bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐C‐116‐01: Effects of T2* On the Accuracy of Two‐Point Dixon Water and Fat Imaging
Authors: Rambow O , Ma J
Published: July 2013

Purpose: To quantify the error caused by T2* decay in two‐point Dixon imaging with flexible echo times. Specifically, we seek the error in the water values as well as the relative background phasor, which is vital for identifying pixels as water‐dominant or fat‐dominant, as a function of the echo times. Understanding how these errors depend on the echo times will enable us to choose echo times that will Result in more accurate fat‐water separation. Methods: In simulation, a model that includes T2* decay was used to generate signals. Water and fat values and the background phasor were then reconstructed from these signals using the traditional model that neglects T2* decay, and the error in these values was calculated. These results were validated experimentally by scanning an oil‐water phantom using a dual‐echo GRE sequence. The first‐echo signal values were taken as the “true” fat and water values, and the error was determined by comparing them to the values obtained using the traditional model. Results: For long T2* values, the error is very small except at TE combinations for which noise performance is also bad. Error is much larger for shorter T2* values and depends strongly on the echo times. For example, error at TE1/TE2 = 1.8/3.0 ms is approximately ten times that at TE1/TE2 = 1.2/2.4 ms. Plots are presented to show dependence on both T2* and echo times. Conclusion: Shorter T2* values Result in greater error, as expected. More interesting is the dependence on echo times, which is similar to error caused by signal noise. For two‐point Dixon imaging, the echo times should be chosen carefully to avoid large errors that can be caused by T2* decay.
WE‐C‐116‐07: Tumor Enhancement Using Deformable Image Registration for Four‐Dimensional Magnetic Resonance Imaging (4D‐MRI): A Feasibility Study
Authors: Yang J , Cai J , Wang H , Chang Z , Czito B , Bashir M , Yin F
Published: July 2013

Purpose: We have previously developed a 4D‐MRI technique using the fast imaging sequence employing steady‐state acquisition (FIESTA) sequence, which has suboptimal tumor‐to‐tissue contrast‐to‐noise ratio (CNR) due to its T2*/T1 weighting. This study investigated the feasibility of enhancing the tumor‐to‐tissue CNR using deformable image registration (DIR). Methods: Five patients with cancers in the liver were included in an IRB‐approved study. 4D‐MRI images were acquired on a 1.5T GE scanner and reconstructed off line using in‐house developed program. All patients were also imaged with a T2‐w fast recovery fast spin‐echo (FRFSE) sequence at the end‐of‐exhalation phase. Deformation vectors between respiratory phases of the 4D‐MRI were determined using commercial software. Pseudo ‘enhanced’ 4D‐MRI was then generated by applying the deformation vectors to the T2‐w FRFSE MR images. Motion trajectories of tumor and diaphragm and tumor‐to‐tissue CNR were compared between the original T2*/T1‐w 4D‐MRI and the ‘enhanced’ T2‐w 4D‐MRI. To validate our method, we performed a simulation study based on a 4D digital human phantom. MR images with T2*/T1‐w and T2‐w with were generated by assigning organ intensities corresponding to those in FIESTA and FRFSE images, respectively. Results: In the phantom study, motion trajectories of the hypothesized ‘tumor’ matched excellently between the original T2*/T1‐w 4D‐MRI and the ‘enhanced’ T2‐w 4D‐MRI. Mean(±SD) absolute difference in motion amplitude was 0.66 (±0.62) mm. In the patient study, tumor and diaphragm motion trajectories closely matched between the two 4D‐MRIs: mean correlation coefficient was great than 0.97 in all directions; the mean (±SD) absolute difference in motion amplitude was smaller than 0.55(±0.19) mm. Tumor‐to‐tissue CNR was significantly improved from 7.57(±5.6) in the original 4D‐MRI to 23.75(±15.8) in the ‘enhanced’ 4D‐MRI. Conclusion: It is feasible to improve tumor‐to‐tissue CNR of T2*/T1‐w 4D‐MRI using the DIR method. The ‘enhanced’ 4D‐MRI retained comparable tumor motion information as the original 4D‐MRI. This work is partly supported by funding from NIH (1R21CA165384‐01A1) and a research grant from the Golfers Against Cancer (GAC) Foundation.
WE‐C‐116‐08: Magnetic Field Homogeneity Evaluated Via the Bandwidth Methodology
Authors: Huff K
Published: July 2013

Purpose: To find a quick, simple and reproducible method for evaluating magnetic field homogeneityMethods: The Bandwidth Difference Methodology utilizes a spherical phantom scanned at isocenter in all three planes using a gradient echo sequence, which enhances field inhomogeneities. The scans are collecting at a low and high bandwidth and the resulting diameter of the spheres are measured in relation to the center frequency. Results: Subtraction yields a value in parts per million and indicates the overall magnetic field homogeneity. The results are highly dependent on field strength and magnet design. General trends have been established and are reported here. Conclusion: Although more robust means are available for determining the magnetic field homogeneity, these methods tend to require the MRI Physicist work directly with a field service engineer or to simply trust the results of the engineer's measurement. The Bandwidth Difference Methodology allows for consistent independent verification.
WE‐E‐108‐05: Evaluation of the XRAD 225Cx MC Source Model in Heterogeneous Mediums
Authors: Pidikiti R , Stojadinovic S , Song K , Speiser M , Solberg T
Published: July 2013

Purpose: This study was performed to benchmark a Monte Carlo source model of the XRAD 225Cx irradiator under heterogeneous conditions. Methods: The BEAM/EGS was used to model 225 kV photon beams from a small animal irradiator (Precision XRAD225Cx). Benchmarking the model in heterogeneous media was performed in a heterogeneous phantom (4×4×4 cm3) composed of solid water and cortical bone. The 10 mm field size virtual source from BEAMnrc was used to compute the 3D dose distribution in DOSXYZnrc. Benchmarking the simulation against measurements was performed using EBT2 film. Heterogeneous conditions were further validated using the phase space file for the 20 mm field size. Gamma analysis was performed to further validate the beam model for the heterogeneous configuration phantom. Results: The MC simulation indicates that there is a 2.4 times increased dose deposition in cortical bone, in agreement with published data. This increased dose deposition, however, was not observed in film measurements and it is investigated further. Gamma analysis was performed for 20 mm field size applicator and the Result of the analysis for a confined region. The single beam with 20 mm diameter circular field irradiation demonstrates a good agreement within the region of interest, with 94% of the calculated data meeting the 5%/0.5 mm criterion. Conclusion: Our kV Monte Carlo source model demonstrates excellent agreement with measurement in heterogeneous conditions.
WE‐E‐108‐07: Design of Open‐Source Binary Micro MLC for Small Animal Radiotherapy: An OSMD Initiative
Authors: Prajapati S , Cox B , Cadman P , Jeraj R , Mackie T
Published: July 2013

Purpose: While stationary collimators are commonly used in micro‐radiation therapy (RT), binary micro‐multileaf collimator (bmMLC) offers superior target conformity and beam modulation. As a part of an Open‐Source Medical Devices (OSMD) initiative, the purpose of this study was to design an open‐source bmMLC for micro‐RT to be integrated into combined micro‐PET/CT/RT system. Methods: The collimator motion is powered by a Dagu micro‐servo motor. The motor rotation pulls and rotates the custom‐designed, 0.5 mm thick brass collimator‐plate into open‐position. A tension spring attached to the collimator‐plate pushes the plate back to its default closed‐position when the motor rotates back. The collimator‐plates are interleaved so that consecutive plates move in opposite directions. Dosimetric tests were performed on the bmMLC using a 250 kVp X‐ray beam with reference to the AAPM Report No. 72. The bmMLC was set up right in front of a Gafchromic EBT2 film for measurement. The film was placed 100 cm from X‐ray source where the field size was 10 × 10 cm2. Primary collimators were not used in this set up. Results: The bmMLC prototype has been tested using ten interleaved collimator‐plates which create a maximum field size of 1.5 × 2cm2 at isocenter (with magnification=2). The leaf opened and closed in 0.5 seconds which is adequate for the expected low dose rate from the X‐ray source. The 80% − 20% penumbra of the bmMLC in direction of leaf movement (horizontal) was 2.6 ± 0.2 mm. The vertical penumbra was 0.4 ± 0.1 mm. The X‐ray transmission by bmMLC was measured to be < 0.1%. The between‐leaf leakage was measured to be 6.5 ± 1%, which can be minimized by further optimizing the design and measurement set up. Conclusion: An inexpensive, open‐source, bmMLC prototype has been designed for a micro‐RT system with potential for IMRT application. Funding Support: Morgridge Institute for Research, Madison, WI
WE‐E‐108‐08: Dosimetric and Biological Benchmarking of a Murine Total Marrow Irradiation Platform
Authors: Azimi R , Alaei P , Takahashi Y , Spezi E , Yagi M , Arentsen L , Sharkey L , Seelig D , Schappa J , Hui S
Published: July 2013

Purpose: Increased radiation dose for recently developed clinical total marrow irradiation (TMI) facilitates bone marrow transplants for high risk leukemia patients but its mechanism and role is completely unknown. To initiate this high impact, clinically relevant, investigation, a murine TMI‐like system has been developed and benchmarked. Detailed dosimetric characterization of the irradiator, toxicity to critical organs, and molecular imaging biomarkers were evaluated. Methods: An orthovoltage x‐ray unit was commissioned and calibrated following TG‐61 protocol. A special irradiation jig utilizing compensators has been developed to reduce the dose to eyes, brain, lungs, heart, and gastrointestinal tract. Validation of the dosimetry has been performed using TLDs, Gafchromic film, ionization chamber, and Monte Carlo calculations. Mice were irradiated for TBI and TMI. Live and longitudinal pre and post radiation (day 2) FDG microPET/CT imaging was performed. Certain organs such as lungs, liver, kidney, gut and brain were harvested post radiation for the purpose of cellular and histological studies using thymidine analog 5‐bromo‐2‐deoxyuridine (BrdU). Results: The dose is verified by performing TLD and film dosimetry on the entrance and exit sides, as well as placing dosimeters inside the subjects. Both absolute doses and planar dose distributions have been determined providing an extensive set of data representing the dose within the subjects. Dose to critical organs was reduced by a factor of two in TMI cases. As a Result metabolic and cellular activities were reduced in TMI mice at the GI and brain compared to TBI mice. Bone marrow proliferation remains the same as bone marrow dose is unchanged. Conclusion: Properly characterized x‐ray beam, accurate dosimetry, and detailed molecular and cellular studies are of importance in radiobiology investigations in support of TMI model which may lead to new therapies for humans. Reduction in side effects such as GI toxicity from radiation is promising for transplantation. This project is supported by NIH.
WE‐E‐141‐01: Accurate Calibration and Measurement of Unflattened Photon Beams
Authors: Sudhyadhom A , Kirby N , Chuang C
Published: July 2013

Purpose: To accurately quantify and account for systematic errors in the measurement of dose for unflattened photon beams due to characteristics specific to these beams. Methods: Dose measurements were taken on five photon beams (6X, 6X FFF, 10X, 10X FFF, and 15X) on a Varian TrueBeam STx using one diode and five ion chambers (PTW Farmer, CC13, CC04, and PTW 3D Pinpoint) which were selected to span a range of dimensions. Errors in the percent depth dose (PDD) due to depth dependent P_ion effects were measured. High‐resolution diode scans for profiles at 6X FFF and 10X FFF were used to create an analytical fit model. This model was used to calculate the reduction in dose (caused by volume averaging) in unflattened beams due to chamber size. Each chamber was cross‐calibrated (using the flattened beams) against the farmer chamber to determine N_D,w(Co‐60). These N_D,w(Co‐60) values were then used to determine the absolute dose in the FFF beams. Results: Changes in P_ion were most pronounced in the 10X FFF beam. This effect resulted in a 1% and 1.5% increase in the measured PDD at depths of 10cm and 20cm, respectively, for 10X FFF with the CC13 chamber. The farmer chamber had the most significant volume averaging effect with a calculated (and measured) dose reduction of 0.35% and 0.72% for 6X FFF and 10X FFF, respectively. An analytical correction factor, P_Flat, was developed to account for this effect. Conclusion: Corrections are necessary to reduce the errors produced when measuring dose in unflattened beams. Two types of errors were quantified that will each lower the measured dose to dmax. When following a TG‐51 calibration, uncorrected absolute dose measurements may Result in a worst‐case error on the order of 2%. We developed an analytical correction factor that substantially reduces this error for common farmer chambers.
WE‐E‐141‐08: Measurements of Secondary Neutron Spectrum and Dose Equivalent From a 250 MeV Passively Scattered Proton Beam Using An Extended Range Bonner Sphere Spectrometer
Authors: Howell R , Newhauser W , Burgett E
Published: July 2013

Purpose: Secondary neutrons from proton therapy have a wide energy range, from thermal to the maximum proton beam energy, which can be as high as ∼250 MeV. Most measurements reported in the literature to date have either not included spectral information or were obtained using detectors with limited response to neutrons above 10 MeV. Therefore, the primary objective of the present study was to measure a secondary neutron spectrum from proton therapy using a spectrometer that was sensitive to neutron energies over the entire energy spectrum. Methods: We performed measurements using an extended‐range Bonner sphere spectrometer (BSS) with high‐atomic‐number shells placed within polyethylene spheres to increase high‐energy response compared to a standard BSS. Measurements were performed for a 250‐MeV passively scattered proton beam with a medium snout and closed aperture. All measurements were performed in air 100 cm from isocenter. Data were unfolded using the MXD_FC33 unfolding algorithm. The a priori spectrum for neutron unfolding was determined using the Bayesian statistical estimator methodology. We used Monte Carlo N‐Particle Code to calculate a response matrix specifically for this measurement system. Results: Total measured fluence was 8.36 ncm2Gy‐1 and included a low energy tail from thermal energies to approximately 1 eV (16% fluence), an evaporation peak from 1 eV to 10 MeV (69% fluence), and a direct neutron peak from 10 MeV to 250 MeV (15% fluence). The total ambient dose equivalent was 2.03 mSvGy‐1 with neutrons in the evaporation peak contributing the highest dose equivalent and neutrons below 1 eV contributing essentially no dose. Conclusion: We report both neutron fluence and dose equivalent spectra for a 250 MeV passively scattered proton beam. These data were measured with a spectrometer that is sensitive over the entire measurable neutron energy spectrum (thermal to 250 MeV) and thus could be a valuable tool for benchmarking Monte Carlo simulations. This research was supported in part, by the National Cancer Institute award 1R01CA131463‐01A1 (W.D. Newhauser, P.I.) and a subcontract of that award (R.M. Howell, P.I).
WE‐E‐134‐01: Preliminary Application of a Multitaper Generalized Spectrum Approach to Quantify Scatterer Nonrandomness in Breast Lesions
Authors: Rosado‐Mendez I , Gerges‐Nasief H , Carlson L , Kohn S , Hall T , Zagzebski J
Published: July 2013

Purpose: The generalized spectrum (GS) has been used to quantify nonrandomness of scattering sources and to characterize breast and liver tissues. In this work, we implement a multitaper GS approach creating parametric images of GS features that describe the degree of nonrandom structure in breast lesions. Methods: This IRB‐approved, HIPAA compliant study recruited subjects who were scheduled for core biopsy of a suspicious breast mass. Subjects were scanned with a Siemens Acuson S2000 using a linear array transducer at 15MHz. Radiofrequency (RF) echo data were obtained in radial (parallel to breast lactiferous ducts) and antiradial planes. Cases (n=34) were selected based on the availability of biopsy results and a lesion size of at least 3mm in both planes. The multitaper GS was obtained by computing the correlation matrix of the Fourier transform of RF signal segments tapered by Prolate Spheroidal Sequences. Nonrandomness was quantified by parameterizing the collapsed average of the GS. A region of interest (ROI) within each lesion and each plane was defined,and the mean and standard deviation of the nonrandomness within it were computed. Results: Cases were grouped into: fibroadenoma (n=12, median diameter (MD)=7.6mm),other benign(n=11, MD=8.2mm), invasive ductal carcinoma (IDC) (n=5, MD=6.3mm), and other malignant(n=6, MD=6.9mm). The IDC nonrandomness inter‐case median of the mean and standard deviation was 64% and 59% of the values from other lesions, and the fractional difference in the standard deviation of the nonrandomness between the radial and antiradial views for the IDC cases was 59% smaller than the values for other lesions. Conclusion: Preliminary results indicate that the spatial distribution of scatterers within IDCs is more homogeneously random compared to other lesions. However, inter‐case variability was comparable to the median values. Future work will expand the population and use beam steered acquisitions to test for anisotropy in these features. This work was supported, in part, by NIH (grants R01CA111289, R21HD061896, R21HD063031, and R01HD072077) and the Consejo Nacional de Ciencia y Tecnologia of Mexico (Reg. 206414).
WE‐E‐134‐07: Ultrasound Image Based Measurements of Myocardial Fiber Structure Within the Left and Right Ventricular Walls of the Heart
Authors: Milne M , Wallace K , Singh G , Miller J , Holland M
Published: July 2013

Purpose: Previous studies from our Laboratory demonstrated that quantitative measurements of myocardial fiber structure for individual hearts at specific transverse planes can be obtained from analyses of echocardiographic images. The objective of this study was to extend these echocardiographic‐based measurements to depict the myocardial fiber structure within the ventricular walls of the entire heart. Methods: A series of 2D apical echocardiographic images were acquired from 7 excised, intact, formalin‐fixed sheep hearts using a commercially available (GE Vivid) ultrasonic imaging system. Myocardial fiber orientations were determined from analyses of the measured transmural (radial) ultrasonic backscatter profiles within the ventricular walls in conjunction with a previously determined relationship between the observed backscatter level and the angle of insonification relative to myocardial fiber orientation. These data were assembled to produce a fiber orientation image map of the entire left and right ventricular walls of each heart. In addition, 3D volumetric, apical echocardiographic images were acquired from a subset of the excised hearts for comparison. Results: Image maps depicting myocardial fiber structure throughout the ventricular walls appear consistent with the known fiber structure of the heart. Images demonstrate left‐ventricular mid‐myocardial fibers oriented within the short axis plane and gradually becoming more longitudinally oriented toward the epicardial and endocardial surfaces. Preliminary data from 3D volumetric, apical echocardiographic images suggest similar results. Conclusion: These results demonstrate that measurements of myocardial fiber structure throughout the entire heart can be successfully derived from analyses of echocardiographic images. Further development of this method may provide a method for mapping the myocardial fiber orientation in individual patients over the heart cycle and provide a means for assessing potentially altered fiber structure associated with congenital and acquired heart diseases. [NIH R01 HL040302]; Funded, in part, by NIH R01 HL040302; Dr. Kirk D. Wallace is an employee of GE Global Research
WE‐F‐105‐04: Evaluation of the Eclipse Electron Monte Carlo Algorithm Based On Patient Specific Dosimetry Measurement
Authors: Wang X , Qi S , Agazaryan N , DeMarco J
Published: July 2013

Purpose: To evaluate the Eclipse electron Monte Carlo (eMC) dose calculation algorithm using patient specific dosimetry measurements, and to investigate possible patient specific QA guideline. Methods: Electron treatments were planned for 58 patients on Eclipse (Version 10.0) using the eMC algorithm for two Varian TrueBeam linear accelerators (Linac‐A and Linac‐B). The dose calculations were based on patient anatomy (patient plan), and a solid‐water phantom (QA plan). The calculation results were compared with physics measurement using a solid‐water phantom and a pinpoint ion chamber. Results: The monitor units as calculated on the QA plans were (2.1±2.0)% higher than the measurement on both accelerators, excluding outliers with small fields (3 cm or less) and extended SSD (above 105 cm). The difference of QA plan and measurement was consistent with the calculation uncertainty of the eMC algorithm (2%). The monitor units as calculated on the patient plans were (8.0±5.0)% (Linac‐A) and (5.5±5.0)% (Linac‐B) higher than the corresponding measurement. However, we observed that the eMC algorithm under‐estimated the dose for one patient treated on nose, by as much as 28.5% for the patient plan and 12.9% for the QA plan. For this patient, a calculation based on an output look‐up table was within 2% of the measurement. Conclusion: The measurements indicate that the eMC algorithm predicts dose reasonably well for QA plans using the same homogeneous phantom. However, for CT‐based patient plans, the eMC algorithm generates a larger number of monitor units versus the QA plan. It may reflect the impact of patient surface curvature and tissue inhomogeneity to the eMC algorithm and further investigation is needed. Caution should be taken for eMC patient plan with small field size and extended SSD. A lookup table of output factors based on measurement can be generated as a quick reference for electron dose calculation.
WE‐F‐WAB‐01: Safety Improvement Through Incident Learning
Authors: Ford E , Ezzell G , Dicker A , Piotrowski T
Published: July 2013

Incident learning is a key tool for improving the quality and safety of procedures. Its use has been linked to better patient‐safety outcomes. This session is designed to provide practical advice to the clinical medical physicist on how to run a successful incident learning system in radiation oncology. The session will draw on engaging examples from clinical practice and will focus on the relevance to smaller clinics. The session will include a presentation from a leading physician on clinical perspectives on quality and safety improvement. The session will also introduce the new national incident reporting system being developed by AAPM and ASTRO. This program employs the Patient Safety Organization (PSO) structure. The concept and structure of the PSO system will be discussed by an expert in the field.

Learning Objectives:

1. Appreciate the value of incident learning for improving patient safety

2. Understand the difference between incident learning at the institutional level vs. the national level, and recognize the issues unique to each

3. Learn about the new national radiation oncology incident learning system developed by AAPM and ASTRO
WE‐G‐500‐01: Identification of High Quality Machine‐Robust CT Image Features
Authors: Hunter L , Stingo F , Kry S , Martel M , Choi H , Court L
Published: July 2013

Purpose: To identify non‐small cell lung cancer (NSCLC) CT image feature sets that are reproducible, non‐redundant, and informative across multiple CT machines. Such feature sets will be ideal for modeling and will yield increased generality and robustness to machine variation. Methods: Non‐contrast‐enhanced, test‐retest CT image pairs were obtained from 56 NSCLC patients imaged on three CT machines from two institutions. 328 quantitative image features were extracted from each tumor based on its geometry, intensity histogram, absolute gradient image, co‐occurrence matrix, and run‐length matrix. Feature reproducibility was quantified using the test‐retest data and the concordance correlation coefficient (CCC). The Dice similarity coefficient (DSC) and the Jaccard index (JI) were used to quantify reproducible feature set agreement between machines. Multi‐machine reproducible feature sets were created by taking the intersection of individual machine reproducible feature sets. Redundant features were removed through hierarchical clustering based on the average correlation between features across multiple machines. Results: Across machines, the average percentage of features that were reproducible (CCC>0.90) was highest for 4D‐CT average images (92.5%), intermediate for 4D‐CT end‐exhale images (73.0%), and lowest for 3D‐CT breath‐hold images (61.0%). For 4D‐CT, end‐exhale image features were relatively machine‐sensitive(DSC = 0.71, JI = 0.55), and average image features were relatively machine‐insensitive (DSC = 0.90, JI = 0.87). Multi‐machine reproducible and non‐redundant feature sets were identified for 4D‐CT average images, 4D‐CT end‐exhale images, and 3D‐CT breath‐hold images. Hierarchical clustering confirmed feature set informativeness: 55 out of 56 test‐retest images were correctly paired using only their reproducible, non‐redundant feature set values. Conclusion: Image feature reproducibility was machine‐sensitive. High quality machine‐robust feature sets were identified for each image type. Compared to end‐exhale 4D‐CT and breath‐hold 3D‐CT, average 4D‐CT derived image features showed superior multi‐machine reproducibility and are the best candidates for clinical correlation.
WE‐G‐500‐03: In‐Beam PET Imaging with Depth‐Of‐Interaction Measurement for Accurate Proton Beam‐Range Verification
Authors: Shao Y , Sun X , Lou K , Zhu X , Mirkovic D , Poenisch F , Grosshans D
Published: July 2013

Purpose: To study the feasibility of using an in‐beam PET with depth‐of‐interaction (DOI) measurement to improve beam‐range verification for proton therapy. Methods: A compact prototype PET with dual rotating DOI‐measurable detector panels was developed based on using solid‐state photomultiplier (SSPM) arrays to read LYSO scintillators with parallel readout ASIC electronics. The system had a 44mm diameter trans‐axial and 30mm‐axial field of view (FOV). A 36mm diameter PMMA phantom was placed inside FOV. Both PET and phantom axes were aligned with collimated 200 MeV beams. The Bragg peak was located within the axial FOV by adjusting phantom position. A total of 9 beams irradiated the phantom with a 20–40 minutes beam separation; each beam delivered ∼50 spills (0.5 sec spill and 1.5 sec inter‐spill time, 800 MU); data from each beam were acquired with detectors at a certain angle; 9 datasets for 9 beams with detectors at 9 different angles over 180o were acquired; each dataset collected both in‐beam and 5 min after‐beam data. Beam‐range was measured from the PET image reconstructed from all 9 datasets, and compared to the results from simulated images. Additionally, a Na‐22 disk‐source was also acquired after each beam to measure the impact of neutrons on system performance. Results: PET performed well except energy photo‐peak positions were reduced slightly after each beam, presumably secondary to neutron exposure of the SSPM. This minor effect was corrected with a shifting 350–650 keV energy window for each dataset. The difference between measured and simulated beam‐ranges was within 1.0 mm, and this can be achieved with in‐beam data alone. DOI‐measurement provided uniform resolutions and high sensitivity to improve the accuracy of range verification. Conclusion: A SSPM‐based DOI‐measureable PET capable of in‐beam imaging may offer significant improvements in the accuracy of proton beam‐range verification. This project is supported by award RP120326 from the Cancer Prevention & Research Institute of Texas.
WE‐G‐500‐04: A Novel Technique for In‐Vivo and Real‐Time Range Verification Based On the Characteristic Prompt Gamma Time‐Structure of Passively Modulated Proton Beams
Authors: Testa M , Min C , Schuemann J , Verburg J , Lu H , Paganetti H
Published: July 2013

Purpose: We propose a novel technique for in‐vivo and real‐time range verification based on the unique temporal dependence of prompt‐gamma produced by passively modulated proton beams Methods: For passively modulated proton beams, the dose delivered to a medium is periodic with the period of the Range Modulator Wheel (RMW) rotation. It has been confirmed experimentally that such periodic dose‐rate functions, measured inside a medium, have a unique correlation with their point of measurement along a Spread‐Out Bragg Peak (SOBP). Therefore, also the time‐structure of prompt‐gammas, generated by proton induced nuclear interactions in the target and detected outside the medium, is expected to be periodic and correlated with their source‐location along the SOBP. To verify such correlation, we employed the Monte Carlo method using TOol for PArticle Simulation (TOPAS). The simulated detection system is constituted by a single‐slit collimated detector placed at 90° from the beam direction. Discrimination of prompt‐γ from background radiation is done trough energy and time‐of‐flight (TOF) selectionResults: We verified that the time‐pattern of prompt‐gamma rate functions (i.e. gamma‐counts vs. RMW rotation‐time) is periodic and correlated with the detection depth along the SOBP. Utilizing this feature it is feasible to predict the range of a SOBP within few millimeters with a single point of prompt‐gamma measurement. The influence of the prescribed dose and collimation setup over the detection statistics is discussed in order to assess the potential clinical application of the technique. TOF selection and background subtraction can significantly increase the signal to noise ratio Conclusion: Our results show that the range of a SOBP can be determined, with a single point of measurement, by analyzing the time‐pattern of prompt‐gamma detected with a single‐slit detection system. This novel technique potentially represents a powerful tool for real‐time range verification for passively modulated proton therapy systems
WE‐G‐500‐06: Offline PET/CT Imaging of Scanned Proton and Carbon Ion Beams: Initial Clinical Experience for Different Tumour Sites
Authors: Parodi K , Bauer J , Kurz C , Unholtz D , Sommerer F , Frey K , Haberer T , Herfarth K , Welzel T , Combs S , Debus J
Published: July 2013

Purpose: To evaluate offline Positron Emission Tomography (PET) /Computed Tomography (CT) for in‐vivo verification of scanned proton and carbon ion irradiation of tumours in different anatomical locations. Methods: At our combined ion therapy facility, in‐vivo PET/CT‐based verification of beam delivery is being performed using a commercial scanner (Siemens Biograph mCT) installed just outside of the treatment rooms. More than 70 patients with tumours in different anatomical locations received at least one 30 min long post‐irradiation scan. PET measurements are compared to expectations using in‐house developed software tools based, among others, on the general purpose FLUKA Monte Carlo code. Results: Activation within the irradiated region could be visualised in all treatment sites, regardless of the ion species and applied dose level. For carbon ions, the most promising results could be obtained for irradiation of compact tumours in the head and neck and hypofractionated treatment of liver lesions with restricted motion. Here, range verification benefits from a marked delineation of the distal activated area, due to the dominant contribution of 11C projectile fragments. For abdominopelvic sites (prostate, sacral chordoma) the typical use of opposed fields, the extremely low counting statistics and the insufficient characterization of biological tissue parameters represent major challenges for range monitoring. Nevertheless, useful feedback on the correctness of the treatment delivery could be inferred in some convenient cases. For protons, the data confirmed the expected higher counting statistics and increased sensitivity to the knowledge of the tissue composition. The latter benefited from an improved tissue classification based on multimodal information in the brain region, while known limitations remain in the pelvic area (prostate). Conclusion: Offline PET/CT imaging of scanned ion treatment is feasible, but its clinical value strongly depends on the anatomical location and treatment strategy (ion species, dose level and multi‐field configuration). Parts of this work have been funded via the FP7 EU Project PARTNER (grant agreement 215840‐2), the BMBF Project DOT‐MOBI (grant agreement 01|B08002F), and the FP7 EU Project ENVISION (grant agreement 241851).
WE‐G‐WAB‐01: Real‐Time Catheter Tracking and Visualization in MR‐Guided Brachytherapy
Authors: Wang W , Gao Y , Mehrtash A , Seethmaraju R , Kapur T , Vishwanathan A , Schmidt E , Cormack R
Published: July 2013

Purpose: The challenge of catheter‐tip visualization for interstitial needle placement in gynecologic brachytherapy remains unmet. We evaluate an approach to actively track tip locations and visualize catheter trajectories and surrounding soft‐tissue in real‐time during an intervention. The methods include development of clinical needles with magnetic resonance (MR) tracked microcoils, an MR tracking and rapid imaging sequence and integration with a graphical workstation for visualization. Methods: An active tracking device was built based on a commercial catheter which consists of a hollow tube and a central needle with microcoils at the distal end. An MR tracking sequence was developed (isotropic resolution: 0.6 mm, frame rate: 40 updates/sec). It runs continuously during navigation or interleaves with real‐time imaging (3 frames/sec), where image position/orientation are automatically set to provide visualization of anatomy around the catheter. The catheter‐tip position/orientation was passed to the workstation for visualization. Needle shapes were superimposed on pre‐acquired high‐resolution images or on the intra‐procedural images. Results: MR‐guided catheter placement procedures were conducted in a gel phantom and an animal model. High‐resolution 3D MR scans were acquired and loaded into the workstation for navigation. During insertion, the catheter tips were visualized advancing on a 3D anatomic model and on assigned planes. Real‐time imaging with slice continuously updating at the instantaneous tip positions was also performed. Both methods served well to guide catheter placement. After insertion, complete catheter trajectories were rendered by recording tip positions as needles were pulled out and overlaid on the images, to support treatment planning. Conclusion: We demonstrated the feasibility of active catheter tracking and visualization in MR‐guided brachytherapy. This will facilitate accurate and time‐efficient catheter insertion by providing on‐line identification of catheter position, and visualization of anatomy ahead of the catheter tip. This enables identifying preferential paths to target locations, and reduces the risk to critical organs. Funding sources: NIH P41 EB015898; AHA 10SDG261039
WE‐G‐WAB‐08: Fiducial Properties of a 3‐Dimensional Bioabsorbable Tissue Marker in Treatment Planning for Breast Cancer
Authors: Simpson J , Benjamin B , Jones S , Ross J
Published: July 2013

Purpose: Improvements in surgical techniques have increased the adoption of breast conservation. However, clearly defining the target volume as well as improving target positioning for the breast remains challenging, thus requiring large treatment margins to insure proper coverage of the target. To better define margin requirements, we evaluated the utility of a novel 3‐D implantable, bioabsorbable tissue marker using multiple types of external beam treatment planning for breast cancer. Methods: The BioZorb, TM tissue marker (a 3‐dimensional bioabsorbable carrier with embedded titanium markers) was implanted into the lumpectomy cavities of 28 breast cancer patients at the time of surgery. Multiple treatment plans (WBI + boost, IMRT, coplanar/non‐coplanar VMAT, 3D‐CRT) were prepared and compared. Results: In all cases, the tissue marker was easily seen on all forms of clinical imaging including mammography, ultrasound, CT, 4D‐CT, cone beam CT and MRI. Utilizing standard CT simulation software, the marker provided a clear region for target delineation/construction as well as positioning using EPID and CBCT. 3‐D target excursions, due to respiration, were easily quantified on 4D‐CT: superior‐inferior, <4 mm; anterior‐posterior, <3 mm; medial‐lateral <1 mm (mean values). Fusion of beams‐eye DRRs with EPID images allowed accurate positioning (uncertainty <1.5mm) for APBI (VMAT, 3D‐CRT) and boost deliveries. When compared to conventional methods for determining treatment volumes, use of the marker significantly reduced PTVs, and in some cases made it possible to utilize accelerated protocols for treatment. On‐board imaging (EPID, and MV/KV CBCT) provided reproducible patient positioning for both partial breast and boost techniques. Conclusion: The utility of this 3‐D, bioabsorbable tissue marker was confirmed when placed into the lumpectomy site during surgery. The marker was consistently visualized, improved the objectivity of target definition for treatment planning and provided unambiguous fiducials for use with IGRT techniques in the treatment of breast cancer.
WE‐G‐WAB‐09: Development of MRI Fiduciary Markers for Interstitial Brachytherapy
Authors: Hu Y , Esthappan J , Du D , Feng Y , Garcia‐Ramirez J , Mutic S , Grigsby P
Published: July 2013

Purpose: To develop MRI (magnetic resonance imaging) visible fiduciary markers to identify the plastic needle locations inside the cylindrical plastic applicator used in interstitial brachytherapy to treat cancers at the virginal apex. Methods: MRI visible fiduciary markers were created using polyimide tubing (outer diameter=1.23mm, inner diameter=1.13mm). The tube was filled with jelly and sealed using bone wax at both ends. MRI fiducials were inserted into the plastic flexi needles that were placed in the interstitial brachytherapy applicator needle holes. The applicator was then placed in a container filled with water and underwent MRI scans. T2‐weighted (T2W) and proton density weighted (PDW) MR images were acquired in the sagittal orientation. The echo time (TE) and repetition time (TR) were 100ms and 5,849ms for T2W images, and 5.5ms and 4,284ms for PDW images. Both T2W and PDW had an in‐plane spatial resolution of 1mm and a slice thickness of 2.5mm. The number of average was 4 for both scans. The total scan time was 4 minutes and 38 seconds for T2W, and 3 minutes and 42 seconds for PDW. Results: Fiduciary markers in all plastic flexi needles were clearly visible in both T2W and PDW images. For sagittal images, the diameter of the fiducial was smaller than the slice thickness. Due to the partial volume effect, signal from fiduciary markers was smaller than that from the water surrounding the applicator. Therefore, the windowing level was adjusted accordingly to visualize the fiduciary markers. Conclusion: We demonstrated the feasibility of creating MRI visible fiduciary markers that could be fit into plastic needles. These markers can be used to determine applicator needle locations for interstitial brachytherapy, making treatment planning based on MRI images possible.
WE‐G‐141‐01: The Imaging and Radiation Oncology Core (IROC) Group: A Proposed New Clinical Trial Quality Assurance Organization
Authors: Followill D , Knopp M , Galvin J , FitzGerald T , Michalski J , Rosen M , Laurie F , O' Meara E , King S
Published: July 2013

Purpose: The NCI is implementing the new National Clinical Trial Network (NCTN) Program in 2014 reducing the number of existing study groups from ten to five. The NCTN Program also requires a new combined Imaging and Radiation Oncology Core (IROC) service to provide a uniform QA program. Methods: The six existing clinical trial QA centers, Radiological Physics Center, Quality Assurance Review Center, RTOG QA Center, Image Guided Therapy Center, ACRIN Core Lab and the CALGB Imaging Core Lab have combined to form IROC. The interdependencies between diagnostic imaging and radiation therapy (RT) will be synergized in IROC eliminating duplication of services within the network and optimizing efficient and effective workflows. A major strength of this new organization will be the development of consistent standard operating procedures for all imaging and RT aspects of the NCTN as well as to facilitate a seamless flow of imaging and RT datasets across the network. Results: IROC, administered though the American College of Radiology will provide the scientific and technical expertise in both diagnostic imaging and RT to the entire NCTN Program capitalizing on existing infrastructure and expertise at QA centers currently providing services to the NCI Cooperative Groups. IROC's organizational structure will allow the delivery of a broad array of imaging and RT QA services including Site Qualification; Trial Design Support; Credentialing; Data Management and Case Review. IROC will work closely with the leadership of each Network Group and NCI to assure them that imaging and RT data used by the Groups for protocol analysis are accurate. Conclusion: The proposed IROC Group has hundreds of collective years of experience conducting clinical trial QA and fully understands the QA needs/dataflow requirements of clinical trials to maintain the highest quality clinical trial data that will not obscure the outcomes of clinical trials. This work was supported by PHS grants CA10953, CA21661, CA029511 and CA081647 awarded by NCI, DHHS.
WE‐G‐141‐03: Diagnostic Quality CT with Soft Tissue Alignment for IGRT Can Safely Reduce Planning Margins For Prostate Cancer: Implication For SBRT
Authors: Li W , Vassil A , Mossolly L Muhieddine , Shang Q , Xia P
Published: July 2013

Purpose: To evaluate whether the use of daily diagnostic quality CT for image‐guided radiation therapy (IGRT) can safely reduce the planning margin using soft tissue alignment for prostate cancer treatment, which can be applied to SBRT. Methods: Nine patients with prostate cancer, who underwent IMRT and daily IGRT using the CT‐on‐rails system, were selected for this study. For all patients, a planning margin of 8mm/5mm posterior was used in the clinically approved plans. For this study, three additional plans were generated with planning margins of 6mm/4mm posterior, 4mm/2mm posterior, and 2mm uniform, resulting a total of four plans for each patient. On the first seven and last seven daily CTs, the prostate, bladder, and rectum were delineated by the same radiation oncologist. Subsequently, for each plan, the corresponding dose distribution on these daily CTs was calculated. The endpoint dose of the prostate was defined as the percentage of the volume receiving prescription dose of 78Gy (V78). V65 and V70 were used for the bladder and rectum, respectively. Results: For 8.7% of the first seven and 13.5% of the last seven fractions (n=126), the daily prostate volumes were 10% higher than those at simulation. Correspondingly, to achieve V78> 95%, the minimum margins of 4mm/2mm posterior and 6mm/4mm posterior were required for the first seven and last seven fractions, respectively. With margin reduced from 8mm/5mm posterior to 6mm/4mm posterior and 4mm/2mm posterior, the average bladder V65 decreased from 17.0±10.6% to 15.2±10.9% (p<0.01) and 9.9±7.4% (p<0.01), respectively. The average rectum V70 decreased from 15.2±8.9% to 13.6±7.9% (p<0.01) and 10.5±6.5% (p<0.01), respectively. Conclusion: A planning margin of 4mm/2mm posterior is sufficient for prostate SBRT with daily IGRT using soft tissue alignment with diagnostic quality CT. Drastic change in daily prostate volumes may increase the planning margin to 6mm/4mm posterior, requiring daily offline dose monitoring. Siemens Medical Solution
TH‐A‐103‐07: A Pan‐Sharpening Approach to Multiresolution Image Fusion for Hybrid Counting/integrating CT
Authors: Rigie D , Riviere P La
Published: July 2013

Purpose: We investigate the application of a pan‐sharpening algorithm to a hybrid CT dataset containing low‐resolution, photon‐counting data and high‐resolution, integrating data to generate images that inherit both the resolution properties of the integrating detector and the spectral information of the photon‐counting detector.Methods and Materials: Our 2D simulation studies include a realistic x‐ray tube spectrum, a photon‐counting detector with 5 energy bins, and an energy‐integrating detector. We used several material‐specific, ellipse‐based phantoms to generate datasets with both detectors, reconstructing panchromatic 512x512 images from the integrating data and multispectral 128×128×5 images from the photon‐counting data. We also separately reconstructed 512×512×5 images from the photon‐counting data, which we regarded as the ground truth. We used a pan‐sharpening algorithm from the remote‐sensing field, which contains 5 tunable parameters that control the balance between resolution recovery and spectral distortion. The optimization‐based algorithm seeks a high‐resolution image that has the spatial detail of the panchromatic image and the spectral characteristics of the multispectral images. The parameters were selected to minimize the mean‐squared error between the pan‐sharpened images and the ground truth. Results: The pan‐sharpened images appear to have recovered nearly all of the detail of the panchromatic image without severe spectral distortion. There is some visible distortion near edges of high‐contrast objects, such as bone. Using pan‐sharpened and ground‐truth images from two of the energy bins of the photon counting detector, we looked at the angular separation of calcium and iodine which agreed to within 0.2 degrees (6%). Conclusions: Our preliminary studies suggest a possible solution to the count‐rate limitations of photon‐counting detectors. Using a high‐resolution image, acquired by a conventional detector as a prior, one may be able to acquire low‐resolution photon‐counting data and then recover spectral images that possess both good spatial resolution and the desired spectral information. This work was supported by Toshiba Medical Systems.