bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐A‐WAB‐07: Evaluation of Local Therapy Response for Locally Advanced Pancreatic Cancer (LAPC) Using PET/CT
Authors: Yue Y , Tuli R , Yang W , Antonuk A , Sandler H , Fraass B
Published: July 2013

Purpose: To quantify local treatment response for pancreatic radiotherapy using PET/CT, and investigate prediction of residual high‐uptake areas using Pre‐radiotherapy scans. Methods: 18FDG‐PET/CT scans were obtained from ten LAPC patients, pre‐RT, 8–12 weeks following treatment (Post‐RT), and at 2 to 4month follow‐up intervals. Four patients received 3 follow‐up scans; others had at least one follow‐up scan. All PET/CT images were registered to the planning CT using object‐specific deformable registration which preserves target volume rigidity while deforming surrounding tissue. Therapy response evaluation is performed by comparing changes in SUVmax and volume pre‐RT and post‐RT. Local response is further evaluated by dividing the volume of interest into 4.8×4.8×4.8mm^3 subvolumes. Each subvolume is characterized with mean uptakes (SUVpre, SUVpost), SUVdiff=SUVpre‐SUVpost, and treatment dose. Local response is evaluated using 3 volumes (VOIs): (1) ITV, (2) volume between PTV and ITV, (3) 3mm expansion around the PTV. For each VOI, the quantified response index is calculated [QR = (#subvolumes with SUVdiff>0)/(#subvolumes)]. A large QR suggests better local control. Subvolumes with SUVdiff<0 are investigated by examining SUVpre and treatment dose. Local response results are correlated to global SUVmax changes, disease volume changes, and clinical radiologist readings. Results: 10 follow‐up scans of 5 patients show strong positive response to treatment, with QRs for all VOIs >0.75 [ITV: 0.97+/−0.07, PTV‐ITV: 0.84+/−0.18, 3mm PTV expansion: 0.76+/−0.29]. Global disease volumes (identified by high‐uptake values) are reduced >70%, global SUVmaxs are reduced more than 50%. Three partial response patients have QR=0.50–0.75 (0.62+/−0.11 for ITV volumes). Two cases (failures) have QR<0.4, with mean 0.26+/−0.06. Conclusion: Quantification of local metabolic response provides a feasible approach for evaluating efficacy of local control of pancreatic cancer treatment. The results can be used to identify persistent and local failure of disease, toward implementing response‐driven adaptive radiotherapy.
TU‐A‐WAB‐08: Strong Evidence for Physiologic Correlation of 4D‐CT Ventilation Imaging with Respiratory‐Correlated Gallium 68 PET/CT in Humans
Authors: Kipritidis J , Siva S , Callahan J , Hofman M , Keall P
Published: July 2013

Purpose: Four‐dimensional CT (4D‐CT) ventilation imaging has been developed as a complement to nuclear medicine (NM) based methods, but has not yet been validated against a quantitative NM based standard. We are performing the first such study with positron emission tomography using 68 Ga‐labelled nanoparticles (Galli‐PET). Methods: Respiratory correlated Galli‐PET ventilation images are obtained for 10 lung cancer patients using a combined PET/CT scanner with Real‐time Position Management system. We begin by calculating the exhale‐to‐inhale 4D‐CT ventilation image (V) by deformably registering the 4D‐CT maximal inhale phase to the maximal exhale phase, and performing quantitative analysis of the deformation vector fields (DVFs). We then simulate a motion‐blurred or time‐integrated 4D‐CT ventilation image. This facilitates comparison with time‐integrated Galli‐PET, which exhibits better signal than for gated images. We study the correlation of V with gated Galli‐PET at exhale, and between time‐integrated 4D‐CT and Galli‐PET ventilation using four distinct ventilation metrics. Ventilation images were compared using the voxel‐wise spearman correlation (r) within the segmented lung volumes, and dice similarity (d) for the lowest functioning (25th percentile) regions of interest. Results: Averaged over the ten patients and four ventilation metrics in this study, the comparison of V with gated Galli‐PET yielded r = 0.38 and d = 0.40. Time‐integrated images exhibited better agreement for all ventilation metrics, yielding r = 0.53 and d = 0.60 on average. Conclusion: Our results demonstrate moderate correlation between 4D‐CT and NM‐based ventilation images. The comparison between time‐integrated images gives better agreement than for gated images as a Result of the improved Galli‐PET signal. Further validation of 4D‐CT ventilation imaging could facilitate improved access to functional lung imaging and functional lung avoidance in radiotherapy. This work is supported by an NHMRC Australia Fellowship, NHMRC project grant 1034060 and US NCI P01CA116602.
TU‐A‐WAB‐09: Functional Tumor Shape Characterization On Baseline 18F‐FDG PET Images Predicts Response to Concomitant Radio‐Chemotherapy in Esophageal Cancer
Authors: Tixier F , Hatt M , Le Rest C Cheze , Visvikis D
Published: July 2013

Purpose: The development of robust 18F‐FDG PET tumor volume delineation methodologies has led to the investigation of several image‐derived parameters for tumor characterization, including metabolic tumor volume (MTV), total lesion glycolysis (TLG), and tracer heterogeneity quantification. Their potential clinical value regarding patient outcome (response to therapy and/or survival) prediction has been recently investigated in several cancer models. They have often demonstrated superior value over standard measurements such as SUVmax or SUVpeak. However, the value of shape characterization (SC) parameters has not been extensively investigated as yet. We therefore studied the predictive value of 7 parameters derived from SC of PET image functional tumor activity distributions within the context of esophageal cancer treated by concomitant radio‐chemotherapy. Methods: Baseline 18F‐FDG PET scans of 50 patients with locally advanced esophageal cancer were retrospectively analyzed. Primary tumors were delineated with the fuzzy locally adaptive bayesian algorithm and 7 features describing the shape of the delineated volumes were extracted. Response to therapy (complete (CR), partial (PR) and non‐response (NR)) was evaluated according to RECIST criteria 1 month after the end of treatment. The correlation between SC parameters was assessed using Pearson coefficients and their corresponding predictive value was evaluated with receiver operating characteristic (ROC) curves analysis. Results: 3D surface and MTV were highly correlated (r=0.97). All other SC parameters were moderately correlated (r<0.75). Maximum diameter within the MTV, as well as the smoothness of its surface allowed the identification of NR (vs. PR+CR) or CR (vs. PR+NR) with areas under the ROC curves of 0.78 and 0.80 respectively. Conclusion: Baseline PET image derived parameters characterizing the shape of the functional tumor uptake may help in predicting response to radio‐chemotherapy in locally advanced esophageal cancer. Future studies will investigate their potential combination with other parameters previously demonstrated as predictive of response, such as intra‐tumor heterogeneity quantification.
TU‐A‐WAB‐10: Estimating Repeatability Coefficients of Diffusion Indices for Assessing Trueness of the Radiation‐Induced Changes in Individual Patients
Authors: Nazem‐Zadeh M , Chapman C , Lawrence T , Tsien C , Cao Y
Published: July 2013

Purpose: To demonstrate the application of repeatability coefficients to assess whether longitudinal changes in diffusion indices of white matter structures are true changes for individual patients undergoing radiation therapy (RT). Methods: Using test‐retest diffusion tensor datasets from National Biomedical Imaging Archive database, as a measure of uncertainty, the repeatability coefficients (RC) of diffusion indices within the segmented cingulum, corpus callosum, and fornix were estimated. Twenty‐two patients with low‐grade or benign tumor treated by partial brain radiation therapy participated in an IRB‐approved MRI protocol. The diffusion tensor images were acquired pre‐RT, 3 weeks during RT, at the end of RT, and 1, 6, and 18 months after RT. The upper and lower limits of 95% confidence interval (CI) of the estimated RC from the test and retest data were used to evaluate whether the longitudinal percentage changes in diffusion indices of the segmented structures in the individual patients were beyond the uncertainty and thus could be considered as true radiation‐induced changes. Results: Diffusion indices of the segmented white matter structures had different uncertainties. The estimated RCs ranged from 5.3% to 9.6% for fractional anisotropy (FA), from 2.2% to 6.8% for mean diffusivity (MD), from 2.4% to 5.5% for axial diffusivity (AD), and from 2.9% to 9.7% for radial diffusivity (RD). Overall, 23% of the patients had FA changes, 44% had MD changes, 50% had AD changes, and 50% had RD changes beyond the uncertainty ranges. In the fornix, 85.7% and 100% of the patients showed changes beyond the uncertainty range at 6 and 18 months after RT, respectively, demonstrating that radiation has a pronounced late effect on the fornix compared to other segmented structures. Conclusion: Assessments of repeatability and confidence interval of diffusion tensor measurements in white matter structures allow us to determine the true longitudinal change in individual patients. Supported in part by RO1 NS064973.
TU‐A‐WAB‐11: Tumor Shrinkage Prediction Using CT Image Features
Authors: Hunter L , Chen Y , Zhang L , Matney J , Stingo F , Kry S , Martel M , Choi H , Liao Z , Gomez D , Court L
Published: July 2013

Purpose: To develop a quantitative image feature model to predict non‐small cell lung cancer (NSCLC) volume shrinkage from standard of care pre‐treatment CT images. Methods: 64 stage II‐IIIB NSCLC patients with similar treatments were all imaged using the same CT scanner and protocol. For each patient, the planning gross tumour volume (GTV) was deformed onto the week six treatment image, and tumour shrinkage was quantified as the deformed GTV volume divided by the planning GTV volume. Geometric, intensity histogram, absolute gradient image, co‐occurrence matrix, and run‐length matrix 3D quantitative image features were extracted multiple times from each planning GTV using a variety of feature extraction parameters. Prediction models were generated using principal component regression with simulated annealing subset selection; performance was quantified using the mean squared error (MSE) between the predicted and observed tumour shrinkages. Cross validation and permutation tests were used to validate the results. Results: The optimal model gave a strong correlation between the observed and predicted shrinkages with r=0.81 and MSE =0.0086. Compared to predictions based on the mean population shrinkage (i.e. predicted shrinkage = mean shrinkage; MSE =0.0251) this resulted a 2.92 fold reduction in MSE. That is, the tumor shrinkage uncertainty was reduced by a factor of approximately three. Conclusion: A quantitative image feature model can use existing CT images to successfully predict tumour shrinkage and provide additional information for clinical decisions regarding patient risk stratification, treatment, and prognosis.
TU‐A‐134‐01: Imaging Informatics 1: Informatics for the Clinical Imaging Physicist: Buying and Testing Equipment for Interoperability
Authors: Walz‐Flannigan A , Weiser J
Published: July 2013

1. Buying Imaging Equipment for Interoperability and Compliance: Beyond DICOM

2. Informatics for the Acceptance Testing of Imaging Equipment

For patient service, safety and regulatory compliance, the quality control of image and image information needs to extend beyond the scanner console to encompass the entire imaging chain. Imaging physicists are often the ultimate quality control professionals and technology experts that are responsible for equipment selection and testing. To aid in these tasks, this session is designed to provide the clinical physicist with practical awareness and tools for equipment selection and acceptance testing that promotes interoperability throughout the imaging chain, protecting image and information quality for smooth clinical operation and patient safety.

Whether the physicist is ultimately responsible for delivering a quality and compliant system or is a part of the process, they need to understand data flow and interoperability in the imaging chain. This involves a basic understanding of the system and stakeholders that determine and interact with the imaging chain. Once an imaging chain (or web in some cases) is understood, physicists can benefit from understanding the standards and interoperability profiles that can help in assessing equipment interoperability throughout that chain.

This session will highlight areas where expectations and current reality for interoperability in an imaging practice may not align. It will cover specific examples of common issues that still plague interoperability two decades after the introduction of DICOM 3.0. We' ll discuss relevant questions to ask of vendors when purchasing equipment from a compliance and interoperability standpoint. The second part of the session will cover strategies and suggestions for ensuring a fully‐functioning imaging system: what aspects related to interoperability might cause problems and what should be assessed with acceptance testing in order to ensure clinical functionality and patient safety?

Learning Objectives:

1. Understand the importance of assessing and testing interoperability for the entire imaging chain when considering or deploying new imaging equipment.

2. Be able to assess the relevant pieces that encompass their clinical imaging chain and the stakeholders involved in configuring, maintaining and using the system.

3. Be aware of common issues with clinical interoperability of imaging equipment

4. Know how to develop, find and use tools for assessing the potential for interoperability prior to purchase and testing after installation.
TU‐A‐116‐02: A Novel Algorithm for Highly Efficient Polyenergetic DRR Calculation
Authors: Folkerts M , Jia X , Jiang S
Published: July 2013

Purpose: It is desirable to compute polyenergetic digitally reconstructed radiographs (DRRs) in many radiotherapy tasks, especially when investigating beam hardening effects in CT/CBCT reconstruction and studying 2D‐3D registration. The standard polyenergetic DRR calculation performs ray‐tracing for each energy bin. The computation time scales with the number of bins in the spectrum and the ray tracing operation for each bin dominates the computation time. This work develops a novel algorithm to enhance the efficiency of polyenergetic DRR computation. Methods: The inputs of our algorithm are 3D density and material arrays along with the energy spectrum. We compute a modified projection by ray tracing through the density data and saving the results from each material into separate 2D arrays. For each energy bin, the product of each density projection and its corresponding energy dependent mass attenuation coefficient is summed over all materials. The exponential of the results from each energy bin are weighted and summed to create a final polyenergetic DRR. Our new algorithm is mathematically equivalent to the standard approach. We use our algorithm to simulate a 512×512 polyenergetic DRR of a 512×512×182 phantom comprised of 3 materials (air, tissue, bone). A realistic 120kVp energy spectrum with 114 bins was used. The computation times and results of the new algorithm are compared to those of the standard algorithm. Results: We successfully improved the efficiency of the polyenergetic DRR calculation by a factor of 63.85 in our testing case. The average error between the results from our algorithm and that from the standard algorithm is on the order of machine precision. Conclusion: We have substantially improved the efficiency of the standard polyenergetic DRR algorithm without sacrificing accuracy. This new approach enables fast and accurate DRR calculations that will facilitate many tasks in radiotherapy.
TU‐A‐116‐06: Pre and Post‐Treatment Temporal Parametric Analysis of Neurovascular Disease Using Gamma Variate Fitting of Time Density Curves From DSA Sequences
Authors: Ionita C , Bednarek D , Dumont T , Siddiqui A , Levy E , Snyder K , Rudin S
Published: July 2013

Purpose: To calculate temporal parameters of contrast flow, using digital subtraction angiography (DSA), and provide parametric imaging (PI) of pre‐and post‐treated neurovascular lesions to aid neuro‐interventionalists decision. Methods: We developed a program to evaluate changes in contrast flow before and after treatment of neurovascular lesions. The program records each pixel value in a DSA sequence and fits the data with a gamma‐variate function. Using the function we calculate parameters such as mean‐transit‐time (MTT), bolus‐arrival‐time (BAT) and time‐to‐peak (TTP) and generate PIs for each quantity. The program was used for pre and post‐treatment parametric calculations for four representative neurovascular lesions: ischemic stroke, intracranial stenosis, arteriovenous malformation (AVM) and intracranial aneurysm treated with a flow diverter. Finally we compared the pre and post‐treatment PIs for changes in temporal parameters of the contrast flow. Results: Processing times for a typical DSA acquisition at 10 frames per second were between 15 and 20 minutes. In the ischemic stroke and intracranial stenosis cases we observed increased flow after clot removal and balloon angioplasty respectively, BAT decreased by 2x while MTT and TTP decreased 1.5x as compared with the pre‐treatment PI. For the AVM the venous arrival time increased three times after glue embolization, indicating decreased flow through the AVM. For the aneurysm treatment the MTT in the aneurysm dome was 5x larger compared with the pretreatment run indicating a reduced flow in the aneurysm. Conclusion: Pre and post‐treatment PIs showed significant differences, indicating reestablished flow for ischemic stroke and intracranial stenosis and decreased flow for the AVM and intracranial aneurysm. Execution time can be decreased significantly if software and hardware is optimized. This kind of information could be a very useful tool for treatment assistance during intracranial minimally invasive procedures in the angiographic suites where CT‐perfusion is not immediately available. Support NIH‐2R01EB002873; Support from NIH Grant 2R01EB002873
TU‐A‐116‐10: Dosimetry Approach for a Retrospective Epidemiological Study On Eye Lens Dose to Interventional Cardiologists and the Occurrence of Radiation‐Induced Lens Opacities
Authors: Farah J , Struelens L , Jacob S , Schnelzer M , Auvinen A , Vanhavere F , Clairand I
Published: July 2013

Purpose: Using whole body dosimetry data to carry out an epidemiological retrospective study on the relation between eye lens dose and lens opacities for interventional cardiologists. Methods: In the framework of the European ELDO project, a method was developed to estimate cumulative eye lens doses for past practices based on whole body doses measured, for routine occupational dosimetry, above the lead apron. The investigation focused on identifying the ratio between eye lens dose and whole body dose measured with APDs at different positions on a Rando‐Alderson phantom in realistic clinical settings. Besides, Monte Carlo simulations were performed to determine the variation of eye lens and whole body dose with tube configurations and with the use of ceiling shields and lead glasses. Another approach was also suggested to estimate eye lens dose when whole body doses above the apron are unavailable. It consists in using the European ORAMED eye lens doses database and accounting for the evolution of the X‐ray systems and procedures over the last 50 years. Results: First, ratios between eye lens doses and whole body doses (at different locations) were determined for procedures without the use of protective equipments. These ratios included different tube projections, tube configurations, beam energies and operator positions. Although eye lens dose correlated best with collar left dose, chest left measurement remains exploitable. Secondly, Monte Carlo simulations provided the necessary coefficients to correct the obtained ratios when protection equipments are used. Meanwhile, for the second approach, information was collected from the manufacturers on the evolution of X‐ray systems to adjust recent eye lens dose values for procedures performed before the years 2000; a correction factor of 2 to 4 was thus identified. Conclusion: This work suggests two methods to assess eye lens dose for retrospective epidemiological studies connecting lens opacities to eye exposure. Research funded by the DoReMi Network of Excellence. No Discolusres.
TU‐A‐116‐11: Maximum Patient Skin Dose From Interventional Radiology Procedures and Definition of Alert Thresholds
Authors: Trianni A , Farah J , Carinou E , Clairand I , Dabin J , Deangelis C , Domienik J , Knezevic Z , Kopec R , Malchair F , Negri A , Novak L , Siiskonen T , Vanhavere F
Published: July 2013

Purpose: To determine patient maximum skin dose (MSD) from interventional radiology procedures and define alerts using kerma‐area product (KAP) and cumulative air kerma (CK) values displayed by equipment manufacturers. Methods: In the framework of EURADOS WG12, nine European Countries participated with measurements of patient maximum skin dose performed during three different types of interventional procedures: neuro‐embolizations (NE), chemo‐embolizations (CE), and coronary angioplasties (PTCA). For each procedure, KAP, CK and fluoroscopy time (FT) values were also collected, as well as other parameters related to dosimetry, such as peak voltage, mAs value, filtration, beam entrance angle and total number of images. Correlations between MSD and displayed dose parameters were investigated. Results: In general, maximum skin dose is weakly correlated to both KAP and FT. Meanwhile, skin dose is quite well correlated with cumulative air kerma. In particular, the best correlation was found for CE procedures, for which relatively small entrance angles are used for the incident beam compared to PTCA and NE procedures. Conclusion: This work provides patient dose levels from some frequent interventional radiology procedures and indicates that CK could be used to define alerts helpful for operators to identify situations associated to high probability of exceeding the dose threshold for deterministic effects. However, definition of alerts applicable at European level remains difficult because of other factors affecting maximum skin dose, including operator's experience and methodology. Funded in the framework of EURADOS WG12.
TU‐B‐134‐01: Imaging Informatics 2
Authors: Clunie D , Peck D
Published: July 2013

Radiation Dose Structured ReportsMultiple diagnostic and/or interventional systems may expose a patient to radiation. The DICOM Information Object Definition (IOD) for these modalities may include acquisition data concerning the irradiation in each image instance produced. Yet, the aggregate irradiation information may not be easily determined from the individual image instances. To alleviate these issues the Radiation Dose Reporting information object was developed. In this session the configuration and organization of DICOM structured reports, and specifically the Radiation Dose Structured Report (RDSR), will be presented. This overview will include the basic construct of structured reporting IOD's and where this content in found in the DICOM standard. The current content and potential future enhancements to the RDSR will be presented. In addition, an overview of a new DICOM work item on the develpment of a Patient Radiation Dose Structured Report and the issues that this new IOD will require will be presented.

Learning Objectives:

1. Understand the basic concepts of DICOM structured reporting.

2. Describe the organization of the DICOM standard in relation to structured reporting with references to the relevant parts and sections.

3. Review the current content and recent extensions to the Radiation Dose Structured Report.

4. Discuss the proposed organization for developing a Patient Radiation Dose Structured Report.
TU‐C‐108‐03: Beyond the Alfonso Formalism for Small Field Dosimetry: A New Metric, New Detectors, Or Both?
Authors: Underwood TSA , Winter HC , Hill MA , Fenwick JD
Published: July 2013

Purpose: The Alfonso et al formalism recommends the use of correction factors to report point‐doses under small field conditions. This work considers whether the requirement for small field point‐dose correction factors may be eliminated via (i) an extension of the Alfonso formalism based upon a new integral dose metric and/or (ii) novel mass‐density‐compensation‐based detector design strategies. Methods: We have developed a mathematical definition of dose area product (DAP) for small detectors used to integrate dose inside and outside the boundaries of a radiation field. Here we test the resulting theorem of ‘inter‐detector DAP invariance’ directly using Monte Carlo (MC) simulations and indirectly using linac experiments. Additionally, MC simulations are used to explore the possibility of mass‐density‐based compensation for a series of hypothetical, spherical detectors (of diameter 0.1 cm and 0.2 cm). Cavities of greater than unit mass‐density are modified using shells of less than unit mass‐density and vice‐versa. A similar MC‐based methodology is used to investigate the potential of modifying the designs of two real radiotherapy detectors: PTW PinPoint 31006 and PTW Diamond 60003. Results: The results demonstrate that the application of conventional (detector‐specific) large‐field calibration factors leads to accurate measurement of the dose area product (integral dose) when small dosimeters are used to integrate dose over enough positions. The simulations of modified detectors also indicate that, if a detector cavity is small enough, it should also be possible to use mass‐density‐compensation to manipulate the small to large field detector response ratio so that it matches that obtained for a “point‐like” water‐structure (under a variety of irradiation conditions). Conclusion: This work presents two novel methods by which the requirement for small‐field point‐dose correction factors may be reduced or eliminated: (i) an integral‐dose‐based reformulation of the Alfonso formulation and (ii) a detector re‐design strategy based upon mass‐density compensation.
TU‐C‐108‐04: Interferometric Phase Shift Measurements to Determine the Absorbed Dose to Water
Authors: Flores‐Martinez E , Malin M , DeWerd L
Published: July 2013

Purpose: To investigate the feasibility of using phase shift measurements of visible light to determine the absorbed dose to water. To determine the minimum resolution of the optical system of a Michelson interferometer for measuring radiation induced changes in the temperature of water and to quantify the additional heating produced by the light. Methods: A Michelson interferometer was modeled with a water‐filled cell in one of its arms. The anticipated phase shift and temperature change was calculated for a 2 Gy irradiation. The observed change in intensity incident on the detector was calculated for different volumes of water and different doses. The heating of water caused by the laser was also estimated. Results: The refractive index of water is related to the dose delivered with a proportionality constant of 2.14E‐8 (λ=532 nm). For the modeled interferometer, the central spot signal in the detector arm is a function of the irradiated length of water and the dose delivered. Changes in intensity of 20 percent would be observed after a 2 Gy irradiation of a 20 cm long cell. Water heating due to the light beam is proportional to the laser power and the decadic absorption coefficient. For a 5 mW laser this would represent about 7.5 percent of the heating rate produced by a dose rate of 1 Gy/min. Conclusion: We showed that visible light phase shift measurements are a reasonable approach to determine the absorbed dose to water. Heating due to the light could be reduced using higher dose rates and/or a pulsed laser. This model provides a measure of the average dose over the beam path and a tomographic reconstruction can be used to ascertain the dose to a point. The reconstructed 2D dose distribution can be useful for small fields in radiation therapy.
TU‐C‐141‐06: Improving Image Quality in 4D‐CT Scans Using Deformable Registration and Selective Averaging
Authors: Aliotta E , Thomas D , Gaudio S , White B , Jani S , Lee P , Lamb J , Low D
Published: July 2013

Purpose: To improve image quality in low‐dose 4D‐CT using a selective averaging algorithm that combines images acquired under free breathing and registered to a single breathing phase. Methods: Five patients were imaged with a low‐pitch helical protocol on a 64‐slice scanner during free patient breathing, as part of an IRB‐approved research protocol. 25 low dose scans were performed in order to image the lungs at varying breathing phases to generate a breathing motion model. The first scan was registered to the subsequent 24 using a b‐spline registration algorithm to produce 25 representations of a single patient scan geometry. These images were averaged using k‐means clustering (k=2 clusters) in conjunction with the arithmetic mean. A gradient mapping algorithm assigned the appropriate mean value to each voxel to produce a composite image. This algorithm calculates the image gradient at each voxel and assigns a cluster mean when the gradient magnitude is above a threshold, otherwise assigning the arithmetic mean. The composite image was compared with the first image in the set as well as the arithmetic mean of all 25 scans. Image noise was calculated in an axial region of the liver. Sharpness was measured as the sum of gradient magnitudes across the image. Results: By combining gradient selective k‐means clustering with the arithmetic mean, image noise was reduced by 78% while maintaining sharpness within 14.5% of the reference image. This improves on the arithmetic mean in sharpness by 14% with less than a 1% increase in noise. Conclusion: Results indicate that 4D‐CT image quality can be improved by co‐registration followed by a gradient selective averaging algorithm. This method greatly reduces image noise while maintaining sharpness that is lost in a simple averaging algorithm. This work supported in part by NIH R01CA096679
TU‐C‐103‐03: On the Relationship of Minimum Detectable Contrast to Dose and Lesion Size in Abdominal CT
Authors: Zhou Y , Scott A , Allahverdian J
Published: July 2013

Purpose: CT dose quantification is typically guided by pixel noise or contrast‐to‐noise ratio that does not delineate low contrast details well. To optimize the dose for lesion specific diagnosis, we utilize the statistically defined minimum detectable contrast (MDC) to study it's relationship to dose and lesion size in typical abdomen CT scans. Methods: An abdomen phantom (CIRS TE‐07) simulating the medium sized patient was used. The phantom contains a cylindrical void of 4 cm diameter, filled with the low contrast insert containing six cylindrical targets (1% and 2% contrast) of 1.2 mm to 7 mm. Helical scans were conducted using a Siemens Sensation 64 (mCT) with 120 kVp and mAs ranged 35‐595 (kernel B30s, pitch 1.4 and width 5 mm). The uniform sections of the contiguous slices were subtracted and the resulted regions were divided by grids of cells sized from 1.37 mm‐6.84 mm. Standard deviations (sd) were computed from the means of all cells and scaled down by square root of 2. The MDC, quantified by the signal to background difference equal to 3.29sd, was fitted to dose D (phantom specific CTDIvol) and cell sizes (d). For validation, independent observations on the targets were made and compared with the measured contrast. MDC versus noise and lesion size was also identified. Results: MDC versus D and d was fitted to a power law (R square 0.993), with power indices of −0.537 and −1.027, respectively. The findings were validated by the independent observations on the larger targets whose contrast can be measured. The MDC was found to be proportional to noise and inversely proportional to d (R square 0.994). Conclusion: The relationships of MDC versus dose and lesion size, and MDC versus noise and lesion size were established. They can be used for task specific dose optimization.
TU‐C‐103‐04: Comprehensive Characterization of Iterative Reconstruction in a Radiation Oncology Setting
Authors: Price R , Chetty IJ , Glide‐Hurst C
Published: July 2013

Purpose: Iterative reconstruction (IR) reduces noise, thereby allowing dose reduction in CT while maintaining comparable image quality to filtered back‐projection (FBP). We sought to characterize image quality metrics necessary for integration of IR into treatment planning.Method and Materials: CTs (Brilliance Big Bore v3.6, Philips Healthcare) were acquired of several phantoms using 120 kVp and 25‐800 mAs. IR was applied at levels corresponding to noise reduction of 0.89‐0.55 with respect to FBP. CT to electron density (CT‐ED) curves were generated over all IR levels. Uniformity, spatial and low contrast resolution were quantified via the CATPHAN. Modulation Transfer Functions (MTFs) of a point source module characterized spatial frequency. Contrast to noise ratio (CNR) was quantified. Line profile and region of interest (ROI) analyses were conducted via scripting functions to quantify boundary changes and noise. Contouring differences were quantified via overlap indices (OI) and Dice similarity coefficient (DSC), and dose calculation was assessed. Imaging dose reduction was determined. Results: No appreciable changes were observed for CT‐ED curves between FBP and IR levels (maximum difference ∼6.7 HU for bone). For uniformity, differences were <1 HU between FBP and IR. Spatial resolution was well conserved; largest MTF width difference at 50% maximum between FBP and IR levels was 0.1 lp/cm. Profile analysis suggested slight edge deterioration (<3 HU), although OI and DSC ranged from 0.994‐0.999. Maximum dosimetric difference was 0.015%. No notable changes in low‐contrast detectability were observed. Substantial noise reduction (∼45% maximum reduction in signal standard deviation) and CNR gain (maximum >200%) were observed, corresponding to ∼70% dose reduction. Conclusion: IR meets the criteria needed for treatment planning. Slight degradation in object edges was observed, however this did not impact contouring ability or dosimetric parameters. IR substantially reduced imaging dose, and a prospective trial is warranted to optimize settings for each anatomical site. The submitting institution holds research agreement with Philips Healthcare.
TU‐C‐103‐05: Image Quality and Dose Reduction Evaluation of a New CT Iterative Reconstruction Algorithm Using Model Observers
Authors: Tseng H , Fan J , Kupinski M , Sainath P , Hsieh J
Published: July 2013

Purpose: To evaluate the impact on image quality of a new iterative reconstruction (IR) algorithm for CT systems and quantitate the amount of dose reduction by using mathematical model observers. Methods: Two phantoms with low‐contrast inserts (head mode and body mode) were used to evaluate task performance for both location known signal detection and location unknown signal detection tasks. The phantom consisted of low contrast cylindrical signals with contrasts ranging from −2 Hounsfield units (HU) to ‐ 10 HU and sizes ranging from 5mm to 7mm. The phantoms were scanned by multi row CT scanner using a range of tube currents 30&– 400mAs, and energy 120 kVp. The performance of a traditional filtered backprojection (FBP) algorithm and the new IR were evaluated using the channelized Hotelling observer. Seven channels designed to match human performance were selected to evaluate the image quality. Area under ROC curves and LROC curves were used to determine the image quality. Results: Evaluation of model observer performances indicates that a 3x dose reduction can be reached using the new IR algorithm in two modes (head and body) while maintaining image quality for location known and location unknown detection tasks. Conclusion: Overall, image quality as measured by task performance is greatly improved by using the IR compared to traditional FBP at equal mAs and kVp. Thus, this study indicates that a significant dose reduction in CT systems can be achieved by using this new IR algorithm. This new IR and the phantoms presented in this study will be used in future investigations of more complicated imaging tasks such as size and contrast estimation. GE Healthcare, Waukesha, WI
IAEA contribution to international harmonization of guidelines for clinical medical radiation physicists
Authors: Meghzifene Ahmed , do Carmo Lopes Maria , Cheung KY , Constantinou Christodoulos , Andreo Pedro , Brandan Maria‐Ester , Castellanos Maria Esperanza , Ige Taofeeq Abdallah , Frey George Henry
Published: July 2013

The IAEA's Technical Cooperation Project INT/6/054 “Strengthening Medical Physics in Radiation Medicine” aims at promoting the recognition of medical physics in radiation medicine and to harmonize educational and clinical training requirements in order to achieve the required standard of patient care in radiation medicine. To achieve this project's objective, the IAEA's efforts were supported by numerous stakeholders from medical physics professional societies and regional counterparts from Europe, Africa, Latin America and Asia. Within this project, the IAEA established four Working Groups (WGs) to address the issues of (i) roles and responsibilities, (ii) education & clinical training requirements, (iii) staffing requirements and (iv) raising awareness on the medical physics profession. The WG1 and WG2 drafted the guidelines on roles and responsibilities, and education & clinical training requirements for clinical medical physicists. The guidelines were compiled into a single report, aiming at providing recommendations on the minimum requirements for the academic education and clinical training necessary for a physicist to become a clinically qualified medical physicist. They include recommendations for accreditation, certification and registration, along with continuous professional development. With the purpose of establishing the grounds for substantiating the recommendation on education and clinical training requirements, the IAEA report includes first the roles and responsibilities of a clinically qualified medical physicist in radiation medicine. The goal of the IAEA report is to establish criteria that support the harmonization of education and clinical training worldwide, as well as promoting the recognition and professionalism of medical physics as a profession internationally. The IAEA report was endorsed by the International Organization for Medical Physics (IOMP) and approved for publication as an IAEA Human Health Report. The main recommendations included in the IAEA report will be presented, together with preliminary plans to support implementation, especially in low and middle income countries. 1 IAEA, 2 Portugal, IOMP, 3 Hong Kong, China, IOMP, 4B.O.Cyprus Oncology Centre, Cyprus, 5 Karolinska University Hospital, Sweden, 6 Mexico, ALFIM, 7 Colombia, ALFIM, 8 Nigeria, FAMPO, 9 USA, AAPM
TU‐E‐108‐03: Optimization of the Beam‐On Latency of An Elekta Linac in the Delivery of Gated VMAT
Authors: Cui G , Housley D , Chen F , Mehta V , Shepard D
Published: July 2013

Purpose: To optimize the beam‐on latency of an Elekta linac in delivering gated VMAT. Methods: Step‐wise optimization was performed using a pre‐clinical gating interface developed by Elekta. Phantom studies were performed where surface motion was simulated using a moving chest plate. Two gating windows 77% and 66% around the end of exhalation were used for the gated VMAT deliveries. The treatment plans from three lung patients previously treated with un‐gated 6 MV SBRT were used for this evaluation. Baseline of the average beam‐on latency of the gated deliveries was first established. Then the average beam‐on latencies between a binned dose rate and a continuously variable dose rate (CVDR) deliveries were compared. With the CVDR delivery, further comparison between two different linac gun hold‐on times 1.35 s and 6.50 s was performed. The dosimetric accuracy of the gated deliveries was evaluated by comparing the measured with planned coronal dose distributions using gamma‐index analyses (3 mm/3% passing rate criteria). Results: The average beam‐on latencies of the gated deliveries with the CVDR were greatly reduced as compared with those of the binned dose rate for gating windows higher than 66%. With the CVDR deliveries, longer gun hold‐on times (6.50 s as compared to 1.35 s) made a dramatic improvement on the beam‐on latency for gating windows equal to and lower than 66%. There were insignificant dosimetric differences between all the gated deliveries and the un‐gated deliveries. Conclusion: For gated VMAT deliveries using an Elekta linac with the CVDR and the gun‐hold time of 6.50 s, the average beam‐on latency was reduced to a level (< 0.3 s) that has minimal impact on clinical results. High dosimetric accuracy was demonstrated for as many as 214 beam interruptions during a single 360‐degree‐arc delivery with gamma‐index passing rates were no lower than 99.0% for all tests. The research is partly supported by a grant from Elekta AB.
TU‐E‐108‐06: Investigation of Prostate Deformation and Associated Dosimetric Implications in IMRT of the Prostate
Authors: Mayyas E , Kim J , Kumar S , Wen N , Elshaikh M , Chetty I
Published: July 2013

Purpose: Prostate deformation is generally considered a secondary correction and is consequently often ignored in planning margin design. In this study we estimated prostate deformation and investigate the associated dosimetric impact on target coverage. Methods: A cohort of ten prostate cancer patients were retrospectively selected for the study, each with three fiducial markers implanted in the prostate. All CBCT images were registered to respective planning CT images using the Velocity AI deformable image registration (B‐spline‐based) software. For cases with accurate prostate registrations (defined by mean marker misalignments of <1.5 mm), deformation‐vector‐fields (DVFs) of the prostate and seminal vesicles (SVs) were quantified using deformation‐volume histograms. For the case with the largest prostate deformation, target coverage degradation was analyzed in each of three treatment plans with PTV margins of 10, 5, and 3 mm. Results: Deformation of the prostate and SVs was most significant in the anterior‐posterior (AP) direction. Maximum prostate deformation of > 10mm, 5mm, and 3mm occurred in 0.5%, 10.0%, and 68.5% of cases, respectively. Based on the deformation‐volume histograms, DVF magnitudes greater than 5mm and 3mm occurred in 2% and 27% of cases, respectively. In general, SV deformation was larger than that of the prostate. For the case with the largest prostate deformation, prostate coverage (D95%) was reduced by 0.5%, 9.0%, and 17.0% for 10mm, 5mm, and 3mm margin plans respectively. Conclusion: These preliminary results are suggestive that prostate deformation over a course of fractionated prostate radiotherapy may not be insignificant, and thereby that proper margin design may be necessary to account for deformation. A consequence of these results is that use of tight planning margins of (e.g. less than 5 mm) must be viewed with severe caution.
TU‐E‐108‐10: Investigation of the Clinical Potential of Scattering Foil Free Electron Beams
Authors: Eldib A , Jin L , Li J , Ma C
Published: July 2013

Purpose: The photon contamination is a common problem for all advanced modulated electron beam therapy techniques. The scattering foil is one of the major accelerator parts contributing to the generation of bremsstrahlung photons. This work aims to characterize the scattering foil free (SFF) beams from the Siemens Artiste accelerator and to study the feasibility of using those beams for breast cancer boost treatment utilizing our in‐house Monte Carlo based treatment planning system. Methods: Percentage depth doses and lateral profiles were measured for all available energies with the primary scattering foil removed. All beam characteristics were compared to those of the conventional electron beams. The SFF electron beams were modeled and simulated using the Monte Carlo method. CT scans of six previously treated breast patients were used for the treatment plan generation. Electron boost plans with conventional beams and the SFF beams were generated, respectively, for all the patients. Results: A significant reduction of the photon component was observed with the removal of the primary scattering foil for beam energies higher than 12MeV. Slight increase in beam energy was only noticed with the 18MeV and 21MeV beams. Ion chamber measurements showed higher dose per monitor unit especially at the higher energies. Flatness was greatly affected, however the difference in flatness between conventional and SFF beams was much reduced for small cone sizes and can be clinically insignificant for breast boosts. Removal of the secondary scattering foil could further reduce photon contamination but the beam flatness was also drastically deteriorated. Results from the electron boost plans showed similar target coverage with much reduced dose to the critical structures. Conclusion: The SFF electron beams can deliver high‐quality dose distributions as conventional electron beams for boost treatments with an added advantage of further reduced dose to the lung and heart. This work has been supported by a UICC American Cancer Society Beginning Investigators Fellowship funded by the American Cancer Society.
TU‐E‐108‐11: Design and Simulation of a Short, 10 MV, S‐Band Linear Accelerator
Authors: Baillie D , St. Aubin J , Fallone B , Steciw S
Published: July 2013

Purpose: To design a short (27.5 cm) S‐band linear accelerator capable of producing a 10 MV x‐ray beam to enable higher photon energies for linear accelerator‐MRI hybrid systems, where the waveguide length and linac‐MR orientation is a concern. Methods: Finite element software COMSOL Multiphysics was used to design an accelerator cavity matching one published in an experiment on breakdown, to ensure that the threshold electric field published are applicable to the final waveguide geometry. This cavity was used as the basis for designing an accelerator waveguide, and the full RF field solution within the waveguide was calculated. This RF solution and an electron‐gun phase space generated using Opera3D/SCALA are input into electron tracking software PARMELA to compute the electron phase space striking the x‐ray target. The resulting electron beam is used for Monte Carlo simulations to calculate PDD curves and the beam penumbra, and compared against those produced by a Varian 10 MV. Results: The shunt impedance, Q factor, and ratio of peak‐to‐mean electric fields of the cavity were matched to those in the published study to within 0.1% error. After tuning the full waveguide, the peak surface fields are 207 MV/m, well below the breakdown threshold of 239 MV/m. The peak of the electron spectrum is centered at 10.4 MeV, with a width of 0.2 MeV, compared with 10.5 MeV and 0.3 MeV, respectively, for a Varian 10 MV linac. Monte Carlo results show dmax is 2.15 cm for a 10×10 cm2 field and the penumbra is 5.0 mm wide at 10 cm depth, compared with dmax at 2.3 cm and 5.6 mm width for a Varian 10 MV linac. Conclusion: This work demonstrates the design and modeling of a waveguide capable of producing 10 MV energy x‐rays yet short enough to be compatible with a linac‐MR system.