bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐G‐141‐07: An Innovative Iterative Neighboring Volume Morphing Algorithm Based On Landmark Mesh to Create 3DCT During Treatment
Authors: Wu H , Lu M , Cheng C
Published: July 2013

Purpose: For the emerging 4D planning radiation treatment, 3DCT during treatment delivery is required. However, it is time consuming or impossible to acquire 3DCT during treatment delivery. This project will generate the 3DCT for any time instant based on a set of motion features (landmarks). Methods: Previously acquired 4DCT is used for landmark selection. The landmarks are monitored in real‐time during treatment delivery using two orthogonal x‐ray images. For any set of landmarks acquired at target phase T, the 3DCT of the nearest 4DCT phase will be selected as the source phase S based on landmark mesh similarity. The iterative morphing algorithm has 8 steps based on neighboring density volume, including landmark selection, isosurface and tumor center identification, landmark mapping using weighted 3‐layer mesh neighbors, landmark mesh similarity comparison, backward morphing based on density volume, and iterative volume morphing. It will generate the corresponding 3DCT at target phase. Results: To validate the morphing algorithm, first, the landmark mapping process using artificial deformation is assessed. The source 3DCT is deformed artificially by non‐linear matrices, which generated a ground truth to evaluate the resulting 3DCT. The iterative algorithm is appraised successfully with the artificial deformation approach. The second validation applies the landmark mapping and the volume morphing on real tumor data. Both the source and target 3DCTs are different phases of a lung 4DCT data. The statistical results, such as the min, max, and histogram of the density difference are summarized, which showed the resulting 3DCT is similar to the target 3DCT. The next step is to apply the whole algorithm to the unknown target 3DCT. Conclusion: The iterative morphing algorithm is innovative and time saving. It has many potential applications in real‐time image guided radiation treatment, such as online treatment error detection and intervention.

Industrail Support from PerkinElmer Inc, Varian Medical Research
TU‐G‐103‐01: Monte Carlo Simulation and Dose Calculation of Chest CT Scan with Tube Current Modulation
Authors: Gao Y , Ding A , Zhang D , Liu B , Caracappa P , Xu X
Published: July 2013

Purpose: To establish the method of organ dose calculation through Monte Carlo simulations for patients taking CT scans with tube current modulation (TCM), and to give the dose results as well as the preliminary comparison of the dose with TCM and the dose without TCM. Methods: The MCNPX Monte Carlo code was used to simulate an armless adult male phantom taking a typical chest CT scan with TCM. The TCM output from a similar scan was provided by the manufacturer (GE Healthcare), and every specific tube current value corresponding to one of the total 15022 projections respectively. The 15022 projections throughout the entire scan were simplified into 274 projections in simulation, and the average tube current was calculated for each projection. With the organ dose per mAs for each projection simulated, the average current, and the rotation time, the organ doses for the entire scan were calculated. This dose simulation was compared to the dose from a constant tube current scan that preserves the same minimum image quality without TCM. Results: As expected, significantly lower dose for the CT scan with TCM was observed. Dose reduction with TCM was found to be from 59% to 72% for different organs, and it was as low as 28% of the dose to thyroid without TCM. Conclusion: The study successfully demonstrated the feasibility of performing Monte Carlo based organ dose calculations for TCM, and suggested the significant dose reduction capability of TCM. One member was funded by the 2012–2013 J. Newell Stannard Fellowship Award from Health Physics Society.
TU‐G‐103‐08: Monte Carlo‐Calculated Patient Dose Distributions From KV‐Cone Beam CT for IGRT
Authors: Hioki K , Araki F , Ono T , Nakaguchi Y , Tomiyama Y
Published: July 2013

Purpose: To calculate patient dose distributions from kV‐cone beam CT (CBCT) for image‐guided radiation therapy (IGRT) with the Monte Carlo (MC) method and to evaluate quantitatively organ doses from dose‐volume histograms (DVHs). Methods: The Varian On‐Board Imager (OBI) and the Elekta X‐ray Volumetric Imager (XVI) systems were modeled using the EGSnrc/BEAMnrc cord system. MC‐calculated doses for both kV‐CBCT were calibrated by converting ion chamber readings measured using a CT water phantom into absolute doses. The chamber measurements were performed by a Farmer chamber with 60Co absorbed dose‐to‐water calibration factor. Then MC‐dose distributions for kV‐CBCT were calculated using patient CT images. In this study, the organ doses of pelvis and head were evaluated from DVHs obtained by the MC‐dose distributions. The beam setting for the pelvis with full scan of 360o was 125 kV and 680 mAs with a half‐bowtie filter for OBI, and 120 kV and 1056 mAs with a full‐bowtie filter for XVI. For the head with half scan of 200o, the beam setting was 100 kV and 145 mAs with a full‐bowtie filter for OBI, and 100 kV and 73.2 mAs without the bowtie filter for XVI. Results: The calculated mean doses for prostate, rectum, and bladder for OBI and XVI were 2.6 and 0.9 cGy, 2.6 and 0.9 cGy, 3.1 and 1.0 cGy, respectively. The absorbed dose in pelvis for OBI was three times higher than XVI. Similarly, mean doses for eye lens, brain stem, and spinal code for OBI and XVI were 0.08 and 0.02 cGy, 0.34 and 0.12 cGy, 0.19 and 0.15 cGy, respectively. The dose for bone increased up to three or four times compared to that of soft tissue. Conclusion: Monte Carlo‐calculated dose distributions are useful to evaluate quantitatively patient doses from kV‐CBCT for IGRT.
TU‐G‐134‐05: MRI Characteristics of Cobalt Dichloride N‐Acetyl Cysteine (C4) as a Contrast Agent Marker for Prostate Brachytherapy
Authors: Lim Tze Yee , Stafford R Jason , Sankaranarayanapillai Madhuri , Martirosyan Karen , Kudchadker Rajat , Frank Steven
Published: July 2013

Purpose: The use of MRI in post‐brachytherapy‐implant evaluation is limited due to challenges in localizing dark‐appearing seeds in the prostatic stroma. Previous studies showed cobalt dichloride N‐acetyl cysteine complex (C4) as a promising positive contrast agent to indicate seed location. In this study, we investigated the potential benefit of using C4, through relaxivity measurements at 1.5T and 3.0T. Methods: Eight vials containing cobalt dichloride at varying concentrations (0%, 0.10%, 0.20%, 0.50%, 1.0%, 1.5%, 2.0% and 5.0%) and a control vial containing water only were imaged in a head coil at two magnetic field strengths, 1.5T and 3.0T. At each concentration, spin‐lattice relaxation time, Ti and spin‐spin relaxation time, Tz were estimated using nonlinear least‐squares fitting of mean signal intensities versus time to standard exponential models. The slopes from linear fits of relaxation rates, Ri and Rz, versus C4 concentrations gave the relaxivities, ri and rz. Results: At 1.5T, ri = 0.151 ± 0.003 mMV1 and rz = 0.208 ± 0.002 mM_1s_1; at 3.0T, ri = 0.148 ± 0.002 mM “is”i and rz = 0.328 ± 0.006 mM' Vi. Accordingly, the relaxivity ratio, rz/ri = 1.38 ± 0.030 at 1.5T and 2.22 ± 0.050 at 3.0T. ri showed a modest decrease with increasing field strength, consistent with the small C4 size. Conversely, rz increased with increasing field strength, thus the rz /ri increased with increasing field strength. The C4 concentration of 1.0% was chosen, which balanced the desired effect of Ti shortening and undesired domineering effect of Tz damping at higher field strengths, to preserve C4 as a positive contrast agent. Conclusion: With these measured relaxation characteristics, we can optimize the pulse sequence parameters for use with C4 by minimizing susceptibility effects and enhancing C4 signal. Overall, this study confirmed the potential of C4 as a positive contrast marker for MRI‐based prostate brachytherapy. Steven Frank and Karen Martirosyan are cofounders of C4 Imaging, LLC.
WE‐A‐103‐01: Ultrasound
Authors: Hangiandreou N , Larson S , Madsen E
Published: July 2013

Ultrasound quality control (QC) testing is often over‐looked in ultrasound imaging practice because there are few regulations requiring regular QC of these systems. Many sites rely on the manufacturer's preventive maintenance program to ensure these systems are functioning optimally. However, the regulatory climate is changing, placing emphasis on safe and effective imaging practice. Regular QC testing of ultrasound equipment is a valuable tool that helps ensure proper function and good image quality in ultrasound imaging. This two‐hour session is organized in two parts. The first hour will cover the basic concepts of ultrasound performance measurement, including the tests that are recommended for acceptance and annual testing as well as routine QC, the rationale for these tests, and specific testing methods. It will also include what the physicist needs to know about ultrasound accreditation. The next hour includes two presentations related to quantitative assessment of ultrasound QC. First presented is the work of the AAPM working group on Quantitative B‐mode Ultrasound QC Test Development. This group has designed software intended to aid in the evaluation of transducer element condition. The second presentation will demonstrate use of a user‐friendly automation software, developed at the University of Wisconsin, for periodic rapid quality assurance (QA or QC) using the tissue‐mimicking conical window phantom described last year. The phantom has been designed specifically for determination of three basic parameters. A method for organizing an electronic filing system for paperless recording of results will also be described.

Learning Objectives:

1. Understand what constitutes an effective ultrasound QC program.

2. Achieve familiarity with common ultrasound QC test methods and phantoms.

3. Understand what the physicist needs to know about ultrasound program accreditation.

4. Learn about a public software tool being developed by the AAPM Ultrasound Subcommittee to detect and assess transducer uniformity artifacts.

5. Learn about a user‐friendly automation software tool to address the most‐recommended ultrasound QC tests.
WE‐A‐108‐01: BEST IN PHYSICS (THERAPY) — A Real‐Time Applicator Position Monitoring System (RAPS) for Intracavitary High‐Dose‐Rate Brachytherapy
Authors: Xia J , Waldron T , Kim Y
Published: July 2013

Purpose: To develop a real‐time applicator position monitoring system (RAPS) for intracavitary brachytherapy using an infrared camera and reflective markers. Methods: 3D imaging‐guided brachytherapy requires high accuracy of applicator localization; however, applicator displacement can happen during patient transfer for imaging and treatment delivery. No continuous applicator position monitoring system is currently available. The RAPS system was developed for continuous applicator position monitoring without additional radiation dose to patients. The RAPS system includes an infrared camera, reflective markers, an infrared illuminator, and image processing software. After reflective markers are firmly attached to the applicator and patient body, applicator displacement are measured by computing the relative change in distance between the markers. The reflective markers are magnetic resonance imaging (MRI) compatible, suitable for MRI‐guided conformal HDR brachytherapy paradigm. In our prototype, a Microsoft Kinect sensor with a resolution of 640 by 480 was used as an infrared camera. A phantom study was carried out to compare RAPS' measurements with known displacements ranging from −15 mm to +15mm. A reproducibility test was also conducted. Results: The RAPS can achieve 4 frames per second using a laptop with Intel Core 2 dual CPU. When the pixel size was 0.95 mm, the difference between RAPS' measurements and known shifts ranged from 0 to 0.8 mm, with the mean value of 0.1 mm and a standard deviation of 0.44 mm. The system reproducibility was within 0.6 mm after 10 reposition trials. At SAD of 60 cm, 7 cm camera position uncertainty in vertical direction introduced 1.0 mm measurement uncertainty. Conclusion: This work demonstrates the feasibility of a real‐time infrared camera based brachytherapy applicator monitoring system. Less than 1mm accuracy was achieved when using an off‐the‐shelf low resolution infrared camera.
WE‐A‐108‐04: Experimental Verification of the Thermal Properties of a Novel LDR Thermo‐Brachytherapy Seed
Authors: Warrell G , Gautam B , Shvydka D , Subramanian M , Ng T , Parsai E
Published: July 2013

Purpose Hyperthermia is a highly effective adjuvant therapy when used with radiation therapy, as shown by multiple groups. A novel thermo‐brachytherapy seed invented by our group combines both modalities by replacing the tungsten radiographic marker in a standard LDR brachytherapy seed with a piece of ferromagnetic alloy. This alloy has a Curie transition temperature of ∼50 degrees‐C, and acts as a self‐regulating source of heat when exposed to an RF magnetic field. We present the results of experimental analysis of the thermal properties of the seed prototypes, and comparisons with computational analysis. Methods Behavior of the seeds in tissue was experimentally investigated by implanting ferromagnetic material and seed prototypes in pieces of ham, serving as a tissue‐mimicking phantom. Induction heating of the seeds was performed with an industrial induction heater fitted with custom coils, and the temperature vs. time was obtained via an infrared camera and a fiber‐optic thermometer. Computational analysis of the thermal properties of the self‐regulating seeds was done via the finite element analysis partial differential equation solver COMSOL Multiphysics 4.3. Results Experimental work shows that hyperthermia can be induced in tissues over reasonable times with clinically‐available magnetic field strengths. There is good correlation between experimental and computational investigations of the temperature rise and distribution for arrangements of thermo‐brachytherapy prototypes in a tissue‐mimicking phantom. The presented work will include quantitative and qualitative comparisons, as well as comparisons between the thermal and simulated radiation dose distributions of the thermo‐brachytherapy seeds. Conclusions For the thermobrachytherapy seed under development with our group, we have demonstrated good agreement between theoretical modeling and measurements for temperature distributions using a tissue‐mimicking phantom. Acknowledgement This research is supported with STTR NIH grant No. R41 CA153631‐01A1; This is supported through NIH grant No. R41 CA153631‐01A1.
WE‐A‐108‐09: Interstitial Rotating Shield Brachytherapy for Prostate Cancer
Authors: Flynn R , Li X , Kim Y , Wu X , Townsend K , Zhang W , Woodin B , Rockey W , Enger S , Breitbach E , Adams Q
Published: July 2013

Purpose: To introduce a feasible interstitial rotating shield brachytherapy (I‐RSBT) system for treating prostate cancer. With I‐RSBT, the radiation sources are surrounded by catheters that contain shields to enable conformal avoidance of healthy tissues, potentially reducing complications relative to conventional high‐dose‐rate brachytherapy (HDR‐BT) techniques. Methods: The I‐RSBT system is based around ten control cartridges with 9.5 mm × 9.5 mm cross sections. Each control cartridge contains a rotational stepper motor, connected to a lead screw, which drives a platinum‐shielded nitinol catheter containing a 37 GBq Gd‐153 source. Gadolinium‐153 is generated by neutron irradiation of europium‐151 or Gd‐152 and is mass‐producible at reasonable cost. For I‐RSBT delivery, the cartridges are arranged in a box‐shaped magazine in a desired delivery pattern and aligned with a template containing implanted 16 gauge interstitial nitinol needles. Each source/catheter travels down a needle in a helical pattern during the dose delivery process. An I‐RSBT delivery using more than ten needles can be accomplished by dividing the treatment into multiple parts, each with a different cartridge arrangement in the magazine. Results: Treatment plans based on Monte Carlo dose calculations and optimized using the linear least squares technique demonstrated I‐RSBT reduced D1% (minimum dose to hottest 1%) for the urethra and rectum by 20% and 10% respectively, relative to conventional HDR‐BT. The prostate D97% was the same for I‐RSBT as for HDR‐BT. The I‐RSBT treatment time for a 20 Gy delivery would be 3 hours with fresh Gd‐153 sources. Since Gd‐153 has substantially lower gamma ray energies than iridium‐192, I‐RSBT treatments can occur in procedure rooms rather than conventional brachytherapy suites, reducing the disadvantage of the longer I‐RSBT delivery times. Conclusions: Treating prostate cancer with I‐RSBT is technically feasible in reasonable treatment times using platinum‐shielded Gd‐153 sources and the proposed delivery system. University of Iowa Research Foundation
WE‐A‐134‐02: Combined MV+kV Beam Optimization for Enabling Real‐Time KV Tumor Tracking
Authors: Grelewicz Z , Wiersma R
Published: July 2013

Purpose: Despite the existence of real‐time kV intrafractional tumor tracking strategies for many years, clinical adoption has been held back by concern over excess kV imaging dose cost to the patient when imaging in continuous fluoroscopic mode. This work aims to solve this specific problem by performing a first time investigation into the use of convex optimization tools to best integrate this excess kV imaging dose into the MV therapeutic dose as to make real‐time kV tracking clinically feasible. Methods: Phase space files for both a 125 kVp kV beam and a 6 MV treatment beam were generated with BEAMNRC, and used to make dose influence matrices in DOSXYZNRC for a lung cancer patient. The dose optimization problem for IMRT, formulated as a quadratic problem, was modified to include additional kV imaging constraints as required for real‐time kV fluorescent tracking. The MOSEK optimization toolkit was used to solve the modified optimization problem. Results: Compared to conventional IMRT optimization, combined MV+kV optimization leads to a 2.4–5.2% reduction in the total number of monitor units assigned to the MV beam due to inclusion of the kV dose. When using an open kV aperture, combined MV+kV optimization allows for a reduction of up to 50% of the excess kV dose compared to standard IMRT with kV fluoro tracking. For all kV field sizes considered, combined MV+kV optimization provided PTV coverage equal to standard IMRT without kV imaging and superior to standard IMRT plus kV fluoro tracking. Skin dose with combined MV+kV imaging was only slightly higher than the no‐imaging case. Conclusion: The use of MV+kV optimization allows for greatly reduced imaging dose to the skin, especially in cases of large kV aperture imaging. Combined MV+kV optimization demonstrates potential for real‐time tumor tracking without excessive imaging dose, paving the way for clinical implementation.
WE‐C‐WAB‐02: Joint FDG‐PET/MR Imaging for the Early Prediction of Tumor Outcomes
Authors: Vallieres M , Freeman C , Skamene S , El Naqa I
Published: July 2013

Purpose: To investigate the potential of joint FDG‐PET/MR imaging features for the prediction of lung metastases at diagnosis of soft‐tissue sarcomas (STS). Methods: A cohort of 35 patients with histologically proven STS was used in this study. All patients underwent pre‐treatment FDG‐PET and MR scans that comprised T1 and T2‐fat suppression weighted (T2FS) sequences. The cohort had a median follow‐up period of 29 months (range: 4–85) during which 13 patients developed lung metastases. An SUV feature (SUVmax) from the FDG‐PET scans and 6 texture features (energy, entropy, contrast, homogeneity, sum‐mean and variance) from the co‐occurrence matrix of the separate (FDG‐PET, T1 and T2FS) and fused (FDG‐PET/T1 and FDG‐PET/T2FS) scans were extracted from the tumor region. Fusion of the scans was implemented using the wavelet transform. Multivariable modeling was performed using logistic regression (LR) and the corresponding performance for lung metastases prediction was assessed using receiver operating characteristic (ROC) metrics on bootstrapping resampling. Optimal texture extraction was carried out through the optimization of intensity quantization, spatial resolution and wavelet band‐pass filtering. Results: Overall, textures extracted from fused scans outperformed those from separate scans for the prediction of lung metastases. The best performance was found using an LR model with the following 4 parameters: SUVmax, FDG‐PET/T1‐‐contrast, FDG‐PET/T1‐‐homogeneity and FDG‐PET/T2FS‐‐variance. The average performance of this model in 10000 bootstrapping testing sets was: AUC=0.956, sensitivity=0.909, specificity=0.925, accuracy=0.916. However, the upper limit on the uncertainty of the texture model due to contouring variations was evaluated to be 15%. Conclusion: Our results demonstrate that fused FDG‐PET/MR texture features can be used to evaluate lung metastasis risk at diagnosis of STS. Accurate risk assessment could improve patient outcomes by allowing better adapted treatments. The methodology developed in this study could be tested on other cancer types and clinical endpoints such as treatment response.
WE‐C‐WAB‐03: Correspondence Between FDG‐PET and Diffusion‐Weighted MRI After Deformable Registration in Locally‐Advanced Non‐Small Cell Lung Cancer
Authors: Hugo G , Olsen K , Ford J , Turlington D , Weiss E
Published: July 2013

Purpose: To develop and evaluate a framework for aligning diffusion‐weighted MR images (DWI) to CT and PET/CT in locally‐advanced lung cancer, and to evaluate the correspondence of FDG‐PET and DWI prior to radiation therapy. Methods: Pretreatment FDG‐PET/CT, 4D fan beam planning CT, and MR were acquired in five locally‐advanced lung cancer patients. Deformable registration was used to align the b=0 s/m2 DWI to a high‐resolution morphological MRI to reduce spatial distortion and respiratory effects. The morphological MRI was then registered to planning CT to map DWI to the planning CT reference frame. Apparent diffusion coefficient (ADC) was computed from DWI. PET/CT was also registered to planning CT. 40% of maximum lesion SUV (SUVmax) threshold was used to delineate primary tumor on PET, and a physician delineated the lesion on DWI. Dice coefficient between PET and DWI primary tumor volumes was computed to assess whole lesion location. To establish correspondence of tumor subvolumes, the region of 70% SUVmax on PET (high SUV) was delineated, and the ADC distribution from the spatially‐registered DWI extracted in this region. This process was repeated for the 40%–50% SUVmax (low SUV) region. Results: All registrations were judged visually acceptable. The PET and DWI‐defined primary tumor Dice coefficient was 0.6 +/‐0.1 after registration. The mean ADC corresponding to the high SUV region was lower than the mean ADC in the low SUV region in 4/5 patients (mean difference of −130 m2/s). One patient had higher ADC in the high SUV region, with a difference of 94 m2/s between regions. This patient had a highly heterogeneous lesion with small hyperintense pockets on ADC images indicating necrosis. Conclusion: Deformable registration of thoracic MR appears feasible to reduce the effects of distortion and motion artifacts. High SUV generally corresponded with the most restricted diffusion signal from DWI.
WE‐C‐WAB‐04: Comparison of 4D‐CT Ventilation Imaging with SPECT Ventilation Imaging for Thoracic Cancer Patients
Authors: Yamamoto T , Kabus S , Lorenz C , Mittra E , Goris M , Hong J , Chung M , Barquero C , Eclov N , Diehn M , Loo B , Keall P
Published: July 2013

Purpose: A novel lung ventilation imaging technique based on 4D‐CT can be used for functional avoidance to spare high‐functional lung regions, and early prediction or assessment of pulmonary toxicity in radiotherapy. However, there has been minimal validation showing inconsistent results in human subjects. The purpose of this study was to compare 4D‐CT ventilation images with SPECT ventilation images as clinical reference. Methods: In an IRB‐approved clinical trial, 4D‐CT ventilation and SPECT ventilation images were acquired in the supine position for 12 thoracic cancer patients. 4D‐CT ventilation was calculated by deformable image registration of 4D‐CT images, followed by analysis of the resultant displacement vector field to quantify regional volume change (Jacobian), a surrogate for ventilation. SPECT ventilation scans were performed by inhalation of 99mTc‐DTPA aerosols. We evaluated the physiologic accuracy of 4D‐CT ventilation by: (1) comparing 4D‐CT ventilation values in SPECT ventilation defect regions with those in non‐defect regions; (2) quantifying Dice similarity coefficients (DSCs) for the spatial overlap of low‐functional lung regions determined by 4D‐CT ventilation and SPECT ventilation; (3) comparing a ventral‐to‐dorsal gradient of 4D‐CT ventilation with that of SPECT ventilation. Results: Five patients showed severe depositions of SPECT DTPA aerosols in central airways, and hence were excluded from the analysis. The 4D‐CT ventilation value in SPECT ventilation defect regions was found to be significantly lower than that in non‐defect regions (0.14±0.06 vs. 0.19±0.07, p=0.01). The DSC for the spatial overlap of low‐functional lung regions was weak (0.29±0.11). 4D‐CT ventilation demonstrated a ventral‐to‐dorsal gravitational gradient, which was consistent with SPECT ventilation. Conclusion: A 12‐patient study demonstrated reasonable correlations between 4D‐CT ventilation and SPECT ventilation as clinical reference, indicating the potential for 4D‐CT ventilation imaging to achieve high physiologic accuracy. However, poor DSCs suggest the need for further studies to improve 4D‐CT ventilation imaging and/or a validation study design. National Lung Cancer Partnership Young Investigator Research Grant; NIH/NCI 2 R01 CA 093626
WE‐C‐WAB‐05: A Novel Integrated X‐Ray and Fluorescence Tomography System for Small Animal Radiation Research Platform
Authors: Wang K , Yang Y , Eslami S , Iordachita I , Patterson M , Wong J
Published: July 2013

Purpose: A novel, low cost, and fast acquisition fluorescence tomography (FT) system was designed and built for preclinical focal radiation research to provide soft tissue guidance as well as to support highly sensitive functional imaging. Materials & Methods: The cone beam (CB) CT/FT system was designed and tested in a standalone form. The mouse is placed prone on a rotation stage. The x‐ray source and flat panel detector for the CBCT are aligned perpendicular to the mouse anterior‐posterior axis. The anatomical information obtained from CBCT is used as prior information to enhance subsequent optical reconstruction by limiting the solution space. Prior to FT acquisition, diffuse optical tomography (DOT) is performed to reconstruct the animal optical properties. Optical fibers at fixed positions in contact with the animal deliver the source light of different wavelengths for DOT. For FT, a diode laser replaces the lamp as the excitation source. A CCD camera with f/1.4 lens is used as the optical detector. The CCD camera response readout was calibrated using an integrating sphere to provide the absolute light fluence rate at the desired wavelength. A mirror system capable of 90 degree rotation around the animal reflects the optical signal to the CCD camera. Results: To test the FT system, pre‐drilled holes in a tissue‐simulating phantom were filled with a solution of indocyanine green (ICG). Several scenarios were used to test the optical system, such as examining the spatial resolution by placing the same fluorophore at variable separations, and reconstructing the ICG and another infrared fluorophore simultaneously to simulate multiple color functional imaging. Our initial results show that FT can localize the ICG source to within 1 mm. Conclusion: The novel CBCT/FT system presents new research opportunities for image guided pre‐clinical radiation research.
WE‐C‐WAB‐08: Measurements and Quantifications for the Lung Nodule Motion Using 4DCBCT Scans Prior to Each SBRT Treatment
Authors: Li S , Charpentier P , Chan P , Neicu T , Valakh V , Micaily B , Miyamotot C
Published: July 2013

Purpose: To measure the lung nodule motion using 4D CBCT, to quantify any potential influences on the motion trajectory, and to derive an analytical approximation for motion trajectory in order to synchronize with external real‐time respiratory motion tracking. Methods: GTV from fast CT and ITV from CT‐PET obtained from rigid or deformable co‐registration with simulation CT are used for SBRT planning. Pretreatment 4D CBCT with ten phases are automatically registered according to the GTV mask. The nodule motion trajectory is quantified by the center, amplitudes, swiping area, major and minor axes in the principal plane (PP), and the PP normal vector. The setup errors and motion margins are assessed by the trajectory center and amplitude, respectively. Detected motion in the PP is analytically approximated by an ellipse with time parameter and the trajactory shape or axes and orentation may be correlated with the lung volume, nodule location, abdominal compression, and restriction force from the neighboring chest wall or other rigid tissue. Those variables in seventy‐two 4D CBCT scans from 34 patients are retrospectively analyzed. Results: After 4D CBCT‐guided setup adjustments of 10±8 mm, the remaining setup errors in any directions increase from 1±1 mm for upper and middle lobes to 1± 2 mm for the lower lobes while the average motion margins in the lateral, longitudinal, and posterior‐anterior directions increase from (1, 2, 1) to (1, 6, 1) mm. No significant difference is observed between the left and right lungs and between the groups with and without abdominal compression. Importantly, most motion trajectories can be analytically approximated and its PP is predicable with the local force. Conclusion: The clinical measurements and detail analysis validate the geometric accuracy and precision of current SBRT and our analytical approximation is potentially useful for synchronization with real‐time respiratory motion tracking for future gated SBRT.
WE‐C‐WAB‐09: A Novel Volumetric Imaging Method Using a Sparse Subset of CBCT Projections
Authors: Zhong Z , Cai Y , Guo X , Kearney V , Jiang L , Wang J , Yordy J , Chen S , Nedzi L , Solberg T , Mao W
Published: July 2013

Purpose: : Over the preceding decade, onboard volumetric imaging utilizing cone beam CT (CBCT) has become an indispensible tool for image‐guided radiotherapy. A novel method has been developed to deform the planning CT to maximize the spatial congruence between the digitally reconstructed radiographs (DRRs) and CBCT projections. This method maps the planning CT images to the current anatomy using a sparse subset of CBCT projections. Methods: A finite element modeling methodology was developed to automatically generate adaptive meshes for a given region of interest without the need for segmentation. In this methodology, more control points are generated at organs boundaries, special tissues, contour boundaries, or high intensity gradients. The displacement of boundaries and important features is directly represented by the displacement of control points, instead of interpolation on regular grids. A splatting method was developed to generate DRRs of the deformed CT. These DRRs were compared with corresponding 2D projections from CBCT scans; as a Result, the displacement vector fields on the CT were optimized iteratively to obtain a final deformed CT image. A digital phantom was used to evaluate this method. Results: Typically 60 projections were needed to reconstruct a set of 3D images while several hundreds of projections were required for a conventional CBCT reconstruction. The feature‐based meshing method led to better results than either regular orthogonal or regular tetrahedral meshes. The image intensity results of the feature‐based meshing method were nearly identical to those of the voxel‐based method (normalized cross correlation efficient (NCC) ∼ 0.9858 vs 0.9872), while the feature‐based meshing method led to much better consistency of displacement vector fields relative to ground truth than voxel‐based method (NCC ∼ 0.8265 vs 0.6261). Conclusion: This feature‐based meshing method is capable of reconstructing volumetric images with significantly fewer projections while retaining the image quality of planning CT. This research is supported by CPRIT Individual Investigator Award RP110329.
WE‐C‐141‐01: Research and Relevance of Brachytherapy Dose Calculation Advancements
Authors: Rivard MJ , Ibbott GS , Ballester F , Tedgren A Carlsson , Mourtada F
Published: July 2013

Research and Relevance of Brachytherapy Dose Calculation Advancements Organizer: Mark J. Rivard Moderator: Geoffrey S. Ibbott Speakers: Facundo Ballester, Asa Carlsson Tedgren, Firas Mourtada Brachytherapy dosimetry is undergoing a renaissance with the scrutiny of the AAPM TG‐43 dose calculation formalism and comparisons with alternate approaches such as the Monte Carlo method, the grid‐based Boltzmann solvers, and the collapsed‐cone technique. Treatment planning systems (TPS) using these more advanced, model‐based dose calculation algorithms (MBDCAs) are now available for clinical use. However, their accuracy and the preferred method for their use have not been established. Thus, it is important for smooth integration of new radiotherapy technology to not interrupt the cohesion of the current paradigm. Consequently, the AAPM, the European Society for Radiation Oncology (ESTRO), and the Australasian Brachytherapy Group (ABG) have forged an alliance to establish clinical benchmark cases for medical physicists to evaluate the TPS that incorporate MBDCA as the dose engine for brachytherapy. This is one charge of the Model Based Dose Calculation Algorithms in Brachytherapy working group. In support of these efforts, comparisons for several MBDCAs are underway and benchmark cases are being prepared.

Learning Objectives:

1. presentation on the background and rationale for MBDCA,

2. quantitative comparisons amongst the MBDCA techniques, and

3. the current status of the benchmark cases with plans for availability to the medical physics community.
WE‐C‐103‐03: Design of a Novel 3D Field Emission Electron Source for High Power X‐Ray Tube
Authors: Xu Y , Li D , Zhang J
Published: July 2013

Purpose: Field emission electron sources today have shown great potentials in various medical imaging applications, such as computed tomography (CT), which demands extremely high emission current. High emission current can be achieved by raising the gate voltage at the expense of increased cathode instability and reduced cathode life. This paper presents the design of a new 3D field emission electron source that has the potential to overcome the limits of conventional field emission cathode in emission current and cathode life. Methods: The 3D cathode design is based on a semi‐enclosed rectangular cavity structure, with one face open to the anode for electron beam emission. All the inner faces of the cavity including four sides and one bottom are set to be the emission surfaces. The 3D cathode has a depth (cavity height) of 5mm along the source axial direction, along with a 10mm×10mm electron beam aperture that is 10mm away from the anode. Results: The performance of both the 3D and conventional 2D cathode was evaluated using the commercial software package CST Studio Suite, under the same operating condition. We have demonstrated that the total emission current of the 3D cathode is 2.4 times the one of the 2D cathode, from a total 3 times emission surface area. The slightly reduced electron transmission rate in the 3D cathode is due to the electron collision inside the cavity structure. Conclusion: We present a novel field emission electron source design based on a 3D semi‐enclosed cavity structure, by utilizing the multiple inner surfaces of the cavity for electrons emission. The 3D cathode has transverse dimensions the same as a conventional single surface 2D cathode, but larger emission area due to its extended space. The 3D cathode design was demonstrated to have the capability of providing much higher cathode current density.
WE‐C‐103‐04: The Optimization of CT Protocols Using Plots of CTDIvol and of Max and Min MA Versus Patient Size for Actual Clinical Scans Using Automatic Exposure Control (AEC)
Authors: Ranallo F , Szczykutowicz T
Published: July 2013

Purpose: To determine the usefulness of the knowledge of CTDIvol and mA variations as a function of patient size for optimizing scan parameters in CT imaging using AEC. Methods: Data was collected from actual patient scans for a number of different CT protocols such as standard chest, body, head, vascular imaging, and pediatric body. A GE LightSpeed VCT scanner was used in Smart mA mode in which the user can select the Noise Index, and the maximum and minimum mA allowed during mA modulation. For each different protocol the CTDIvol, minimum mA, maximum mA and patient size where determined for at least 40 patients, along with information on when the mA had reached its specified minimum or maximum value. Plots were made of the CTDIvol versus patient size and of the maximum and minimum mA versus patient size. Results: Initial results demonstrated a significant variation in CTDIvol over the range of adult patient sizes of more than a factor of ten for abdominal imaging. The observation that clinical scans frequently reached the minimum allowed mA indicated that reduction of the rotation time and lowering of the minimum mA parameter would allow lower patient dose and better operation of the AEC system. These results also led us to create separate protocols for small, medium, and large patients, each with a different optimized Noise Index, kV, rotation time, and mA range. These were created in consultation with our radiologists in determining the lowest dose that would provide a clinically acceptable image after the AEC was deemed to be operating optimally. Conclusion: The above analysis can provide significant help in improving CT protocols and lowering patient dose. The plots of CTDIvol versus patient size also helped to educate radiologists in the dose variations to be expected for a range of patient sizes. Equipment grant from GE healthcare.
WE‐C‐103‐07: Standardization of CT Scanner Performance in Routine Clinical Exams: A Pilot Survey
Authors: Duan X , Zhang Y , Leng S , Yu L , McCollough C
Published: July 2013

PurposeThe goal of this project is to standardize CT scanner performance across scanner models, software versions, and patient sizes. In this pilot study, we measured image quality and radiation dose for several CT systems for 3 patient sizes to determine the amount of variation that exists within our practice for our routine abdomen/pelvis scan protocol parameters. Methods4 CT scanners used in a single practice were studied. A wire phantom was used to measure the modulation transfer function (MTF), a foil phantom to measure section sensitivity profile (SSP), and semi‐anthropomorphic abdomen phantoms of three sizes (15 year old, medium and large adults) to measure noise and assess automatic exposure control (AEC) performance. Scans of the abdomen phantom were performed by a clinical technologist as if the phantom were a patient, with all parameters per our clinical protocols. Wire and foil phantoms were scanned with AEC off using overlapping thin images, but with the same reconstruction kernel. ResultsThe 10% values of MTFs were 6.6, 6.4, 6.8 and 6.6 lp/cm and full‐widths‐at‐half‐maximum of SSP were 4.9, 5.0, 5.0 and 5.3 mm. The coefficients of variation of recorded CTDIvol were 18%, 20% and 24% for 15 year old, medium adult and large adult phantoms across the four scanners, with noise coefficients of variation of 11%, 6% and 19%.ConclusionFor routine abdomen scans performed in a single practice using different scanners, there were negligible differences in spatial resolution (MTF or SSP). For a 15 yo and medium adult phantoms, variations of dose and noise were present, but modest. For a large adult, a factor of 1.8 in dose and 1.6 in noise were observed between the lowest and highest dose or noise values, demonstrating an opportunity to adjust our AEC settings to make the dose and noise more consistent across scanners. This work was supported in part by NIH grant R01 EB071095 from the National Institute of Biomedical Imaging and Bioengineering.
WE‐C‐103‐11: Impact of Patient Parameters On the Repeatability of DCE‐CT Kinetic Analysis
Authors: Fontaine M La , McDaniel L , Kubicek L , Chappell R , Forrest L , Jeraj R
Published: July 2013

Purpose: A mixed‐effects model can separate and quantify effects according to randomness and measurable patient parameters such as weight or blood pressure. Using data acquired with a high signal‐to‐noise ratio (SNR) and limited patient motion in test‐retest‐retest scanning, we investigated the impact of various patient parameters on the repeatability of dynamic contrast enhanced CT (DCE‐CT) kinetic analysis. Methods: Eleven canine patients with sinonasal tumors received three pre‐treatment DCE‐CT scans on consecutive days. To ensure sub‐millimeter reproducibility, patients were anesthetized and immobilized with a patient‐specific bite‐block, dental mold, and vacuum mattress. Kinetic analysis was performed using the distributed parameter model to compute values for blood flow (F), blood volume ratio (BVR), transit time, and permeability (PER). The repeatability of each parameter was evaluated by the Bland‐Altman repeatability coefficient. The impact of patient parameters was determined by a hierarchical mixed‐effects model. Results: The repeatability coefficients were calculated for F (45%), BVR (39%), transit time (29%), and PER (37%). Between patients, the patient parameters with significant influence on the kinetic parameters were patient weight, area underneath the curve (AUC) of the artery, and AUC of the vein (p<0.05). However, within a patient, patient weight did not have a prominent bearing on the repeatability as it was found stable with a standard error of measurement (SEM) of 2%. As the AUC of the artery increased by one SEM, F decreased by 24% and BVR by 40%. In addition, PS decreased by 14% when the AUC of the vein increased by one SEM. Conclusion: Despite high SNR and limited patient motion, the AUCs of the artery and vein had a notable impact on the repeatability within patients for F, BVR, and PER. This indicates the need for reliable vessel selection in order to minimize kinetic analysis uncertainty.
WE‐C‐116‐03: Spectral Parameter Estimation in the Presence of Macroscopic B0 Variations Using Fast Chemical Shift Imaging
Authors: MacLellan C , Hazle J , Stafford R
Published: July 2013

Purpose: To assess the ability to correct for macroscopic B0 variations to obtain accurate estimates of T2* and amplitude in voxels containing multiple chemical species. Methods: A solid lipid/water phantom was constructed by adding 1.5% (w/v) agarose and 1.4% (w/v) lecithin to a mixture containing equal parts water and lard by volume. The phantom was imaged using fast multi‐echo GRE sequence (TEmin=3.8ms, ΔTE=2 ms, 10 echoes) while a linear gradient was applied in the slice direction at six linearly spaced values ranging from 32 to 200 μT/m. The decay of the complex data was corrected assuming an ideal (boxcar) slice profile and Gaussian slice profile estimated from phantom measurement. At each gradient strength, the T2* and amplitude of both chemical species was estimated using an autoregressive moving average (ARMA) model on the corrected and uncorrected data. Results: Before correction, the observed decrease in T2* over the range of gradient strengths was greater in water (ΔT2*=−37%) compared to fat (ΔT2*=−23%ms). The Gaussian slice profile assumption led to a better estimation of T2* (ΔT2*=−7% (water), +3%ms (fat) ) compared to the ideal slice profile assumption (ΔT2*=−18% (water); −9%ms (fat) ). Without any correction, the water fraction was overestimated by 2.8% compared to .7% and 1.1% for the Gaussian and boxcar slice profile assumptions, respectively. Conclusion: The method described in this work allows the T2* and amplitude of multiple chemical species to be corrected for the effects of linear B0 variations in the slice direction. In general, B0 variations have a greater effect on water T2* than fat T2*. The Gaussian slice profile provides a more robust correction for both T2* and amplitude estimates. Future work will focus on investigating the sensitivity of this model over a range of spectral parameters. This research is supported in part by the MD Anderson Cancer Center Support Grant CA016672 and the National Center for Advancing Translational Sciences of the National Institutes of Health under Award Number TL1TR000369.
WE‐C‐116‐05: Residual Respiratory Motion Management Within a Gating Window Using Quasi‐Breath‐Hold (QBH) Biofeedback
Authors: Kim Taeho , Lee Danny , Keall Paul , Lee Rena , Kim Siyong
Published: July 2013

Purpose: The aim of the project is to test the hypothesis that quasi‐breath‐hold (QBH) biofeedback improves the residual respiratory motion management within a gating window, reducing respiratory motion artifacts in gated 3D thoracic MR images. Methods: A QBH biofeedback system has been employed with gated 3D thoracic MRI acquisitions. The QBH biofeedback system utilized (1) the external marker position on the abdomen using an RPM system (Real‐time Position Management, Varian) to audio‐visually guide a human subject for 2s breath‐hold at 90% exhalation position in each respiratory cycle and (2) the gated T2 weighted SPACE MR pulse sequence of 3 T Siemens MRI for 3D thoracic imaging. The improvement in the upper liver breath‐hold motion reproducibility within the gating window using the QBH biofeedback system has been assessed for a group of volunteers. Each subject underwent two imaging sessions for the assessments of the residual respiratory motion management within the gating window and respiratory motion artifacts in 3D thoracic MRI both with/without QBH biofeedback. Results: The residual upper liver motion within the gating window during MR acquisitions (∼6 minutes) has been considerably reduced using QBH biofeedback, resulting in the reduction of respiratory motion artifacts in lungs and liver of 3D thoracic MR images. Additionally, average RMSE (root mean square error) of abdomen displacement obtained from the RPM has been reduced from 2.3mm of free breathing to 0.8mm of QBH biofeedback breathing: 65% of average displacement error reduction with QBH biofeedback. Conclusion: The study demonstrated the improvement of the upper liver breath‐hold motion reproducibility using QBH biofeedback during 3D thoracic MR imaging. This system can provide clinically applicable motion management of the internal anatomy for gated radiotherapy.