bluuebunny/crossref_metadata_2025 huggingface dataset:
TH‐C‐230A‐06: High‐Energy Proton Acceleration Driven by Ultra‐Intense Ultra‐Clean Laser Pulses
Authors: Maksimchuk A , Bulanov S , Chvykov V , Brantov A , Bychenkov V , Kalintchenko G , Matsuoka T , Rousseau P , Reed S , Yanovsky V , Litzenberg D
Published: July 2006

Purpose: To improve the contrast ratio of the multi‐terawatt Chirped‐Pulse Amplification (CPA) Ti:Sapphire laser to 1011 to allow Coulomb explosion regime of ion acceleration in the interaction of ultra‐short high‐intensity laser pulses with ultra‐thin (< 1 micron) foils. Method and Materials: The cross‐polarized wave generation (XPW) technique in BaF2 crystals was implemented. This technique improves contrast by rejecting the low‐intensity amplified spontaneous emission (ASE) preceding the main laser pulse. Particle‐in‐cell (PIC) simulations were conducted under the anticipated experimental conditions: 225 TW in a 6.75 J, 30 fs laser pulse with no prepulse, focused to a spot size of 2.4 microns (FWHM) on thin foils of varying thickness. Results: Implementation of the crosspolarized wave generation technique resulted in a contrast improvement of three orders of magnitude to approximately 1011. The performed PIC simulations show that for a 0.2 μm thick hydrogen foil, protons with energy of about 200 MeV can be generated. In the case of the two‐layer aluminum‐hydrogen foil the maximum energy of accelerated protons is about 150 MeV, but the proton spectrum has a flatter distribution, which may be more advantageous for therapy applications. Conclusion: We demonstrated that pulse cleaning based on cross‐polarized wave generation (XPW) using two BaF2 crystals yields a 1011 contrast ratio for a 50 TW laser system. Such contrast may be sufficient for a preplasma‐free interaction of sub‐Petawatt laser pulses with a sub‐micron thickness foils at intensity of ∼1022 W/cm2. Modeling of this interaction with PIC simulations demonstrated proton energies that are of interest for the radiation therapy.

This study was supported by the National Science Foundation through the Frontiers in Optical and Coherent Ultrafast Science Center at the University of Michigan and the National Institute of Health.
TH‐C‐230A‐07: Reconstruction of Spatially Varying Optical Properties of Human Prostate During Metexafin Lutetium PDT
Authors: Zhou X , Zhu T , Hahn S , Pogue B
Published: July 2006

Purpose: The purpose of this study is to characterize the internal optical absorption and reduced scattering distribution of human prostate during the interstitial metexafin lutetium photodynamic therapy (PDT). These distributions could be utilized in PDT treatment planning, which optimizes the arrangement and weighting of interstitial light sources to ensure sufficient photon are delivered to the treatment volume. Method and Materials: A continuous‐wave diffuse optical tomography system has been developed using a finite element reconstruction algorithm based on diffusion approximation of light distribution in biological tissue. Reconstructed images are presented from simulated data and clinical data acquired from prostate cancer patient being treated by PDT. Sourcedetector arrangement is identical in simulated data and patient data. The contour of prostate was obtained using ultrasound imaging. The meshes were generated by MATLab PDE Toolbox. Results: The synthetic measurement data were calculated for a rectangular phantom containing a single absorption anomaly and a single scattering anomaly. The model had a background of , . The absorption anomaly was located at (15mm,15mm), with a radius 5mm, ; the scattering anomaly was located at (35mm,10mm), with a radius 5mm, .A total number of 5 sources and 12 detectors yielded 60 measurements (12 detectors ×5 sources). The reconstruction basis uses a coarser mesh (100 nodes) to reduce the degree of freedom. The reconstruction images successfully recover the both anomalies with good localization. The clinical DOT imaging was performed on 70‐year old male subject. The reconstructed prostate μa varied between 0.025 and 0.07 mm−1 and μ′s ranged from 1.1 to 2 mm−1. These results are consistent with previous measurement using a point‐by‐point method. Conclusion: We have shown that this modeling and reconstruction algorithm can produce fast and reliable images of internal optical properties with fast computation time.
TH‐C‐230A‐08: A Prototype Rotational Immobilization System for a Proposed Static‐Gantry MicroRT Device with Tomographic Capabilities
Authors: Hope A , Stojadinovic S , Deasy J , Hubenschmidt J , Grigsby P , Low D
Published: July 2006

Purpose: Proposed small animal irradiation devices are typically isocentric gantry systems. Multi‐axis gantry systems require significant resources to develop and maintain. A static gantry system could provide the functionality of a multi‐axis gantry via subject rotation if subject motion could be minimized. In this study, we evaluated internal organ motion of mice within a prototype immobilization device during rotation. Method and Materials: Mice were anesthetized and immobilized in a prototype device designed to rigidly support animal positioning during rotation along the cranio‐caudal axis. The head and tail of the mouse were allowed to extend beyond the immobilization device as an internal control. Validation of internal and external immobilization was assessed using computed tomography imaging at multiple rotation angles. CT images were co‐registered (translated/rotated) using our research treatment planning system (CERR) into a common reference frame. Internal organ motion was assessed qualitatively by examination of internal anatomy in overlaid multiplane CT images. Quantitative evaluation of organ motion was assessed by delineating organ structures in CERR and comparing relative organ volumes and centers of mass. Results: CT imaging demonstrated minimal exterior contour changes (<1mm) in the immobilized regions during rotation. Un‐immobilized regions demonstrated the expected gravitational positional changes. Internal organs demonstrated sub‐millimeter changes in organ centers of mass (heart and lung) and small (<5 mm3) changes in volume during rotation. These variations were similar to the differences when the same CT was re‐contoured multiple times by the same operator and likely represent intra‐observer contouring variations. Conclusion: A microRT device with a stationary irradiator, collimator, tomographic imaging system, and rotating subject would reduce the overall cost and complexity of the unit. This study demonstrates rotational immobilization of small animals is feasible.

This work supported in part by NIH R21 CA108677 and by a grant Varian, Inc.
TH‐C‐230A‐10: A General Software Framework for Investigations in Radiation Therapy Planning
Authors: Rehbinder H , Andersson J , Ericson S , Eriksson K , Forsgren C , Hårdemark B , Korevaar E , Larsson M , Liander A , Lundin A , Riddersporre J , Rosseau D , Sundgren C , Uhrdin J , Löf J
Published: July 2006

Purpose: To be able to experiment with various topics in advanced radiation therapy planning using a stand‐alone Windows‐based software. Method and Materials: Product code for IMRT planning was merged with research code for adaptive radiation therapy and dose computations. An architecture and graphical user interface tailor‐made for representing adaptive treatments was designed. Code for proton dose computation and treatment planning was developed and integrated into the system. Results: A software package that executes on a standard PC or advanced laptop has been developed. The system is capable of IMRT treatment planning using dose‐volume based functions, EUD, Poisson‐LQ and LKB biological models, both as objectives and hard constraints. Pencil beam and heterogeneity corrected collapsed cone dose computations can be used. The system can optimize every relevant combination of pencil beam weights, SMLC segments, gantry, couch and collimator angles. It is possible to perform intensity modulated proton therapy planning. Models for tumor repopulation and repair are included and irregularities in the fractionation scheme can be compensated for by allowing the dose to vary between fractions during optimization. The system exhibits a comprehensive GUI and functionality for simulation and evaluation of adaptive/IGRT treatments with algorithms for deformable dose accumulation based on information from portal imaging and 3D imaging modalities such as onboard CT scanners. Errors due to patient setup and organ motion can be counteracted and compensated for by couch shift and on‐ and offline IMRT replanning. Conclusion: A software environment suitable for studying various advanced topics in modern radiation therapy has been developed. The system has proven useful in research and development in IMRT optimization, biological models, proton therapy and adaptive radiation therapy. Conflict of Interest: The authors are employees and stock owners of the submitting company.
TH‐C‐224C‐01: Relative Biological Effectiveness(RBE) and Dosimetry of Low Energy Photons(8keV) Generated Using Miniature X‐Ray Tubes
Authors: Srinivasan M , Yudelev M , Gutman G , Burmeister J , Lyons K , Joiner M
Published: July 2006

Purpose: To study the Relative Biological Effectiveness(RBE) and dosimetric characteristics of an 8keV photon beam generated by an insertable miniature electronic brachytherapy device developed by Advanced X‐ray Technology, Inc.(AXT). Method and Materials: The AXT X‐ray needle consists of a primary conventional X‐ray tube with silver anode producing a 22 keV beam focused through a collimator into the applicator needle which has a secondary copper target generating an 8 keV fluorescent beam. The radio‐resistant human tumor cell lines HGL21(glioblastoma) and MCF7 (breast) were irradiated at 22°C using the AXT miniature needle and compared with a Co‐60 beam at dose rates of approximately 6cGy/min and 12cGy/min. An extrapolation chamber was used in gradient mode to determine the dose rate within the AXT beam after initially determining the effective area of the collecting electrode in a Co‐60 beam using the Bragg‐Gray relationship. Results: Cell surviving fraction (SF) was the primary end point in assessing the radiobiological effect. For the 8 keV beam, SF was found to be 0.056 for HGL21 and 0.018 for MCF7 for a dose of 2 Gy. This yields an RBE of 4.4 for HGL21 and 5.5 for MCF7 cells lines. The dose rate in the 8keV beam was found to vary linearly as a function of extrapolation chamber electrode spacing. This allows the use of the slope of the ionization gradient to determine the dose. The dose rate measured in free space at the location where the cells were irradiated was found to be 15.4 cGy/min.Conclusion: These high RBE values are not surprising given the stopping power of the very low energy recoil electrons produced in this beam, and support the premise that the AXT device will be an effective tool to treat tumor sites like brain, breast and prostate in which radio‐resistance might limit conventional radiotherapy.
TH‐C‐224C‐03: EUCLID: A New Outcome Analysis Tool for High‐Dimensional Clinical Studies
Authors: Gayou O , Miften M
Published: July 2006

Purpose: To develop a clinical outcome statistical analysis tool available for clinicians and researchers to perform univariate and multivariate analysis of a clinical study with a possibly large number of clinical, biological, physiological and dose‐volume variables. Method and Materials: The program was developed using the MATLAB software. The bases for this work were laid out in the DREXLER software, developed at Washington University. New functions were added, including data histogramming and equivalent doses calculations (EUD, gEUD, BED), as well as the possibility to apply a threshold on variables to select a subset of patients. A new user interface was developed with the goal of allowing easy manipulation and analyzing of large clinical studies along with the graphical and tabular reporting of outcomes and correlations with useful statistical information. Results: EUCLID provides a user‐friendly graphical interface that allows several aspects of the analysis at the same time, using several windows. The input data can include for every patient an unlimited number of clinical, biological, physiological variables, outcomes and dose‐volume histogram (DVH) points. The univariate analysis includes plotting and histogramming the variables individually. If survival time is available, the Kaplan‐Meier method is used to calculate the survival curve. The multivariate analysis allows the user to show a map of correlation coefficients between all possible pairs of variables. The user may also perform a logistic regression analysis to use clinical and DVH variables to predict an outcome. The predictive power of the model can be visualized on a cumulative probability histogram, contour plot, octile plot or Receiver‐Operating Characteristic (ROC) curve. If DVH data are present, the DVH can be displayed, and the TCP, NTCP and equivalent doses can be analyzed. Conclusion: EUCLID is a powerful, user‐friendly tool that allows researchers to quickly obtain a complete statistical analysis of potentially large clinical studies.
TH‐C‐224C‐04: Radiobiological Concerns On Prolonged IMRT Delivery for Head‐And‐Neck Carcinoma
Authors: Qi X , Yang Q , Wang D , Li X
Published: July 2006

Purpose: Radiobiological effect of the prolonged IMRT delivery time on head‐and‐neck cancer has remain to be defined. The purpose of this work is to estimate a plausible set of radiobiological parameters (α/β, sublethal damage repair halftime, potential doubling time) for squamous cell carcinomas of head‐and‐neck (SCCHN) based on in vitro measurement and clinical data, and to examine the potential radiobiological influence due to the prolonged delivery time using the newly estimated parameters of SCCHN. Methods and Materials: In vitro cell survival measurements were performed for two cell lines of SCCHN irradiated by a series of specially‐designed single and split dose regimens using a 6 MV machine. The obtained survival data were fitted to the Linear‐Quadratic (LQ) model using the least χ2 technique. Other radiobiological models, such as equivalent uniformly dose (EUD) and tumor control probability (TCP), were used to analyze published clinical outcome to validate the parameters estimated from the in vitro data. Results: Based on the present in vitro measurements, we have estimated a set of radiobiological parameters for SCCHN: repair half‐time Tr = 16 ± 21 min, the potential doubling time Td = 48 ± 10 hours, radiosensitivity parameters α/β = 7.9 ± 4.5 Gy, α = 0.22 ± 0.08 Gy. This set of parameters was found to be able to fit the available clinical data. The calculation based on these parameters indicated that prolonged delivery time, if comparable/longer with the repair half‐time, would result in noticeable reduction in treatment effectiveness. For example, an IMRT delivery time of 30 minutes would result in a reduction of 11% in tumor EUD (compared to a 5‐minute fraction). Conclusions: The present measurement and analysis show that the repair half‐time and potential doubling time for head‐and‐neck cancer are relatively short, indicating that optimal IMRT delivery time needs to be clinically considered.
TH‐C‐224C‐05: Analysis of Radiation‐Induced Pneumonitis in Lung Cancer Patients
Authors: Gayou O , Parda D , Miften M
Published: July 2006

Purpose: To study clinical, physiological, biological and dose‐volume factors in lung cancer patients who developed symptomatic radiation‐ induced pneumonitis (RP). Method and Materials: Data from two‐hundred patients with non‐small cell lung cancer who received 3D conformal radiotherapy (RT) treatment were analyzed using an in‐house developed MATLAB‐based analysis tool, EUCLID. The effect of 52 clinical, physiological and biological factors, as well as dosimetric variables extracted from the lung dose‐volume histogram (DVH) was analyzed using univariate and multivariate approaches. Results: Thirty nine patients (19%) developed RP. In the univariate analysis, the forced expiratory volume in 1 second (FEV1) post‐treatment, normal tissue complication probability (NTCP), mean lung dose, history of smoking, level of TGF‐β post‐treatment and nodal stage were associated with RP (p‐range 0.001–0.033). When considering the percentage of volume of lung receiving more than a specified dose, we found that 60 Gy (V60) yields the strongest correlation with RP (p=0.0001). In the multivariate analysis, a logistic regression analysis was performed using different sets of uncorrelated variables. The predictive power of the model was quantified using the area under the Receiver‐Operating Characteristic (ROC) curve. The best result was obtained with V30, FEV1, age, time of chemotherapy (before, after or concurrent with RT) and Lobe (location of tumor inside the lung). The area under the curve for these variables was 0.85. While only the regression coefficients of V30 and FEV 1 determined a correlation with RP with a p‐value less than 0.05, the exclusion of the other three variables led to a lower area under the curve. Conclusion: V30 and FEV 1 were the best predictors of symptomatic RP after external beam RT for lung cancer. Multivariate analysis showed that other clinical factors that are not individually strongly associated with RT can be included in a regression model to increase the predictive power of that model.
TH‐C‐224C‐06: Using Quality of Life Information to Rationally Incorporate Normal Tissue Effects Into Treatment Plan Evaluation and Scoring
Authors: Miften M , Gayou O , Parda D , Marks L
Published: July 2006

Purpose: Modern radiotherapy treatment planning systems provide an increasing number of competing plans. The decision to select a particular plan for treatment is generally made by a radiation oncologist based on training and clinical experience. The criteria applied are often poorly‐defined, qualitative, and largely based on tradition and familiarity. A “realistic” approach utilizing decision analysis tools to evaluate/rank treatment plans based on quality adjusted life years (QALY) expectancy was developed. Method and Materials: The decision analysis methods were applied to the concept of uncomplicated tumor control probability (UTCP). The expected outcome for an anticipated course of radiation was described as a series of probabilities: alive, free of disease without complication; alive with disease; alive with complication, etc. For each of these states of health, a utility can be assigned based on published work or empirical estimates. The total QALY' for a particular treatment plan represent the product of duration‐weighted states of health. The formalism for UTCP was generalized to incorporate the total QALY (UTCPQALY) for a particular treatment. Results: This approach was applied to compare the clinical treatment plans of 200 patients who received high‐dose external‐beam for unresectable non‐small cell lung cancer. Thirty nine out of the 200 patients developed radiation‐induced pneumonitis with the grade distribution of 8.7%, 69.6%, and 21.7% for grades 1, 2, and 3, respectively. The plan ranking based on the traditional UTCP and pneumonitis QALY‐weighted UTCP (UTCPQALY) values were different. The UTCP varied significantly, reaching values of 0.5. Using UTCPQALY scoring, the mild complications importance is downplayed compared to the severe complications, with all UTCPQALY values above 0.85. The QALY‐weighted UTCP's appear to provide better clinical realistic differentiator between plans. Conclusion: The construct presented represents a potential improvement in the current methods used to compare plans. Formulas presented can be readily incorporated into planning systems.
TH‐C‐VaIA‐03: Accurate Dosimetry in Narrow Stereotactic Photon Fields
Authors: Gibbons J
Published: July 2006

Dosimetric measurements for stereotactic radiosurgery or radiotherapy fields typically include determination of relative output factors, tissue maximum ratios and off‐axis beam profiles. Accurate measurements of each of these quantities are made more difficult when the measured field sizes are either comparable to the detector size, or less than the distance required for lateral electronic equilibrium. These difficulties are present when measuring either single, static‐field cone or micro‐MLC linac‐based delivery systems, or simultaneous multiple‐field Gamma Knife delivery systems.

Several detector characteristics should be considered when choosing a measurement system. The detector size in the radial direction will determine the extent of the beam profile integrated in the reading. Typically solid‐state detectors or film (radiographic or radiochromic) have been used to reduce this volume‐averaging effect. Several other detection systems have also been used, including pin‐point ionization chambers, thermoluminescence dosimetry, and diamond and scintillation detectors. Techniques exist to correct for finite detector volume, including the extrapolation of measured results to zero‐volume, and deconvolution of measured data with the detector response function.

The detector energy response also should be considered due to the variation in the number of low energy scattered photons with field size and depth. Additionally, for field sizes below lateral electronic equilibrium, variations in the stopping power ratios affect the conversion of ionization to dose, particularly for higher‐energy measurements. Both of these effects increase with beam energy and depth.

This lecture will provide an overview of the measurement techniques used to determine dosimetric quantities for stereotactic fields. Recommendations for measurement systems will be made, and limitations to each system will be discussed. Estimations of error will be provided, both for individual measurements and in the overall planned dose. When available, comparisons will be made with results predicted by theoretical Monte Carlo calculations.

Educational Objectives:

1. Understand the basic principles and practical aspects of clinical dosimetry for stereotactic radiosurgery.

2. Understand the limitations and applicability of various detector types and sizes for small field measurements.

3. Understand current techniques available to correct data measurements in small fields.
TH‐C‐VaIA‐05: Accurate Dose Measurements in Heterogeneous Phantoms
Authors: Huq M
Published: July 2006

The human body consists of tissue types that have radiological properties that are different from water. These include, for example, lung, bone, and oral cavities. Presence of such tissue types and cavities in the treatment fields of high‐energy photon beams creates potential dosimetric problems. For inhomogeneities with density less than that of water electronic disequilibrium situations can be severe. Lateral electronic disequilibrium is present for small field sizes (i.e., 5 cm × 5 cm) and high energy beams (i.e., 15 MV) in a low density inhomogeneity such as lung. Perturbations at air‐tissue interfaces are complex to measure or calculate due to lack of electron equilibrium. The trend of data published in the literature show that for low density media i) dose generally increases beyond the depth of dose maximum; ii) build‐up and build‐down regions exist within tissue near the low density media‐tissue interfaces; the severity of these effects increase with increasing energy and decreasing field size; iii) the penumbra increases with energy in the region of low density region. For high density media the dose is found to decrease beyond the depth of dose maximum.

The dosimetric effects of these heterogeneous tissues become even more complicated for IMRT beams. This is because i) small radiation beams are inherently difficult to measure; ii) standard ion chambers have dimensions that are large compared to the beam and do not have the spatial resolutions that are needed to resolve the narrow central region of uniform dose and the sharp dose gradient regions of the penumbra and iii) the chambers may have a dose rate dependence.

The dosimetric impact of the presence of heterogeneous tissues in megavoltage photon beams have been addressed with varying degrees of success by various investigators i) experimentally by the use of specially designed ionization chambers, film, TLD and other dosimeters in specially constructed phantoms, ii) theoretically by the development of various dose calculation algorithms and iii) by the use of Monte Carlo simulation.

Educational Objectives:

Develop an appreciation of

1. the challenges involved in accurate dose measurements in heterogeneous phantoms

2. the clinical implementation of the results of such measurements, various dose calculation algorithms and/or Monte Carlo simulations to various disease sites that involve the presence of various types of heterogeneous tissues.
TH‐C‐VaIA‐06: Accurate Dosimetry Measurements for IMRT and 4D Delivery
Authors: Ma C
Published: July 2006

The use of conformal radiotherapy, especially with the IMRT technique, is a major departure from the way radiotherapy is currently delivered. Although the use of multileaf collimator (MLC) provides the possibility of achieving better dose distributions conformed to tumor targets, it also increases the treatment complexity. The sequences of leaf movement and their associated effects on the dose delivered to the patient may vary significantly depending on the accelerator and the MLC design. Accurate measurement of IMRT dose distributions in a clinical setting is not an easy task since many factors may affect the measurement results. In this presentation we will review various factors affecting IMRT dose distributions including the variation of the accelerator head scatter component in the MLC‐collimated beam, the amount of photon leakage through the leaves, and the scatter from the leaf ends, the “tongue and groove” effect, and the effect of back‐scattered photons from the moving jaws and MLC leaves on the monitor chamber signal. We will describe the use of different detectors commonly used for absolute and relative dose determination with both static and dynamic beam delivery. We will discuss the effects of electron disequilibrium, detector perturbation and patient heterogeneous anatomy on the measurement accuracy.

Below are the educational objectives of this presentation:

1. Review dosimeters for absolute and relative IMRT dose measurements.

2. Discuss the process for dose determination under electron disequilibrium conditions.

3. Describe the use of Monte Carlo simulations to derive detector correction factors.

4. Discuss major factors affecting IMRT dose measurement accuracy.
TH‐D‐330A‐02: An Electronically‐Collimated Gamma‐Ray Detector for Intraoperative Localization of Radiation Sources
Authors: Smith B , Matthews K , Hill W , Lackie A , Wang W‐H , Cherry M
Published: July 2006

Purpose: We are developing a radiation detector for locating radiation sources, e.g. for intraoperative localization of sentinel lymph nodes and metastases. The design emphasizes compact size and portability, wide field of view, and efficiency and accuracy in source localization. Room‐temperature cadmium‐zinc‐telluride (CZT) detectors and electronic collimation via Compton‐scatter detection are used to achieve the design goals. Method and Materials: The detector design was simulated in GEANT4 to assess feasibility and optimize the design. The simulation model was a 6‐sided box with one detector module on each end and two modules per side. One end is the primary scatter detector; the other modules detect the scattered photons, operating in coincidence with the primary module. The simulations allowed variations of detector dimensions, pixel size, energy resolution, and source energies. Experimental measurements with a 3‐module partial prototype were used to validate the simulations; each module is a 16×16‐pixel 38×38×5‐mm3 CZT detector. Results: The simulations indicated ∼15% of incident gamma rays produce valid direction measurements; 30–70% of these events are Compton‐photoelectric interaction pairs. The measured angular resolution varied from a few degrees for 100‐keV gamma‐rays up to about 10° FWHM at 1 MeV. Above ∼1.5 MeV, multiple Compton‐scatter events limit accurate measurement of Compton cone angles; below ∼50 keV, few Compton‐scatter events occur. Experimental validation with the prototype system is in progress.Conclusion: Efficiency and angular resolution vary with source energy but reasonable performance seems achievable for radioisotopes from Am‐241 through Co‐60. Ongoing work is investigating the effect on performance of design parameters such as pixel size and detector thickness. Coupled with concurrent development of real‐time methods to calculate the directional information, this system provides localization of radiation sources with high sensitivity. Acknowledgment: Supported by Homeland Security Advanced Research Projects Agency, and Space and Naval Warfare Systems Center San Diego; Contract N66001‐05‐ C‐6024.
TH‐D‐330A‐04: A Novel PET Respiratory Gating Algorithm to Reduce Lung Tumor Blurring Using the 4D NCAT Phantom
Authors: Wang J , McGoron A , Byrne J , Franquiz J
Published: July 2006

Purpose: Develop and validate a PET gating algorithm based on the amplitude of respiration to correct for abnormal respiratory cycles. Method and Materials: Using the 4D NCAT phantom model, 3D PET images were simulated in lung and other structures at different times within a respiratory cycle. To compare the amplitude gating algorithm with time gating, NCAT phantom was used to simulate a case with 5 different respiratory periods. We generated 6–10 frames over one respiratory cycle (corresponding to 3–5 s respiratory periods) and summed the results to mimic clinical imaging. Images were reconstructed with and without respiration motion. Comparison was performed for gated and un‐gated images, and for the new amplitude binning algorithm with the time binning algorithm by calculating the mean number of counts in the ROI. Lesion‐to‐background ratios were 2.5, 5 and 8. Lesion diameters were 6 mm, 8.5 mm, 10 mm and 20 mm. Simulated images were created using a Gaussian distributed random number generator. Blurring due to the finite PET image resolution was simulated by the convolution of each slice with a Gaussian filter with FWHM of 1.6 pixel. Results: As both the L/B ratio and lesion size decreases, image degradation due to respiration increases. The greater benefit for smaller diameter lesion and lower L/B ratio indicates a potential improvement in detecting more problematic lesions. Little improvement is gained for large lesions with high L/B ratios. But these are relatively easy to diagnose and gating is probably not necessary. Conclusion: From the study made using 4D NCAT simulation, it was observed that in each selected ROI, the relative activity values in four cases are: Ideal PET images (without respiratory motion) > Amplitude Gated PET images > Time Gated PET images > Un‐gated PET images, here greater value means better and more accurate lesion detection.
TH‐D‐330A‐05: Modeling and Correcting for Respiratory Motion in PET
Authors: Vyas N , Schleyer P , Hill D , Marsden P
Published: July 2006

Purpose: To model and correct for respiratory motion in PET Method and Materials: Regular arrays of lesions of different sizes and contrast were incorporated into the NCAT Torso phantom. SimSET was used to simulate data acquisition and data was reconstructed using the filtered back projection algorithm at 16 phases of the respiratory cycle. Affine registrations were performed on the images to create a single summed motion corrected PET frame. The transformations were derived from (i) the PET images themselves and (ii) simulated CT images at the same respiratory phases. Results: Respiratory motion both blurs lesions and decreases the accuracy of quantification of PET images. These effects varied with lesion size and SUV. Lesion size is seen to increase and uptake values decrease in lesions undergoing motion. Smaller and lower contrast lesions show more differences between static, time average and motion corrected frames. Preliminary comparisons between corrected and static frames show that the CT corrected frame is closer to the static frame than the PET corrected one. Conclusion: We have developed a complete simulation of the PET data acquisition and reconstruction process based on the NCAT and SIMSET software packages, to assess the effect of respiratory motion and our proposed motion correction technique on PET data. For the small number of lesions of sizes described here, the differences in volume and SUV confirm that respiratory motion both blurs lesions and decreases the accuracy of the quantification of PET images. The simulation and assessment methods above were used to evaluate motion correction methods used to correct simulated PET data. Results show that smaller and lower contrast lesions show more differences in volume and SUV between the corrected, static and time average frames. Future work will involve looking into ways to improve the correction scheme, and application of the technique to clinical data.
TH‐D‐330A‐06: Registration of Gated PET Images Using Wavelet Denoising
Authors: Mawlawi O , Qiao F , Yue Y , Lofton B , Pan T
Published: July 2006

Objective: Gated PET images are characterized by low signal to noise ratio which results in poor image registration. The aim of this abstract is to evaluate the accuracy of image registration of gated PET images following wavelet denoising. Methods: A NEMA/IEC phantom containing 6 spheres of varying diameters (1–3.7cm) was filled with F‐18 water and positioned on a unidirectional translating platform in the FOV of a DST PET/CT scanner. A sinusoidal waveform (5 sec cycle, 2cm peak to peak) was used to drive the platform during the PET data acquisition. The platform motion was tracked using an RPM device which sent a trigger signal to the PET scanner at a specific phase of every repeating cycle of the waveform. PET data was acquired in 2D for 30 minutes using LIST mode and then rebinned using a gated prescription (10 bins of 500 msec each) into 13 different scan durations ranging from 1 min to 30 min. This scheme resulted in 13 gated image sets each corresponding to a different scan duration. The same experiment was then repeated using four different sphere/background ratios of 2, 3.4, 7.4 and 13.5. PET images were then reconstructed using OSEM. At each contrast ratio and scan duration, the gated images were first processed using wavelet denoising and then registered to the first bin. The estimated motion from this registration was then compared to that without wavelet denoising as well as to the true motion. Results: Wavelet denoising decreases the background noise without blurring the image. The effect of wavelet denoising on image registration decreased with increasing sphere‐to‐background ratio and increasing scan duration. Plots showing the difference between image registration with and without wavelet denoising will be presented. Conclusion: Wavelet denoising improves image registration. This improvement quickly diminishes with increasing scan duration and/or contrast ratio.
TH‐D‐330A‐07: Model‐Based Statistical Image Reconstruction for 4D PET
Authors: Li T , Thorndyke B , Schreibmann E , Yang Y , Xing L
Published: July 2006

Purpose: Four‐dimensional (4D) PET can be acquired with gated, dynamic or list mode. In reality, a major problem limiting its clinical application is the poor statistics, since the total coincidence counts in conventional 3D PET are divided into several phase bins and each of them is treated as an independent entity in 4D image reconstruction. We develop a mathematically rigorous system approach that allows one to maximally enhance the signal‐to‐noise ratio (SNR) of 4D PET by simultaneously considering the coincidences acquired at all time points when reconstructing the phase‐resolved images. Method and Materials: A GE Discovery‐ST PET/CT scanner was used to acquire 4D‐CT/PET images. A Real‐time Position Management (RPM) system was used to determine the respiration phases and to correlate temporally the PET and CT images. By deformable registration of the 4D‐CT images, a patient‐specific motion model was derived and incorporated into our “spatial‐temporal PET reconstruction” algorithm based on the maximum likelihood principle. The approach was quantitatively evaluated with numerical and physical phantom experiments. Five clinical studies of pancreatic, lung and liver cancer patients were then carried out. Results: Via a novel concept of “virtual curved line‐of‐response”, we proved that the PET “4D likelihood” can be maximized with a modified expectation‐maximization algorithm. Numerical/physical phantom experiments and patient studies showed that the algorithm converged monotonically. In the former two cases, the “ground truths” were reached within 40 iterations, and the SNRs were enhanced by more than 80% over the regular 4D PET and 35% over 3D PET. Similar level of improvement was observed for the patient studies. Conclusion: A spatial‐temporal reconstruction formalism has been established to fully take advantage of the coincidence information acquired in the 4D acquisition process when reconstructing phase‐resolved PET images. It allows us to obtain the statistically optimal 4D solution and substantially improved SNRs in 4D PET.
TH‐D‐330A‐08: A New Arterial Input Free Method of Deconvolution in Functional CT
Authors: Kim S , Cho Y , Haider M , Milosevic M , Yeung I
Published: July 2006

Purpose: In functional CT (fCT), the arterial input function (AIF) and tissue curve are measured and used for calculating the functional parameters by deconvolution. A new method of deconvolution without the requirement of AIF is presented. Method and Materials: The AIF is determined by the injection profile (IF) and the dispersion due to the patient's physiology (i.e. “patient function”, PF). Eight patients with cervix carcinoma participated in a fCT study, in which X‐ray contrast of 1.5ml/kg was injected at 4ml/sec. At the same time, a cine CT set was performed at a fixed slice at 1 rotation/sec for 120 sec. The AIFs are obtained from the CT scans and the PFs were determined by deconvolution of IF from AIF. The characteristics of PF were quantified and correlated with the patients' weight. The proposed method incorporates IF and PF into the deconvolution for the determination of functional parameters, as IF is known while PF can be partially determined in a population of patients. The method makes use of the strong correlation between PF and weight as constraint for deconvolution. The adiabatic tissue homogeneity model was examined. Functional parameters calculated with the conventional and new approach were compared. Results: The correlation coefficients of the maximum amplitude, peak‐to‐peak time, and amplitudes at 80 and 100 sec of PE, when correlated with patient' weight, were found to be −0.84, 0.45, −0.97 and −0.98 respectively. The spreads of the differences in blood flow, mean transit time, extraction fraction, and extravascular volume between the two methods were 2.83, 3.3, 6.29, and 6.45 % respectively. The mean differences of functional parameters between these two methods were <1 % except for extraction fraction (7 %). Conclusion: This study showed the feasibility to extract the patient function and incorporating it in deconvolution for fCT without the requirement of AIF.
TH‐D‐330A‐09: Factor of Ten Dose Reduction in CT Perfusion Imaging
Authors: Supanich M , Chen G , Rowley H , Hsieh J , Mistretta C
Published: July 2006

Purpose: To reduce by a factor of ten the patient dose in contrast enhanced CT Neuro Perfusion protocols while maintaining SNR and physiologic information relative to standard full dose CT Neuro Perfusion protocols. Method and Materials: Our group's newly developed undersampling algorithm for contrast enhanced MRI, HighlY constrained back Projection (HYPR), is applied to a contrast enhanced CT Neuro Perfusion protocol. By using temporally redundant information in the time series, a reduction in the number of required projection angles for each time frame is possible. The time series data is acquired using interleaved and equally spaced projections. A composite image consisting of projection information from either the entire time series or a limited number of time frames is first constructed by the standard filtered back projection technique. Next, a HYPR time frame is reconstructed by multiplying the composite image by backprojections for each projection angle in the time frame after normalizing them by the corresponding projection from the composite image. Results: HYPR time frames with similar SNR to fully sampled images and containing equivalent physiologic information for the creation of perfusion parameter maps have been obtained. The simulated reduction in the number of projection angles for the studies completed would result in a reduction in dose by a factor of 10. Computed parametric maps of CBV, CBF, and MTT are qualitatively similar to that of full dose maps, and arterial and venous input functions show excellent agreement with full dose input functions. Conclusion: The application of HighlY constrained back Projection (HYPR) to contrast enhanced CT Neuro Perfusion protocols allows a potential reduction by an order of magnitude to the delivered patient dose while maintaining SNR and physiologic information in the form of CBV, CBF, and MTT maps and arterial, venous and tissue input functions.
TH‐D‐VaIB‐01: Correction of Couch Artifacts in KV Cone‐Beam CT From An On‐Board Imaging System
Authors: Ali I , Lovelock D , Kriminski S , Chang J , Amols H , Ali I
Published: July 2006

Purpose: To evaluate artifacts caused by treatment couch attenuation on 3D image reconstruction for a new kV on‐board‐imager (OBI) and cone beam CT (CBCT) system and to develop an algorithm that filters couch effects from two‐dimensional radiographic projections prior to inputting to the 3D reconstruction algorithm. Material and methods: A standard quality assurance phantom was scanned in air and on couch top using both full and half fan cone‐beam scanning modes with and without bowtie filter combination. A spatial domain filter algorithm was developed to remove couch attenuation from each radiographic projection. This filter is based on a pixel‐by‐pixel subtraction technique of radiographic projections of cone‐beam scans of the couch from the corresponding radiographic projections of scans with phantom on top of the couch. The net couch‐filtered radiographic projections were used to reconstruct CT images. Results: CT numbers for scans of the phantom on couch top are less uniform than for scans of the phantom in air. The couch artifacts vary the linearity of the CT numbers by 5–15%, depending on the density of the material. Noise of the scans with phantom on couch top (3.5%) is higher than that with phantom in air (1.5%). The increased noise hinders the ability of the CBCT system to resolve low‐contrast regions when the couch is present. Pre‐reconstruction processing of the couch suppresses noise (< 1.5%) improves uniformity by a factor of 2 and removes ring and streak artifacts in the couch‐filtered reconstructed CBCT images. Conclusion: The treatment couch produces streaking artifacts, enhances noise, and causes drifting of CT numbers in the reconstructed OBI CBCT images. The developed couch pre‐processing algorithm suppresses noise, improves CT number uniformity by a factor of 2 and removes ring and streak artifacts in the couch‐filtered reconstructed CBCT images.

Conflict of Interest: Supported by NCI Grant P01‐CA59017.
TH‐D‐VaIB‐03: Unified Algorithm for KV and MV Scatter and Beam‐Hardening Correction Using the Convolution‐Superposition Method
Authors: Maltz J , Gangadharan B , Hristov D , Paidi A , Bose S , Bani‐Hashemi A
Published: July 2006

Purpose: Quantitative cone beam CT (CBCT) is essential for advanced radiation oncology (RO) applications such as portal image‐based 3D dose reconstruction. Quantitative CT requires accurate modeling of scatter, beam‐hardening and detector response. Scatter correction methods are typically semi‐empirical in nature and are designed to reduce visible artifacts while incurring low computational cost. In contrast, Monte Carlo (MC) methods are accurate but impractically slow. Convolution‐superposition (CS) scatter models offer a good balance between accuracy and computational complexity. We show how CS can be employed to implement a unified correction method that enables quantitative kV and MV imaging. Method and Materials: (1) We perform detailed MC modeling of the kV and MV cone beam imaging systems. (2) Using MC, we generate calibration data that map intensities recorded on the flat panel imagers to water‐equivalent thicknesses (WETs). (3) The MC models are used to generate pencil beam kernels for water cylinders of varying thickness. (4) Scattergrams are generated from acquired projection images via the CS method using these kernels indexed by the WET at each pixel. (5) Scattergrams are iteratively refined using a multiplicative correction formula that ensures that the estimated primary image remains non‐negative even when scatter‐to‐primary ratios are very high. (6) The FDK reconstruction algorithm is applied directly to the thickness maps corresponding to the estimated primary images. Results: The algorithm is able to reduce maximum non‐uniformity in the reconstruction of a 16cm cylindrical homogeneous tissue equivalent phantom from 11.7% to 1.5%. When applied to a challenging 35cm × 22.5cm oblong water phantom, a non‐uniformity reduction in from 36% to 2.5% is achieved. A dataset of 200 1024×1024 projections can be processed in 25 seconds. Conclusions: CS methods can be used at both kV and MV energies to enable reconstruction of quantitative CBCT images. Conflict of Interest: Supported by Siemens.
TH‐D‐VaIB‐04: Patient Alignment Using Megavoltage Cone‐Beam CT
Authors: Morin O , Gillis A , Aubin M , Chen J , Mu G , Bucci K , Pouliot J
Published: July 2006

Purpose: The growing use of conformal radiotherapy techniques has motivated the development of in‐room imaging systems capable of producing a patient 3D image that can be compared with the planning CT. We report on the Megavoltage Cone‐Beam CT (MVCBCT) positioning accuracy and its first clinical use for alignment of head and neck patients. Method and Materials: Using a standard treatment unit equipped with a flat panel detector, we compared a 2D setup technique using digitally reconstructed radiographs and portal images with a 3D setup technique using a diagnostic CT and MVCBCT. A gold seed placed at isocenter was imaged over time to measure the MVCBCT absolute positioning accuracy and stability. A Rando head phantom was imaged at 23 different locations in the treatment field to measure the capability of both setup techniques to determine shifts. A total of 18 MVCBCTs and corresponding pairs of orthogonal portal images were acquired on 8 patients undergoing treatment for head and neck cancers. Results: The absolute positioning accuracy of MVCBCT was better than 1.5 mm over several weeks. The mean and standard deviations of the differences between applied and measured shifts on Rando were (0.0±0.5) and (0.0±0.9) mm for MVCBCT and portal imaging respectively. For patient images, bony anatomy and soft‐tissue was visualized on MVCBCT while only bony structures could be used for alignment on portal images. The shift measurements made with the two methods were within 2 mm of each other in 68% of cases. However, differences as large as 4 mm were observed. Conclusion: The phantom measurements indicate that portal imaging and MVCBCT have the potential to verify patient shifts with sub‐millimeter precision. MVCBCT performed on patients showed translation shifts, rotations and anatomy deformations not always appreciated using portal imaging. Conflict of Interest: Research sponsored by Siemens OCS.