bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐F‐211‐01: Delineation of Functional Thalamic Subregions: A Comparison of Probabilistic Diffusion Tractography and Electrophysiology
Authors: Sudhyadhom A , McGregor K , Okun M , Foote K , Trinastic J , Crosson B , Bova F
Published: November 2011

Purpose: To delineate functional subregions of the thalamus through probabilistic diffusion tractography and electrophysiology. Methods: We acquired diffusion weighted MRI scans in a set of five thalamic deep brain stimulation (DBS) subjects in order to employ probabilistic diffusion tractography (PDT) for localization of connections from the thalamus to somatosensory cortex (S1) and primary motor cortex (M1)/supplementary motor area (SMA). We defined and implemented a novel model to delineate PDT based thalamic functional subregions, i.e. connectivity defined regions (CDR). In this “mixture” model, a voxel can be considered to be comprised of multiple functional circuits. This model is compared against the “separation” model whereby a voxel is functionally associated with the dominate circuit that inhabits that voxel. The ability for these models to correctly classify a voxel as corresponding to sensory or motor was determined by comparison against a “gold standard” (ie. electrophysiology). Results: In the separation model, both sensory and motor responsive cells (from electrophysiology) were found to lie within the motor CDR (with the exception of one sensory responsive cell). Separation model defined CDRs grossly overestimated the extent of the motor CDR and further underestimated the extent of the sensory CDR. A threshold (between 1 % and 8% of the total number of fibers in a voxel) was used to create a mixture model sensory CDR that spatially maximizes inclusion of sensory cells and minimizes inclusion of motor cells. A mixture model motor CDR at similar thresholds spatially included all motor cells but also included all sensory cells suggesting that motor circuits strongly innervate areas with sensory cells but that the reverse is not necessarily true. Conclusions: Mixture model delineation of CDR offer a significant improvement in delineation of functional subregions (as compared with electrophysiology). The data from this study suggests that tractography derived data may correlate with electrophysiology.
MO‐F‐211‐02: Higher Order Diffusion Tensor Metrics in the Evaluation of Traumatic Brain Injury
Authors: Zhuo J , Gullapalli R
Published: November 2011

Purpose: Knowledge of tissue alterations at an early stage following traumatic brain injury (TBI) is critical for injury management and prevention of secondary damage to the brain. In this study we investigate whether diffusion kurtosis imaging is sensitive to the microstructural changes in water diffusion in various grey and white matter regions in a controlled cortical impact (CCI) injury rat model at both the acute (2 hours) and the sub‐acute (7 days) stages following injury. Methods: 12 adult male Sprague‐Dawley rats were subjected to left parietal CCI injury. Imaging was performed on a 7 Tesla Bruker system using a four channel receive coil. Diffusion tensor images of the entire brain was obtained at an in‐plane isotropic resolution of 200 microns and a slice thckness of 1mm with diffusion encoding in 30 directions. Images were precessed for fractional anisotropy (FA), mean diffusivity (MD) and mean kurtosis (MK). Immunohistochemistry staining for astrocytes using anti‐GFAP was obtained for correlation with imaging findings. Results: Changes in standard diffusion tensor parameters, including FA and MD that normalized by the sub‐acute stage. However, MK was significantly elevated and remained elevated at 7 days in the ipsilateral regions of the hippocampus, cortex and the external capsule. Further, at 7 days abnormal MK was observed in the contralateral regions while no changes were observed with MD and FA. An increase in mean kurtosis was directly associated with increased reactive astrogliosis from immunohistochemistry analysis in the cortex, hippocampus, corpus callosum and the external capsule. Conclusions: This study for the first time provides direct evidence for the ability to detect in vivo via MK, the increased astrocytic activity that leads to microstructural changes. Monitoring changes in MK allows the investigation of molecular and morphological changes in vivo due to reactive astrogliosis and may complement information available from standard DTI parameters.
MO‐F‐211‐05: GPU Computation for Voxelwise Kinetic Modeling of Hepatic Perfusion
Authors: Wang H , Cao Y
Published: November 2011

Purpose: To accelerate computation speed of time‐consuming voxelwise hepatic perfusion estimation from dynamic contrast enhanced (DCE) imaging using graphics processing unit (GPU) hardware, thus facilitating high resolution DCE analysis of large tissue regions for perfusion assessment. Methods: Voxelwise perfusion estimation for large tissue regions are assigned to a GPU for parallel computation with a CUDA block for one voxel computation. The Nelder‐Mead simplex algorithm for the nonlinear least squares fitting of a hepatic kinetic model is executed in each block. To compute the convolution in the cost function in frequency domain, the general Cooley‐Tukey algorithm with the radix‐2 inverse FFT is implemented in a block. The algorithms are programmed using CUDA 3.2 on the GPU of NVIDAˈs Tesla C2050. Simulated dynamic curves are used to evaluate the GPU implementation. The computation time of the GPU perfusion estimation per voxel is compare with that from a CPU. By varying the number of time points in the dynamic curves, we also examine the performance improvement with respect to the share memory usage. Results: The perfusion estimation with single precision float GPU computation has accuracy of greater than 99% of the truth. The GPU implementation is approximately 30 times faster than the CPU computation for the number of voxels greater than 100. The result also shows less share memory usage produces higher performance. Conclusions: We implement the voxelwise hepatic perfusion estimation from DCE imaging on GPU, which significantly accelerates the computation speed. Further optimization of the GPU codes, such as share memory usage, will improve the performance. The GPU programs are valuable for a study of liver perfusion after irradiation as well as useful for other DCE imaging modeling for high performance

The work is supported in part by PO1CA59827 and RO1CA132834.
MO‐F‐211‐06: Characterization of Through‐Plane Flow Effects on Vascular Input Function Definition and Subsequent DCE‐MRI Imaging Biomarkers
Authors: Bosca R , Jackson E
Published: November 2011

Purpose: Quantitative analysis of dynamic contrast‐enhanced (DCE)‐MRI data is becoming increasingly utilized in early phase clinical trials as a means of assessing therapy response. The aim of this study was to characterize the effect of vascular through‐plane blood flow on the quantification of DCE‐MRI data in salivary glands and nodal tumors of the head and neck. Methods: Patients (n=8) were imaged using an axial 3D FSPGR sequence that acquired a frame every 6.4s. Gd‐DTPA was administered (0.1mmol/kg) using a power injector. Pharmacokinetic parameter (Ktrans, kep, vp) maps derived from non‐linear fits of the general kinetic model were calculated using various vascular input functions (VIFs) calculated from pixels selected by an automatic detection algorithm in either an internal jugular vein or carotid artery. Only VIFs for which 90% or more of the vesselˈs area was selected by the algorithm were considered. One‐way analysis of variance (ANOVA) was performed and coefficients of variation (CVs) calculated for all pixels in each of the submandibular/parotid glands and nodal disease sites for individual patient maps calculated from each VIF. Results: One‐way ANOVA results showed that kinetic parameter VOI averages for all sets of VIFs across axial slices were not equivalent (p≪0.001). CVs ranged from 15% to 70% and 11% to 127% for all kinetic parameters calculated using the jugular vein and carotid artery, respectively. Of the 20 slices, 11 ±2 slices in the imaging volume were above selection threshold for arterial defined VIFs compared with 14±3 slices using a jugular‐derived VIF. Conclusion: Flow effects produced substantially more variation in DCE‐MRI imaging biomarker measures when using arterial input functions to calculate pharmacokinetic parameters as opposed to venous‐derived. Choosing a VIF defined in the jugular vein 2–3 slices below the volumeˈs center provides reproducible results over several slices in this patient population.
MO‐F‐211‐07: Quantifying Magnetic Susceptibility of Veneous Blood by the Complex Sum Method in MRI
Authors: Hsieh C , Cheng Y , Stafford R , Haacke E
Published: November 2011

Purpose: Changes of venous blood oxygenation level leads to direct changes in the magnetic susceptibility of veins. The oxygenation level reflects the physiological state of a given vein. Therefore, susceptibility quantification of veins has been a strong interest in MRI. Here we will demonstrate a general approach to extracting magnetic susceptibilities of veins at arbitrary orientations from only two or three echoes of a standard 3D gradient echo sequence. Methods: The complex sum method is used. The complex MR signal of each voxel is added around a long cylindrical object of interest. Previous work has accurately quantified effective magnetic moments of given cylindrical objects. If an object has no MR signal, its volume and susceptibility can be further determined by the spin echo approach. On the other hand, when an object of interest (e.g., vein) has an MR signal, the susceptibility of the object and its volume may be uniquely solved using this method. Images acquired with two different echo times in a typical gradient echo sequence are sufficient to quantify the magnetic susceptibility and volume of veins. Several small isolated human cerebral veins were measured at TE=11.6 ms and 19.2 ms in 4.0T. Due to low signal to noise ratio, images at TE=19.2 ms were Bilateral filtered, to preserve the edge but reduce noise. The uncertainties of magnetic susceptibilities were quantified by the error propagation method. Results: The measured susceptibility of veins at two different echo times agrees with the value in the textbook (0.40 ppm) within the uncertainty. The volumes of venous vessels, the spin density inside and outside these vessels are also obtained. Conclusions: The in‐vivo measurements demonstrate our method can be used to quantify the magnetic susceptibility of a given narrow and long cylindrical object in human imaging.
MO‐F‐211‐09: Scalar Coupling Effects on Lipid Composition Determination Using Localized 1H Magnetic Resonance Spectroscopy at 9.4 T
Authors: Yahya A. , Fallone B.G.
Published: November 2011

Purpose: To improve lipid composition determination by localized proton magnetic resonance spectroscopy (MRS) at 9.4 T by minimizing J‐coupling modulations of the 2.1 ppm, 2.3 ppm, and 2.8 ppm lipid peaks. Methods: Experiments were conducted on corn oil and sesame oil phantoms at 9.4 T. A regular PRESS (Point RESolved Spectroscopy) sequence was used to obtain spectra from the oils with echo times (TEs) of 20, 30, 40, 50, 80, 120, 180, and 240 ms. A modified PRESS sequence designed to minimize signal losses due to J‐coupling was also utilized to acquire spectra of the 2.1 ppm, 2.3 ppm, and 2.8 ppm resonances of the oils with TEs of 40, 50, 80, 120, 180 and 240 ms. The areas of the three lipid resonances obtained by both sequences were plotted as a function of echo time and the resulting curves were fitted to the function Moexp(−TE/T2), where Mo is proportional to the proton concentration of the target resonance. Oil compositions (% linoleic acid, % oleic acid, and % saturated fatty acids) were determined from extrapolated Mo values for the three resonances and from equations established in the literature. Results: The responses of the three proton groups to a regular PRESS sequence were modulated due to J‐coupling interactions. However, the responses to the modified PRESS sequence fit well to monoexponentially decaying functions. Oil compositions determined with the PRESS sequence designed to minimize J‐coupling effects agreed with results reported in the literature unlike those calculated from spectra acquired with the regular PRESS sequence. Conclusions: Lipid compositions determined by localized proton MRS can contain significant errors (as high as 49 %), even if they are determined from short‐ TE PRESS spectra corrected for T2 relaxation, if the influence of J‐coupling is not considered.
MO‐F‐220‐01: The Future of Ultrasound Systems and Imaging
Authors: Metz S
Published: November 2011

A brief look at the history of Ultrasound systems and imaging and a look into the future driven by miniaturization and advances in system electronics and imaging systems.

The promise of ubiquitous Ultrasound is fast approaching. Advanced in analog and digital hardware as well as the miniaturization of computer and embedded systems is allowing manufacturers to produce compact Ultrasound systems with solid imaging performance.

This talk will look at the history of ultrasound and what advances in systems and software are driving the use of ultrasound in new environments and what issues are related to workflow and simplification of the ultrasound exam.

Learning Objectives:

1. Understanding of the history of Ultrasound in the current age.

2. Understanding how miniaturization and new advances are making Ultrasound available in new clinical area.

3. Understand issues related to operator independence and workflow issues to simplify the Ultrasound exam.
MO‐F‐220‐04: Quantitative Ultrasound Imaging
Authors: Rognin N
Published: November 2011

The objective measurement of tissue pathological state by medical imaging plays an increasing role in clinical practice. The ultrasound imaging modality offers dedicated solutions based on image‐derived quantitative measurements for evaluating a variety of diseases in cardiology, radiology and oncology. Our presentation will show three solutions developed by Toshiba for quantifying myocardial contractility, liver fibrosis and tumor perfusion, respectively.

The first part of the presentation will demonstrate a solution for quantification of left ventricular contractility, which is an important clinical indicator of the cardiac function. To quantity regional motion abnormalities, a 3D wall motion tracking technique was implemented in an analysis software application. The technique tracks the speckle pattern, frame‐by‐ frame, over a cardiac cycle to calculate a field of motion vectors in 3D. This field is then processed to measure clinical parameters, such as strain values in different directions (longitudinal, circumferential and radial) and volumetric values (left ventricle ejection fraction).

The second part of the presentation will demonstrate a solution for evaluating liver fibrosis. Tissue characterization consists in differentiating subtle changes in ultrasound speckle patterns, indicative of the tissue microstructures, which remain non perceptible to human visual inspection. The solution, named Acoustic Structure Quantification (ASQ), was developed to quantify the homogeneity of the speckle pattern using the probability function (PDF) of the echo amplitude in a region of interest. The PDF is estimated using a modified chi‐square distribution. The peak value of that distribution was found to be a promising quantitative parameter to distinguish fibrotic tissue from normal tissue in liver.

The last part of the presentation will describe a solution for quantifying perfusion using dynamic contrast enhanced ultrasound (D‐CEUS). The technique utilizes an intravenous injection of microbubble contrast agent, which supports ultrasound imaging of macro‐vascularization. The D‐CEUS technique is a promising application for monitoring tumor response to cancer therapies. Our approach uses a mathematical function to model the contrast uptake (or time‐intensity‐curve) in a region of interest outlining a tumor. From that function, quantitative parameters are derived that are indicative of blood flow dynamics, which vary during the course of the therapy.
MO‐G‐BRA‐01: Evaluation of Prostate Post‐Implant Dosimetry by Tracking Edema Resolution with Deformable Image Registration
Authors: Zhai Y , Jiang Y , Papademetris X , Roberts K , Nath R , Chen Z
Published: November 2011

Purpose: To evaluate post‐implant dosimetry of prostate implants by tracking edema‐induced movements of implanted sources and tissue sub‐volumes using deformable image registration on post‐implant serial CT images. Methods: Post‐implant serial CT imaging was used to characterize the variations of prostate volume and movements of implanted sources during edema resolution. Seven post‐implant time points, up to 42 days, were selected. Deformable image registrations performed between each consecutive pair of CT images were used to track the spatial movements and tissue deformation using the Yale BioImage Suite non‐rigid image registration algorithm. The history of tissue movement was used in a 4D dose calculation approach to determine the dose actually received by each tissue sub‐volume in presence of prostate edema. Results: Tracking of tissue sub‐volume was validated using simulated datasets with known tissue deformations. Post‐implant dose rate distributions calculated at different post‐implant times were accumulated to corresponding tissue sub‐volumes. The dose distributions determined with full considerations of source migration and tissue deformation were compared to conventional approach using one static post‐implant image set. We observed that the hot and cold spot positions were moving around with edema evolution. Overdose at the peripheral of prostate would cause problems to the adjacent organs. The edema‐induced tissue and source movements caused overdose and deficit dose magnitudes were up to 1.12E04 cGy and −1.23E+04 cGy respectively, and overdose and deficit dose volumes were up to 10.37% and 10.26% respectively, and the percentage of hot or cold volume dynamically varied from 1.4% to 20.63% with post‐implant timing. Conclusions: Post‐implant dosimetry based on actual source position and tissue deformation during edema resolution was obtained using serial post‐implant CT imaging and deformable image registration. It provides a more realistic documentation of the actual dose delivered and could be used to compensate edema‐induced dose deficits and assess the risk of overdose.

This research project is currently funded by the NIH grant R01CA134627‐ 01 “Prostate Edema in Permanent Interstitial Brachytherapy”.
MO‐G‐BRA‐03: The Study of Needle Insertion Force and Its Effect on Deflection in Brachytherapy
Authors: McGill C , Moore J , McLaughlin P , Shih A
Published: November 2011

Purpose:To quantify needle deflection and study the relationship between the deflection and the force that is produced during insertion into a homogeneous phantom. A proposed model can be used to estimate needle deflection using the force that occurs on the needle during insertion into the phantom. Methods: A model was developed that correlates needle insertion force to needle deflection. Experiments were performed to validate this model. Using a needle grid, a 30° bevel trocar was inserted bevel up and then bevel right into two separate areas within a homogeneous phantom. During and after needle insertion, a force dynamometer was used to measure the y‐directional force data. After insertion and obtaining force data, needle deflection was quantified using a measurement apparatus that consisted of a digital depth gauge and two datum surfaces. A second experiment used a linear stage to bend a trocar inside the phantom, while force and needle deflection were measured. Using Matlab, the y‐force directional data of the bevel up and bevel right were analyzed. After matching up peeks of both data sets, the force of interest was obtained via bevel up data minus bevel right data. Results: With a sample size of n = 3 for the bevel up and bevel right experiments, a force reading of 0.23 ± 0.04 N and trocar deflection of 3.63 ± 0.5 mm were obtained. Similarly, the linear stage experiment was performed to obtain the Youngˈs modulus of the needle and phantom system. The deflection and force results validate the model created, providing the experimentally determined Youngˈs modulus of the needle and phantom system. Conclusions: Two sets of experimental apparatus was constructed to obtain force and deflection data. A model was developed to correlate the needle force to needle deflection and validated with experimental data.
MO‐G‐BRA‐05: Sequencing Method To Reduce Treatment Time for Intensity‐ Modulated Brachytherapy
Authors: Edwards D , Kim Y , Wu X , Flynn R
Published: November 2011

Purpose: Bulky (>40 cc) cervical cancer brachytherapy (BT) tumor dose conformity is often poor since symmetric BT dose is limited by the presence of the nearby bladder, rectum, and sigmoid. Rotating shield intensity modulated brachytherapy (RS‐IMBT) can theoretically improve tumor dose conformity, but at the cost of significantly increased treatment times. We developed a time efficient method of improving cervical cancer dose distributions with multi‐rotating‐shield IMBT (MRS‐IMBT) that drastically reduces the delivery times relative to RS‐IMBT. Methods: We developed a shield sequencing method that optimally divides a set of finely sampled IMBT shielding patterns into a combination of coarse and fine shields that delivers the same dose distribution but with a reduced treatment time. The resulting MRS‐IMBT method was applied to eight cervical cancer patients who were treated with MRI‐guided conventional BT. The treatment planning was done with an in‐house treatment planning system. Results: The MRS‐IMBT method significantly reduced treatment times relative to finely‐sampled IMBT without losing tumor coverage. When using shields that provided adequate coverage (22.5°), the sequencing method on average decreased the treatment time by a factor of 4. For the finest shields considered (5.625°), MRS‐IMBT decreased the treatment time by a factor of 12 on average. Conclusions: While RS‐IMBT causes treatment times to rise exponentially with the number of emission directions when a single shield emission angle is used, treatment times for the MRS‐IMBT method increase linearly with the number of emission directions. MRS‐IMBT makes IMBT delivery clinically feasible, which could lead to mean better tumor dose conformity and improved outcomes.
MO‐G‐BRB‐05: Quantitative Evaluation of Non‐Uniform Dose Patterns for Preclinical Radiobiology Studies
Authors: Stewart J , Lindsay P , Jaffray D
Published: November 2011

Purpose: Prompted by a desire to increase the complexity and precision with which radiation can be distributed at the small scale demanded by preclinical studies, several institutions have developed dedicated platforms for small animal irradiation research. Such systems have the potential to probe the physiological response of spatially inhomogeneous dose distributions in the controlled preclinical environment. The performance of such a system (Xrad225Cx, Precision X‐Ray, Inc., North Branford, CT) in terms of its ability to spatially modulate dose was assessed for a dose pattern broadly characterized as ‘grid’ therapy. Methods: By programming the animal positioning stage to move between a series of irradiations, complex dose patterns can be delivered. A spatially modulated grid irradiation pattern consisting of a 5×11 array of irradiations delivered with a fixed 1 mm diameter circular collimator and a 2 mm distance between the isocenter of each irradiation was delivered. Individual irradiations were performed for 30 seconds at an energy of 225 kVp and current of 13 mA. Gafchromic EBT2 radiochromic film placed between two 4.9 mm thick water equivalent slab phantoms was used for quantitative dosimetric analysis. After irradiation, the films were scanned at a resolution of 400 DPI (∼0.06 mm/pixel). Results: The 55 separate irradiations forming the ‘grid’ pattern were delivered with 93% of the irradiations within 0.15 mm of the desired 2.0 mm spacing. Dose falloff from each individual irradiation was rapid with a typical falloff of 1.24 Gy / mm (57% / mm). The dose‐depth curve was roughly exponential with a decay constant of 0.040 / mm. Conclusions: The preliminary characterization of the delivered dose demonstrates the ability of the small animal irradiation platform to deliver precisely modulated dose distributions comparable to that employed in ‘grid’ therapy. This dosimetric capability holds promise for in vivo radiobiological studies of complex radiation delivery schemes.

Some of the co‐authors are inventors of the small animal irradiation system described herein, and may financially benefit through its successful commercialization by Precision X‐Ray, Inc.
MO‐G‐BRC‐04: Normal Liver Tissue Density Dose‐Response in Patients Treated with Stereotactic Body Radiation Therapy for Liver Metastases
Authors: Howells C , Stinauer M , Diot Q , Westerly D , Schefter T , Kavanagh B , Miften M
Published: November 2011

Purpose: To investigate normal liver tissue density changes as a function of dose and time for patients with metastatic liver tumors treated with stereotactic body radiation therapy (SBRT). Methods: Seventy‐one non‐ contrast follow‐up computed‐tomography (CT) scans of 18 patients with liver metastases were retrospectively analyzed from the time of treatment to their final follow‐up scan [range, 1–24 months] [median, 8.2 months]. All patients received a prescription dose of 40–60 Gy [median, 57 Gy] in 3–5 fractions delivered with 3DCRT or dynamic conformal arcs. The follow‐up scans were binned into the following time periods: 3, 6, 9, 12, 18, and 24 months. The liver volume was contoured on all scans for each patient and registered to the planning CT. Dose‐response curves (DRC) were calculated by averaging Hounsfield unit changes (HU) in liver regions (excluding PTV) receiving the same dose in 5 Gy intervals. Results: For early follow‐ ups, a small decrease in normal liver CT numbers (up to −10 HU) was observed from the first to the second follow‐up periods (3 to 6 months); however, this decrease was not observed from treatment to the first follow‐ up period. For later follow‐ups (9, 12, and 18 months), a significant increase in liver CT numbers was seen [up to 20 HU]. A return to the baseline planning CT values was observed for the last follow‐up period (24 months), but only within lower dose regions [< 25 Gy]. Conclusions: The early pathologic veno‐occlusive disease response [Olsen et al., IJROBP 2009] in normal liver after SBRT produces minimal quantitative density change despite its characteristic hypodense CT appearance. The subsequent tissue regenerative process involves transiently increased density that appears to consolidate over time. The high dose region tissue changes are possibly triggered by the mechanism of sinusoidal endothelial cell disruption described in preclinical models [Yamanouchi et al., Hepatology 2009].
MO‐G‐BRC‐06: Potential for Improved IQ Using Volumetric Modulated Arc Therapy Compared to Conventional 3D Conformal Radiation for Whole Ventricular Radiation in Children
Authors: Qi S , Stunauer M , Roger B , Liu A.
Published: November 2011

Purpose: Radiation treatment for localized pure germinoma includes treatment to the whole ventricles followed by a boost to the tumor. Our goal was to compare Volumetric Modulated Arc Therapy (VMAT) with 3D conformal radiation therapy (3DCRT) in the treatment of these children. We compared coverage of the target, doses to normal tissues, and modeled the effect of the dosimetric differences on IQ. Methods: Ten children with intracranial germinomas were used. The prescription doses was 23.4 Gy to the ventricles followed by 21.6 Gy to the tumor located in the pineal region. For each child, two‐lateral 3DCRT plans (CMS XiO, Version 4.4) and full arc VMAT plans (MONACO, Version 2.03.01) were generated. Coverage of the target was assessed by computing a conformity index (CI) and heterogeneity index (HI). Mean dose to the temporal lobe was used to estimate IQ five years after completion of radiation, using a patient age of 10 years old. Results: VMAT compared to the 3DCRT plan improved conformality (CI 1.85 versus 1.10), with similar heterogeneity (HI 1.09 versus 1.06). The averaged mean doses for left and right temporal lobes were 31.3 and 31.7 Gy for VMAT plans and 37.74 and 37.6 Gy for the 3DCRT plans. This difference in mean temporal lobe dose resulted in an estimated IQ difference of 3.1. If the temporal lobes were explicitly included in the VMAT optimization, for a representative case, the mean temporal lobe dose is further reduced by 5.6 Gy, resulting in an estimated IQ difference of an additional 3.0 points. Conclusions: For treatment of children with intracranial pure germinomas, VMAT compared to 3DCRT provides increased conformality and reduces doses to the temporal lobes. This may result in improvements in IQ in these children.
TU‐A‐224‐01: Practical Research Advice: NIH Navigation and Grantsmanship
Authors: Paganetti H , Jeraj R , Beddar S
Published: November 2011

This 1‐hour symposium will be aimed at introducing new (or junior) AAPM members engaged in research to NIH funding. Recently there have been new changes to the grant submission process. and new initiatives to enhance research using “Multiple‐PI” models. We plan to have two segments. The first segment would be to present some of the tools available within the NIH website and how to navigate through it; present briefly the new changes to the submission process and focus on the new scoring system and the new review criteria that would be essential to submitting a successful grant. The second segment will cover aspects on how to set‐up a clinical research program. This would include practical advice for those researchers who are not at the “NIH submission” level yet as well as the many medical physicists that do not have protected research time but are still eager to do clinically relevant research that sometimes could lead to NIH funding. The symposium will be followed with a 10–15 min interactive Q&A session with the audience.

Learning objectives:

1. Navigate the NIH website and learn about the new tools

2. New changes to the NIH scoring system

3. New NIH review criteria

4. Practical advice for those researchers who are not at the “NIH submission” level yet.
TU‐A‐BRA‐01: Planning, QA, and the Role of Imaging of Localization for Head and Neck Treatments
Authors: Mayo C , Garces Y , Dong L , Howell R
Published: November 2011

This educational session is designed to provide practical perspective on head and neck treatment planning and delivery. The panel will draw from their own and the shared experiences of the other panelists to provide a comprehensive discussions of the issues and decisions encountered daily as part of treating patients with head and neck cancer.

Contouring, PTV and Organ at Risk Doses: a Physicianˈs perspective ‐ How a physician approaches the question of a practical balance between doses to target and proximal normal tissues will be explored and implications of contouring approaches will be considered.

• Use and implications of hand drawn PTV vs CTV + margin = PTV

• Organs at risk

• Dose trade‐offs

• Planning process: When is it good enough? Is the difference between plans clinically observable or art? What dose levels, that can be affected in planning, produce results that are observed in practice?

Treatment Planning ‐Strategies in beam selection, contouring of dose sculpting structures and in setting of constraints to enable for driving IMRT opimizers to achieve the balance sought by the physician for targets treated at multiple concurrent dose levels will be discussed. Process flow and time to create plans will be discussed.

• Dose Sculpting Structures

• Beam selection (IMRT vs VMAT)

• Optimization strategies

Patient Positioning Options and Imaging Strategies — The ability of the treatment plan to accurately reflect delivered doses, is linked to the ability to reliably set up and verify the same patient position as in the original CT. A range of typical questions and practical approaches will be discussed. • Patient Positioning Options: Head cup + aquaplast,vac‐loc bag, alpha cradle based,bite block, etc.

• Imaging

∘ kV vs Conebeam

∘ Image treatment fields or just setup fields?

∘ How frequently should fields be imaged?

∘ Decision tree for use of MV, kV, ConeBeam

∘ Use of blended imaging tools for checking measured vs predicted DRR or ConeBeam?

∘ When it doesnˈt align, then what?

IMRT QA — There area wide array of devices and measurements for QA of IMRT fields. This presentation will address issues encountered in designing practical approaches to demonstrate that the dose planned for a patient can be delivered with acceptable accuracy. The strengths and weaknesses of QA approaches will be discussed.

• Measurement devices, strategies and basis for choice

• Is gamma analysis alone sufficient? What else is used instead?
TU‐A‐BRB‐01: Convex Optimization Techniques for Handling Delivery Time and Plan Complexity in Multi‐Criteria VMAT Optimization
Authors: Craft D , Bortfeld T
Published: November 2011

Purpose: To explore the joint trade‐offs of target coverage, organ sparing, and delivery time for volumetric modulated arc therapy (VMAT).Methods: One measure of beam‐on time in IMRT is the “sum of positive gradients” (SPG) of the intensity maps. We adapt this measure to VMAT planning. The adaptation is based on the fact that while the beam rotates through a specified arc length, a certain amount of modulation can be achieved “for free”, that is, without slowing down the gantry. The resulting convex optimization formulation is applied to minimizing or constraining delivery time in VMAT. We also consider the selection of collimator angle, and we explore the following: finding the single collimator angle which offers the quickest delivery while maintaining a specified dosimetric plan quality. Results: We demonstrate the optimization routines on three cases: a pancreas, a prostate, and a lung. We find that SPG smoothing decreases delivery time by a factor of 2 for the pancreas and lung cases and 2.7 for the prostate. For the pancreas case, we examine collimator rotation. Compared to the default angle of 0 degrees (i.e. leaf motion perpendicular to gantry rotation direction), a well‐chosen single collimator angle (23° in this case) can reduce the delivery time by an additional 8%. Conclusions: Although the VMAT problem is fundamentally non‐convex, due to the non‐convex mapping from leaf positions to voxel doses, we can use a modified SPG function, which is convex, to compute VMAT plans that correctly slow down the beam where it should. Our method is exact for leaves that move infinitely fast, and practically useful in the finite leaf speed case. It can straightforwardly be embedded into a multi‐criteria system allowing the user to explore the trade‐offs of target coverage, organ sparing, and delivery time.

Funding support from NIH R01 Grant
TU‐A‐BRB‐02: An Estimator of Deformable Organ Variation Probability Density Function in IMRT of H&N Cancers
Authors: Nie X , Liang J , Yan D
Published: November 2011

Purpose: To create a deformable organ variation probability density function (PDF) estimator for the purpose of treatment dose estimation and adaptive inverse planning optimization in the clinical applications of adaptive radiotherapy.Methods: Principle Component Analysis (PCA) was applied to variations of organs of interest manifested on multiple treatment CBCT images. Utilizing the PCA model for deformable organ PDF estimation includes the determination of the eigenvectors and the corresponding coefficients. The coefficients can be either random variables or random functions of treatment time depending on the characteristics of organ deformation as stationary or non‐stationary random process. The least square regression method with time‐varying weighting parameters was applied on the pre‐collected patient images to determine the function form of the coefficients. Seven h&n cancer patients, 31 images per patient, were included in the construction of the estimator and the optimization of the corresponding weighting factor in the estimator. The estimator was evaluated using total 19 organs of interest of another eight patients. Results: The deformable variation of organ can be accurately represented by 3 to 4 eigenvectors. These vectors change and need to be updated with the new image observations during the treatment course. The estimation error in the mean of the organ PDF is less than 3 mm for cord and CTV for elective nodes, and less than 2 mm for the other organs of interest. The estimation error in the standard deviation of the organ PDF is less than 1 mm for all organs of interest. Conclusions: Deformable organ variation estimator is feasible to perform acceptable estimation for deformable organ PDF during the h&n cancer radiation treatment. This estimator will provide an important role in the treatment course of adaptive radiotherapy.

This study is partially supported by the research grant from Elekta Oncology System, Inc.
TU‐A‐BRB‐06: Evolving and Optimizing IMRT Treatment Plans with PARETO ‐ a Novel Treatment Planning System Based on a Multi‐Objective Genetic Algorithm
Authors: Fiege J , Potrebko P , Champion H , Cull A , McCurdy B
Published: November 2011

Purpose: We introduce a novel multi‐objective treatment planning system called PARETO (Pareto‐Aware Radiotherapy Evolutionary Treatment Optimization), which simultaneously optimizes beam angles and fluence patterns by treating the PTV conformity and dose to OARs as separate objectives that are optimized by a powerful multi‐objective parallel genetic algorithm (GA).Methods: PARETO treats radiotherapy treatment planning as a single monolithic optimization problem, in which beam angle configurations and fluence patterns are explored to simultaneously optimize the PTV dose conformity and a dose objective for each OAR. We use a Pareto‐ranking scheme to discover necessary compromises between objectives. A final non‐dominated database of solutions is compiled from all plans evaluated during the run such that no solution in the database is superior to any other solution in all objectives. A graphical tool allows rapid navigation of the pre‐optimized database to select a final treatment option for the patient.Results: PARETO is at the stage of a working prototype. Solutions are of high quality, as judged by DVH curves and dose distribution, and consistent results are obtained between runs. Only minor differences in trade‐off surfaces result from four different fluence parameterizations of varying complexity, but they differ by a factor of ∼4 in speed. A novel feature allows optimization of the number of beams and a realistic test case shows that no further improvements in conformity are found for more than ∼9 beams. A newly implemented GPU‐based ray tracer, including convolution with a patient dose kernel, results in a speedup factor of ∼3 compared to CPU‐based computation. Conclusions: This work demonstrates PARETOˈs feasibility as a treatment‐planning tool, which replaces manual iterative optimization of treatment plans with a rapid graphical exploration of pre‐optimized solutions. Clinically acceptable run times of less than an hour appear within reach by combining several of our GPU‐based systems in parallel.

J. Fiege discloses authorship of the Ferret GA (used by PARETO) and ownership of nQube Technical Computing Corporation, which distributes this optimization software.
TU‐A‐BRB‐07: VMAT and IMRT: The Best of Both Worlds
Authors: Matuszak M , McShan D , Fraass B
Published: November 2011

Purpose: To introduce a hybrid VMAT/IMRT optimization strategy that combines the delivery efficiency of VMAT with the superior intensity modulation possible with IMRT. Methods: A beamlet‐based inverse planning system was enhanced to combine the advantages of VMAT and IMRT into one comprehensive system. In the hybrid system, IMRT plans are created with many beams and optimized to convergence, taking note of the beam intensity map variation (BIMV) at each angle. Second, all beams are converted to VMAT segments and optimized for a set number of cycles. Then, the previous BIMV values and current cost function gradients with respect to the beamlets are used to define a gradient modulation factor (GMF). Beams with the highest GMF are converted from segments to beamlets and optimization proceeds with the mixed variable set until convergence or until additional beams are selected for conversion. This strategy was characterized on phantom and clinical cases. Comparisons were made between the hybrid plans, standard IMRT plans, and VMAT plans. Results: In a simple phantom, a hybrid VMAT/IMRT plan with 3 converted beams achieved superior dosimetric quality and required 30% fewer MU compared to 7‐beam IMRT. The hybrid plan also had a 20% reduction in final cost compared to VMAT. In a pancreas case, a 3 converted beam hybrid plan had improved and equivalent dosimetric quality compared to VMAT and 7‐beam IMRT, respectively. The hybrid and VMAT plans were more delivery efficient than IMRT. Conclusion: A hybrid VMAT/IMRT strategy was implemented to find the best compromise between gantry‐angle and intensity‐based degrees of freedom. This optimization method will allow patients to be simultaneously planned for dosimetric quality and delivery efficiency without switching between delivery techniques. Phantom and clinical examples suggest that the conversion of only 3 VMAT segments to modulated beams results in a good combination of quality and efficiency.

Supported by NIH‐P01‐CA59827
TU‐A‐BRC‐02: Hyperpolarized 13C MRSI for Assessing Radiation Response of Prostate Cancer in Transgenic Mice
Authors: Senadheera L , Mayer D , Josan S , Darpolor M , Luong R , Yen Y , Spielman D , Xing L
Published: November 2011

Purpose: To assess the tumor response to radiation in transgenic mouse model of prostatic adenocarcinoma (TRAMP) by hyperpolarized MR spectroscopic imaging (MRSI) of [1–13C]pyruvate.Methods: The TRAMP mouse model used in this study develops an autochthonous tumor in the prostate at the onset of puberty. The progression of tumors was volumetrically monitored by T2‐weighted MRI at 7 T. Four mice with tumor volumes of 400–1500 mm3 underwent hyperpolarized 13C MRSI at 3 T. Two of them received fractionated X‐ray radiation (200 kV, 20 mA, 1.21 cGy/s, 1 mm Cu HVL) doses of 10 and 20 Gy to the tumors, followed by the 13C MRSI at the fourth day of postirradiation. Dynamic 13C MRSI was performed following an intravenous bolus injection of 300 μL of 80 mM hyperpolarized [1–13C]pyruvate to obtain the transient fate of 13C‐labeled metabolites in a 3D volume encompassing the tumor with a nominal spatial resolution of 2.7×2.7×3 mm3. The average time‐resolved signal intensities of pyruvate and its downstream products lactate and alanine were measured in the tumors from reconstructed metabolic images. Metabolic response was characterized in terms of lactate/pyruvate ratio and apparent rate constant of pyruvate‐to‐lactate conversion, kpl, by fitting data to a two‐site exchange model. Results: Based on MRI volumetry, the TRAMP tumors exponentially grew with doubling time of 7±3 d and shrank in response to radiation by 50% in volume within 4±1 d. The untreated tumors that grew to larger volumes over a similar postirradiation period exhibited increased lactate/pyruvate ratio and kpl compared to the treated tumors. Alanine was in noise levels and hence not considered for analysis. Conclusions: Preliminary data indicate the feasibility of utilizing hyperpolarized 13C MRSI to assess therapeutic response of prostate cancer to radiation in TRAMP mice. Further investigations are underway to obtain additional data.

This work is partly supported by DOD PCRP (W81XWH‐10‐10498) research award.
TU‐A‐BRC‐03: A Novel Technique to Use CT Images for in Vivo Detection and Quantification of the Spatial Distribution of Radiation‐Induced Damage to the Esophagus
Authors: Court L , Tucker S , Gomez D , Liao Z , Zhang L , Kry S , Martel M , Dong L
Published: November 2011

Purpose: Current dose‐response studies use symptom endpoints (e.g. grade 2 esophagitis) as substitutes for data about actual tissue damage. CT imaging could provide objective spatial data on radiation‐induced damage to the esophagus in lung cancer patients. Methods: Deformable image registration techniques were used to register weekly CT images taken during radiotherapy treatment with the original planning CT image. The esophagus contours were automatically mapped. The impact of day‐to‐day variations in the degree of collapse of the esophagus was reduced by using thresholding to remove air from the esophagus. The cross‐sectional area of the esophagus was then calculated for each CT slice. The results from surrounding slices were averaged to reduce apparent abrupt steps in cross‐ sectional area between adjacent CT slices caused by varying undulations/folds in the esophagus. Finally, the relative expansion of the esophagus was calculated as the ratio of the cross‐sectional area of the esophagus in the weekly CT (minus air) to that on the corresponding CT slice in the planning image. This technique was applied to weekly CT images of 5 lung cancer patients (35 CTs), with acute esophageal toxicity grade 0 to 3. For these patients we examined (1) The correlation between the relative expansion of the esophagus and the clinical toxicity grade, and (2) the correlation between the spatial dose distribution and the spatial variation in esophageal expansion. Results: The average maximum esophageal expansions for toxicity grades 0, 2, and 3 were 1.2, 1.7 and 1.9, respectively. The difference between grade 2 and 0 was statistically significant (p=0.008). The location and degree of variation of the changes in esophagus cross‐section were found to be related to the high dose given at the same location. Conclusion: Radiation‐induced injury to the esophagus can be detected in CT images. This has potential for use in dose‐response studies.
TU‐C‐214‐11: Interfractional Variations in Partial Breast Irradiation: Prone vs Supine
Authors: Morrow N , Carver M , White J , Li X
Published: November 2011

Purpose: To compare interfractional patient setup and anatomy variations and their dosimetric consequences between prone and supine positioning in partial breast irradiation (PBI). Methods: Daily CT data acquired for 10 breast cancer patients (5 prone and 5 supine) during IGRT PBI treatments were analyzed. The patients were clinically setup to skin marks. Daily pre‐ treatment CTs were acquired using CT‐on‐Rails (CTVision, Siemens). Each daily CT was registered with corresponding planning CT prior to treatment to obtain repositioning shifts based on lumpectomy cavity. Contours of breast, lumpectomy, PTV and critical structures on daily CTs were generated using an auto‐segmentation tool (ABAS, CMS) based on deformable image registration. For each patient, original treatment plan was applied to the daily CT twice, once based on the setup isocenter (setup plan), and then on the IGRT repositioning isocenter (repositioning plan). Dosimetric variations were measured by a series of dose‐volume parameters and compared for the two plans. Results: The variation of daily repositioning shifts for supine cohort was statistically significantly less than that for prone patients. The comparison of the daily setup plans shows that the variations in PTV D95 and D98 (dose received by 95% and 98% of PTV) are smaller for supine cohort and varies from 0.5–3% (opposed with 2– 8% for prone). The repositioning plans show a reduction in variation for the PTV dose criteria for both cohorts; however the D95 reduction for prone patients is not statistically significant and is patient dependent. The impact of repositioning on OAR DVH is dependent on location of the lesion and is small. Conclusions: Larger variation in IGRT repositioning shifts and in DVH parameters in the setup plans indicate the challenge of daily reproducibility of prone setup. Improvement in the plan quality with repositioning suggests the need of IGRT to increase reproducibility of prone setup for PBI.