bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐G‐BRA‐01: Development of a Web‐Based Dosimetry Training Tool for Therapy and Dosimetry Education
Authors: Schreiber E , Hannum W , Zeman E , Kostich M , Tracton G , Church J , Dean R , Adams R
Published: June 2012

Purpose: Training in clinical dosimetry is an important component of radiation therapy, dosimetry, and medical physics training programs. Based on our in‐house treatment planning system, PLanUNC, we are developing and assessing a web‐based dosimetry teaching tool to augment existing training programs. Methods: We surveyed radiation therapy program directors to assess the need for clinical dosimetry training tools. Based on survey results, we are developing a web‐based dosimetry‐training tool consisting of 10 modules containing didactic content based on the ASRT curriculum, student assessment, and hands‐on treatment planning exercises. External content specialists reviewed the self‐paced modules for accuracy and content validity. Two external dosimetry students were observed as they completed three sections, and were interviewed in‐depth to evaluate the modules. This qualitative analysis combined features of usability testing with formative evaluation of instructional products. We revised the modules based on these data. Our next phase, quantitative evaluation, will assess the effectiveness of the modules, the quality of the interactivity and the degree of student engagement when completing the modules. Results: Sixty‐four percent of program directors indicated they had insufficient local resources for dosimetry training, and over 90% indicated interest in web‐based training tools as teaching supplements. External evaluators indicated module content was appropriate and accurate. Students indicated the modules were easy to use with clear and understandable content. They were engaged when using the modules and motivated by the interactive components. They placed value on the exercises and the feedback they received. Conclusions: Inter‐institutional evaluation improves the quality and generalizability of instructional modules. Carefully designed online learning modules are viewed as effective teaching tools by dosimetry students. The clinical dosimetry teaching tool will be made accessible to therapy and dosimetry training programs worldwide. This work is supported by NCI grant 5R25‐CA134307
WE‐G‐213CD‐08: Initial Experience with the Clinical Implementation of a Deep Inspiration Breath Hold for Left Breast Radiotherapy Using Surface Imaging and Visual Aid
Authors: Harry T , Rahn D , Yashar C , Einck J , Pawlicki T , Jiang S , Cervino L
Published: June 2012

Purpose: To evaluate the clinical implementation of a deep inspiration breath hold (DIBH) treatment for left breast radiotherapy using surface imaging and visual aid. Methods: A CT scan of the patient at DIBH is acquired and used for treatment planning. The plan and skin contour, containing isocenter and surface information are exported from the treatment planning system and imported into the surface imaging system (SIS). The skin contour constitutes the treatment reference surface or target DIBH position. A region of interest (ROI) consisting of the sternum and medial breasts is selected in the SIS. A set of video goggles allows the patient to view their breathing signal within the SIS, aiding in producing a reproducible and stable DIBH similar to simulation. Once the patient is set up at free breathing, she performs a DIBH while being monitored with the SIS. Shifts to minimize displacements from their reference DIBH surface are made. The surface image and patient setup are validated with weekly MV images. The beam is enabled when the two surfaces are within a predetermined tolerance. Results: Data for evaluation of the implementation was acquired for 4 patients throughout treatment. Average treatment time was 16.8 minutes and 14.2 minutes for setup. The average displacement from the reference surface was 0.4 mm during DIBHs. The average reduction of heart mean dose and volume receiving 50% of the prescribed dose between DIBH and FB was 38% and 89% respectively. A total of 15 patients have completed this new treatment. 2 were excluded for inability to achieve reproducible and stable DIBH.Conclusion: The workflow we have implemented has proven to be effective and efficient for clinical purposes. Surface imaging provides adequate real time information valuable to the treatment process. Visual aid has helped patients achieve DIBH with high reproducibility and stability.
WE‐G‐213CD‐09: Quality Assurance of the Surrogate Signal‐Based Dynamic Tumor‐Tracking Irradiation with Vero4DRT (MHI‐TM2000)
Authors: Mukumoto N , Nakamura M , Sawada A , Suzuki Y , Takahashi K , Miyabe Y , Kaneko S , Mizowaki T , Kokubo M , Hiraoka M
Published: June 2012

Purpose: To perform the quality assurance for the dynamic tumor‐tracking (DTT) irradiation with Vero4DRT (MHI‐Tm2000). Methods: Vero4DRT swings its gimbaled 6‐MV C‐band x‐ray head along the pan and tilt direction to track a moving tumor. Surrogate signal‐based DTT system implemented in Vero4DRT was used. Before DTT irradiation, the correlation model (4D‐model) between motion of the IR markers on the abdominal wall and the tumor position was created with synchronously monitoring by the IR camera and orthogonal kV x‐ray imaging subsystem. During beam delivery, the 4D‐model predicted the future tumor position from the displacement of the IR markers in real‐time, and then contentiously transferred the corresponding tracking orientation to the gimbaled x‐ray head.Water‐equivalent phantoms were set on a 1D motor‐driven base with IR markers. A film placed at a depth of 10 cm in the phantom was irradiated under the following conditions: stationary state, and tracking and non‐ tracking state for sinusoidal patterns. In addition, the geometric accuracy was evaluated using a 3D moving phantom and Polaris Spectra for the previously‐acquired patient's respiratory pattern. Results: Compared to the stationary conditions, reductions in lateral distance between 95% doses of the dose profile were 1.2 mm for tracking and 29.6 mm for non‐tracking state for (amplitude [A], period [T]) = (20 mm, 2 s); and 0.2 mm and 29.4 mm for (A, T) = (20 mm, 4 s); and 0.0 mm and 11.2 mm for (A, T) = (10 mm, 2 s), respectively. In the geometric accuracy testing, 95th percentile of the tracking error was 0.5 mm in left‐right, 1.0 mm in superior‐inferior, and 0.5 mm in anterior‐posterior direction. Conclusions: We demonstrated that Vero4DRT substantially reduced the blurring effects on dose distribution with high tracking accuracy, and confirmed the safety of the DTT irradiation for a clinical application. This research was supported by the Japan Society for the Promotion of Science (JSPS) through its Funding Program for World‐Leading Innovation R&D on Science and Technology (FIRST Program), and sponsored in part by Mitsubishi Heavy Industries, Ltd.
WE‐G‐217BCD‐04: Diagnostic Image Quality Evaluation of a Dedicated Extremity Cone‐ Beam CT Scanner: Pre‐Clinical Studies and First Clinical Results
Authors: Muhit A , Zbijewski W , Stayman J , Thawait G , Yorkston J , Foos D , Packard N , Yang D , Senn R , Carrino J , Siewerdsen J
Published: June 2012

Purpose: To assess the diagnostic performance of a prototype cone‐beam CT (CBCT) scanner developed for musculoskeletal extremity imaging. Studies involved controlled observer studies conducted subsequent to rigorous technical assessment as well as patient images from the first clinical trial in imaging the hand and knee. Methods: Performance assessment included: 1.) rigorous technical assessment; 2.) controlled observer studies using CBCT images of cadaveric specimens; and 3.) first clinical images. Technical assessment included measurement of spatial resolution (MTF), constrast, and noise (SDNR) versus kVp and dose using standard CT phantoms. Diagnostic performance in comparison to multi‐ detector CT (MDCT) was assessed in controlled observer studies involving 12 cadaveric hands and knees scanned with and without abnormality (fracture). Observer studies involved five radiologists rating pertinent diagnostics tasks in 9‐point preference and 10‐point diagnostic satisfaction scales. Finally, the first clinical images from an ongoing pilot study were assessed in terms of diagnostic utility in disease assessment and overall workflow in patient setup. Results: Quantitative assessment demonstrated sub‐mm spatial resolution (MTF exceeding 10% out to 15–20 cm‐1) and SDNR sufficient for relevant soft‐tissue visualization tasks at dose <10 mGy. Observer studies confirmed optimal acquisition techniques and demonstrated superior utility of combined soft‐tissue visualization and isotropic spatial resolution in diagnostic tasks. Images from the patient trial demonstrate exquisite contrast and detail and the ability to detect tissue impingement in weight‐bearing exams. Conclusions: The prototype CBCT scanner provides isotropic spatial resolution superior to standard‐protocol MDCT with soft‐tissue visibility sufficient for a broad range of diagnostic tasks in musculoskeletal radiology. Dosimetry and workflow were advantageous in comparison to whole‐body MDCT. Multi‐mode and weight‐bearing capabilities add valuable functionality. An ongoing clinical study further assesses diagnostic utility and defines the role of such technology in the diagnostic arsenal. ‐ Research Grant, Carestream Health ‐ Research Grant, National Institutes of Health 2R01‐CA‐112163
WE‐G‐217A‐01: Fast Recovery Driven Equilibrium with Automated Switching to Avoid Artifacts
Authors: Edmonson H , Bernstein M
Published: June 2012

Purpose: To reduce image artifacts from the unnecessary use of driven‐ equilibrium. Driven‐equilibrium methods known as fast recovery, RESTORE, or DRIVE enable reduction of repetition time (TR) and hence acquisition time in RARE (FSE or TSE) imaging by applying additional RF pulses following each echotrain to accelerate T1 recovery. Fast recovery (FR) techniques are most useful when TR is less than 4*T1. For neuroimaging, the benefit of FR diminishes as TR increases beyond ∼3s. In regions of rapid susceptibility change such as near metallic implants, FR techniques can introduce artifact because the magnetization is not properly rephased when the FR pulses are applied. In our clinical practice we observe that technologists frequently adjust TR over a range of 2–5s on a patient‐ specific basis to minimize scan time. We do not observe, however, that technologists reliably disable FR when TR is long enough, introducing possible artifacts. Methods: An FR‐FSE pulse sequence was modified to automatically disable the FR feature whenever TR exceeded a user‐defined threshold (TR0). Under IRB approval, a healthy volunteer was scanned with the sequence using TRs ranging from 1–5s, and TR0=900ms or 6s. Contrast‐ to‐noise measurements were made between CSF, gray matter and white matter for each dataset. Results: The volunteer study shows decreasing benefit of FR as TRs increase beyond 3s. A patient with bilateral auditory brainstem implants scanned with and without FR demonstrates FR‐induced artifacts. Conclusions: We demonstrate an FR‐FSE pulse sequence that automatically disables fast‐recovery whenever TR exceeds an operator‐ selected threshold. The pulse sequence avoids unnecessary artifacts in regions of rapid susceptibility changes, while retaining the advantages of FR when TR<TR0. Clinical images from a patient with bilateral auditory brainstem implants demonstrate potential artifacts introduced by FR, and the benefits of automatically avoiding unnecessary use of FR.
WE‐G‐217A‐05: Automatic Method for RF Coil Assessment in Clinical MRI: A Three‐Dimensional Approach
Authors: Peng Q
Published: June 2012

Purpose: MRI RF coil assessment is usually evaluated with region‐of‐interest (ROI) analysis from a single 2D phantom image. This simple approach has worked well for large volume coils or phased‐array coil with large receivers, but not the high density phased‐array coils characterized by 3D array arrangement of their multiple receivers. This abstract proposes a novel approach for quantitative coil assessment based on 3D imaging and 3D ROI analysis. Methods: To characterize all receivers of the coil of interest, a large uniform phantom (preferably a corresponding anthropometric phantom) and a large 3D geometric coverage fully includes the coil sensitivity volume was applied during MR imaging. After imaging, data from all receivers were used to reconstruct a composite 3D image, and to reconstruct 3D images from each individual receiver, leading to a total of N+1 3D image datasets (where N is the number of coil channels). IDL programs were developed to automatically perform ROI analysis on the composite image and on the individual receiver images. Instead of choosing one single 2D slice out of each 3D dataset, the whole 3D dataset was treated as a 3D image, and 3D ROIs were automatically generated for coil assessment. Results: This 3D coil evaluation approach could be applied to all clinical coils including quadrature body/head coils, and phased‐array coils with 2 to 32 channels. 3D sensitivity map could be generated to check receiver function visually. 3D mean SNR, max SNR, and uniformity could be obtained from composite and individual channel 3D images fully automatically. Coil/receiver performance assessment was very fast and straightforward, regardless of the number of receivers of the coil. Conclusions: 3D imaging in combination with 3D automatic ROI analysis is a fast, convenient, and less subjective approach for quantitative coil assessment, particularly for high density phased‐array coils.
WE‐G‐217A‐09: Phase Imaging Measurement of Static Magnetic Field Homogeneity
Authors: Hsieh C , Stafford R , Reeve D
Published: June 2012

Purpose: The ACR MRI accreditation program requires measurement of the magnetic field homogeneity (MFH) in the annual QA. Full implementation of vendor methods can be very time consuming and incorporates techniques not available to clinical physicists. Conversely, many of the less involved techniques proposed tend to be less inaccurate and/or precise. Here, we propose a robust approach to MFH analysis using a simple phase mapping acquisition which is a time efficient compromise. Methods: The root mean square (r.m.s.) for MFH measurement is commonly used over multiple slices (∼24). In regions with high SNR, the MR signal can be reasonably assumed Gaussian distributed. Therefore, the standard deviation of phase values in ROI is equivalent to the r.m.s. of those. The standard deviations of phases in x, y and z are assumed uncorrelated. Thus, only axial, sagittal and coronal planes need to be acquired to approximate the MFH as opposed to a full 3D acquisition. To investigate this concept, phase images were acquired on four 1.5T clinical scanners and one 3.0 clinical scanner (MAGNETOM Espree, Siemens Medical Systems, Signa Excite HD 1.5T, and 3.0T GE Healthcare Technologies). The manufacturer phantoms were scanned using two echo times (delta_TE=TE2−TE1<5ms) using a simple 2D gradient echo acquisition to produce phase images. After acquiring phase difference images in three orthogonal planes, the standard deviation was calculated in three circular ROIs (Diameter=10, 20 and 30cm) in each plane, respectively, to estimate the MFH for the effective DSV. Results: The MFH values in five scanners using this method were within vendor specifications for the DSV. Additionally, the measured MFH values compared favorably with vendor planned maintenance records with <0.1 ppm discrepancy. Conclusions: This proposed method may be a reliable and practical for regular MFH measurement in QA programs and providing an independent check of the vendor measurement.
WE‐G‐218‐02: The Measurement of Absorbed Dose to Active Intravenous Cardiac Devices in Patients Undergoing Radiotherapy
Authors: Reft C
Published: June 2012

Radiotherapy departments are seeing an increasing number of patients presenting for treatment with active intravenous cardiac devices (AICDs). This is due to an increasing aging population and technology advances in these devices. The AAPM TG‐34 addressed the radiation effects in these devices and provided recommendations for patients with these devices undergoing radiotherapy. The current devices utilizing CMOS technology are more sensitive to radiation then the older bipolar devices. Therefore, it is important to estimate the dose to the device to ensure that the radiation does not adversely affect the performance of the device. This is particularly important for patients dependent on their accurate functioning. The dose to the device is generally from secondary radiation and is typically below 0.05 Gy with most of it coming from lower energy scatter radiation. Treatment planning systems can be used to estimate the dose to the device. However, these systems do not accurately calculate doses at distances more than 2–3 cm from the field edge. For these out–of–field dose measurements the dosimeter requires a high sensitivity and a relatively flat energy response. Thermoluminescent detectors and optically stimulated luminescent detectors satisfy these requirements and they are relatively unobtrusive. The newer formulations of radiochromic film with higher sensitivity can also be used. The detector should be place under 0.5 to 1.0 cm of bolus to minimize the contaminating head‐scatter electrons provide a more realistic measurement of the dose to the device.

Learning Objectives:

1. List the reasons for estimating the dose to the AICDs

2. Provide a discussion on the various methods which include calculations and measurements to estimate the dose to the device as well as the uncertainties in these estimates.

3. Identify detectors that satisfy the requirements for these in‐vivo out‐of‐field dose measurements as well as describe the appropriate correction factors to apply for accurate dose measurements.
TH‐A‐211‐02: Effects of Different Parameters on Deformable Image Registration
Authors: Kim J , Zhong H
Published: June 2012

Deformable image registration algorithms generally consist of three components, similarity metric, transformation, and optimization. In addition to these components, the optimization also includes one or more regularization terms such as the smoothness of the underlying deformation or restrictions based on the physical properties of organs. It is also common for most of the algorithms to take a multi‐resolution approach to capture large initial deformations as well as to speed up the registration process. Understanding and proper choice of such parameters are critical to a successful registration. The effects of different choices of parameters will be presented using public domain algorithms as well as commercial software.

Learning objectives:

1. To understand the basic constituents of deformable image registration algorithms.

2. To understand the consequences of the different parameter choices.
TH‐A‐213AB‐04: Improving VMAT Delivery Accuracy by Using an Aperture Complexity Penalty during Optimization
Authors: Younge K C , Matuszak M M , Moran J M , McShan D L , Fraass B A , Roberts D A
Published: June 2012

Purpose: Apertures optimized during VMAT planning can be small and irregular, resulting in dosimetric inaccuracies during delivery. Our purpose is to develop and integrate an aperture‐regularization objective function into the optimization process for VMAT, and to quantify the impact of using this objective function on dose delivery accuracy and optimized dose distributions. Methods: An aperture‐based metric (‘edge penalty’) was developed that penalizes complex aperture shapes based on the ratio of MLC side edge length and aperture area. To assess the utility of the metric, VMAT plans were created for an example paraspinal SBRT case with and without incorporating the edge penalty in the cost function. To investigate the dose accuracy, Gafchromic EBT2 film was used to measure 15 sample individual apertures and composite plans with and without the edge penalty applied. Films were analyzed using a triple‐channel uniformity correction and measurements were compared directly to calculations. Results: Apertures generated with the edge penalty were larger, more regularly shaped and required 22% fewer monitor units than those created without the edge penalty. DVH analysis showed that the changes in doses to organs at risk and normal tissues were minimal. Edge penalty apertures showed a significant decrease in the number of pixels disagreeing with calculation by more than 10%. The number of pixels passing in the composite dose distributions for the edge penalty and non‐edge penalty plans were 52% and 96%, respectively. Employing gamma criteria of 3%/1mm resulted in a 79.5% (without penalty) / 95.4% (with penalty) pass rate for the two plans. Conclusions: The use of the edge penalty during optimization has the potential to significantly improve dose delivery accuracy for VMAT plans while minimally affecting optimized dose distributions.
TH‐A‐213AB‐10: Improved Multi‐Criteria Optimization for Intensity Modulated Proton Therapy Using Iterative Resampling of Randomly Placed Pencil‐Beams
Authors: van de Water S , Kraan A , Breedveld S , Teguh D , Madden T , Kooy H , Heijmen B , Hoogeman M
Published: June 2012

Purpose: In treatment planning for spot‐scanned intensity modulated proton therapy (IMPT), a fine‐grid pencil‐beam distribution is used to guarantee high‐quality treatment plans. This may lead to very large optimization problems with excessive planning times, especially for large target volumes. To improve the trade‐off between plan quality and optimization times, we have developed a new pencil‐beam placement method called ‘resampling’. Methods: Resampling is based on repeated multi‐criteria optimizations. In each iteration, a new sample of randomly placed pencil‐beams is optimized together with favorable (high‐weight) pencil‐beams of the previous solution. In previous studies, resampling was successfully applied for Cyber Knife plan optimization. In this study, IMPT resampling plans for four head‐and‐ neck cancer patients were compared with traditional IMPT plans, generated using a regular grid with typical spacing (5×5×4mm3). For resampling, sample sizes of 3000, 5000, 7000, and 9000 pencil‐beams per iteration were tested, storing the (intermediate) plans after each of in total 7 iterations. The same dose prescription and 3‐beam arrangement was used in all plans. Results: For similar optimization times and target coverage, resampling resulted in lower doses to organs‐at‐risk than the traditional approach. Mean doses were reduced by 0.4Gy on average (1.7%, range: 0Gy–0.9Gy) for both parotid glands, by 2.5Gy (7.1%, range 0.5Gy– 3.8Gy) for both submandibular glands and by 3.3Gy (9.6%, range: 2.3Gy–4Gy) for the swallowing muscles. Maximum doses to spinal cord and brain stem were on average reduced by 4.1Gy (25.7%, range: 2.3Gy–5.8Gy) and 3.4Gy (31.4%, range:−0.4Gy–9.5Gy), respectively. For comparable doses to organs‐at‐risk, optimization time was reduced by 38.7% on average (range: 6.7%–54.8%), being proportional to the target volume. Conclusions: Pencil‐beam resampling is an efficient method for IMPT plan optimization, allowing for clinically relevant improvements in plan quality and/or planning time, especially for large problem sizes. It opens possibilities for dealing with large‐scale problems such as beam‐angle optimization.
TH‐A‐BRA‐06: Optimal PTV Margin Expansions along Six Anatomic Directions in Oropharyngeal IGRT
Authors: Yock A , Zhang L , Court L , Garden A , Dong L
Published: June 2012

Purpose: To determine the optimal PTV expansions along six anatomic directions for a population of patients receiving CT‐guided IMRT of the oropharynx. Methods: For 20 patients, daily‐acquired CT‐on‐rails images used for patient alignment to the C2 vertebral body were deformably registered to the patients' planning CT. The positions of volume elements originally within the CTV (target voxels) or within a 1cm shell surrounding the CTV (normal tissue voxels) on the patients' planning CT were determined on the daily CTs. The geometric target coverage and included normal tissue were the proportion of target voxels and normal tissue voxels, respectively, that were within a margin for a particular proportion of treatment fractions. Geometric target coverage was evaluated for 15,625 margins created in MatLab representing the 56 combinations of 1, 2, 3, 4, and 5mm expansions along the posterior, anterior, lateral, medial, inferior, and superior directions. The optimal margin minimized the normal tissue values at 10, 50, and 90% of treatment fractions while providing adequate geometric target coverage for at least 90% of patients. Four target coverage criteria were selected requiring at least 90 or 95% of target voxels be covered during at least 90 or 95% of treatment fractions. Results: Optimization according to each geometric target coverage criterion yielded a unique, anisotropic margin. Margins ranged from 1–5, 3–5,1–3, 4–5, 2–5, and 3–5mm in the posterior, anterior, lateral, medial, inferior, and superior directions, respectively. These optimal margins included 9.8 to 44.8% less normal tissue than isotropic margins while providing equivalent target coverage. Conclusions: Due to characteristics of non‐rigid setup errors and anatomical changes during the course of treatment, the optimal margin for oropharyngeal patients was anisotropic. Anisotropic margin expansions could reduce normal tissue exposure without compromising geometric target coverage. Funding support provided by the University of Texas Graduate School of Biomedical Sciences at Houston and the University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
TH‐A‐BRA‐08: Retrospective Accuracy Estimation for Motion Compensated Robotic Radiosurgery of the Liver
Authors: Krause J , Blanck O , Duerichen R , Wurster S , Andratschke N , Rades D , Hildebrandt G , Dunst J , Schweikard A , Schlaefer A
Published: June 2012

Purpose: The CyberKnife™ compensates translational target motion by moving the beams synchronously. While the system was found to operate with sub‐millimeter accuracy in phantoms, determining the clinical accuracy is challenging. Measuring the delivered dose distribution inside a patient is impractical. Hence an analysis of treatment data is typically used to estimate residual errors. Methods: We implant 3‐5 fiducials for target tracking and treat liver tumors in 3‐5 fractions with 45Gy at 80% to the PTV (CTV+3mm). Patients are aligned based on X‐ray images in expiration breath hold. During delivery, X‐ray images are acquired every 60‐90s, and the translational and rotational misalignment is computed. We grouped this data into 10 respiratory phases. The mean misalignment for each phase was used to simulate the translation and rotation of the target with respect to the alignment center. The resulting dose distribution was computed and compared to the planned dose. Additionally, the quality of motion prediction was evaluated. Results: We analyzed 5 cases with a total of 17 fractions. The maximal target motion per fraction ranged from 9.2mm to 25.7mm (3D trajectory). The mean error for each patient ranged from ‐0.76/‐0.01/‐ 0.32mm to 0.35/0.17/0.10mm (Translation IS/LR/AP) and ‐0.94/‐0.82/‐2.07 degrees to 0.24/1.95/2.36 degrees (Rotation roll/pitch/yaw). The dose simulation showed point dose difference for each patient ranging from ‐ 0.10Gy to ‐0.76Gy (Mean) and ‐1.13Gy to ‐5.05Gy (Max). The resulting reduction in coverage ranged from 0.37% to 4.19% (PTV) and ‐0.43% to +0.94% (CTV). Finally, the mean prediction error over all fractions was 0.33mm. Conclusions: We demonstrated that while maximum point dose differences can be considerable, the coverage of the CTV is maintained even in the presence of substantial respiratory motion. The results indicate that the standard 3mm system uncertainty margin can account for errors due to rotation and deformation during robotic radiosurgery for tumors in the liver.
TH‐A‐213CD‐04: A Bone Artifact Reduction Algorithm for Differential Phase‐Contrast CT Based On Statistical Iterative Reconstruction
Authors: Hahn D , Thibault P , Noel P , Bech M , Pfeiffer F
Published: June 2012

Purpose: The purpose of this work is a reduction of the influence of dense materials, e.g. bones, on the reconstruction of grating‐based differential phase‐contrast computed tomography (PCCT). These strongly absorbing materials introduce streaking artifacts, in look and feel similar to metal artifacts in conventional absorption CT. Methods: An iterative reconstruction algorithm, which statistically models the differential phase‐ contrast imaging process, was developed. It allows for individually introducing a statistical weight for each sinogram pixel, i.e. its influence on the resulting reconstruction. In grating‐based imaging the absorption and phase‐contrast signals are simultaneously retrieved from the same set of raw projection images and are thus inherently registered. This can be utilized for getting information on the position of highly dense materials, e.g. bones, from the absorption signal. The statistical weights are then modified according to this information to reduce the influence of sinogram pixels that contain dense material and are likely to cause artifacts. This concept was applied to a tomographic dataset of a mouse acquired with a grating interferometer at the European Synchrotron Radiation Facility in Grenoble, France. Reconstructed with a standard filtered backprojection, the sample dataset suffers from very strong streaking artifacts in the region surrounding the spine. Detail contrast in the soft tissue around the spine is lost due to these streaks. Results: Comparing reconstructions performed with a standard filtered backprojection and with the newly developed algorithm shows a significant reduction of streaking artifacts and a strong improvement in soft tissue contrast in regions influenced by dense material. Conclusions: This work significantly expands the potential of grating‐based differential phase‐contrast computed tomography. It is now possible to offer the high soft‐tissue contrast of phase‐contrast imaging in cases where dense materials such as bones, are present. D.H., P.T., M.B. and F.P. acknowledge financial support through the DFG Cluster of Excellence Munich‐Centre for Advanced Photonics and the European Research Council (FP7, Starting grant #240142).
TH‐A‐213CD‐06: Study of a New X‐Ray Scatter Rejection Technique Based On Frequency Division Multiplexing
Authors: Zhang J , Chang S , Lu J , Zhou O
Published: June 2012

Purpose: X‐ray scatter may significantly degrade imaging performance in x‐ray radiography applications in terms of soft tissue contrast reduction, potentially severe image artifacts, and increased patient dose. We recently developed a new x‐ray scatter rejection method based on nanotechnology‐enabled frequency division multiplexing x‐ray (FDMX) imaging technique. In this study we report our recent work on developing this new scatter rejection method and evaluating its performance. Methods: The key enabling technology is the carbon nanotube (CNT)‐based multi‐beam field emission x‐ray (MBFEX) source technology. The proposed FDMX imaging system has a MBFEX source with an array of x‐ray tubes. The x‐ray radiation from each individual x‐ray tube is modulated at a certain given frequency. The collimated x‐ray beams passed through the object and were captured by a high speed x‐ray detector. A demultiplexing algorithm was applied to reject the scatter radiation from the primary radiation based on their different modulation frequencies. Results: The x‐ray images generated by the FDMX imaging technique clearly demonstrated improved imaging quality in terms of lower scatter‐to‐primary‐ratio (SPR) and higher contrast‐ to‐noise‐ratio (CNR). It shows great potential of improving x‐ray imaging performance and reducing patient dose. Conclusions: We recently developed a novel x‐ray scatter reduction method based on nanotechnology‐ enabled frequency division multiplexing x‐ray (FDMX) imaging technique. The FDMX imaging system has a MBFEX source with an array of x‐ray tubes. The x‐ray radiations from the MBFEX source were modulated at different frequencies. The scatter radiations were decoupled from the primary radiations based on their different modulation frequencies. This novel scatter reduction method, once fully developed, will have a great potential in improving x‐ray imaging quality and reducing patient dose.
TH‐A‐217BCD‐01: Challenges and Opportunities with Photon Counting CT
Authors: Danielsson M
Published: June 2012

There is currently a large interest in photon counting CT detector research in both academia and industry. There are several detector systems and strategies to handle major challenges such as the very high count‐rate, while the energy information for each photon is retained. Another challenge is cross talk, which may compromise the energy estimation for the photons and can cause double counts, which gets worse with smaller pixel size. If implemented in the clinic, photon counting CT will likely enable a dose reduction when this is important, as for example in pediatric CT. Photon counting CT will also make possible quantitative measurements, energy weighting and/or tissue decomposition techniques that can be of great importance for a number of imaging tasks
TH‐A‐217BCD‐11: A Practical Approach to Evaluate the Performance of Automatic Exposure Controls in Digital Mammography
Authors: Zhou Y
Published: June 2012

Purpose: To establish a practical methodology to quantify the performance of different automatic exposure controls (AEC) options in digital mammography in terms of dose efficiency. Methods: A Hologic Selenia digital mammography system was used in the study. A figure of merit (FOM), defined as the squared signal difference to noise ratio normalized by the mean glandular dose (MGD), was utilized to delineate the AEC performance. The measurements and analyses were conducted under different AEC options on a realistically shaped tissue equivalent phantom (CIRS 18‐222). The phantom consists of simulated masses, fibers, and microcalcifications. Slabs of BR12 were added to reach different thicknesses. Based on the results, a computer simulation was performed for lesions on the images of an anthropomorphic breast phantom (Gammex, Rachel) acquired under the same AEC options. The pathological findings from the resulted images were compared. Results: For the mammography system used in the experiment, it was found that as compared with the default AEC, the lower kVp and Mo‐Mo target‐filter AEC table results in a FOM improvement on low contrast by 11% to 20%, except for 7 cm thickness where the FOM is reduced by 17%. The FOM improves negligibly on high contrast details for the thicknesses of 4.5 – 6 cm and decreases by 18% for the thickness of 7 cm. The simulated lesions on the Rachel phantom showed enhanced contrast with the lower kVp and Mo/Mo option, but the enhancement gradually decreases for the thicker breast. Conclusions: A methodology was established to quantify the performance of different AEC options using the figure‐of‐merit and the commercially available phantoms. For the tested mammography system, the lower kVp and Mo/Mo option is preferred if the breast thickness ranges 4.5 – 6 cm, whereas the default AEC is recommended if the breast thickness is 7cm and above.
TH‐A‐218‐01: Managing Fat in MRI: A Technical Perspective
Authors: Ma J
Published: June 2012

Water and fat are the two predominant sources of signal for in vivo MRI. Because fat is omnipresent in many parts of our body and because fat appears bright in many types of basic MR images, it is often essential to be able to successfully suppress the fat signal. Chemical shift selective saturation (CHESS) and short‐tau inversion recovery (STIR) are the two well‐known techniques for this purpose. Despite their widespread use and success, CHESS and STIR have fundamental limitations and as a consequence, poor fat suppression is one of the most frequently‐encountered image quality issues in clinical practice. Further, it is difficult to implement the CHESS or STIR‐based techniques for some emerging applications such as fast dynamic imaging. Another MRI technique for managing fat that has gained increasing clinical use only in the last few years was first published by Tom Dixon in 1984. The original idea of the so‐called Dixon techniques is to collect two images that have water and fat signals in‐phase and 180o out‐of‐phase, respectively. These two images can be added and subtracted to yield a “water‐only” image and a “fat‐only” image. Thus, the Dixon techniques have the potential for simultaneous fat suppression and fat quantification. Additionally, it was recognized and is now demonstrated that the Dixon techniques can be made highly insensitive to magnetic field inhomogeneity and highly SNR and scan time efficient. In this talk, I will provide an overview of some major development of the techniques for managing fat in MRI. I will focus particularly on the physical basis as well as the respective pros and cons of the different fat management techniques in MRI.

Learning Objectives:

1. Understand the physical basis and advantages and disadvantages of several major fat management techniques in MRI

2. Understand some major issues and technical development of the Dixon techniques for water and fat imaging

3. Understand some remaining challenges and future opportunities for fat imaging and applications by MRI
TH‐B‐218‐01: Iterative Reconstruction Methods in Computed Tomography
Authors: Stayman J
Published: June 2012

Sophisticated iterative reconstruction methods for computed tomography have seen more widespread adoption with the availability of increased computational power and the desire for improved dose utilization. While improved image quality and dose reduction are possible with iterative approaches, there is a (sometimes confusing) diversity of algorithm choices. This presentation will introduce the basic concepts behind iterative reconstruction and statistical methods, including how such approaches are formed and illustrating different classes of reconstruction algorithm. Differences between iterative approaches and traditional reconstructions will be discussed ‐ both in terms of how data is processed as well as the differing image properties that arise from each type of algorithm. The lecture will highlight advantages and limitations of iterative reconstructions and provide listeners with a basic introduction of the inner workings of the iterative methodology.

Learning Objectives:

1. Understand the fundamentals of how iterative methods are formed and how to identify particular classes of iterative methods.

2. Gain intuition into the flexibility of iterative methods and why these approaches can have an advantage over other techniques.

3. Learn about the nature of iteratively reconstructed images and how images produced by these methods can have significantly different image properties from those produced by traditional analytic approaches.

This talk may contain research sponsored by Siemens, Varian Medical Systems, and/or Carestream Health.
TH‐C‐213AB‐02: Improved Predictive Modeling of Radiation Pneumonitis in Lung Cancer Patients Using Machine Learning Techniques
Authors: Oh J , Apte A , Robinson C , Bradley J , Deasy J
Published: June 2012

Purpose: Early prediction of radiation pneumonitis (RP) could help physicians provide locally advanced non‐small cell lung cancer (NSCLC) patients at high risk of RP with targeted radiotherapy. To date, several RP predictive models have been developed using statistical methods and machine learning techniques. We designed an improved risk model for predicting RP using a recently introduced machine learning method. Methods: We retrospectively analyzed a single NSCLC dataset collected at Washington University School of Medicine, which consisted of 123 NSCLC patients who received 3D conformal radiation therapy with a median prescription dose of 66 Gy and had a median follow‐up of 17 months. In this analysis, 59 patients with grade=2 were considered to have RP. Using clinical variables and lung and heart dose‐volume variables extracted from this dataset, we built a novel RP predictive model based on multivariate logistic regression and supervised principal component analysis (SPCA). The performance of our proposed method was compared with that of multivariate logistic regression alone. Results: Using lung‐related dosimetric variables, SPCA‐based logistic regression model had a Spearman correlation coefficient (Rs) of 0.33 (p=0.0001), whereas logistic regression model had Rs=0.20 (p=0.014). Using heart‐related dosimetric variables, Rs=0.42 (p < 0.0001) and Rs=0.40 (p < 0.0001) were obtained in the SPCA‐based logistic regression and logistic regression models, respectively. Interestingly, when clinical variables alone were used, logistic model showed better performance with Rs=0.34 (p < 0.0001) than SPCA‐based logistic regression model with Rs=0.32 (p < 0.0001). Integrating all variables, SPCA‐based logistic regression model obtained the best performance with Rs=0.44 (p< 0.0001) while logistic model had Rs=0.37 (p< 0.0001). Conclusions: Incorporating multivariate logistic regression with a new machine learning method allowed us to produce a better predictive RP model that should be further tested for potential clinical use.
TH‐C‐213AB‐09: State‐Driven Mathematical Model Simulations of Tumor Response to Radiotherapy: How Does High FDG Uptake Relate to Classical Radiobiological Principles?
Authors: Jeong J , Deasy J O
Published: June 2012

Purpose: High FDG‐PET tracer tumor uptake is well‐established to correlated to increased local failures and shorter overall survival. However, the relationship between uptake and classical radiobiological mechanisms is unclear. We explore the potential relationship between FDG‐PET uptake and classical radiobiolocial mechanisms using a mathematical framework. Methods: Tumor response was simulated using a novel, state‐driven tumor response model, including proliferating, hypoxic, and intermediate cell sub‐populations. Different potential relationships between FDG uptake and these cell populations were simulated. The uptake of FDG was assumed to be associated either with (1) the total number of viable cells, (2) the number of proliferative cells or (3) the number of intermediate cells. The predicted tumor doses for 50% control (TD50) in 2 Gy/fx were estimated for all possible initial conditions and correlated with the FDG uptake level for each assumption. Results: When the FDG uptake pattern was assumed to reflect the level of proliferation, the TD50 decreased with high FDG uptake. When the FDG was assumed to reflect the fraction of viable cells, only a weak positive correlation was observed between FDG uptake and TD50. As a surrogate of metabolically‐viable hypoxic cells, FDG uptake exhibited a strong positive correlation with TD50, consistent with clinical observations. Conclusions: Several different FDG uptake patterns were simulated using the model. Given the established clinical fact that FDG uptake correlates to a requirement of higher dose to achieve local control, the results support a potential avidity of FDG for cells in the intermediate stress state between being well‐oxygenated (and proliferating) and very poorly oxygenated (extremely hypoxic). Supported by the Enid A. Haupt Endowment for Medical Physics
TH‐C‐213AB‐11: LET‐Guided Biological Optimization in IMPT
Authors: Giantsoudi D , Grassberger C , Craft D , Niemierko A , Trofimov A , Paganetti H
Published: June 2012

Purpose: To investigate the feasibility of linear energy transfer (LET)‐ guided biological dose optimization in intensity modulated proton therapy (IMPT). Methods: Multi‐criteria optimization (MCO) module was utilized to generate Pareto‐optimal IMPT plans, each one corresponding to defined objectives (base plans), for a pediatric chordoma case. A Monte Carlo (MC) platform was used to calculate the corresponding LET distributions for each base plan, as well as for a linear combination of the initial base plans (resulting in clinically acceptable plans). Comparison among calculated LET distributions was performed in terms of dose and LET volume histograms (DVH and LVH) for the target and organs at risk (OARs). For verification purposes, the LET distribution of the clinically acceptable plan was also calculated as the dose weighted average of the LET distributions of the contributing base plans. It was then compared to the corresponding MC LET calculation. Results: Significant differences were observed among the LET distributions for different Pareto‐optimal base plans. Target LVHs demonstrated up to 10% differences in LET values within the range of 30% to 95% of the target volume. Plotted LVHs for the OARs showed more significant differences, more than 50% in the range of 10% to 90% of the structure volume. Comparison between the MC calculated and dose weighted averaged LET distributions for the clinically acceptable IMPT plan showed no significant differences. This verifies the accurate calculation of the LET distribution as a dose weighted average of pre‐calculated LET distributions. Conclusions: By demonstrating the variability of LET distributions among Pareto‐optimal IMPT plans in MCO and verifying the accuracy of the LET calculation method, our study suggests the feasibility of MCO‐based planning optimization system, where the user will have access to both the LET and dose distributions while navigating on the Pareto‐surface, towards effect‐driven treatment planning. Federal Share of program income earned by Massachusetts General Hospital on C06 CA059267
TH‐C‐213AB‐12: On the Importance of Heterogeneous Calculation in Brachytherapy: A Radiobiological Point of View
Authors: Afsharpour H , Verhaegen F , Beaulieu L
Published: June 2012

Purpose: The purpose of this work is to investigate the importance of heterogeneity corrections for dosimetry in brachytherapy. In particular, we are interested to see how the estimations of the a/b parameter for prostate cancer may change if accurate dose calculations are implemented in brachytherapy. Methods: A Monte Carlo dose engine called ALGEBRA (Based on GEANT4) is used to accurately calculate dose distributions for 30 prostate cancer patients treated with brachytherapy at our institution. The equivalent uniform BED (EUBED) is used to take the high spatial dose heterogeneity of BT into account for estimating the biological efficiency of treatments. For the same level of clinical outcome, the EUBED of BT can be assumed is‐effective with BED of external beam radiotherapy to extract the a/b value for prostate cancer. Results: When the heterogeneities are neglected, a/b value equals 3.1 Gy as reported in the literature. When heterogeneities are considered in BT, an a/b value of 5.4 Gy is predicted for prostate cancer. Conclusions: The importance of a precise dosimetry method in plan evaluation has been recognized but its importance on the radiobiological evaluations is usually neglected. This study shows that by using an accurate dosimetry method in BT, the estimation of a/b can change considerably with regard to the reported value of 3.1 Gy in the literature.