bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐G‐213CD‐01: Risks and Realities of Radiation Dose in Medical Imaging
Authors: Hendee W , McCollough C , O'Connor M
Published: June 2012

Several publications over the past few years have predicted thousands of cancers and cancer deaths in the US population caused by radiation exposures from medical imaging. The predictions are derived from risk estimates in the National Academy of Sciences BEIR VII report. These risk estimates are highly speculative with wide confidence intervals, and the BEIR VII committee has warned against using them to estimate cancer risks to individuals or populations. They are based on risk models derived from the linear no‐threshold hypothesis of radiation risk at low doses, a hypothesis that has been challenged by experiments at the cellular and animal levels as well as by data of cancer incidence in medically‐, occupationally‐, and environmentally‐exposed individuals. The main source of data for the BEIR VII risk estimates are the survivors of the Japanese A‐bomb explosions, a population greatly different from the US population that was exposed to radiation conditions greatly different from those of medical imaging. Collectively, the uncertainties in the derivation of the BEIR VII risk estimates, and the intrinsic speculative nature of the risk estimates themselves, cause predictions of cancers and cancer deaths to be more hypothetical than real in populations exposed to medical imaging. Unfortunately, these hypothetical predictions are themselves a health risk, because they create anxiety in patients resulting in a reluctance to undergo medical imaging procedures prescribed for their benefit.
WE‐A‐217BCD‐01: Medical Physics Ethics in Action
Authors: Fahrig R , Frey G , Halvorsen P , Hendee W , Ozturk N , Prisciandaro J , Serago C , Starkschall G
Published: June 2012

In 2009, the AAPM formally adapted a Code of Ethics for its‘ members based on the recommendations of Task Group 109. The intention of the code is to provide a set of ethical principles to members and affiliates to help guide them to behave in an ethically professional manner with respect to patients, colleagues and the general public. Although the principles are not law, it is expected that as professionals, we would honor and respect them. However, even the best intentioned may find themselves at one time or another in a moral gray zone, and feel that these principles or their application to a specific scenario may be open for interpretation.During this two hour panel session, medical physics experts in the area of education, ethics, professionalism, and research will discuss ethical scenarios and their interpretation of the TG 109 report with respect to these scenarios. The panel will be moderated by the chair of the Ethics Committee, Chris Serago. Several of the scenarios will be based on anonymized responses from the survey on Ethics and Professionalism in Medical Physics circulated by the AAPM to its members in February 2012.

Learning Objectives:

1. Discuss the meaning of ethics and professionalism.

2. Review AAPM Code of Ethics.

3. Discuss ethical scenarios and interpretations of AAPM Code of Ethics with respect to these scenarios.
WE‐A‐218‐01: NCICT a Computer Program for Organ and Effective Dose Calculation for Pediatric and Adult Patients Undergoing Computed Tomography
Authors: Lee C , Kim K , Long D , Bolch W
Published: June 2012

Purpose: To develop a computer program for users to conveniently assess organ and effective doses for patients undergoing computed tomography (CT) examinations by using patient‐ and scan‐specific parameters. Methods: A comprehensive organ and effective dose database previously published by the authors was employed in this study. A series of pediatric and adult hybrid computational phantoms representing the International Commission on Radiological Protection (ICRP) reference data was coupled with a reference CT scanner model within Monte Carlo transport code to establish a set of five dimensional dose matrix, D (33 organs, 6 age groups, 2 genders, 3 tube potentials, scan positions with 1 cm z‐resolution). A graphical user interface (GUI) was designed using Visual Basic computer language to obtain user input (patient age and gender, scanner manufacturer and models, head/body filter, pitch, tube potential, tube current, a single rotation time, and scan start and end position). The GUI was then coupled with the dose matrix and a dose calculation routine was written. Organ doses were compared with the values obtained from previous CT dosimetry tools. Results: A computer program, named NCICT, was developed using pre‐ calculated dose matrix. As a result, a total of 33 organ doses and two effective doses based on ICRP Publication 60 and 103 are displayed. Major organ doses were calculated for head, chest, and abdomen‐pelvis scans and compared with the values from CT‐Expo and CTDosimetry. The comparison revealed that use of phantoms with realistic anatomy is crucial to improved accuracy in CT organ dosimetry. Conclusion: NCICT, a user‐ friendly computer program for CT dose calculation was developed and validated. The program provides more realistic patient anatomy, higher age resolution, advanced skeleton dosimetry, and several convenient features compared to the previous tools. The NCICT is under beta testing and will be available for research purpose in the near future.
WE‐A‐218‐05: Do Weight‐Based Pediatric CT Abdomen Protocols Provide Similar Size‐Specific Dose Estimates for Similar Patient Effective Diameters?
Authors: Supanich MP
Published: June 2012

Purpose: The use of weight‐based acquisition techniques for CT examinations of pediatric patients is a common practice in the imaging community. AAPM Report 204 reported on conversion factors for Size Specific Dose Estimates (SSDE) based on patient effective diameter. This study examines the relationship between the use of weight‐based Pediatric CT abdominal acquisitions at one institution and the resultant SSDE. Methods: A total of 36 Pediatric Abdomen and Pelvis CTs acquired on scanners from 2 different manufacturers at 120 kVp and using fixed tube current based on reported patient weight were analyzed. The fixed tube currents at each weight range were chosen to match CTDIvol (32 cm phantom) across scanners. Effective diameter was established by thresholding the mid‐scan range image to determine patient area and was calculated using eXposureTM from Radimetrics. The area is then converted to a circle of equivalent diameter. SSDE was determined using the effective diameter for each study and the recorded CTDIvol. The eXposureTM software utilized AAPM Report 204 look‐up‐tables (LUTs) of conversion factors and interpolation to determine the correct normalization factor for each study which is then used to scale the CTDIvol to the final SSDE value. Results: Weak correlation was observed between effective diameter and SSDE, with SSDE values varying by as much as a factor of 2 for effective diameters within 0.5 cm. A slight decrease in average SSDE was observed at larger effective diameters. Conclusion:The weight‐based acquisition protocols analyzed in this study do not effectively match patient effective diameter and radiation dose. Technique parameters based on patient effective diameter should provide better dose equivalence for patients of equal cross‐sectional area. Assessment of image quality and the evaluation of acquisition protocols based on diameter will be pursued in the future. The Presenting Author is the PI on a Research Grant funded by Siemens Medical Solutions.
WE‐C‐213AB‐02: Preparing for the ABR Initial Certification Board Exam
Authors: Chinsky B
Published: June 2012

Starting the process of ABR board certification in medical physics can be complex and overwhelming. The first step is the Initial Certification computer‐based exam, commonly known as Part I. It is important to understand the eligibility requirements and application process, as well as the exam format and topics, to prepare for and pass the exam. The first portion of this talk will discuss current and future exam eligibility requirements and the exam set‐up. The second portion will discuss the exam experience, the wide range of topics potentially covered on the exam, helpful texts, and mock Part I type questions. This talk is not designed to be a comprehensive review of Part I study material. Instead, this presentation will focus on introducing candidates to the exam process, eligibility, study methods and topics.

Learning Objectives:

1. Understand the prerequisites and application process for the ABR Medical Physics Initial Qualification Examination.

2. Understand the examination format and day‐of testing experience.

3. Learn about potential topics and helpful study materials for the Part 1 examination.
WE‐C‐BRB‐01: Dosimetric Changes Realized from Extended Bit‐Depth and Metal Artifact Reduction in CT
Authors: Glide‐Hurst C , Zhong H , Altman M , Chen D , Chetty I
Published: June 2012

Purpose: High‐Z material in CT yields metal artifacts that degrade image quality and may cause substantial errors in dose calculation. This study couples a metal artifact reduction (MAR) algorithm with enhanced 16‐bit depth (vs. standard 12‐bit) to quantify potential dosimetric differences. Methods: Extended CT to electron density (CT‐ED) curves were derived from tissue characterization phantom with Titanium and Stainless Steel inserts scanned at 90–140 kVp for 12 and 16‐bit reconstructions. MAR was applied to sinogram data (Brilliance BigBore CT scanner, Philips Healthcare, v.3.5). Single/double hip prostheses were simulated using Cerrobend rod(s) embedded in a pelvic phantom and two dosimetric verifications were performed to elucidate changes between 12 and 16‐bit data: (1) BEAMnrc/Dosxyz Monte Carlo simulation (MC‐SIM) (400,000,0000 histories, 6×, 10×10 beam traversing Cerrobend rod) and (2) Gafchromic film analysis for plans calculated with Anisotropic Analytic Algorithm (AAA, Eclipse) and Monte Carlo (MC‐BL, Brainlab). Five patients with metal implants were reconstructed using both bit depths, with plans calculated using AAA and derived CT‐ED curves. Dose profiles and matrices were evaluated. Results: For 12‐bit images, Titanium and Stainless saturated at 3071 HU, while for 16‐bits (120kVp), mean CT numbers were 8088+/−336 and 13,971+/−1460 HU for Titanium and Stainless, respectively. MC‐SIM was well‐matched between 12 and 16‐bit images except downstream of metal, where 16‐bit dose was ∼6.4% greater than 12‐bit. In treatment planning phantom cases, dose profiles were well‐matched in the buildup region, but deviated in the shadow of metal where ∼12% differences between AAA 16‐bit and 12‐bit doses were observed. Similar results were obtained in patient cases. The largest discrepancy was at a tissue‐metal prosthetic interface, with 12‐bit dose yielding 23.8% less dose than 16‐bit. Conclusions: Dosimetric differences revealed between 12‐ and 16‐bit images were substantial. Further dosimetric verification is warranted. These results support implementing MAR‐corrected, 16‐bit images in treatment planning. This work supported in part by a grant from Philips Medical Systems, Cleveland . Titanium and Stainless Steel inserts were provided by Gammex Inc. in exchange for 16‐bit depth information.
WE‐C‐BRB‐03: Effect of Scattered Photons When Determining Dose Rate Constants Spectroscopically
Authors: Rodriguez M , Rogers D
Published: June 2012

Purpose: To determine the effect of scatter from the seed when establishing the dose rate constant of 125I and 103Pd seeds using the spectroscopic method of Chen and Nath (Med Phys 34 (2007) 1412) which is based on the main peaks in the spectrum. Methods: The energy spectra generated by two 125I and one 103Pd seeds were calculated in vacuo at 10 cm from the source using the EGSnrc BrachyDose Monte Carlo code. Energy bin width was 0.2 keV and statistical uncertainty was 0.02%. The energy spectra generated by the seeds were then used as a 3 mm line source in a Monte Carlo simulation to calculate the dose rate constant. Two simulation were performed; one using the full energy spectrum and the other using only the main peaks. Statistical uncertainty in air kerma strength and dose rate was 0.1%. Results: The differences between the average energy of the full spectrum and the average energy of the main peaks generated by the three seeds were 0.07% or less. Differences in air kerma strength and dose rate constant were 0.5% or less and the difference in the dose rate was lower than the statistical uncertainty (0.1%). Conclusions: Air kerma strength, dose rate at the reference point and dose rate constant were calculated by Monte Carlo simulation using both the full energy spectrum and the main peaks only of three brachytherapy seeds. The differences in the calculation of these clinical parameters were less than 0.5%. This difference is substantially lower than the reported uncertainty in establishing the dose rate constant spectroscopically, which can reach up to 3.9% and 2.6% for the 125I and 103Pd seeds respectively. Therefore, the effects of scatter on determining the dose rate constant spectroscopically is absorbed by the other uncertainties in the method.
WE‐C‐BRB‐09: Development of a GPU‐Based Monte Carlo Dose Calculation Package for Proton Radiotherapy
Authors: Jia X , Schuemann J , Paganetti H , Jiang S
Published: June 2012

Purpose: Monte Carlo (MC) simulation is considered to be the most accurate method for proton therapy dose calculation. However, the long computation time limits it from routine clinical applications. Recently, graphics processing units (GPUs) have been widely used to accelerate computationally intensive tasks in radiotherapy. The purpose of this project is to develop a fast MC dose calculation package, gPMC, for proton dose calculation on a GPU. Methods: gPMC supports proton transport in the energy range of 0.5∼300 MeV. Proton transport is modeled by the Class II condensed history simulation scheme with continuous slowing down approximation. Ionization, elastic and inelastic proton nucleus interactions are considered. Energy straggling and multiple scattering are modeled. Secondary electrons and charged nuclear fragments are not transported and their energies are locally deposited. Secondary protons are stored in a stack and transported after the primary protons finish, while secondary neutral particles are neglected. gPMC is implemented on GPU under the CUDA platform with each GPU thread responsible for the transport of a single proton. A high performance random number generator and hardware linear interpolation are utilized. Results: We have validated gPMC in various cases including homogeneous phantoms with different materials and a phantom of a half slab geometry. A mono‐energetic mono‐directional proton beam is used. Good agreements between results from gPMC and Geant4 are observed, and the gamma passing rate for 3%/3mm criterion is over 99.9% in the region with dose greater than 10% maximum dose. It takes 6.3∼24.1 sec to simulate 10 million source protons depending on the phantoms and the energy. A high efficiency has been achieved compared to the computational time of tens of CPU hours for Geant4. Conclusions: We have developed a GPU‐based MC proton dose calculation package, gPMC. The achieved accuracy and efficiency is promising for clinical applications.
WE‐C‐BRB‐10: Acceleration of Proton Monte Carlo Simulations Using the Macro Monte Carlo Method
Authors: Jacqmin D
Published: June 2012

Purpose: This work describes a new macro Monte Carlo method for proton beam dose calculation. Originally developed for electron beams, macro Monte Carlo (MMC) is designed to provide better computational efficiency than traditional MC without sacrificing accuracy. Methods: The proton MMC method performs dose calculation using pre‐calculated steps derived from MCNPX simulations. Simulations of mono‐energetic proton pencil beams ranging from 5–200 MeV impinging on homogenous cylinders of varying length, radius and material were carried out using MCNPX. The energy loss, trajectory and exit position of the exiting protons and secondary particles have been determined and used to create a pre‐calculated step database. The database is used to transport protons through an absorbing geometry in a step‐by‐step manner. Energy loss is scored in a 3D dose grid during each step. The creation of secondary particles is tracked as well. For validation purposes, the dose distributions for many monoenergetic proton beams have been calculated using proton MMC and MCNPX for single‐ and multi‐layered phantoms. The resulting central‐axis depth dose curves and dose profiles have been compared. The materials tested include water, bone, fat, soft tissue and lung. Results: The calculated central‐axis depth dose curves agree better than 1% or 1 mm for all pencil beams near the Bragg peak. The lateral dose profiles agree to better than 1% or 1 mm for all pencil beams near the Bragg peak. Away from the Bragg peak, the depth dose curves and lateral profiles agree better than 1% or 1 mm for energies below 100 MeV. Above 100 MeV, disagreement can reach 5%. The computational efficiency of proton MMC is about 100 times greater than for MCNPX. Conclusions: The results from the dose comparisons show that proton MMC is accurate and more efficient than traditional Monte Carlo.
WE‐C‐BRB‐12: Comprehensive Image‐Based Dosimetric Analysis of Alpha Particle Dose in Bone Marrow
Authors: Pan J , Watchman C
Published: June 2012

Purpose: In this study, a comprehensive analysis of alpha particle dose to bone marrow was developed. Using autopsy spongiosa samples and an in house Monte Carlo program, dosimetry data was calculated for macroscopic dosimetry (MIRD schema) to microdosimetric methods. This investigation provides a uniform comparison of these different methodologies. Methods: Autopsy samples of spongiosa from two bone sites (iliac crest and vertebrae) were sectioned and immunohistochemically stained (anti‐CD34) to identify hematopoietic stem and progenitor cells (HSPC). Digitized 2‐dimensional image was segmented based on pixel intensity to differentiate between bone trabeculae, red bone marrow and adipocytes. Individual HSPC were also identified. The processed image was used as input for an alpha‐particle Monte Carlo radiation transport program where dosimetric data was calculated for absorbed fractions, hit probabilities and z‐values. Results: Energies of 0.5‐10 MeV were investigated. Source distributions (bone, fat, red bone marrow and bone surface) of alpha particles were obtained. Absorbed fraction of each tissue region and HSPC were obtained. Probability of receiving hit of alpha particles of HSPC and nucleus were also calculated. Data for each source and target combination indicated significant dose differences to the HSPC depending on the methodology used to calculate the final dose estimate. Conclusions: Results of this study indicate the discrepancy between macroscopic and microscopic dose methods. While the microscopic methods provide a more detailed assessment of HSPC dosing they lack clinical utility. Additional work is required to bridge these two dosimetric spatial domains before bone marrow dose calculations may be clinically implemented.
WE‐G‐BRCD‐03: Improvement in Robustness and Delivery Efficiency of Intensity‐Modulated Proton Therapy Using Single‐Field Optimization with Energy Absorber
Authors: Quan E , Liu W , Li Y , Zhang X , Zhu X , Mohan R , Wu R
Published: June 2012

Purpose: Intensity‐modulated proton therapy (IMPT) using multi‐field optimization (MFO) could generate highly conformal dose distributions but it is more sensitive to setup and proton range uncertainties than IMPT using single‐field optimization (SFO). This work evaluates the effectiveness of SFO treatment plans with the use of energy absorbers (EAs) to improve the robustness and delivery efficiency of IMPT for head and neck cancers. Methods: IMPT treatment plans were generated using 2‐field SFO with an EA in each field (EA‐SFO) for four patients with head and neck cancers. We compared the plan quality, robustness, and delivery efficiency of the EA‐ SFO plan with a 3‐field MFO plan that was used to treat the patient. Robustness analysis of each plan was performed to generate two dose distributions, consisting of the highest and the lowest possible doses from spatial and range perturbations at every voxel. Dosimetric indices and the numbers of energy layers required in the EA‐SFO and MFO plans were compared. Results: All the nominal EA‐SFO plans are clinically acceptable. They achieved similar levels of target coverage compared to the MFO plans; the differences in D95 of the GTV and CTVs between the two plans were within 3.5%. Although some of the OARs received higher dose in the EA‐ SFO plan, they were all within tolerance. The EA‐SFO plans yielded an average of 38.5% reduction of plan sensitivity to uncertainties in the targets and 18.5% overall. The EA‐SFO plans used an average of 79 (46%) fewer energy layers than the MFO plans, which corresponds to nearly 3 minutes shorter delivery time. Conclusions: The use of energy absorber greatly facilitated the design of clinically acceptable SFO treatment plans. Compared to MFO, EA‐SFO not only improved the robustness to setup and range uncertainties, but also reduced the time required for delivery and patient QA.
WE‐G‐213CD‐01: 4D Optimization for Scanned Ion Beam Tracking Therapy for Moving Tumors
Authors: Eley J , Graeff C , Lüchtenborg R , Durante M , Howell R , Newhauser W , Bert C
Published: June 2012

Purpose: To apply scanned ion radiotherapy to patients with moving tumors, motion mitigation approaches are needed. The purpose of the current study was to determine whether 4D optimized ion beam tracking therapy could reduce dose to critical structures near a moving target while maintaining target dose coverage. Methods: A conjugate gradient minimization algorithm was developed to incorporate 4D organ motion data in the optimization of scanned ion pencil beam fluences. Treatment plans for 3D and 4D optimized carbon beam tracking were prepared using an in‐ house code for a sphere target volume moving in water with a proximal avoidance volume. For 1 lung cancer patient, 3D and 4D optimized carbon beam tracking treatment plans were designed to provide uniform dose coverage to a clinical target volume and minimal dose to the heart. For both the water phantom and patient case, 4D dose distributions were calculated. Differences between 3D and 4D optimized beam tracking were analyzed using dose colorplanes, dose‐volume histograms, and dose‐volume statistics. Results: For the sphere target, 3D optimized beam tracking achieved target dose coverage of (100.0 ± 0.3)% and a mean and maximum avoidance volume dose of 26.1% and 89.4%, respectively. 4D optimized beam tracking achieved target dose coverage of (99.9 ± 0.4)% and a mean and maximum avoidance volume dose of 7.7% and 42.2%, respectively. For the lung patient, 3D optimized beam tracking achieved target dose coverage of (101.0 ± 5.9)% and a mean and maximum heart dose of 7.7%and 103.4%, respectively. 4D optimized beam tracking achieved target dose coverage of (100.0 ± 0.1)% and a mean and maximum heart dose of 8.7% and 100.3%, respectively. Conclusions: 4D optimized ion beam tracking therapy may be used to reduce the maximum dose to critical structures near a moving target, compared to 3D optimized ion beam tracking therapy. Work supported by the Rosalie B. Hite Fellowship, The University of Texas M. D. Anderson Cancer Center, Houston, Texas.
WE‐G‐213CD‐05: Beam's‐Eye‐View Prostate Motion Detection during Arc Radiotherapy
Authors: Yue Y , Nguyen P , Rottmann J , Berbeco R
Published: June 2012

Purpose: To track prostate motion during clinical arc radiotherapy using a novel statistical motion tracking algorithm in both phantom and patient systems. Methods: For the phantom study, a dynamic phantom with a custom tumor model and radiopaque fiducials was used. For the patient study, the clinical data from two prostate patients were acquired during volumetric modulated arc therapy (VMAT). For each patient, two gold fiducials (X‐Mark, 1cm and 2cm in length) were implanted in the prostate. A total of 35 fractions with 2‐field full arcs were delivered. Beam's‐eye‐ view (BEV) images were acquired in cine mode every five fractions at a frame rate of 2 fps.The prostate motion was measured by two sequential steps: fiducial detection and motion estimation. In the first step, a wavelet‐ based block matching filter was used to suppress the noise and enhance the fiducials in the BEV images. A trajectory of detected fiducials was generated along the projection angles. Sequentially, the prostate motion was tracked using a statistical maximum a posteriori (MAP) algorithm. The 3‐D fiducial position was estimated by maximizing the probability of displacement of 2‐D projections. Results: A total of 8,400 BEV images were processed for this study. The phantom experiments showed that the baseline accuracy of estimation is 0.69+/−0.56 mm. For patient 1, intra‐ fraction prostate motion was measured to be 0.98+/−0.51 mm for all fractions, and individual fraction motion less than 1 mm. For patient 2, intra‐ fraction motion was 1.12+/−0.65 mm for all fractions. However, an exceptionally large displacement was measured as 4.9+/−0.74mm in one of the fractions. Conclusions: Prostate motion during arc‐therapy can be rigorously tracked to an accuracy of one millimeter. This technique is well suited for in‐treatment room target tracking and post‐therapy evaluation. Varian Medical Systems Inc
WE‐G‐217BCD‐06: Fully Incorporated Scanning Geometry for Improved Accuracy in C‐Arm CBCT Image Reconstruction
Authors: Han X , Silver M , Oishi S , Zhang Z , Bian J , Sidky E , Pan X
Published: June 2012

Purpose: The adoption of C‐arm cone‐beam CT (CBCT) can minimize interruption to the interventional workflow. However, C‐arm gantry rotation can be susceptible to gravity and mechanical instability, therefore resulting images with contamination of tilting and wobbling motion. The purpose of this work is to investigate and demonstrate potential improvement of C‐arm CBCT images by tailoring and applying an innovative iterative algorithm that can fully incorporate accurate scanning geometry. Methods: A clinical C‐arm CBCT system (Toshiba Infinix‐i, Japan) was used for collecting projection data of a patient's brain with aneurysm. A mask scan was performed before contrast was injected, and a contrast scan was performed during continuous contrast feeding. During each scan, 108 projections were acquired over a range of approximately 200 degrees within about 4.6 seconds. Logarithm subtraction was then carried out view by view to obtain 108 projections of virtually only the vasculature. An iterative algorithm, referred to as the ASD‐POCS algorithm, was modified to fully incorporate calibration data characterizing the actual scan geometry that deviates from a circular trajectory due to gantry tilting and wobbling. We then applied both FDK and ASD‐POCS algorithms to reconstructing image from the acquired patient data. Results: In FDK reconstructions without considering C‐arm tilting and wobbling motion, artifacts can be observed, which break vessel continuity and compromise image's clinical utility. We then performed FDK reconstructions by incorporating the system geometry in the back‐projection step and obtained improved vessel continuity. Finally we applied the ASD‐ POCS algorithm by incorporating calibration data in the forward‐ and back‐ projector, and obtained reconstructions with further improvement on the recovery of small, secondary vascular branches. Conclusions: Appropriately developed iterative algorithms can improve C‐arm CBCT image quality by fully incorporating scanning geometry, and can potentially enable spatial‐resolution demanding applications which can be challenging to achieve with the FDK algorithm.
WE‐G‐217BCD‐07: Implementation and Evaluation of Helical On‐Board CBCT and Exact Image Reconstruction
Authors: Tan J , Li H , Parikh P , Izaguirre E , Li H , Yang D
Published: June 2012

Purpose: Longitudinal coverage of CBCT, which is 17 cm for head scan and 15.5 cm for body scan, is not enough to cover the entire PTV for over 90% of head/neck and gastrointestinal/genitourinary/gynecologic patients if lymph nodes are involved. Helical CBCT, which was accomplished using external beam LINAC in its research mode, is one promising way to extend the CBCT longitudinal coverage. Aim of this study is to compare Katsevich's exact algorithm with traditional FDK algorithm for helical CBCT image reconstruction. Methods: CBCT projection raw data were acquired on a TrueBeam LINAC machine (Varian Medical Systems) in the research mode in helical trajectories that encompass a 360 degree rotation, 25 cm pitch, 100 kVp, 80 mA, and 25 ms, with a Catphan 600. Reconstruction was done with Katsevich's exact and FDK approximate algorithms. Scatter correction, beam‐hardening correction, and non‐uniform gantry angle correction, are performed on projection data to reduce artifacts and noise. Image qualities (CT number accuracy, uniformity, SNR) were evaluated and compared between the reconstruction algorithms. Results: Images reconstructed by Katsevich's algorithm show better qualities, compared to ones by FDK algorithm and HU numbers have higher uniformity and accuracy. The HU‐density calibration curve closely conforms to the manufacturer recommended values. The level of noise computed as the standard deviation in the phantom uniform region is 28.07 for the Katsevich algorithm, compared to 44.64 for the FDK algorithm. Conclusions: Katsevich's exact reconstruction algorithm provided better image qualities than FDK for helical CBCT scans. This result will very useful for our ongoing investigation of helical CBCT, which would lead to improvement of CBCT longitudinal coverage of PTV and would be essential for future image‐guided adaptive radiation therapy applications. Varian Research Agreement with Washington University in St. Louis
WE‐G‐217A‐04: Segmenting Limbic Circuit Fiber Tracts for Quantifying Changes in Diffusion Indices Due to Partial Radiation Therapy
Authors: Nazem‐Zadeh M , Chapman C , Lawrence T , Tsien C , Cao Y
Published: June 2012

Purpose: To segment the cingulum, fornix and the corpus callosum using diffusion weighted images, in order to evaluate the radiation‐induced damage on these important white matter structures Methods: We propose a seed‐based tractography algorithm for segmenting the entire cingulum into the left and right anterior, superior, and posterior subdivisions. In that algorithm, multiple ROIs (regions of interest) for tractography are automatically created from seeded points by a level‐set segmentation algorithm. Moreover, we propose new ROI placements for fornix tractography. Furthermore, a new subdividing method is proposed for supporting the possible rotation in the corpus callosum longitudinal axis in presence of glioma tumors. To test the reproducibility of the proposed algorithm for segmenting the cingulum, test‐retest diffusion tensor data‐sets of twelve patients were chosen from the National Biomedical Imaging Archive database. We calculated the Dice coefficients of the volumetric overlap between the test and retest cingulum segments. Twenty‐two patients with low grade brain gliomas underwent 6‐week fractionated radiation therapy (RT). The patients prospectively enrolled MRI with diffusion tensor imaging up to 18 months after starting RT. The fornix and subdivisions of cingulum and corpus callosum were segmented. Results: The Dice coefficients between test and retest data were 0.878, 0.899, 0.951, 0.954, 0.926, and 0.929 for the anterior right and left, the superior right and left, and the posterior right and left cingulum segments respectively, suggesting our method's high reproducibility. Amongst the fornix and subdivisions of cingulum and corpus callosum, the most significant changes in fractional anisotropy, mean, axial, and radial diffusivity were observed in fornix throughout all dose volumes, indicating that both axonal degradation and dysmyelination are prominent radiation effects in the fornix. Conclusions: The proposed seed‐based tractography method segments the cingulum accurately and completely with dramatically reducing the operator's interaction time and effort in manual depicting large number of ROIs. Supported in part by National Institutes of Health grants RO1 NS064973
TH‐A‐213AB‐09: An Investigation of the Impact of Spot Spacing on Plan Quality Using IMPT Optimization Incorporating Deliverable Monitor Unit Constraints
Authors: Cao W , Li X , Lim G , Li Y , Zhu X , Zhang X
Published: June 2012

Purpose: To investigate the impact of spot spacing on intensity modulated proton therapy (IMPT) plan quality based on a new IMPT optimization method which incorporates deliverable monitor unit (MU) constraints and therefore eliminates the dose distortion effect of post processing while using small spot spacings in the current treatment planning system (TPS). Methods: We introduce a two‐stage linear programming (LP) based model to solve the deliverable spot intensity optimization (DSIO) problem by incorporating deliverable minimum MU constraints. The first‐stage LP solve selects a sub set of pre‐arranged spots without considering MU constraints, and the second‐stage LP solve optimizes intensities of selected spots with forced MU constraints. A quadratic programming (QP) based model to simulate the conventional spot intensity optimization (SCIO) without MU constraints is used for comparison. Four prostate cancer cases were studied in this work. Plans optimized by both the DSIO and CSIO were evaluated for different settings of spot spacing of 3, 4, 5, 6 and 7 mm. Results: Patient studies demonstrated improved dose‐volume metrics of DSIO optimized IMPT plans, i.e., better rectum and bladder sparing, compared with CSIO optimized plans with the same spot spacing. With decreased spot spacings, improvements on dose‐volume metrics were relatively marginal. There was no pronounced improvement achieved when spot spacing reduced below 4 mm. In addition, the DSIO model can automatically create a non‐uniform spot arrangement using only a fraction of scanning spots required by plans optimized by CSIO in our study. Conclusions: The proposed DSIO method can firstly avoid the discrepancy between optimized and delivered plans in the current IMPT TPS, and secondly, allow the use of small spot spacings to improve target coverage and normal tissue sparing. Evaluations on four prostate cancer cases found that spot spacing less than 4 mm could not achieve pronounced dosimetric improvements.
TH‐A‐BRA‐05: Linear Regression Analysis of 2D Projection Image Data of 6 Degrees‐ Of‐Freedom Transformed 3D Image Sets for Stereotactic Radiotherapy
Authors: Lin C , Winey B
Published: June 2012

Purpose: To improve accuracy and speed of identifying the 6 degrees‐of‐ freedom (DoF) transformation during patient positioning alignment for stereotactic radiotherapy by determining the linear relationship between two real‐time orthogonal 2D projection images and two digitally reconstructed radiographs (DRRs) generated from a 3D volume image. Methods: Each 2D image representing an independent transformation was characterized and defined by a shape function, a function parameterized by distance and pixel value. A principal component analysis was developed to find the linear relationship between the 2D projection images and the two DRRs generated from the 3D volume image for small‐scale transformations by matching the 2D images to a set of base functions established from singular transformations. The patient‐positioning algorithm calculates the 6 DoF transformation of the patient based upon two orthogonal real‐time 2D images and from the linear relationship established. The algorithm has been validated against classical image registration methods on patient data for runtime and positioning accuracy. Results: The algorithm has accuracy to at least 1 pixel (equivalent to 0.5 mm accuracy given this image resolution). The shape function characterizes each 2D image on an average of 1.78 seconds. The algorithm interprets the evaluated transformation as a linear combination of separate 6 DoF transformations. The principal component analysis allows for rapid and accurate position matching of the images, and provides the transformation needed to align the orthogonal images to the volume on an average of 3.32 seconds. Conclusions: The linear relationship developed from the shape function algorithm affords speed and accuracy of patient positioning during stereotactic radiotherapy treatment. The algorithm is fast and accurate for small‐order 6 DoF transformations. This algorithm indicates the potential for high precision of patient positioning from the interpolation and extrapolation of the linear relationships. This project is supported by the NCI Federal Share of program income earned by Massachusetts General Hospital on C06 CA059267, Proton Therapy Research and Treatment Center.
TH‐A‐213CD‐02: BEST IN PHYSICS (IMAGING) ‐ The Feasibility of Multiplexed Biomarker Detection Using X‐Ray Stimulated Fluorescence Imaging
Authors: Kuang Y , Pratx G , Meng B , Qian J , Bazalova M , Xing L
Published: June 2012

Purpose: A feasible way of enhancing diagnosis reliability is to detect multiple biomarkers at the same time via simultaneously using multiple probes to achieve multiplexed molecular imaging. However, no routine approach to directly measure multiple biomarkers currently exists via X‐ray CT, which is the most commonly used imaging modality in the clinic. In this study, we investigated the feasibility of multiplexed biomarker detection using X‐ray stimulated fluorescence CT (XSF‐CT). Methods: This method utilizes high atomic number (Z) nanoprobes, i.e. Gold (Au), Gadolinium (Gd) and Barium (Ba), that emit XSF photons when excited by ionizing photons. Since the XSF spectrum is unique to each element, this provides a means of detecting the presence of multiple nanoparticles coated with antibodies or peptides that specifically bind to biomarkers found only in tumor. In this study, a polychromatic X‐ray source was used to stimulate emission of XSF photons from the probes. XSF‐CT used a first‐generation CT geometry. The data were collected using a cadmium telluride detector to sort out a set of spectra. The spectra were then used to generate sinogram. The biodistribution and concentration of each element were reconstructed with the ML‐EM algorithm. Results: The acquired XSF spectra showed sharp peaks emitted from Au, Gd and Ba molecules with small FWHM values, which supports the potential of XSF‐CT for multiplexed imaging. The distributions of Au, Gd and Ba molecules in the phantom were clearly identifiable on the reconstructed XSF images. In addition, our results also showed the linear relationships between the XSF intensity of each tested element and their concentrations, respectively. Conclusions: XSF imaging would transform the CT landscape into a multiplexed biomarker detection feature for early detection of cancer and/or imaging the intervention processes in vivo. It could have major predictive value for the clinical outcome in the long term patient care. This work was supported by NIH/NCI grants (CA133474, CA153587), an NSF grant (0854492) and a grant from the Friends for an Earlier Breast Cancer Test Foundation.
TH‐A‐213CD‐03: Polychromatic Cone‐Beam X‐Ray Fluorescence Computed Tomography of Gold Nanoparticle‐Loaded Objects
Authors: Jones B , Manohar N , Karellas A , Cho S
Published: June 2012

Purpose: To determine the spatial distribution and amount of gold nanoparticles (GNPs) within small‐animal‐sized objects using polychromatic cone‐beam x‐ray fluorescence computed tomography (XFCT) under realistic constraints on x‐ray dose, scan time, and image resolution. Methods: 6‐mm‐diameter cylindrical tubes containing saline solution and 0.5–2.0 wt. % of GNPs were inserted into a cylindrical polymethyl methacrylate (PMMA) phantom, 3 cm in diameter and 5 cm in height. The phantom was irradiated by a cone‐beam of polychromatic 105 kVp x‐rays filtered by 0.9 mm of tin. Energy‐sensitive cadmium telluride detectors behind a 2.5 mm diameter lead pinhole collimator collected the spectrum of emitted gold K‐shell fluorescence and Compton scattered photons at an angle of 90° relative to the beam central axis as the phantom was rotated to a series of 60 projection angles in 6° steps. Sinograms of gold fluorescence photon signals were constructed by extracting the gold fluorescence peak height from the Compton background, and the image of GNP location and concentration was reconstructed using a maximum likelihood iterative reconstruction algorithm. Results: Using the measured sinograms, XFCT images of GNP‐loaded objects were successfully reconstructed, accurately determining both the GNP location and concentration. The x‐ray dose delivered during the XFCT scanning was measured using the AAPM TG‐61 protocol, and it was determined that, using an array detector, it would be possible to acquire these images in one hour with a tissue dose of approximately 20 cGy. Conclusions: With a few easily achievable modifications, the current benchtop setup would be capable of producing useful XFCT images of small animals injected with GNPs with the total scanning time and a tissue dose comparable to other modalities currently available for routine pre‐clinical in‐vivo imaging such as micro‐CT. Supported in part by NIH/NCI grant 1R01CA155446. Supported in part by NIH/NCI grant 1R01CA155446
TH‐A‐217BCD‐06: Characterization of Brain Foci of Susceptibility Into Hemorrhagic Or Calcific Etiologies Using Gemstone Spectral Imaging‐CT
Authors: Nute J , Roux L Le , Chandler A , Schellingerhout D , Cody D
Published: June 2012

Purpose: Calcific and hemorrhagic foci of susceptibility are frequently encountered in routine brain MR studies and are difficult to distinguish. Single‐energy CT can be used to identify lesions with attenuation over 100 HU as calcific however those lesions with lower attenuation cannot be reliably identified1. While calcific lesions are unlikely to cause harm, hemorrhagic lesions carry a risk of subsequent intracranial bleeding. A methodology was developed using dual‐energy Gemstone Spectral Imaging‐CT (GSI‐CT) to take advantage of the unique attenuation properties of calcium and iron to distinguish between these two etiologies. Methods: Ferric oxide and hydroxyapatite were used to model hemorrhage and calcification respectively. A uniform distribution of these compounds was suspended in 1 % agarose gels to model elemental concentrations of iron and calcium over a range of 0.005M to 0.25M. The gels were imaged in an anthropomorphic head phantom with a single‐energy routine brain protocol. These scans were utilized to create HU matched gels of calcium and iron from 0 to 100HU which were verified using the single‐energy routine brain protocol. The HU matched gels were imaged with a dual‐energy protocol which had similar dose and imaging parameters to the single‐energy protocol. Material decomposition was used to create water and calcium density images from the dual‐energy data. Water/calcium scatterplots were created from measurements on the material density images. For each HU matched pair, the separation between the mean values along each axis was measured and plotted against the HU. The uncertainty in the separation was calculated as the quadrature sum of the standard deviations along both the water and calcium axes. Results: Matched HU pairs yielded separation greater than the uncertainty for 40HU and above along both the calcium and water axes of the material decomposition scatterplot. Conclusions: HU matched iron and calcium gels of 40HU and above could be distinguished using dual‐energy GSI‐CT.
TH‐A‐217BCD‐08: BEST IN PHYSICS (IMAGING) ‐ Quantification of Breast Density with Spectral Mammography
Authors: Ding H , Ducote J L , Molloi S
Published: June 2012

Purpose: To investigate the feasibility of quantification of volumetric breast density using photon‐counting spectral mammography. Methods: A computer simulation model using polyenergetic spectra from a tungsten anode x‐ray tube and a Si‐based photon‐counting detector has been evaluated for breast density quantification. The figure‐of‐merit (FOM), which was defined as the signal‐to‐noise ratio (SNR) of the dual energy image with respect to the square root of the mean glandular dose (MGD), was chosen to optimize the imaging protocols, in terms of beam energy and splitting energy. A scanning multi‐slit photon‐counting spectral mammography system was used in the experimental study to quantitatively measure breast density using dual energy decomposition with glandular and adipose equivalent phantoms of uniform thickness. Four phantom studies were designed, which covered various thicknesses ranged from 2.0 to 8.5 cm and densities ranged from 0% to 100%. In addition to the standard calibration fitting function used for dual energy decomposition, a modified third order fitting function was also investigated. Results: The optimal splitting energies for breast density quantification with clinically relevant beam energies were suggested from the FOM simulation for various breast thicknesses. In the physical phantom studies, the RMS errors in breast density quantification were approximately 1.54% and 1.35% for measurements using the standard and the modified calibration fitting function, respectively. Conclusions: The results of the current study suggest that photon‐counting spectral mammography can be implemented in screening exam to measure volumetric breast density with high accuracy, which can potentially have a high impact in the assessment of breast cancer risk.
TH‐A‐217BCD‐10: Feasibility of Performing 2D Mammography Using CNT Source Array Designed for Tomosynthesis
Authors: Shan J , Gidcumb E , Inscoe C , Qian X , Lu J , Zhou O
Published: June 2012

Purpose: Digital breast tomosynthesis (DBT) is the top rival of 2D mammography. Two common approaches to DBT are continuous and step‐and‐shoot tube motion; presenting problems with source motion blur and long scan time, respectively. Stationary DBT (s‐DBT) has the potential to overcome both issues. We recently developed an s‐DBT scanner utilizing a CNT (carbon nanotube) x‐ray source array, and demonstrated its enhanced spatial resolution and faster scanning speed. This work explores the possibility of expanding the capabilities of current CNT s‐DBT technology to 2D mammography when necessary. Methods: A testing chamber was configured to mimic the most recent iteration of the s‐DBT technology. Simulations of heat loading on the tungsten anode were conducted to predict the maximum power the anode could withstand. The minimum goal was to test if a single CNT cathode could output 50mAs in 4s, giving similar exposure of one traditional 2D view. Further testing explored the current limits of the cathodes. Results: Results show that a single CNT cathode can easily reach the minimum requirement for a 2D mammography image and can reliably administer up to 50mAs with a 3 second pulse width at 35kVp, which is an equivalent exposure to one 2D mammography image. Conclusions: A single CNT cathode in the electrode configuration of the current s‐DBT design can successfully administer enough current to perform a 2D mammography screening image. The heat loading on the anode was sufficient for this purpose, with the limiting factor being the current design of the CNT cathodes. This work is supported by the National Cancer Institute through the Carolina Center for Cancer Nanotechnology Excellence under grant number U54CA119343 and R01CA134598, the Lineberger Comprehensive Cancer Center and University Cancer Research Fund at UNC