bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐E‐141‐10: Automated Patient Identification and Localization Error Detection Using X‐Ray Setup Images
Authors: Lamb J , Reyhan M , Agazaryan N , Low D
Published: July 2013

Purpose: To show that planar x‐ray radiotherapy setup imaging can be used to perform computer‐based automated patient identification and localization error detection. Methods: For this proof‐of‐concept study, setup imaging from a sample of 100 cranial radiotherapy patients, 100 prostate patients, and a group of 83 patients treated for spinal lesions was analyzed. The patients were treated using a commercially‐available image‐guided radiotherapy system that derives setup corrections by performing 2D‐3D registration. The 2D‐3D registration is performed by dynamically generating digitally‐reconstructed radiographs (DRRs) with varying translational and rotational shifts until a measure of the similarity between the x‐ray projections and DRRs is optimized. Using the cranial patients, and separately the prostate patients, we investigated whether the value of the optimized image similarity measure could be used to discriminate between cases where x‐ray projections and DRRs from the same patient (correct match) and from different patients (incorrect match). Using the spinal patients we investigated whether the optimized similarity measure could be used to discriminate between localizations performed to the correct vertebral body and to vertebral bodies off by one from the correct body. Results: A threshold value of the similarity measure could be chosen to separate correct and incorrect patient matches and correct and incorrect vertebral body localizations with excellent accuracy for the patient cohorts studied. A 10‐fold cross‐validation using linear discriminant analysis yielded misclassification probabilities of 0.000, 0.0045, and 0.014 for the cranial patient identification, prostate patient identification, and spinal localization cases respectively. Conclusion: Automated patient identification and localization error detection can be performed with excellent accuracy using an IGRT system with 2D‐3D matching. This technique can be used to reduce errors in radiotherapy with very little procedural overhead. Our group is currently extending this methodology to the more common case of image guided radiotherapy systems which use 2D‐2D matching.
WE‐E‐141‐11: Optical Cone Beam 3D Tomography of Radiation Beams Using Cerenkov‐Excited Fluorescence
Authors: Glaser A , Davis S , Zhang R , Gladstone D , Pogue B
Published: July 2013

Purpose: Here, we explore a novel medical physics application of the Cerenkov effect for the dosimetric profiling of megavoltage beams used in radiation therapy. The technology to achieve these images has recently progressed from capturing single 2D projections with an intensified charge‐coupled device, to full 3D optical tomography using parallel beam back projection and a telecentric lens. In the current study, the method is extended to 3D imaging with a standard CMOS commercial camera and lens, using cone beam tomography algorithms for the reconstruction. Methods: Projection images of the induced Cerenkov light from a 20×20 cm2 6 MV beam operating at a dose rate of 600 MU/min incident on a water tank with a 1.0 g/L concentration of Quinine Sulfate were captured from 0–360° with a 3° angular resolution and 5.0 second exposure time, resulting in a total scan time of 10 minutes. The resulting projection images were used in a Feldkamp‐Davis‐Kress (FDK) cone beam tomography algorithm to reconstruct the imparted 3D dose distribution. An accuracy analysis was performed by comparing the reconstructed lateral profile at a depth of 10 cm and a percent depth dose curve to a reference dose distribution from the treatment planning system (TPS). Results: A 3D dose distribution was successfully reconstructed from the captured projections yielding results which were within +/− 8% of the TPS dose distribution. Conclusion: Optical cone beam 3D tomography of radiation beams using Cerenkov‐excited fluorescence has been demonstrated for the first time. The proposed technique has several advantages over alternative methods (e.g., ionization chambers, scintillation, and gel dosimetry) including speed, flexibility, and necessitates only water, which serves as a cheap, abundant, and easily standardized tissue equivalent medium. Upon future refinement and improved accuracy the proposed modality may prove to be an important dosimetric tool with both clinical and research applications.
WE‐E‐134‐02: High Resolution Acoustic Angiography for Early Assessment of Tumor Response to Radiation Treatment in Rat Tumor Model
Authors: Chang S , Gessner R , Wang S , Lee Y , Dayton P
Published: July 2013

Purpose: To test the hypothesis that acoustic angiography would enable early assessment of tumor response to radiation therapy at multiple timepoints after a single‐fraction radiotherapy treatment. Methods: 15 fibrosarcoma tumor‐bearing rats were irradiated (field‐size:1.8×1.8cm) by 6MV photon beam from a clinical linac. Tumors were implanted subcutaneously in the lower flank area and treated 14 days later (Mean‐diameter: 7.03+/−1.62mm). Animals were randomized into three groups (doses of 0, 5 or 20 Gy). Tumors were imaged prior to treatment (Day 0) using both acoustic angiography (microbubble contrast‐based microvessel imaging) and standard high frequency b‐mode, and then again at Days 3, 6, 9, 12, and 18. Tumor volume, and perfused volume ratio (PVR ‐ the ratio of tumor volume with perfused voxels, to total tumor volume) were quantified at each timepoint. Results: The tumors in the 0 or 5 Gy groups continued to grow exponentially after treatment. All animals in the 20 Gy group experienced an inflection point in their growth curve at Day 3, and tumor volume reduced exponentially until Day 12. Three of these tumors are non‐responders(20Gy‐NRs) and had second inflection point at Day 12, and proceeded to increase in volume, on average to their original Day 0 tumor size by Day 18. The other two tumors in the 20 Gy group are responders(20Gy‐R' s) and reduced to undetectable tumor volumes by Day 18. The PVR metric for vascularization revealed differences in the 20Gy‐NR and 20Gy‐R groups at Day 12, which correlated with tumor volumetric differences. Conclusion: Our preliminary data indicate that the acoustic angiography‐derived PVR metric can detect rat fibrosarcoma tumors responded (N=2) and those which did not (N=3) to 20 Gy radiation six days before there is a detectable difference in tumor volumes.
WE‐E‐134‐03: Ultrasonic Tissue Characterization of Parotid‐Gland Injury Following Head‐And‐Neck Radiotherapy Using Nakagami‐Parameter Imaging: A Feasibility Study
Authors: Liu T , Yu D , Beitler J , Tridandapani S , Bruner D , Curran W , Yang X
Published: July 2013

Purpose: Radiotherapy (RT) is an important modality in the multidisciplinary approach to treating head‐and‐neck malignancies. However, xerostomia (dry mouth), secondary to parotid‐gland injury, is a distressing side‐effect affecting up to 90% of patients post head‐and‐neck RT. The purpose of this study is to develop an ultrasonic tissue characterization technique based on Nakagami‐parameter imaging to evaluate parotid‐gland injury. Methods: A preliminary clinical study was conducted with 12 post‐RT patients and 12 healthy volunteers. Each participant underwent one ultrasound study in which ultrasound scans were performed in the longitudinal, i.e. vertical, orientation on the bilateral parotids. For the 12 patients, the mean radiation dose to the parotid glands was 37.7 ± 9.5 Gy, and the mean follow‐up time was 16.3 ± 4.8 months. All enrolled patients experienced grade 1 or 2 late salivary‐gland toxicity (RTOG/EORTC morbidity scale). The normal parotid glands served as the control group. From Nakagami imaging, Nakagami scaling and shape parameters were computed from the RF data to quantify radiation‐induced parotid‐gland changes. Results: Significant differences in Nakagami parameters were observed between the normal and post‐RT parotid glands. The mean Nakagami scaling parameter values were (3.77 ± 1.70)10E8 for the normal parotid glands, and (2.77 ± 1.69)10E8 for the irradiated parotid glands (p<0.001). The mean Nakagami shape parameter values were 2.16 ± 0.95 for the normal parotid glands, and 1.29 ± 0.68 for the irradiated parotid glands (p<0.001). Radiation‐induced parotid‐gland injury appears to be associated with decreased Nakagami parameters. Conclusion: In this study, we demonstrate the feasibility of using Nakagami parameters to evaluate parotid‐gland injury. Nakagami imaging, which complements conventional B‐mode imaging, has the potential of providing key imaging signatures for ultrasonic characterization of radiation‐induced changes in the parotid glands. This imaging method may be useful as we try to address xerostomia in patients following radiotherapy for head‐and‐neck malignancies.
WE‐E‐134‐04: Computerized Detection of Breast Cancer On Automated Breast Ultrasound for Women with Dense Breasts
Authors: Drukker K , Sennett C , Giger M
Published: July 2013

Purpose. Develop a computer‐aided detection method and investigate its feasibility for detection of breast cancer in automated 3D ultrasound for women with dense breasts.Methods. The HIPAA‐compliant study involved a dataset of 3D automated breast ultrasound image volumes (views) acquired with a U‐Systems SomoV ABUS system for 185 asymptomatic women with dense breasts (BI‐RADS Composition/Density 3 or 4). For each patient, three 3D views per breast were acquired. A total of 52 patients had breast cancer (61 cancers) and 31 patients (32 cancers) had a screening‐mammogram, clinically‐assigned BI‐RADS Assessment Category 1 or 2, i.e., were mammographically negative. All software was developed in‐house and involved 3 steps: 1) detection of initial tumor candidates, 2) characterization of candidates, and 3) elimination of false‐positive detections. Performance was assessed through the cancer detection sensitivity as a function of the number of marks (detections) per view. Results. At a single mark per view, i.e., 6 marks per patient, the median detection sensitivity of our computerized method was 50.0% (16/32) for the patients with a screening mammogram assigned BI‐RADS category 1 or 2, similar to the 49.9% on average obtained for these by patients by 17 radiologists in a reader study. At 3 marks per view, the sensitivity was 69% (22/32)+/−5% for the BI‐RADS 1 and 2 patients, and 64% (39/61)+/−3% for all patients.Conclusion. Promising detection sensitivity was obtained for this 3D ultrasound dataset of women with dense breasts at a rate of false‐positive detections that may be feasible for clinical implementation. Conflict of interest statement: M.L.G. is a stockholder in R2 Technology/Hologic and receives royalties from Hologic, GE Medical Systems, MEDIAN Technologies, Riverain Medical, Mitsubishi and Toshiba. K.D. received royalties from Hologic. It is the University of Chicago Conflict of Interest Policy that investigators disclose publicly actual or potential significant financial interest that would reasonably appear to be directly and significantly affected by the research activities. Funding: This work was supported in part by NIH S10 RR021039 and P30 CA14599. and the Department of Radiology of the University of Chicago
WE‐E‐134‐08: Characterization of Carotid Plaque with Histology and Quantitative Ultrasound
Authors: Wang X , Salamat S , Varghese T , Dempsey R
Published: July 2013

Purpose: To compare and correlate localization and registration of calcified, fibrous and lipid regions within heterogeneous plaque using histology and ultrasound quantitative imaging, and to better characterize carotid plaque. Methods: Atherosclerotic plaque excised after carotid endarterectomy, was imaged ex vivo using a VisualSonics Vevo 770 ultrasound system. Attenuation coefficient images were obtained from the three‐dimensional radiofrequency data collected and rendered into a 3D volume. Fixed plaque tissue was then longitudinally sectioned in increments of 5 um, and sections separated by 100 um were acquired. The thickness of each section of the sample was 5 um. Histopathology images were digitized using a PathScan Enabler IV. The two‐dimensional histology information obtained were registered using Matlab and reconstructed into a 3D volume. Different regions such as the lumen, calcified, fibrous and lipid region were segmented by a pathologist and digitally color‐coded into the 3D histology data. We then compared similar tissue types from the 3D histology volume to the estimated 3D attenuation coefficient using quantitative ultrasound methods. Results: Our results indicate that calcified, fibrous and lipid regions in the two volumes showed a good correlation. Calcified regions delineated on the histology volume correspond to the high attenuation coefficient region (2.48 dB/cm/MHz) in the 3D attenuation coefficient volume, while lipid regions tend to have lower attenuation coefficient values (1.47 dB/cm/MHz). Fibrous regions in histology, correlate to the lowest attenuation coefficient value (0.86 dB/cm/MHz). Conclusion: Most plaques are heterogeneous and difficult to characterize precisely. This work demonstrates a direct correlation between pathology and ultrasound quantitative imaging characterization of plaque. It provides a promising way for direct localization of plaque regions and structures, and for improved determination of plaque composition. This work was supported in part by NIH grants R21 EB010098‐02, R01 NS064034‐04, and 2R01 CA112192‐06.
WE‐E‐134‐11: Ultrasound Cardiac Strain Imaging of Left Ventricle Using Lagrangian Tracking
Authors: Ma C , Varghese T
Published: July 2013

Purpose: Lagrangian description of myocardial tissue deformation is essential for accurate regional strain estimation of left ventricular wall over time. Failure to couple the estimated displacement and strain information with the correct myocardial tissue structure will lead to erroneous displacement and strain estimation. Methods: In this study, a method to obtain Lagrangian based deformation tracking is presented. Myocardial tissue is divided into a fixed number of pixels whose deformation is tracked over the cardiac cycle. An algorithm that utilizes a polar‐grid generated between the estimated endocardial and epicardial contours for the left ventricle in cardiac short axis images is proposed to ensure Lagrangian description. Displacement estimations from consecutive radiofrequency frames were then mapped onto the polar grid to obtain a distribution of the cumulated displacement that is mapped to the polar grid over time. Results: This method was validated against a finite element analysis (FEA) based canine heart model coupled to an ultrasound simulation program. Segmental analysis of the accumulated displacement and strain over cardiac cycles show excellent agreement between the ideal Results obtained directly from the FEA model and our Lagrangian approach for deformation mapping. Eulerian based estimation results on the other hand, show significant deviation from the ideal Results. A comparison of the displacement and strain estimated on parasternal short axis view on a healthy volunteer is also presented. Conclusion: Lagrangian deformation tracking using a polar grid demonstrates accurate results when validated against finite element cardiac model. In addition to the cardiac application, this approach can also be applied to transverse scans of arteries.
WE‐E‐116‐01: Grantsmanship and Funding
Authors: Beddar S , Deye J , Romeijn E , Mackie T , Paganetti H , Jin J , McGuire S
Published: July 2013

This symposium is organized by the Working Group on Funding and Grantsmanship (WGFG: http://www.aapm.org/org/structure/?committee_Code=WGFG); one of the WG of the AAPM Research Committee. The main goal of this symposium is to introduce to the membership two Federal Funding Agencies (NSF and DOE) that are typically less frequently approached for funding medical physics research than the NIH. Speakers representing all funding agencies will inform the audience of their roadmap initiatives and the type of research they will most likely fund, including highlights of their respective research opportunities.

1. NIH Updates: James A. Deye, Ph.D., Program Director

2. NSF Funding: Edwin Romeijn, Ph.D., Program Director

3. DOE Funding: Rock Mackie, Ph.D.

A Grantsmanship keynote presentation is dedicated to NCI R01 and R21 applications, followed by two perspectives to writing a winning grant proposal which will be presented by two New Investigators (one from the Therapy side and the other from the Imaging side).

4. “Grantsmanship for NCI R01 and R21 applications”: Harald Paganetti, Ph.D.

5. New Investigator's perspectives to writing a winning grant proposal:

a) Therapy investigator: Jian‐Yue Jin, Ph.D.

b) Imaging investigator: Sarah McGuire, Ph.D.

The symposium will be followed with a 20 minutes Q&A session between the audience and all the speakers.
WE‐F‐105‐02: Fano Cavity Test of the Monte Carlo Codes GEANT4 and PENH for Proton Transport
Authors: Sterpin E , Sorriaux J , Vynckier S , Bouchard H
Published: July 2013

Purpose: In the scope of reference dosimetry of radiotherapy beams, Monte Carlo (MC) simulations are widely used to compute ionization chamber dose response accurately. Uncertainties related to the transport algorithm can be verified performing self‐consistency tests, e.g. the so‐called Fano cavity test. The Fano cavity test is based on the Fano theorem, which states that under charged particle equilibrium (CPE) conditions, the charged particle fluence is independent of the mass density of the media as long as the cross‐sections are uniform. Such tests have not been performed yet for MC codes simulating proton transport. The objectives of this communication are 1) presenting a new methodology for Fano cavity test of MC codes for protons and other charged particles; 2) applying the methodology for two MC codes: GEANT4 and PENELOPE extended to protons (PENH). Methods: The geometry considered is a 10×10 cm2 parallel virtual field and a cavity (2×2×0.2 mm3) in a water phantom with dimensions large enough to ensure CPE. Virtual particles of energy E and attenuation coefficient μ are transported. During each interaction, the virtual particle triggers a proton with kinetic energy E and is then regenerated. Assuming no nuclear reactions and no generation of other secondaries, we theoretically demonstrate that the computed cavity dose should equal μE/ρ times the incident fluence. Simulations satisfying those assumptions were implemented in GEANT4 and PENH. Results: For conservative user‐inputs (small step sizes), both GEANT4 and PENH pass the FANO cavity test within 0.1%. However, differences of 0.6% were observed for PENH using larger step sizes. The difference was attributed to the random‐hinge method that introduces an artificial energy straggling if step size is not small enough. Conclusion: Using safe user‐inputs, both PENH and GEANT4 pass the Fano cavity test for proton transport. Our methodology is valid for any type of charged particle. Jefferson Sorriaux is sponsored by a public‐private partnership IBA ‐ Region Wallonne
WE‐G‐108‐01: A Computer Assisted Treatment Events Recognition System (CATERS) For Radiation Therapy
Authors: Xia J , Mart C , Bayouth J
Published: July 2013

Purpose: To develop an automated treatment event detection system to safeguard radiation therapy patients by analyzing electronic treatment records and reporting treatment events. Methods: CATERS is to make the treatment monitoring process more efficient by offloading repetitive tasks to the computer. Treatment events are defined as possible deviations from physician's intention, such as inconsistent or wrong treatment parameters. CATERS consists of a user interface, the CATERS core, and a data interface. CATERS core is responsible for all logic analysis and treatment event recognition. Through the user interface, users can access CATERS from either mobile devices or desktop computers. The data interface provides methods for retrieving electronic treatment records. A five months study was conducted to compare CATERS with manual chart checks. Results: From July 2012 to November 2012, 491 patients were treated at our clinics for total of 7692 fractions. From these fractions, 553 events were detected by CATERS, none of the events has significant dosimetric impacts on patient treatments. On average, it takes about one second to check one patient. During the trial, CATERS was able to efficiently detect all events that were discovered with a manual chart check when used side‐by‐side. The top three types of events were couch position override (3.2%), cone beam CT frequency (1.85%), and significant couch position deviation (1.31%). CATERS is clinically deployed and routinely used by all the physicists in our clinics. Conclusion: CATERS offers an effective method to detect and report treatment events. With CATERS, radiation treatments can be monitored and treatment events can be reported on a daily or even an hourly basis. Caters has the potential to improve treatment check efficacy and minimize the possibility of a misadministration.
WE‐G‐108‐02: Oncospace: A Database Designed for Personalized Medicine in Radiation Oncology
Authors: McNutt T , Evans K , Moore J , Yang W , Herman J , Quon H , Sharabi A , Wong J , DeWeese T
Published: July 2013

Purpose: The Oncospace database aggregates treatment planning and clinical information about prior patients facilitating extraction of knowledge from prior courses of care. The goal is to use this knowledge to influence clinical decisions, quality and safety of care for new patients. Methods: The Oncospace website, built in C# and ASP.NET, accesses the MS SQLServer database for analysis. The data tables are designed to support patient geometry, targets and organs at risk (OAR) and their spatial relationships, dose distributions, toxicities, diagnosis and disease progression, chemotherapy and medications, laboratory values, patient histories and demographics. Data is collected directly from the treatment planning system and the oncology information system (OIS). Point of service data collection is facilitated with tablet (iPad) forms linked to the OIS. Results: Web pages have been built to answer the following: A) For a selected toxicity and OAR, display the dose volume histogram (DVH) and colorize them by the maximum toxicity grade of the patient while identifying a selected patients DVH B) For a selected OAR and percent volume (%V), find the lowest dose achieved from all patients whose %V is closer to the selected target volume? C) For a given diagnosis, toxicity and treatment, display the aggregate trend in toxicity from start of treatment (acute) through several year follow‐up (late)? Oncospace currently supports: and a full H&N database, a multi‐institutional pancreatic stereotactic trial, and shape database for automated planning pancreas cancer. Conclusion: Oncospace can provide fast access to large amounts of data through complex queries designed to answer specific clinical questions to influence the safety and quality of care for new patients. This system can be used in the clinical setting to assess both plan quality and outcome expectations for new patients based on the data of prior patients. Funding for this research was provided by the Commonwealth Foundation, Elekta/IMPAC Medical Systems, Inc., Philips Radiation Oncology Sytems, and the Johns Hopkins University.
WE‐G‐108‐06: Evaluating Pre‐Treatment IMRT & VMAT QA Techniques Quantitatively Using Receiver Operating Characteristic (ROC) Analysis
Authors: Mitchell A , Adamson J
Published: July 2013

Purpose: Pre‐treatment IMRT and VMAT QA techniques are often commissioned without knowledge of their sensitivity to clinically relevant delivery errors. The purpose of this work is to develop a method to quantify the sensitivity and specificity of pre‐treatment IMRT and VMAT QA techniques to treatment delivery errors. Methods: To evaluate a QA technique, a population of treatment plans and a population of clinically relevant delivery errors are defined. For each delivery error, a threshold magnitude is determined that induces a substantial change in clinically relevant dosimetric indices. Errors at the threshold magnitude are introduced into the plans and QA is performed with and without intentionally introduced errors. The QA technique is treated as a binary classifier to predict error plans using Receiver Operator Characteristic (ROC) analysis. We applied this technique to evaluate portal imager and 2D ion chamber array based QA for VMAT treatment of brain lesions. Delivery errors included discrepancies in MLC positioning (single leaf and leaf bank); lag of MLC trajectory; and discrepancy in dose rate per control point or gantry angle. The threshold magnitude was determined by achieving a 5% change in target conformity index. Results: The area under the curve (AUC) for the ROC analysis was 0.592 and 0.509 for the ion chamber array and portal imager, respectively, using a gamma index of 3%, 3mm. The AUC increased to 0.632 and 0.777 when 2%, 2mm was used for the ion chamber array and portal imager, respectively. Comparison based on 3% dose agreement resulted in an AUC of 0.557 and 0.693, respectively. Conclusion: For both portal imager and ion chamber array based QA, stricter tolerance than 3%, 3mm is needed to detect clinically relevant delivery errors. This method can be used to quantitatively compare the sensitivity of various QA techniques to clinically relevant dosimetric errors.
WE‐G‐108‐07: EPID Dosimetry Comparisons and Corrections: Portal Image Prediction Vs. Portal Dose Conversion
Authors: Bailey D , Kumaraswamy L , Bakhtiari M , Podgorsak M
Published: July 2013

Purpose: To compare the pretreatment quality assurance robustness of two forms of EPID dosimetry: dose image prediction and dose plane conversion. Both systems are tested for accuracy in all areas of the detecting surface, for both symmetric and asymmetric field sizes, and various levels of modulation intensity. Both EPID dosimetry techniques are sensitivity‐tested for their ability to identify crucial TPS errors. Methods: Over 50 IMRT fields, from low‐modulation breast electronic compensation to high‐modulation head/neck plans, were measured and analyzed via a commercial portal dose prediction package and a commercial portal dose conversion package. Various beam characteristics and dose calibration errors were induced into the TPS, then dose planes and dose predictions for several IMRT fields were recalculated for comparison to respective measurements. A common diode array system was also used in these studies, representing a standard for dose comparison. Results: For IMRT fields with no induced errors, both EPID dosimetry systems perform similarly, except for large and/or off‐axis fields where the EPID prediction system underestimates EPID response by up to 15%. In these cases, a 2D matrix correction developed by the authors and applied to individual EPID predictions brings the portal dose prediction system into good agreement with measurements. The portal dose prediction system, which uses actual fluence as an input, is able to catch some TPS errors, such as erroneous MLC transmission or dosimetric‐leaf‐gap values, but not errors downstream from the leaf‐motion calculation. The portal dose conversion system, which compares measured absolute dose planes to TPS dose planes, is sensitive to errors anywhere in the fluence/dose calculation. Conclusions: All EPID dosimetry systems are not created equal. Empirically‐derived prediction algorithms may need substantial correction techniques, and may be insensitive to some TPS errors. Portal image conversion to dose matrix is a more comprehensive form of pretreatment IMRT QA.
WE‐G‐108‐09: Modulation Severity as a Predictor for Patient‐Specific IMRT QA Delivery Failure
Authors: Price R , Veltchev I , Ma C
Published: July 2013

Purpose: The goal of this work was to determine if highly modulated fields contribute to decreased passing rates for patient‐specific IMRT delivery QA. Methods: Data for 10 Varian Eclipse‐planned patients in each of 3 categories were collected: IMRT, carriage shift, and RapidArc. Total plan modulation was calculated as the ratio of total MU to dose per fraction. Applied modulation, in cGy, was determined for each field as the ratio of total MU per field to total plan modulation. The difference between applied modulation and dose from the planning system on a per beam basis was calculated and the mean values found for each patient and each category. Limits were applied based on the category mean plus 3 standard deviations for 2 beams as well as maximum limits for a single beam. Data were evaluated with respect to these limits for 889 patients. The individual results were compared with the IMRT delivery QA data collected with the IBA Matrixx using absolute 3% dose and 3mm DTA acceptance criteria. Results: Modulation limits were exceeded for IMRT plans in 64%, 44% and 22% of cases and for RapidArc plans in 43%, 22% and 2% of cases for delivery QA passing rates of 92%, 95% and 98%, respectively. The mean passing rate for delivery QA was approximately 97% (range 90.4–100%). Conclusion: There is a definite trend indicating lower delivery QA passing rates with severe modulation for both modalities. However, given an arbitrary acceptable passing rate of 95% with the modulation test failing 44% and 22% of the time for IMRT and RapidArc, respectively, modulation may not be a strong predictor of delivery QA acceptability. The cause(s) of severe modulation should be evaluated on a case‐by‐case basis with appropriate time and attention allotted for all phases of the QA process.
WE‐G‐500‐02: BEST IN PHYSICS (JOINT IMAGING‐THERAPY)‐Proton Beam Range Verification Using Proton Activated Fiducials and Off‐Site PET
Authors: Cho J , Ibbott G , Gillin M , Gonzalez‐lepera C , Titt U , Mawlawi O
Published: July 2013

Purpose: Proton range uncertainty places limits on the accuracy of proton therapy. PET imaging of activated endogenous tissue following proton treatment has been suggested as a tool for proton range verification. However, this approach is limited due to the weak activation of tissue near the proton distal fall off and the need for expensive in room PET scanners. To overcome these limitations, we investigated the use of patient implantable proton activated elements such as Zn68(p,n)Ga68 which is strongly activated by low energy protons and decays by positron emission with a 68min half life. This study compares PET signals from irradiated Zn68 enriched foil and a tissue substitute polycarbonate,(C16O3H14). Methods: Zn68 (>97%) enriched foils simulating implanted fiducials of 10 mm3 (10 × 10 × 0.1 mm thick) and polycarbonate sheets simulating tissue volumes of 305 mm3 (20 × 20 × 0.76 mm thick) were irradiated with a 160 MeV, 10‐cm SOBP proton beam. 2 foils and 2 sheets were placed at each of four depths over the distal fall‐off range (100% ∼ 40% of SOBP dose). A dose of 12.5 Gy was delivered, simulating thoracic SBRT. 47 min following activation a 2.5 hour PET scan was acquired and the corresponding images were reconstructed. The PET signal intensity of each foil and sheet was then measured and normalized to the results of the shallowest depth. Monte Carlo simulation was also performed for comparison. Results: Normalized mean activity concentration for Zn68 (polycarbonate) at the distal fall off region at 100∼99%, 99∼98%, 93∼81%, 62∼40% dose were 100±8% (2.6±0.4%), 83±11% (1.4±0.5%), 96±48% (1.4±0.8%), 64±2% (2.4±1.0%). Monte Carlo simulation agreed with measurements and were 82% (6%), 100% (2%), 84% (1%), 38% (0%). Conclusion: The higher activation of Zn68 over the distal fall‐off suggests the possibility of using Zn68 as proton activated fiducials for proton range verification.
WE‐G‐500‐08: Novel Multilayer Detector Design Using Polycrystalline CdTe for Radiation Therapy Imaging Applications
Authors: Shvydka D , Karpov V , Paudel N , Parsai E
Published: July 2013

Purpose: In radiation therapy treatments the standard approach of taking a planar portal or CIAO image offers setup verifications crucial to accurate radiation delivery. A substantial detector thickness necessary for MV photon absorption is a limitation due to large signal spreading; the requirements of large areas (up to 40×40 cm) and commercial viability dictate the use of non‐crystalline semiconductors. We propose a detector based on thin‐film CdTe technologies recently developed for photovoltaic applications. It utilizes a stack of CdTe photovoltaic layers, each having a built‐in electric field. This 3D structure adds a depth signal reading to the traditional 2‐D pixilation allowing for the photon energy and position resolution. Methods: We modeled the energy deposition under mono‐energetic photon sources of 0.5 to 18MV with depth by Monte Carlo simulation package MCNP5. The results yield the charge carrier generation profiles in structures having 3 to 30 layers, and CdTe thickness of 2–10 microns. The profiles were used as input for modeling of current‐voltage (I–V) characteristics with device operation modeling software SCAPS‐1D. Results: Based on the modeled I–V we established variations of the output signal in each layer with depth (layer number), and developed an algorithm for extracting the position dependent source energy. Our design includes an original read‐out approach where, under the global short circuit conditions, the voltages across individual layers are exponentially sensitive to their corresponding generation rates, a ∼1% difference in deposition energies translates into ∼100% difference in the corresponding voltage readings. Conclusion: The micron‐range thickness of layers overcomes known limiting factors of the low hole mobility and electron trapping typical of thick crystalline CdTe detectors. A new algorithm allows extracting information on radiation intensity and spectra from the data on the layer photo‐voltages leading to enhancement in spatial resolution.Acknowledgment: this research is supported through NRC grant No.: NRC‐HQ‐12‐G‐38‐0042; This project is part of a faculty development award supported by the NRC grant No.: NRC‐HQ‐12‐G‐38‐0042
WE‐G‐500‐09: Robotic Multi‐Pinhole Scenarios for SPECT Molecular and Functional Imaging Onboard and in Other Applications
Authors: Bowsher J , Yan S , Yin F
Published: July 2013

Purpose: Single Photon Emission Computed Tomography (SPECT) is one of the two predominant modes of nuclear emission tomography, the other being Positron Emission Tomography (PET). An important recent advance has been region‐of‐interest (ROI) SPECT for cardiac imaging. For SPECT imaging onboard radiation therapy machines, we have proposed a robotic, multi‐pinhole SPECT approach. Robotic maneuvering facilitates navigation of the SPECT system about patient, patient table, and gantry, and it also enables more flexible positioning of the pinholes. Even more pinhole‐positioning flexibility can be provided by enabling more degrees of freedom (DOFs) in the motion of pinholes relative to one another. This will likely increase imaging performance, but also system cost. The purpose of this study is to investigate imaging performance as a function of DOFs in relative pinhole motion. This has bearing for molecular and functional imaging onboard radiation therapy machines, and also for other applications of SPECT ROI imaging. Methods: A 49‐pinhole system which we have previously presented is considered for imaging ROIs smaller than, equal in size to, and larger than the ROI for which the system was optimized. This system has one internal DOF which enables relative motion among the seven 7‐pinhole pods that comprise the system. Also considered is a second system in which 7 additional DOFs enable relative motion of the pinholes within each pod. Imaging performance of these two 49‐pinhole systems is compared over a range of ROI sizes. Results: The additional DOFs can improve proximity to smaller ROIs and thereby improve SPECT sensitivity and resolution for those ROIs. Conclusion: SPECT ROI imaging can be advanced by a multi‐pinhole approach that enables greater relative motion of pinholes. This work was supported by PHS/NIH/NCI grant 5R21CA156390.
WE‐G‐WAB‐04: Ultra‐Fast Dynamic MRI for Lung Tumor Tracking Based On Compressed Sensing and Low‐Rank Decomposition in the Spatial‐Temporal Domain
Authors: Sarma M , Hu P , Ennis D , Thomas A , Lee P , Sheng K
Published: July 2013

Purpose: Dynamic MRI is an attractive tool for internal organ motion monitoring but its speed is yet to be improved for real time 3D imaging. The purpose of the study is to accelerate the imaging acquisition using a hybrid compressed‐sensing and low rank decomposition method (k‐t SLR) exploiting data sparsity in the spatial‐temporal domain. Methods: Six retrospective lung cancer patients were included in the study. For each subject, 120 continuously dynamic 2D MR images were acquired using a fast steady state precession imaging sequence. To test the feasibility of accelerated MR acquisition, fully sampled k‐space data were down‐sampled by 5–20 folds before reconstruction. The under‐sampled low rank spatial‐temporal matrix was recovered by a k‐t SLR method computing the matrix of minimum nuclear norm that fits the data. The k‐t SLR results were compared against conventional total variation (TV) reconstruction of individual dynamic MR frames. Results: High imaging fidelity and low noise levels were achieved with the k‐t SLR method even at the most aggressive down‐sampling ratio while TV reconstruction showed substantial loss of details and subsequently greater tracking errors. The k‐t SLR method resulted in an average normalized mean square error less than 0.05 as opposed to 0.23 by using the TV reconstruction on individual frames. In addition to the high correlation coefficients (>0.90) in the tumor trajectories automatically tracked from the original images and the k‐t SLR reconstructed images, less than 6% points showed tracking errors greater than 1 mm with 20 fold down‐sampling, as opposed to the lower correlation coefficient (0.87) and 15% tracking error from using TV alone with 10 fold data down‐sampling. Conclusion: We have demonstrated the potential to significantly reduce the amount data samples required for lung MR image reconstruction in the radiotherapy context where long imaging acquisition of a repetitive anatomic process is performed. The study is supported in part by NIH 1R21CA144063 and R21CA161670
WE‐G‐WAB‐06: Three‐Dimensional Visualization Using Magnetic Resonance Imaging for Episcleral Brachytherapy
Authors: Rodriguez V , Bertelsman C , DeWees T , Hu Y , Rao P Kumar , Garcia‐Ramirez J , Grigsby P , Esthappan J
Published: July 2013

Purpose: Conventional treatment planning for episcleral plaque brachytherapy entails creating a two‐dimensional (2D) isodose plan based on the tumor dimensions and distances to critical structures as defined by ultrasound and fundus photography. The purpose of this study was to compare 2D‐based metrics of the tumor and normal eye anatomy with magnetic resonance (MR)‐based metrics. Methods: Thirty‐five patients with ocular melanoma were prescribed to receive 85 Gy over 96 hours using episcleral plaque brachytherapy with iodine‐125. The plaque size and seed source strength were determined from the tumor characteristics as defined by ultrasound and fundus photography. The patients were imaged on a 1.5‐Tesla MR unit using T1‐and T2‐weighted techniques. Images were exported to a brachytherapy planning system for contouring of tumor and normal eye anatomy, and identifying points of interest for critical structures, e.g., fovea and optic disk. The tumor apex height, basal dimensions, distances between tumor edge to fovea and to optic disk were averaged over all patients, and compared between 2D‐and MR‐based methods using statistical Signed test analysis. Results: There were no statistically significant differences between 2D‐and MR‐based methods for mean tumor apex height, basal dimensions, and distance to optic disk and to fovea. Four patients presented with tumors located anteriorly in the ciliary body. This tumor location proved to be challenging in estimating distances to optic disk and fovea based on 2D methods. These distances were measurable on MR regardless of tumor location. Conclusion: We have shown that tumor dimensions and distances measured using 2D‐based methods can be reproducibly defined on MR. Future work will evaluate isodose plans on the MR images and compare them to 2D‐based isodose plans. Additional work will include investigating different MR imaging techniques to enhance soft‐tissue visualization.
TH‐A‐103‐05: Characterization of An Energy‐Resolved Photon‐Counting Si Strip Detector for Breast CT Imaging
Authors: Cho H , Ding H , Barber W , Iwanczyk J , Molloi S
Published: July 2013

Purpose: To investigate the characteristics of a high resolution energy‐resolved photon‐counting Si strip detector for breast CT imaging. Methods: A prototype Si strip detector was studied for breast CT imaging. A bench‐top CT system was constructed using a tungsten anode x‐ray source with a focal spot of 0.8 mm and a single line Si strip detector with 256 pixels and pixel pitch of 100 μm. A 38 μm diameter tungsten wire phantom was used to determine the point spread function (PSF) of the detector. The tungsten wire phantom was positioned 110 and 7.5cm from the x‐ray tube focal spot and detector, respectively. The system MTF was measured using reconstructed images. For the noise power spectrum (NPS), three different exposures 16, 31, and 46 μGy were used. Flat field images were acquired with and without electric noise at each exposure to investigate the effect of detector's electric noise on the noise property. The simulations with the same phantom and system geometry were also performed for validation purposes. A 16 cm water phantom, which contains various diameters (76, 102, 152, 203, and 254 μm) of aluminum (Al) wire was investigated to confirm the simulation and experimental results. Results: The desired resolution of 100 μm, corresponding to a spatial frequency of 5 lp/mm was demonstrated in both simulation and experimental results. A higher normalized NPS was measured when electronic noise included. The relationship between measured and known diameter for Al wires was quite linear except for the smallest Al wire which is smaller than detector pixel size. Conclusion: The performance of the prototype Si strip detector was evaluated using MTF and NPS. The results show that the investigated detector has excellent potential for high resolution breast imaging at low radiation dose levels.
TH‐A‐103‐09: Bowtie Filter Designs for Dedicated Breast CT
Authors: Kontson K , Jennings R
Published: July 2013

Purpose: To design bowtie filters with improved properties for cone‐beam breast CT in order to improve image quality and reduce dose to the patient. Methods: In breast CT, the relatively uniform composition and approximate rotational symmetry of the object being imaged invite the application of analytic methods to the bowtie filter design problem. It is possible to eliminate the beam hardening effect in the reconstructed image by adjusting the bowtie filter thickness so that the effective attenuation coefficient for every ray is the same. Other effects for which compensation can be achieved include spectral change only, or spectral change and variation of overall intensity. The designs that compensate for spectral change or spectral change/intensity require additional software corrections to the calibration scan while the beam hardening design does not. Results: Examples of designs that satisfy the criteria described above are presented. Verification of the performance of the design that eliminates the beam‐hardening effect was done by reconstructing simulated projection data. Reconstruction of an experimental data set using a bowtie filter that compensates for spectral change showed a marked reduction in the ring artifact. The performance of the designs depends only very weakly on incident spectrum and tissue composition. By varying the material used in the fabrication of the filter, it is possible to minimize the dynamic range requirement on the detector by dividing it between the calibration scan and patient scan. The designs were based on a cylindrical phantom. Extension of the method to a more realistic shape is straightforward. Conclusion: The special properties of breast CT permit the use of rational design methods. Simulation and preliminary experimental results for our test geometries are encouraging. The next steps are further experimentation and analysis of performance with non‐ideal design parameters.
TH‐A‐116‐03: Photon and Proton Radiotherapy of the Lung Would Benefit From 4D Dose Calculation Techniques
Authors: Matney J , Chen Y , Park P , Li H , Bluett J , Sahoo N , Court L , Liao Z , Mohan R
Published: July 2013

Purpose: To compare the effects of respiratory motion by calculating four‐dimensional (4D) dose accumulation on proton and photon radiotherapy plans for a stage III lung cancer cohort.Methods and Materials: This study used passively scattered proton therapy (PSPT) and photon intensity modulated radiotherapy (IMRT) plans designed to meet the same criteria for an ongoing clinical trial. For 20 patients, 4D dose evaluation was calculated on both the PSPT and IMRT plans by accumulating individual phase dose using an intensity‐based in‐house deformable image registration algorithm. The resulting 4D dose accumulation method was compared against current standard of three dimensional (3D) dose as calculated on the average CT. Results: Both proton and photon plans demonstrated dosimetric differences when accounting for respiratory motion using 4D dose calculation methods. Reported 4D‐3D values are mean plus one standard deviation. 4D‐3D difference in PTV 95% dose coverage was >2% for 5 IMRT (0.5±1.1Gy) and 4 PSPT plans (0.5±0.8Gy). The structural doses most affected by respiratory motion were normal structures distal to the tumor, such as esophagus V65 (IMRT: −0.5±1.2Gy, PSPT: −0.4±1.4), mean heart (IMRT: − 0.4±0.6 Gy, PSPT: −0.3±0.9 Gy) and spinal cord maximum (IMRT: 0.0±0.2Gy, PSPT: 1.5±2.9Gy). No correlations were found between tumor motion and the change in 4D dose difference for any lung, heart, or spine dose‐volume index. Conclusions: The use of 4D dose evaluation techniques at time of treatment planning revealed small but significant respiratory motion induced deviations from the 3D planned dose for both photon and proton therapy. In both modalities, differences between 3D and 4D dose distributions are patient dependent; no population trends were found correlating dose differences to the extent of tumor motion. The implementation of 4D dose calculation methods for proton and photon lung cancer radiotherapy plans may help identify patients for whom respiratory motion alters the planned dose distribution. This project is supported by grant P01CA021239 from the National Cancer Institute.