falling. There is much we can learn from our past experiences to be applied towards the new risk‐based assessments.

Learning Objectives:

Understand the impact of clinical and technical quality on outcomes

Understand the importance of quality care in radiation oncology

Learn to assess the impact of quality on clinical outcomes

D. Followill, NIH Grant CA180803
WE‐AB‐BRA‐01: Biodistribution of Paclitaxel‐Loaded Nanodroplets for Prostate Cancer Management Using Ultrasound‐Mediated Drug Delivery Under MRGuidance
Authors: Gupta R , Cvetkovic D , Wang B , Chen L , Ma C
Published: July 2016

Purpose:

To study the biodistribution of paclitaxel‐loaded nanodroplets in vivo in order to evaluate the efficacy of focused ultrasound (FUS)‐mediated drug delivery under MR‐guidance to prostate tumor.

Methods:

Poly {ethylene oxide}‐co‐poly {D, L‐lactide} (PDLA) nanodroplets loaded with fluorescently labeled‐paclitaxel (F‐PTX) were synthesized using solid dispersion technique. Human prostate cancer, LNCaP cells were implanted orthotopically in prostates of male nude mice. Tumor‐bearing mice (n=3) were injected with 0.1% F‐PTX, 2% PDLA nanodroplets using tail vein. At chosen time points (30min; 2h; 4h; 6h; 12h; 24h) animals were anesthetized, blood was collected by eye bleed, animals were sacrificed, tumor and vital organs (liver, spleen, lung and heart) were excised, cut and weighted. Then the organ was homogenized, incubated in lysis buffer and centrifuged. The lysates were read using fluorescence spectrophotometer (Excitation‐ 496nm, Emission– 524nm). Fluorescence readings were compared with values from the standard calibration curve. Tumor‐bearing mice (n=3) were also injected with 0.1% F‐PTX solution (fluorescent drug in free form).

Results:

Quantitative analysis showed 20% of the injected drug‐loaded nanodroplets in the tumor, 30 min after systemic injection; which increased to 30% after 2h; 35% after 4h; then decreased to 27% after 6h; 11% after 12h and 5% after 24h. When drug in free form was injected, drug accumulation in the tumor was 7% within 30mnt; 8% within 2h; 10% within 4h; 9% within 6h, 3% within 12h and 2% within 24h. Liver showed major drug accumulation for drug‐loaded nanodroplets while heart and lung showed less. For drug in free form, liver and spleen showed maximum drug concentrations while heart showed concentrations similar to that in tumor.

Conclusion:

Present work indicates that the optimum time for applying focused ultrasound is after 4h of systemically injecting drug‐loaded nanodroplets. This would increase treatment efficacy and provide preclinical data for FUS‐mediated drug delivery under MR‐guidance.
WE‐AB‐BRA‐08: Correction of Patient Motion in C‐Arm Cone‐Beam CT Using 3D‐2D Registration
Authors: Ouadah S , Jacobson M , Stayman JW , Ehtiati T , Siewerdsen JH
Published: July 2016

Purpose:

Intraoperative C‐arm cone‐beam CT (CBCT) is subject to artifacts arising from patient motion during the fairly long (∼5–20 s) scan times. We present a fiducial free method to mitigate motion artifacts using 3D‐2D image registration that simultaneously corrects residual errors in geometric calibration.

Methods:

A 3D‐2D registration process was used to register each projection to DRRs computed from the 3D image by maximizing gradient orientation (GO) using the CMA‐ES optimizer. The resulting rigid 6 DOF transforms were applied to the system projection matrices, and a 3D image was reconstructed via model‐based image reconstruction (MBIR, which accommodates the resulting noncircular orbit). Experiments were conducted using a Zeego robotic C‐arm (20 s, 200°, 496 projections) to image a head phantom undergoing various types of motion: 1) 5° lateral motion; 2) 15° lateral motion; and 3) 5° lateral motion with 10 mm periodic inferior‐superior motion. Images were reconstructed using a penalized likelihood (PL) objective function, and structural similarity (SSIM) was measured for axial slices of the reconstructed images. A motion‐free image was acquired using the same protocol for comparison.

Results:

There was significant improvement (p < 0.001) in the SSIM of the motion‐corrected (MC) images compared to uncorrected images. The SSIM in MC‐PL images was >0.99, indicating near identity to the motion‐free reference. The point spread function (PSF) measured from a wire in the phantom was restored to that of the reference in each case.

Conclusion:

The 3D‐2D registration method provides a robust framework for mitigation of motion artifacts and is expected to hold for applications in the head, pelvis, and extremities with reasonably constrained operative setup. Further improvement can be achieved by incorporating multiple rigid components and non‐rigid deformation within the framework. The method is highly parallelizable and could in principle be run with every acquisition.

Research supported by National Institutes of Health Grant No. R01‐EB‐017226 and academic‐industry partnership with Siemens Healthcare (AX Division, Forcheim, Germany).
WE‐AB‐BRA‐09: Registration of Preoperative MRI to Intraoperative Radiographs for Automatic Vertebral Target Localization
Authors: De Silva T , Uneri A , Ketcha M , Reaungamornrat S , Goerres J , Vogt S , Kleinszig G , Wolinsky J , Siewerdsen JH
Published: July 2016

Purpose:

Accurate localization of target vertebrae is essential to safe, effective spine surgery, but wrong‐level surgery occurs with surprisingly high frequency. Recent research yielded the “LevelCheck” method for 3D‐2D registration of preoperative CT to intraoperative radiographs, providing decision support for level localization. We report a new method (MR‐LevelCheck) to perform 3D‐2D registration based on preoperative MRI, presenting a solution for the increasingly common scenario in which MRI (not CT) is used for preoperative planning.

Methods:

Direct extension of LevelCheck is confounded by large mismatch in image intensity between MRI and radiographs. The proposed method overcomes such challenges with a simple vertebrae segmentation. Using seed points at centroids, vertebrae are segmented using continuous max‐flow method and dilated by 1.8 mm to include surrounding cortical bone (inconspicuous in T2w‐MRI). MRI projections are computed (analogous to DRR) using segmentation and registered to intraoperative radiographs. The method was tested in a retrospective IRB‐approved study involving 11 patients undergoing cervical, thoracic, or lumbar spine surgery following preoperative MRI. Registration accuracy was evaluated in terms of projection‐distance‐error (PDE) between the true and estimated location of vertebrae in each radiograph.

Results:

The method successfully registered each preoperative MRI to intraoperative radiographs and maintained desirable properties of robustness against image content mismatch, and large capture range. Segmentation achieved Dice coefficient = 89.2 ± 2.3 and mean‐absolute‐distance (MAD) = 1.5 ± 0.3 mm. Registration demonstrated robust performance under realistic patient variations, with PDE = 4.0 ± 1.9 mm (median ± iqr) and converged with run‐time = 23.3 ± 1.7 s.

Conclusion:

The MR‐LevelCheck algorithm provides an important extension to a previously validated decision support tool in spine surgery by extending its utility to preoperative MRI. With initial studies demonstrating PDE <5 mm and 0% failure rate, the method is now in translation to larger scale prospective clinical studies.

S. Vogt and G. Kleinszig are employees of Siemens Healthcare