bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐HH‐BRB‐03: Correction for Multiple and Coherent Scatter in First Generation Incoherent Scatter CT for In‐Vivo Breast Imaging
Authors: Aviles JE Alpuche , Pistorius S
Published: August 2010

Purpose: We are currently working on a bench top system to investigate the benefits of reconstructing electron density (ED) images of the breast. Single incoherently scattered photons can be directly related to ED but multiple and coherent scatter cause additional scattering which lead to image artifacts. This work presents a correction for multiple and coherent scatter in first generation incoherent scatter CT of the breast. Method and Materials: Monte Carlo (MC) simulations were used to quantify the increase of scatter for breasts with different sizes and compositions. Scatter increase correction ratios (SICR) as a function of radiological path length were fitted to an empirical equation. The equation allows us to analytically calculate SICR using transmission CT. The accuracy of the correction was tested by reconstructing ED images of MC simulated scans for a homogeneous and an inhomogeneous breast. Results: Coherent scatter contributes ∼9% to the total scatter signal for a typical breast, demonstrating that multiple scatter is the major source of image artifacts. The fitted equation corrects for multiple and coherent scatter with errors of 11% ± 2% for the homogeneous breast and 21% ± 10% for the inhomogeneous breast. The errors in ED images are of − 9% ± 4% for the homogeneous breast and −4% ± 3% for the inhomogeneous breast. The corrected ED image is twice as accurate as the uncorrected image and twice as precise as the image based on the linear attenuation coefficient. Conclusion: The scatter increase due to multiple and coherent scatter is weakly dependent on breast size and composition. This allows an empirical equation to be used to correct multiple and coherent scatter artifacts. Our study shows the feasibility of reconstructing ED breast images using our approach and future efforts will be devoted to its practical implementation.
SU‐HH‐BRB‐05: Variations in 6MV Photon Energy Spectra Impact the Response of TLD
Authors: Scarboro S , Kry S , Howell R , Followill D
Published: August 2010

Purpose: TLD exhibits a response that is dependent on photon energy; however, the specific energy response is typically determined only for the photon spectrum at the standard dose calibration point (depth of maximum dose on central axis from a 10cm×10cm field). Variations in the energy spectra as a result of field size, measurement location, or the presence of heterogeneities have not been previously considered. Therefore, we sought to quantify these variations from a 6‐MV beam, as well as to characterize the corresponding changes in energy response of thermoluminescent dosimeters (TLD). Method and Materials: Photon energy spectra from a 6MV beam were simulated at various locations throughout a water tank using Monte Carlo. This was done for fields sizes ranging from 5cm×5cm to 20cm×20cm, and for locations up to 20cm deep and 50cm from the central axis. We also calculated the spectra with the addition of 9cm of bone and lung material. The range of calculated energy spectra were then used to determine theoretical energy correction factors of TLD through the application of Burlin cavity theory. Results: The photon energy spectrum varied with location and field size, and was most substantially different outside of the treatment field. The presence of heterogeneities had little impact on the spectrum. Correspondingly, within the treatment field, as well as in the presence of heterogeneities, there was only a small perturbation to the dose measurement of the TLD (<1%). The most substantial energy response was for dose measurement outside of the treatment field, which varied up to 8% relative to the central axis calibration location. Conclusion: Variations in photon energy spectrum do not greatly impact the TLD response under most in‐field conditions. A single additional energy correction factor of 0.95 should be applied to out‐of‐field measurements using TLD to correct for changes in photon energy spectra.
SU‐HH‐BRB‐07: Thin Film CdTe Photovoltaic Detector Performance under Diagnostic X‐Ray Beams
Authors: Jin X , Parsai I , Shvydka D
Published: August 2010

Purpose: Recent development of thin‐film cadmium telluride (CdTe) deposition techniques allows manufacturing of low cost large‐area devices, having the direct detection design with superior imaging capabilities, and outstanding radiation hardness. We investigate the performance of a thin‐film CdTe‐based radiation detector operating in a photovoltaic mode under the range of energies relevant to diagnostic imaging applications. Methods: The energy deposition in CdTe layer of varying thickness was evaluated by Monte Carlo simulations under diagnostic X‐ray beams, yielding the charge carrier generation profiles across the film thickness. These profiles were used for modeling of current‐voltage (I–V) characteristics with device operation modeling software SCAPS, routinely employed for photovoltaic devices. The results for the thinnest devices were compared to those measured under Varian Ximatron simulator in our clinic. Results: Performance of CdTe detector having thickness from 3 to 1000 microns was studied under X‐ray beams with 70 to 120kVp energies. Output voltages and currents were extracted from I–V characteristics modeled with SCAPS. The output parameters for thicker devices were found to gradually decrease with thickness. The two major factors responsible for these trends are the limited average photon penetration depth of about 150 m, and enhanced charge carrier separation near the CdS/CdTe junction region. The X‐ray beams of higher input energies produced higher output signals. The measurements on experimental 3 and 10 micron thick CdS/CdTe devices confirmed some of the general trends found through the modeling, though the output signal was lower than modeled. Conclusions: Device operation modeling led to estimates of expected output signals and their dependence on CdTe layer thickness and input X‐ray beam energy and intensity, provided important insights into device operation. The experimental results demonstrated that even at the thinnest detector has signal sensitivity and linearity adequate for use in quantitative measurements under diagnostic X‐ray beams.
SU‐HH‐BRB‐08: Blood Flow and Volume Changes during Simulated Mammography
Authors: Busch DR , Minkoff DL , Choe R , Durduran T , Schnall MD , Rosen MA , Yodh AG
Published: August 2010

Purpose: Ascertain effects of mammographic compression on microvascular blood flow and thus understand potential confounding factors due to compression on contrast agent distribution. Method and Materials: An X‐ray mammogram simulator was constructed to hold optical fibers for diffuse correlation spectroscopy measurements of blood flow and diffuse optical spectroscopy measurements of hemoglobin concentration and oxygenation. 15 healthy subjects were recruited for experiments consisting of 3 serial compression‐release cycles. Results: Small (∼15% or ∼1cm) changes in plate separation resulted in dramatic changes in blood volume (∼47%) and flow (∼65%) in measurements of 15 subjects. However, there was significant inter‐ and intra‐ subject variation in response within the population. Conclusion: The distribution of contrast agents injected during mammographic compression will be affected by the average and inhomogeneous changes in blood flow measured in this study. This study is currently being expanded and instrumentation improved to identify the cause of inter‐subject variation in blood flow changes.
SU‐HH‐BRB‐12: IGRT Via Machine Learning from Limited Angle Projection Images
Authors: Chou C , Pizer S , Frederick B , Chang S
Published: August 2010

Purpose: To yield accurate patient treatment setup correction from few numbers of projection images in tomosynthesis‐based IGRT approaches using cone‐beam CT (CBCT) and the novel carbon nanotube stationary tomosynthesis (NST) devices. Method and Materials: Our method uses a machine learning strategy that has a two‐stage process: training and IGRT. In the training stage we perform a patient‐specific training that samples from a range of potential patient movements, and for each such movement we generate 2D projections by transforming and re‐projecting the patient's planning CT. We compute a linear regression between the patient movements and the differences between the projections of the moved CT and those of the CT in the planning position. In the IGRT stage, the learned regression model is applied iteratively to the successive residues between the real‐time projections and those of the moving CT transformed by the previously predicted parameters. This iteration yields the predicted transformation with sub‐voxel accuracy. The re‐projection process is implemented on GPUs to speed up the real‐time image guidance that will be enabled by the carbon nanotube based stationary tomosynthesis IGRT system NST. Results: We tested our method using three patients' head‐and‐neck CTs. A total of 180 test movements were simulated with combination of both translations and rotations that were randomly picked within −2 to 2 cm and −5 to 5 degrees, respectively. The NST and the 44‐degree CBCT IGRT devices are simulated in our tests. The mean of the vector error distance are 0.1270 cm with 12 NST image projections and 0.1116 cm with 5 image projections from the 44‐degree CBCT. Conclusion: Our method can yield accurate patient's position and orientation correction with limited projection images, which is important for image‐guidance during treatment delivery and the reduction of imaging radiation dose. Conflict of Interest: Research sponsored by Siemens Medical Solutions.
MO‐SAM‐201B‐01: Optimizing CT Dose and Image Quality for Different Patient Sizes
Authors: McNitt‐Gray M
Published: August 2010

CT technology has improved dramatically over the past decade and its clinical utilization has increased significantly as well. While CT can yield exquisite descriptions of anatomy that were not previously possible (at least not with noninvasive techniques), its increased utilization has led concerns over radiation dose; CT has now been identified as the single largest contributor to medical radiation dose to the population and accounts for approximately 50% of medical exposure. Methods to reduce radiation dose have been the focus of all stakeholders (medical physicists, technologists, radiologists, manufacturers and regulators). Reducing dose while maintaining acceptable image quality can be complex and this is made even more complex when considering patients of different sizes.

This talk will first describe methods currently used, and some being developed, to estimate radiation dose in patients. This will include a discussion of measurement techniques as well as Monte Carlo simulation‐based techniques. Specific attention will be paid to the differences in dose to patients of different sizes ranging from pediatric patients to obese adult patients. Tradeoffs in image quality and radiation dose will also be described in this context as well. Radiation dose reduction techniques, including a review of various tube current modulation schemes currently being employed will also be described. The effect of these dose reduction methods on both radiation dose and image quality will be discussed, again with attention to how they can be deployed with patients of different size.

Learning Objectives:

1. Understand how radiation dose for CT studies is currently estimated

2. Understand the trade‐offs of dose and image quality, especially for large (obese) patients and in pediatric patients

3. Review of the manufacturers' dose modulation methods and how these affect dose in different patients
MO‐D‐201C‐03: Advances in MR: State of the Art Today and Future Directions — MR‐Guided Interventions
Authors: Stafford R
Published: August 2010

Image‐guidance of minimally invasive interventions for diagnosis and therapy has been a rapidly evolving field, particularly with respect to incorporation of increasing advanced imaging equipment for the planning, targeting, monitoring and assessment of procedures. Traditionally, these vascular, therapeutic and biopsy procedures have been carried out using fluoroscopy, ultrasound or CT. MRI is an inherently 3D, non‐ionizing imaging modality offering multiple soft‐tissue contrast mechanisms as well as functional imaging in a single locale. Because of these unique properties, use of MRI for guidance of interventions has been of growing interest in recent years for a number of procedures requiring stereotactic localization and planning or real‐time image guidance and monitoring, such as biopsy and thermal therapy delivery.

However, despite the recent proliferation of commercially available hardware and software solutions for MR guided procedures, integration of MRI into an intraoperative and interventional environment remains a challenge. Because of the cost associated with equipment acquisition and siting, careful attention should be paid to specifying the MR system as well as the location of the facility. The specification of hardware and software, as well as the layout of the suite, strongly influence workflow and domain of possible procedures that can be realistically performed in the suite. Last, but certainly not least, the safety of patients and staff working in the MR environment must be considered and programs put in place to continuously educate staff who work in these suites.

This talk aims to provide an overview of MR‐guided interventional procedures which are currently performed clinically on high‐field (≥1.5T) cylindrical bore systems with an emphasis on the potential for guidance of thermal ablative therapies. Illustrations of the use of MRI for planning and targeting lesions as well as monitoring and assessing thermal therapy delivery (i.e., cryotherapy and laser ablation) will be presented and challenges associated with these procedures discussed.

Learning Objectives:

1. Understand some of the enabling technology facilitating MR‐guided interventions as well as be able to identify challenges and safety concerns.

2. Understand some of the tradeoffs in MR imaging of tumors for treatment planning, targeting, real‐time monitoring and post‐therapy assessment of thermal therapy.
MO‐D‐201B‐02: Distributed X‐Ray Source Development
Authors: Frutschy K , Neculaes B , Inzinna L , Mani V , Caiafa A , Reynolds J , Zou Y , Zhang X , Gunturi S , Cao Y , De Man B , Roffers R , Lounsberry B , Pelc N
Published: August 2010

This work is funded in part by NTH grant R01EB006837 and General Electric Global Research. Distributed x‐ray sources have unique capabilities, which can enable break‐through medical imaging system performance. In particular, the distributed x‐ray source or “multisource” from GE has high instantaneous power, fast source switching, consistent focal spot sizes, large angular coverage, and high reliability [1]. This multisource is scalable from 1 to 2 rows of sources with source spacing in each row at 25mm currently with potential reduction down to 10mm. The multisource is being scaled up from 8 to 32 sources for the Inverse Geometry Computed Tomography (IGCT) application [2,3], which offers up to 70% x‐ray dose reduction, cone‐beam artifact reduction, and higher temporal resolution compared to conventional CT systems. Another multisource application is digital breast tomosynthesis (DBT). Today's DBT systems rely on physically moving a conventional x‐ray source over an arced path to obtain views at the required angles. A multisource not only eliminates mechanical motion and provides a faster scan, it also allows for multiple x‐ray spectrums (W, Rh, Re) at interleaved positions. Lastly, an x‐ray multisource enables vascular surgeons to see a real‐time 3D view of an interventional tool inside the blood vessels that they are navigating through. The ability to adjust electron beam current for each source (i.e, virtual bow‐tie) provides the precise amount of x‐ray dose required at each view for a particular patient's size thus eliminating excess dose in both IGCT and vascular tomography. This paper summarizes the current multisource development work, challenges, and application benefits.

Learning Objectives:

1. understand x‐ray multisource architecture and performance

2. understand medical imaging system benefits from x‐ray multisource
MO‐EE‐A2‐02: Failure Mode and Effects Analysis (FMEA) on Xoft®
Authors: Palaniswaamy G , Richardson S , Rangaraj D , Mutic S
Published: August 2010

Purpose: To perform failure mode and effects analysis on Xoft®, the alternative Brachytherapy source. The purpose of FMEA analysis is to identify the weak links in the process and develop quality management (QM) measures to reduce the likelihood of such failures. Methods and Materials: FMEA is a strategic activity employed in various industries to recognize and evaluate potential failures of a process/product, estimate the effects caused due to any failures/events and take corrective measures to reduce or eliminate the probability of occurrence of such failures. The entire process is quantified using an RPN (Risk Priority Number) score calculated as RPN = S × O × D, where S is the severity of the event when it occurs, O is the frequency of occurrence of such an event and D is the probability of detection when an event occurs. All the factors are on a scale of 1 (low) to 10 (high). The higher the RPN score, the higher the risk due to the event. The RPN scores were estimated initially assuming that there were no QM measures in place, and then reassessed after implementation of QA/QC procedures, to evaluate the effectiveness of he QA program. Results: Four processes were analyzed and 14 failure modes identified; 4 modes with significant RPN scores above 230. A wrong dose delivery due to a calibration error had the highest RPN score of 400 when there was no QA process which reduced to 192 when QA procedures were established. The event with the next highest RPN score of 300 was source positioning error caused due to transit error which reduced to 120. Conclusion: The QA/QC procedures established for the Xoft® system were found to be effective in educing RPN scores and establishment of a systematic QM program.
MO‐EE‐A2‐06: The Puzzle of Repair Half‐Time in Mouse Lung Irradiation — Application of the GLQ Model
Authors: Wang J , Huang Z , Lo S , Yuh W , Mayr N
Published: August 2010

Purpose: The repair half‐time of radiation damage for mouse lung remains controversial. To solve the puzzle, we reanalyzed the existing data using the generalized LQ (gLQ) model that was developed to address the dilemma of LQ model in high dose region. Method and Materials: An animal dataset of mouse lung irradiation (Vegesna et al. IJMB 1985;47:413) was studied. In this experiment, mouse lung was irradiated with repeated dose from 1.15 Gy to 13.43 Gy. The endpoint was death due to radiation pneumonitis. A repair half‐time of 1.5 hour derived from the data of reciprocal of LD50 (lethal dose for 50% mortality) vs. dose‐per‐fraction was much longer than the repair half‐time of 0.4 hour published in the literature. In this study, the same data set was reanalyzed using both the LQ and the gLQ models. The c2 min method was adopted to fit the data and to evaluate the figure of merit for the two models. Results: Fixing the repair half‐time to 0.4 hour, the gLQ model fit the data much better than the LQ model: the reduced c2 min is 0.39 vs. 2.8 respectively. The a/b ratio was also quite different: 1.7 Gy for the gLQ model, and 3.3 Gy for the LQ model. While the gLQ model correctly predicted the high dose response based on low dose data, the LQ model could not reproduce the downward curvature shown in the LD50 plot. Conclusion: Our results indicate that the gLQ model provides a consistent interpretation of the mouse lung data across fraction sizes up to 13 Gy and naturally solves the puzzle of repair half‐time faced by the LQ model. Therefore, the gLQ model is useful to extend our clinical experience accumulated from conventional low‐dose fractionation to high dose irradiation schedules, including SRS/SBRT and HDR brachytherapy.
MO‐E‐BRA‐03: Adjustment of Lateral and Longitudinal Size of Scanned Proton‐Beam Spots Using a Pre‐Absorber
Authors: Titt U , Mirkovic D , Sawakuchi G , Perles L , Newhauser W , Taddei P , Mohan R
Published: August 2010

Purpose: To evaluate the efficacy of adding a pre‐absorber in the exit of a scanning proton beam head to reduce the lateral beam spot size, increase the longitudinal spot size and extend the interval of clinically useful beam ranges to shallower depths. Method and Materials: We investigated a method for adjusting the lateral and longitudinal spot size that utilizes downstream plastic pre‐absorbers located near a water phantom. The spot size adjustment was characterized using a validated Monte Carlo model of a modified commercial scanned‐beam treatment head. Results: Our results revealed that the pre‐absorbers can be used to reduce the lateral full width at half maximum of dose spots in water by up to 14 mm, and to increase the longitudinal extent from about 1 mm to 5 mm at residual ranges of 4 cm and less. A large factor in manipulating the lateral spot sizes is the drift space between the pre‐absorber and the water phantom. Increasing the drift space from 0 cm to 15 cm lead to an increase in lateral FWHM from 2.15 cm to 2.87 cm, at a water equivalent depth of 1 cm. Conclusion: Our findings suggest that it is possible to improve dose spots delivered from a scanning proton beam treatment head. By using pre‐absorbers we were able to reduce the lateral spot size for shallow target sites (< 17cm). Additionally, we were able to increase the longitudinal spot size and therefore reduce the amount of energy levels necessary to cover the target volume. This method may lead to improved penumbrae for scanned proton treatments of shallow sites, such as head and neck cancer.
MO‐E‐204C‐04: Improving Robustness of Phase Retrieval in X‐Ray Phase Contrast Imaging
Authors: Wu X , Yan A , Liu H
Published: August 2010

Purpose: The phase retrieval, retrieving tissue phase maps from the x‐ray phase contrast images, is an important task in x‐ray phase‐sensitive imaging. The robustness of phase retrieval algorithms is of critical importance for reducing radiation doses in clinical applications. We show that the conventional phase retrieval method is actually unstable against the quantum noise. We present a more robust phase retrieval method that we developed. Method and Materials: We first studied the phase retrieval by means of the conventional Transport of Intensity Equation (TIE) method for phantom imaging (such as a nylon air bubble wrap). For improvement we developed a robust phase retrieval method based on our notion of the phase‐attenuation duality and attenuation partition, and derived a robust iterative phase retrieval algorithm. This algorithm had been applied to experimental phase contrast imaging with phantoms. In addition the phase retrieval accuracies had been analyzed with computer simulations of phase contrast imaging of a digital phantom of breast tissue characteristics. Results: We found that the TIE‐based phase‐retrieval suffers from an intrinsic singularity. The phantom imaging showed that the TIE‐based phase retrieval method is unstable against the noise and misalignment in phase contrast imaging, even if the Tikhonov regularization was employed. In contrast, our method based on the phase‐attenuation duality and attenuation partition is singularity‐free, and is robust in terms of the phase‐map image quality and phase‐map accuracies against the noise and misalignment, as is verified by means of experimental phantom imaging and computer simulation. Conclusion: The conventional TIE‐based phase retrieval method is unstable against noise and image misalignment. Our phase retrieval method method based on the phase‐attenuation duality and attenuation partition is robust against the noise and image misalignment. Research supported in part by DoD Breast Cancer Research Program.
MO‐E‐204C‐05: X‐Ray Luminescence Computed Tomography Via Selective X‐Ray Excitation
Authors: Pratx G , Carpenter C , Sun C , Xing L
Published: August 2010

Purpose: X‐ray luminescence computed tomography (XLCT) is proposed as a new molecular imaging modality for imaging X‐ray‐excitable phosphorescent nanoparticles three‐dimensionally, in living subjects. Some of these nano‐sized particles can emit near‐infrared (NIR) light when excited with X rays and are particularly well suited for in‐vivo biomedical imaging because the signals can propagate long distances in tissue. Method and Materials: The imaging mechanism used in XLCT consists in irradiating the subject using a sequence of programmed X‐ray beams, while sensitive photo‐detectors measure the light coming out of the subject. By restricting the X‐ray excitation to a single, narrow beam of radiation, the origin of the light photons can be inferred regardless of where these photons were detected, and how many times they scattered in tissue. By including an X‐ray detector in the system, anatomical imaging is performed simultaneously with molecular imaging via standard X‐ray computed tomography. The molecular and anatomical images are spatially and temporally co‐registered. Simulations of an XLCT system were performed using an analytical beam model. A preliminary experiment was also conducted using a superficial treatment beam and an EM‐CCD camera. Results: Tracer uptake in a 2 mm‐diameter target can be detected and quantified with sub‐picomolar sensitivity using less than 1 cGy of radiation dose, a result that makes XLCT potentially more sensitive than PET, currently one of the most sensitive molecular imaging modalities. Provided sufficient signal‐to‐noise ratio, the spatial resolution of the system can be made as small as needed by narrowing the beam aperture. In particular, 1 mm uniform spatial resolution was achieved for a 1 mm‐wide X‐ray beam. Images reconstructed from experimental XLCT measurements showed good agreement with the simulation model. Conclusion: Preliminary simulations and experiments show that XLCT is a feasible approach for small objects, such as research animals or dedicated organ imaging.
MO‐E‐204C‐06: Validation of In‐Air Micro‐CT Measures of Excised Tumor Volume as Gold Standard for Tumor Size Response in Rodent Models
Authors: Lee Y , Goins B , Fullerton G
Published: August 2010

Purpose: The treatment efficacy of anticancer drugs is often assessed by measurement of tumor size change. Radiologic assessment of tumor size has been performed using one‐dimensional measurement (RECIST), area calculated from two linear dimensions (WHO criteria), and volume calculated from two or three linear dimensions using a variety of equations or other volumetric techniques. However, one‐ and/or two‐dimensional measurements may misrepresent change in tumor size by disregarding the second and/or third dimension. It is frequently proposed that the weight of an excised tumor is the most consistent and reproducible reflection of its volume. The aim of this project is to validate that in‐air micro‐CT imaging volume of an excised tumor can be gold standard in place of mass. Methods and Materials: Ultrasound, micro‐CT and MR imaging of twenty head and neck rat tumor models (SCC‐4) ranging in size from 4.19 mm3 to 1436.76 mm3 were performed followed by caliper measurements. Tumors excised from rats were weighed and in‐air micro‐CT images of the excised tumors were obtained. In‐air micro‐CT imaging volume of excised tumors was calculated using a voxel counting method of Analyze software. NIST‐traceable acrylic phantoms were used to validate accuracy and precision of micro‐CT imaging volume. In situ tumor size measurements were made in three perpendicular dimensions for each modality. 1D (RECIST), 2D (WHO) and 3D (volume) analysis was performed for each modality as well as the caliper method, and compared with excised tumor volume. Results: The accuracy (∼ 0.4%) of in‐air micro‐CT imaging volume of excised tumors was confirmed using acrylic phantoms. In situ volumes in three modalities were linear to “gold standard” excised tumor volumes and showed statistically to be the most likely model. Conclusion: It is concluded that in‐air micro‐CT imaging volume of excised tumors is a more direct gold standard and nearly equivalent to mass.
MO‐E‐204B‐01: JUNIOR INVESTIGATOR WINNER: A New Simple, Accurate, and Quantitative Approach for Routine Quality Assurance in Digital Radiography
Authors: Kuhls‐Gilcrist A , Bednarek D , Rudin S
Published: August 2010

Purpose: We report on a new approach for measuring the MTF, instrumentation‐noise‐equivalent exposure (INEE), and DQE that is easily implemented, highly accurate, and does not require specialized measurement devices. No slits, edges, alignment devices, or other costly accessories are needed. Method and Materials: A method has been developed to obtain the MTF, INEE, and DQE using only the noise characteristics in dark‐ and flat‐field images. For demonstration, measurements were done on three different detector technologies: an x‐ray image intensifier, a flat‐panel detector, and a solid‐state x‐ray image intensifier. Ten dark‐field and flat‐field images (obtained at one exposure level using RQA 5) were acquired according to standard guidelines and the NPS was measured for each set of images. The electronic part of the NPS (constant, irrespective of exposure) and the quantum part of the NPS (proportional with exposure) could then be separated. MTFs were determined from the quantum part of the NPS using the new noise‐response (NR) method. Frequency‐dependent INEEs were measured by determining the exposure where quantum and electronic noise would be equivalent, thereby quantifying the quantum‐limited operating range of the detector. DQEs were determined from the measured MTFs and NPSs. A software package was written to automate the analysis. Results: Using this simplified approach, we observed agreement within 5% at the detector Nyquist frequency (even better agreement at lower spatial frequencies) with the most rigorous metric measurement methods. Measurements took less than 10 minutes per detector and were stable over a three‐month period, indicating no changes in, or problems with, detector performance. Conclusions: This work describes a simple technique for quantitative measurement of detector performance in terms of resolution (MTF), noise (INEE), and signal‐to‐noise ratio (DQE) that can be practically implemented into routine QA programs to assist in the verification of proper imaging system performance. (Support: NIH Grant RO1EB008425)
MO‐E‐204B‐02: X‐Ray Spectroscopy with a Room Temperature CdZnTe Detector
Authors: Fritz SG , Shikhaliev PM
Published: August 2010

Purpose: To investigate room temperature CdZnTe detectors for x‐ray spectroscopy. Method: X‐ray spectroscopy with accurate, simple, and room temperature detectors are of interest. The CdZnTe semiconductors are recognized as a good candidate. However, CdZnTe detectors suffer from hole trapping and spectral tailing which is unstable and difficult to correct. We investigated two CdZnTe detectors with different configurations for x‐ray spectroscopy. A 1×1 cm2 planar detector with 3 mm thickness and a 5×5×5 mm3 capacitive grid detector were used. Tilted angle irradiation was used to decrease hole trapping. Spectra were first acquired from isotopes sources 241Am, 59.5 keV, and 57Co, 122 keV. Each source was measured at normal and tilted angle incidence of radiation and peak‐to‐total ratios were compared. X‐ray spectra were acquired at 40, 60, 80, 100, and 120 kVp tube voltages. Monte Carlo calculations were used to simulate Cd and Te K x‐ray escape from CdZnTe. The measured x‐ray spectra were corrected for K x‐ray escape using the stripping procedure. The corrected x‐ray spectra were then compared to theoretical spectra simulated using published methods and verified software. Results: It was shown that tilted angle irradiation can virtually eliminate hole trapping and spectral tailing thus increasing peak‐to‐total ratios by more than 40% and 130% for 59.5 and 122 keV photons, respectively. X‐ray spectra showed major improvement with tilted angle irradiation. The capacitive grid detector has shown overall better performance compared to planar detector. Conclusion: Tilted angle of the x‐ray beam with respect to the detector surface virtually eliminates hole trapping and spectral tailing. Tilted angle increases K x‐ray escape, however, this can be simulated with high accuracy and corrected for, while hole trapping is not stable and difficult to correct. The capacitive grid detector has shown better performance in tilted angle configuration due to its inherently higher energy resolution.
MO‐E‐204B‐04: Interventional Fluoroscopy Procedure Skin Dose Assessment Using DICOM Dose Structured Reports
Authors: Schueler B , Pavlicek W , Khodadadegan Y , Zhang M , Paden R , Fetterly K , Wu T , Langer S
Published: August 2010

Purpose: Patient skin injury due to radiation exposure during interventional fluoroscopy procedures is a concern. The FDA has recommended dose be monitored, along with the dose distribution on the patient's skin. Modern fluoroscopy equipment provides a readout of the accumulated reference point air kerma. However, this parameter is a poor estimate of localized skin dose since it does not take into account beam movement. Acquisition information needed to calculate skin dose can be recorded as a DICOM Dose Structured Report (Dose SR), which has recently become available on new fluoroscopy equipment. We have developed a system that uses the Dose SR to produce a skin dose map, along with determination of the peak skin dose. Method and Materials: The Dose SR provides data for each irradiation event (fluoroscopy footswitch or acquisition): kerma‐area‐product, reference point air kerma, C‐arm angulation and table position. Using the position of the patient on the table, backscatter and table attenuation, the air kerma to 1‐cm2 regions on the patient's surface is calculated. The patient surface is approximated as a mathematical model using SolidWorks simulation software, with model size varied based on patient parameters. Results: The method was validated using a Siemens Axiom Artis angiography system. Measurements made with an ionization chamber and lucite phantom were compared to calculated skin dose values for a range of C‐arm angles, table positions and exposure levels. Errors ranged from 2–10% with higher errors corresponding to increased C‐arm angulation. Conclusion: A system has been developed to estimate skin dose and generate skin dose maps from an interventional procedure Dose SR. The system allows for a more precise determination of localized skin dose and assists with planning appropriate entry ports for future procedures to minimize skin injury. Application to any vendor platform providing a Dose SR is possible.
MO‐E‐204B‐05: A Novel Organ Dosimetry in an Anthropomorphic Phantom Using XRQA‐2 Radiochromic Film
Authors: Brady S , Yoshizumi T , Toncheva G , Anderson‐Evans C , Fredrickson M , Frush D
Published: August 2010

Purpose: A novel method to measure organ dose distributions in a phantom of heterogeneous tissue composition was established using radiochromic XRQA‐2 films. Film response accuracy was validated using thermoluminescent dosimeters (TLDs). Method and Materials: Film response accuracy and sensitivity in CT exposure geometry were verified by comparing TLD responses between two CTDI head phantoms. The phantoms were placed end‐to‐end to allow for a uniform scatter environment. TLDs and films were placed between cross‐sectional slabs of a 5‐yr old anthropomorphic phantom's thorax and abdomen regions. Software was written for dosimeter comparison within a complex anthropomorphic phantom. Film accuracy within the anthropomorphic phantom was measured by comparing TLD results within the lung, liver, and kidney organs. Results: Film and TLD dose response differences were measured for CTDI phantom, 45% (SD ± 2%), and for the anthropomorphic phantom in the lung, 28% (SD ± 8%), and liver/kidneys, 15% (SD ± 4%). Due to consistent response differences in low and high organ dose, a tissue specific correction was applied to the film organ responses. Corrected film response agreed to better than 3% (SD ± 2%), for CTDI scans, and 3% (SD ± 3%) for lungs, 5% (SD ± 3%) for liver, and 4% (SD ± 3%) for kidneys. Film measured a heterogeneous dose distribution within the organ volumes; the extent of which was not measured with the TLDs. XRQA film demonstrated an advantage over the TLD method by discovering a 15% greater maximum dose to lung in a region unmeasured by TLDs. Conclusion: XRQA films demonstrated lower sensitivity to absorbed dose measurements due to geometric inefficiencies of measuring dose from a beam situated end‐on to the film. Corrected film responses demonstrated equivalent measurement accuracy as TLD detectors with the added advantage of measuring high‐resolution dose distributions throughout an organ volume.
MO‐FF‐A1‐01: Optimal Schedule for Localized Radio‐Sensitization of 125I Prostate Implants
Authors: Cormack R , Nguyen P , D”Amico A , Sridhar S , Makrigiorgos M
Published: August 2010

Purpose: Localized radiosensitization may improve the therapeutic ratio of 125I prostate brachytherapy. Spacers used in permanent implants may be manufactured from a drug‐releasing polymer. Loading the polymer with radio‐sensitizer would allow spacers to deliver protracted release of radio‐sensitizer localized to the prostate. Such devices will have a limited drug‐loading capacity, and the drug release schedule that optimizes outcome, under such a constraint, is not known. This work seeks optimal drug release schedules for 125I prostate brachytherapy and demonstrates the manufacture of such spacers. Method and Materials: Mathematical models of cell kill based using quadratic (LQ) models were used to compare biologic effectiveness of a number of drug release schedules where sensitization is present for a limited time (T). A range of radiosensitizations (S) was simulated by incorporating time dependent α and β values in the LQ model and calculating cell survival fractions. To avoid model dependence, a range of baseline α/β values were considered. A limited drug capacity was simulated by comparing schedules with equal products of sensitization and time (ST). To evaluate the ability to create drug‐releasing spacers, a gold fiducial marker was coated with a polymer loaded with fluorescent molecules. Results: Comparing cell kill for schedules with equivalent ST shows that the cell kill is increased more by delivering a substantial sensitization over a shorter time than by sensitizing less for a longer time. Extended duration of radio‐sensitization requires a time scale of weeks to achieve increased cell kill given sensitization levels reported for taxol. Polymer coated fiducials show 2‐week drug release is technically feasible. Conclusion: Using brachytherapy spacers to produce localized radio‐sensitization over the time scale relevant to prostate brachytherapy is feasible. Both traditional sensitizers and repair inhibitors may be employed to improve the therapeutic ratio of prostate brachytherapy.
MO‐FF‐A1‐02: Tolerance of Source Position Accuracy in HDR Brachytherapy in the Era of 3‐Dimensional Treatment Planning
Authors: Gao M , Roeske J , Albuquerque K
Published: August 2010

Purpose: 3D CT/MRI based treatment planning has largely replaced 2D radiographs in HDR brachytherapy. Although dose‐volume‐histogram provides better estimate of organ dose than ICRU point, its accuracy suffers from source position errors due to intrinsic high dose gradients. The actual source dwelling position deviates from the position shown in plan because: applicator gets pushed in or pulled out during transportation between OR, CT/MRI and HDR; slice thickness of CT/MRI images introduces localization error in reconstructed applicator; HDR machine has ∼1mm mechanic error in specification. In this study, we estimated the dosimetric changes due to source position errors. Method: Nineteen fractions from ten cervical patients were included. Prescription was 6 Gy using tandem/ovoids. CT‐based plans were evaluated following GYN‐GEC‐ESTRO guidelines (D90 for CTV, D2cc for OAR). H point and ICRU bladder/rectal point dose were also calculated. For each plan, source positions were shifted to mimic source position error, and resulting dosimetric changes were computed. Two levels of error were studied: 2.5 mm and 5.0 mm. Results: For a 2.5 mm error, CTV D90 changed by 1.8% while H point dose changed by 2.2%. D2cc for bladder, rectum and sigmoid changed by 4.8%, 3.4% and 3.9% respectively. ICRU bladder and rectal point dose changed by 11.4% and 3.3% respectively. For a 5.0 mm error, CTV D90 changed by 3.7% while H point dose changed by 4.6%. D2cc for bladder, rectum and sigmoid changed by 10.9%, 6.6% and 8.4% respectively. ICRU bladder and rectal point dose changed by 23.8% and 6.9% respectively. Conclusion: Volumetric parameters are less sensitive to source position errors than ICRU points. Tumor coverage is not affected much by such errors. ICRU bladder point is extremely sensitive to such errors. To achieve an overall accuracy of 5% in dose delivery, combined source position error should be kept within 2.5 mm.
MO‐FF‐A1‐03: Comparison of Inter‐ and Intra‐Observer Variability in Prostate Definition with Tissue Harmonic (H) and Brightness (B) Mode Imaging
Authors: Sandhu G , Dunscombe P , Meyer T , Pavamani S , Khan R
Published: August 2010

Purpose: To compare the image quality of tissue harmonic (H) with brightness (B) mode transrectal ultrasound (TRUS) images of the prostate gland, by studying the interobserver and intraobserver variation in prostate delineation. Method and Materials: Transrectal ultrasound images of the prostates of 10 patients were acquired using both B and H ultrasound imaging modes. The prostates on all image sets were contoured by an experienced radiation oncologist (RO) and five equally trained observers. The volumes of the prostate glands were calculated and compared among the observers, and against the RO. Prostate contours for one of the patients were drawn five times by four observers in order to evaluate the intraobserver variability. The prostate volumes were also compared to observe the inter mode (B vs H) variation. Results: A one sample student t‐test showed that the volumes outlined by the five observers are in close (p>0.05) agreement with that of the RO in both imaging modes. Based on a paired student t‐test it was found the prostate volumes with H mode were significantly smaller (p=0.008) than that of B mode. Inter‐ and intraobserver consistency was estimated based on standard deviations as percentages of mean volumes and concordance indices (CIs). It was found that for smaller prostate glands (≤ 35 cc) H mode provides more consistency amongst observers (higher CI) compared to B mode; however for larger glands (≥ 35 cc) B mode provides more consistent results. Intraobserver consistency was also higher for H mode compared to B mode. Conclusion: Prostate volumes defined with H mode are significantly smaller compared to B mode. H mode improves inter‐ and intraobserver consistency in volume differentiation for smaller to medium prostate glands. In larger glands, H mode does not show any advantage over the B mode.
MO‐FF‐A1‐04: An Innovative Needle Tip Detection Method for TRUS‐Guided Prostate HDR Brachytherapy
Authors: Zheng D , Gilbert V , Todor D
Published: August 2010

Purpose: In the TRUS‐guided prostate HDR brachytherapy, the needle tip defines the distal end of possible dwells. Needle tip detection plays a critical role in the distance accuracy of dwell positions and hence has a significant impact on dosimetry. However, directly finding the needle tip on the ultrasound images is nothing but an uncertain art. Therefore, the current study was conducted to design and evaluate a novel method to turn this uncertain art into an accurate measurement‐based detection. Method and Materials: Our method used real‐time‐measured residual needle length and offline‐established coordinates to calculate the needle tip position on the TRUS images. Coordinates were established and populated to a lookup table through measurements at possible template‐to‐probe configurations. With the known full length of a needle, the tip position can be calculated using an online‐measured residual length and this lookup table. To evaluate our method, we conducted an experiment in water. The needle tip positions were detected by (1) x‐ray radiographs which we use as the gold‐standards; (2) our measurement‐based method; and (3) direct detection on ultrasound images. 5 different template‐to‐probe configurations were tested, and at each configuration the equipments were assembled for 3 times to assess the assembling reproducibility. Results: With the 5 tested configurations, the reproducibility was found based on the gold‐standard radiographs to be within 0.2 mm. Relative errors using our method and the direct detection method were from 0.6 to 0.8 mm and from 0.9 to 2.3 mm, respectively. Conclusion: A simple and effective method to accurately detect the needle tip on the TRUS images for HDR prostate brachytherapy was developed based on physical‐measurement‐defined coordinate systems. The validity and accuracy of the method was tested and established. The easy‐to‐implement method is clinical‐ready.
MO‐FF‐A1‐05: On‐line CT Verification of Needle Applicator Positions in HDR Prostate Brachytherapy
Authors: Huang Y , Miller B , Doemer A , Nurushev T , Chetty I , Aref I
Published: August 2010

Purpose: Needle applicators have shown displacement between fractions during HDR prostate brachytherapy, which will degrade plan quality. Typically, displacement is determined by analyzing catheters on a verification CT (vCT) or port films obtained before treatment relative to fiducials or bony landmarks. We present a procedure to verify applicator positions to achieve planned dose distributions by registering vCT directly to planning CTs (pCT). Method and Materials: Patients received a vCT prior to each fraction. This was imported to BrachyVision (Varian Medical Systems) and fused to the pCT by rigid‐body registration based on matching urethra and three prostate‐implanted gold fiducials. Then, applicators in the vCT were compared to applicators in the pCT in a reconstructed plane through each catheter and any difference larger than 3mm was manually adjusted by a radiation oncologist before treatment. To assess treatment quality, the prostate volume was copied from pCT to vCT and the planned dwell positions/time was applied to the vCT applicators. Results: Two consecutive patients were treated using our CT registration needle verification method. Both patients required applicator adjustments in the first two fractions. Patient one had an average 7mm cranial‐to‐caudal applicator displacement, corresponding to 23% and 12% fractional drop in V100prostate respectively; Patient two had displacement in both cranial‐to‐caudal and caudal‐to‐cranial directions up to 9mm, but due to minimum loading of affected applicators, no significant decrease in V100prostate was seen. Neither patient required applicator adjustment at the Srd/last fraction. Despite differences in applicator displacement, post‐adjustment, the achieved V100prostate at each fraction deviated from planned value by less than 4% for both patients. The distances between fiducials in vCTs were consistent with those in pCTs within 3mm, confirming that fiducials are appropriate landmarks for registration. Conclusion: We have successfully treated two patients using this method. This technique ensures the treatment quality closely matches plan quality.