bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐E‐332‐05: Dose Reduction in Detection of Pulmonary Thrombotic Embolism with Computed Tomography
Authors: Hodge G , Merrill R , Wu X , White J , Singh S
Published: July 2008

Purpose: Due to recent concerns raised regarding excessive doses acquired by CT, it is prudent to review and audit the amount of radiation acquired by a patient who undergoes a procedure. Included is an assessment of a proposed dose‐reduced CT scan protocol for detecting a pulmonary thrombotic embolism (PTE). An alternative protocol for the PTE scan involves a reduction in the peak voltage of the x‐ray tube from 120 kV to 80 kV for young female patients. Method and Materials: An assessment of the dose was done using Monte Carlo simulation data provided by the U.K. Health Protection Agency publication NRPB‐SR250 (D G Jones and P C Shrimpton 1993). Using a FORTRAN program, the data can be used to determine organ dose along with a concise calculation of the effective dose upon a statistically average human. This dose model was compared to a measurement of the dose under equivalent scanning conditions for verification of the accuracy and reliability of the computer model. Results: Calculations from the computer model show a difference in breast dose is nearly a factor of six reduction. Comparisons to weighted CTDI suggest at least a factor of four dose reduction under equivalent conditions. Contrast‐to‐Noise (CNR) actually improves under sample cases due to increased response of the contrast media at lower tube voltages and smaller patient size. Conclusion: The results of the computer modeling clearly demonstrate a considerable dose savings, as young female patients can be expected to have a breast dose reduction of nearly 83%, while maintaining an acceptable level of efficacy in the scan protocol by reassigning the image's window level and window width to help compensate for the shift in contrast media signal in an 80 kV scan.
TH‐SAMS‐332‐01: Dosimetry and Common Pitfalls in the ACR CT Accreditation Program
Authors: Pfeiffer D
Published: July 2008

Facilities participating in the American College of Radiology Computed Tomography Accreditation Program require significant support from Medical Physicists. A number of presentations in prior years have covered the mechanics of preparing a submission to the program. Recently, changes and clarification were made to the program. Rather than covering the basics of scanning the phantom, this presentation will focus on these recent changes and some common pitfalls and how to avoid them. Issues around dosimetry measurements will be covered. Finally, areas where Medical Physicists can provide additional support to facilities will be briefly discussed.

Educational Objectives:

1. To become aware of the new dose limits of the ACR CT Accreditation Program.

2. To gain an understanding of some of the common application pitfalls and how to avoid them.

3. To gain insight regarding the role of the Medical Physicist within a clinical CT program.
TH‐SAMS‐332‐03: Design and Performance Evaluation of Cone Beam CT Systems : Cone Beam Angio CT
Authors: Fahrig R
Published: July 2008

Conebeam CT using C‐arm mounted large area flat panels (FPs) is becoming more commonly used in neuro‐ and body‐interventional suites. The ability to visualize vascular geometry in 3D along with soft tissue during an intervention is providing information that may increase accuracy, shorten procedure time and may even change the course of treatment. However, acquisition of the projection data required for volume imaging requires dose to the patient, and understanding the trade‐offs between acquisition parameters, dose and image quality is critical to the appropriate adoption of this imaging technique.

Unlike conventional CT, the beam length in conebeam CT can cover the entire length of the object to be imaged or can be varied with the use of collimation, and the concept of CTDI is not, therefore, the metric of choice for measurement of dose. In addition, most C‐arm conebeam CT systems use a short‐scan (pi plus fan‐angle) acquisition, and the dose distribution within the object is not cylindrically symmetric. Finally, since FP design has been optimized for fluoroscopy, image quality when used for CT must be carefully evaluated.

This lecture will describe a dose metric that is appropriate for conebeam CT and allows direct comparison with the CTDIw of conventional CT. A perception study using the CATPHAN 600 phantom for a range of acquisition parameters will be described, and the relationships between kVp, image noise, dose and contrast perception will be discussed.

Research sponsored by Siemens Medical Solutions AG, AX Division, by NIH grant R01 EB003524 and by the Lucas Foundation.

Educational Objectives:

1. Understand how differences in acquisition geometry between conebeam and conventional CT affect dose distribution and dose measurement.

2. Understand how contrast perception in conebeam CT images depends on acquisition parameters.
TH‐A‐342‐01: ACR MR Accreditation Update: The Role of the Medical Physicist
Authors: Price R
Published: July 2008

In 2006, the ACR council approved a resolution requiring the current ACR MRI Accreditation Program to be redesigned into a modular program. The current program is limited to only whole‐body and cardiac accreditation. The new modular program will offer six clinical modules and is designed to allow a facility to have an accreditation that is more appropriately matched to the individual practice and the patient population being served. The six modules are: body, head, MR angiography (MRA), spine, musculoskeletal and cardiac. A breast MR accreditation program is currently under development; however, will not be one of these MR modules. Instead, it will be part of the Breast Imaging Accreditation Program. Also, an accreditation program specifically designed for special‐purpose orthopedic systems is under development.

This continuing education course will review the current status and requirements of the ACR Whole Body MRI Accreditation Program, anticipated changes related to the proposed modular program and anticipated changes in the MRI Quality Control Manual as related to the Annual Medical Physicist Performance Survey.

Educational Objectives:

1. Review the role of the Medical Physicist in the current Whole Body Accreditation Program with emphasis on the requirements of the annual performance survey.

2. Discuss the status of the proposed ACR modular accreditation program as well as the new initiatives into cardiac and orthopedic accreditation and the anticipated impact that these changes will have on the role of the medical physicist.

3. Discuss special accreditation considerations related to 3T systems and for systems with parallel imaging capability.
TH‐B‐AUD C‐01: Functional Imaging for Therapy
Authors: Cao Y
Published: July 2008

The clinical value of in vivo functional and physiological imaging (perfusion, diffusion, and diffusion tensor imaging) for assessment of therapeutic responses has been demonstrated in recent years. In vivo functional and physiological imaging can provide early prediction for treatment outcomes and organ and tissue complications, compared to conventional clinical methods and anatomic imaging. The advantage of early assessment is to allow for re‐optimizing individual patients' treatment plans, including decisions of total dose, modifying risks of critical normal tissue, and optimizing use of concomitant therapies. Clinical applications of perfusion, permeability, diffusion and diffusion tensor imaging are increasing rapidly.

This lecture will provide an overview of physiological origins of perfusion, permeability, diffusion and diffusion tensor imaging, as well as clinical applications, typical imaging acquisition protocols, and image processing methods. The limitations of these techniques will also be discussed.

Educational Objectives:

1. Understand the physiological origins of perfusion, diffusion and diffusion tensor imaging.

2. Understand typical imaging acquisition protocols and basic image processing methods.

3. Understand clinical applications and limitations.
TH‐C‐350‐06: Laser‐To‐Proton Energy Transfer Efficiency in Laser‐Plasma Interactions
Authors: Fourkal E , Veltchev I , Ma C
Published: July 2008

Purpose: In recent years there has been an explosion of research work concerning the topic of charged ion acceleration using high‐power lasers. The maximum particle energy and the shape of the distribution function are the two main parameters influencing the potential utilization of the new technology in radiation therapy. Low energy transfer efficiency from the laser pulse to protons (∼ 5%) is one of the detrimental factors limiting the production of particle beams in the therapeutic energy range. In this study we show that the energy transfer efficiency can be significantly increased through a process of splitting the single interaction stage (conventional interaction design) into multiple sub‐stages. Method and Materials: 2D Particle in Cell simulation code and 3D theoretical model were used to simulate interaction of laser sub‐pulses with multiple targets in a sequential manner. The thin layer of protons is initially located only at the back surface of the first target. The remaining targets are devoid of any contaminant hydrogen‐rich materials. Results: It was shown that in a three‐stage setting, there is ∼ 60% increase in the energy efficiency of the laser accelerator as compared to a single interaction scheme. At the same time according to the results of our 3D model, it should be possible to increase the energy efficiency by more than 100% for a six‐stage interaction setting without using more powerful lasers. Conclusion: The splitting of a single interaction site into multiple stages is an effective way of reducing an irreversible component in the energy exchange process between the laser and protons. As a result more laser energy is transformed into proton kinetic energy, thus increasing effectiveness of the “pump”.
TH‐C‐AUD A‐03: A New Approach for Afterloading Brachytherapy Inverse Planned Dose Optimization Based On the Accurate Monte Carlo Method
Authors: D'Amours M , Carrier J , Lessard E , Pouliot J , Verhaegen F , Beaulieu L
Published: July 2008

Purpose: In brachytherapy, considering the perturbations from the heterogeneities in the planning system will give a better dose conformity for specific sites. The goal of this work is to demonstrate the feasibility of replacing the TG43 analytical approach by a Monte Carlo (MC) dose calculation engine in the optimization process. Method and Materials: The novel method is based on pre‐computed 3D dose kernels. The CT clinical images and the dwell positions (DWP) are loaded from the DICOM‐RT files to create a voxel based simulation of the treatment. MC dose calculation is used to create the dose kernel specific for each possible DWP. Density and tissue compositions are fully taken into account in MC. The Inverse Planning Simulated Annealing (IPSA) algorithm is used for the optimization process. IPSA reads and analyzes the MC dose kernels before the beginning of the optimization process; it replaces the TG43 parameterization. A breast interstitial HDR plan is used to demonstrate the approach. Results: Computation of precise 3D‐kernels is the most time consuming portion and is proportional to the number of DWP. However, the optimization process itself takes the same amount of time as a standard (TG43) optimization. The breast, TG43/MC plan shows an underdosage in the CTV relative to the TG43/TG43 plan by 4.3 % on D90 and 3.2 % on D50. For the surgical bed, the difference is 4.2 % and 3.5 % for D90 and D50 respectively. This was corrected in the MC/MC plan, with a minimal dose increase of the skin. Conclusion: MC optimization improved the dose conformity. The method presented is straightforward and can be applied to any site and any afterloading process (HDR or PDR) using various type of sources, from Ir‐192 to micro‐XRay devices, as long as a precise MC model is made.
TH‐C‐AUD A‐08: Evaluation of Electronic Equilibrium Conditions Near Brachytherapy Sources
Authors: Perez‐Calatayud J , Granero D , Rivard M , Melhus C , Pujades M , Ballester F
Published: July 2008

Purpose: For high‐energy photon‐emitting brachytherapy sources such as , , , and , the main contribution of the systematic uncertainty in the dose distributions near the sources is understanding of electronic equilibrium and the contribution of β‐rays due to radioactive disintegration. Thus, it is important to study these effects in detail to accurately depict dose distributions near these brachytherapy sources. This work studies the relative importance of β‐ray contributions to total dose (β + γ + x‐ray), and feasibility of using the approximation “collision kerma equals dose in electronic equilibrium conditions.” Method and Materials: Characteristics of kerma and dose distributions were studied for spherical , , and sources with composition, encapsulation, and dimensions similar to those existing in the literature. Dose contribution of β‐rays and γ+x‐rays were individually examined using the GEANT4 Monte Carlo radiation transport code. Results: The comparison of kerma and dose rate distributions indicate ∼ 20% electronic disequilibrium within 1 mm of sources, with have the most pronounced effect. When examining the dose contribution of β‐rays, again had the most pronounced effect out to 5 mm beyond the capsule, with β‐rays contributions for and 1.5 and 0.5 mm beyond the capsule, respectively. Conclusion: The dosimetric effect of β‐rays for high‐energy photon‐emitting radionuclides and the influence of the electronic disequilibrium near of the sources were studied using Monte Carlo methods. For and brachytherapy sources, electronic disequilibrium has an important role near the source. For the main perturbing dosimetric effect near the source is from β‐ray contributions and not electronic disequilibrium.
TH‐C‐AUD A‐09: Monte Carlo (MCNP5) Dose Calculation for Eye Plaque Therapy
Authors: Palaniswaamy G , Rangaraj D , Yaddanapudi S , Loyalka S
Published: July 2008

Purpose: To model the geometry of eye plaque therapy using MCNP5 and study the dose distribution at specific points in the eye. Effects of tissue heterogeneity and coverage for small tumors (<10mm) which have poor clinical outcomes are concentrated. Method and Materials: Geometry of the eye plaque for eye plaque therapy is modeled using MCNP5. The dose at the tumor base and apex has been calculated and compared against published data. For this work, a simple geometry of the eye plaque has been studied. The eye diameter, tumor base diameter, plaque diameter, plaque thickness and depth are chosen to be in compliance with the COMS standards. This model uses 14 radioactive NASI MED 3631 A/M mode I‐125 seeds. The source energy distribution for this problem defines only the photon energies and not the beta energies as they are absorbed by the titanium capsule in the I‐125 seed. Results: Dose at the tumor apex was calculated using *F8 and F6 tallies in MCNP5. Results show that F6 tally gives more accurate results than *F8 for this problem. So, F6 tally was used further in this research. Dose at tumor base and depth dose profile were studied for this problem using F6 tally. 54540 source particles were simulated using MCNP5 and the resulting particle trace was obtained. Conclusion: The geometry of the eye plaque has been modeled using MCNP5 and the dose distribution at specific points of interest has been studied. The MCNP5 results were found to be agreeable with the published data for several treatment techniques. The effects of tissue/tumor heterogeneity have been studied and the reason for poor tumor control / toxicity outcomes for small tumors is found using Monte carlo dose calculation due to lack of coverage which could not be realized with 2D/3D planning.
TH‐C‐351‐06: Evaluation of a Compartmental Model for Estimating Tumor Hypoxia Via FMISO Dynamic PET Imaging
Authors: Wang W , Georgi J , Nehmeh S , Narayanan M , Paulus T , O'Donoghue J , Zanzonico P , Schmidtlein C , Lee N , Humm J
Published: July 2008

Purpose: To evaluate a pharmacokinetic compartmental model for identifying intra‐tumor hypoxia using dynamic positron‐emission‐tomography (PET) imaging with 18F‐fluoromisonidazole (FMISO) radiotracer. Method and Materials: The compartmental model used for this work is an irreversible generic two‐tissue type implemented within a pharmacokinetic modeling program called Voxulus by Philips Research. A dynamic PET image dataset (spatial and time) was simulated with 3 tissue regions: normoxia, hypoxia and necrosis, and with an image‐based arterial input function. Each voxelized tissue time‐activity‐curve (TAC) simulation used typical kinetic parameters, generalized from 6 head‐and‐neck cancer patient FMISO‐PET data. The dynamic image was first produced without any statistical noise, to ensure that correct kinetic parameters were reproducible by Voxulus. Next, to investigate the stability of kinetic parameter estimation in the presence of noise, 1000 noisy samples of the dynamic image were generated, from which 1000 noisy samples of kinetic parameters were calculated, and used to estimate sample mean and covariance matrix. To further investigate how bias in the arterial input function affected the kinetic parameter estimation, a shift error was introduced in the peak amplitude, peak location and tail amplitude of the input TAC, and the bias of various kinetic parameters computed. Results: Without noise, the estimated kinetic parameters matched their true values perfectly. With noise, the hypoxia rate constant k3 had more variation than other parameters. The plasma‐to‐tissue and tissue‐to‐plasma rate constants (k1 and k2) for diffusible compartment, and vascular density β were highly correlated with each other; while k3 had no correlation with others. Voxulus was applied to estimate parametric image maps of hypoxia for 6 head‐and‐neck cancer patients. Conclusion: Mathematical phantom studies have been used to determine the statistical accuracy of Voxulus, which provides us guidance and confidence in clinical dynamic FMISO‐PET data analysis.
TH‐C‐351‐07: Partial Volume Effect Correction in PET Using Regularized Iterative Deconvolution with Variance Control Based On Local Topology
Authors: Kirov AS , Piao JZ , Schmidtlein C Ross
Published: July 2008

Purpose: To present a new partial volume effect (PVE) correction method for PET with variance control, which is not dependent on prior anatomical information: a necessity for radiation treatment planning. Method and Materials: The method performs post‐reconstruction iterative deconvolution using a 3D Maximum Likelihood Expectation‐Maximization algorithm. To achieve convergence a One Step Late (OSL) regularization procedure that follows the work of Alenius et al is used. This technique was further modified to selectively control the variance depending on the local topology of the PET image. Different regularization weights can be selected by the user for different parts of the image based on the signal‐to‐noise ratio. The procedure was tested for isotropic gaussian deconvolution functions with FWHM ranging from 6.31 mm to infinity. The method was applied to simulated and experimental scans of the NEMA NU‐2 image quality phantom with the GE Discovery LS PET/CT scanner and on patient scans. Results: Optimal sphere‐activity‐to‐variance ratio was obtained, when the deconvolution function was replaced by a few voxels wide step function. In this case the deconvolution method converged in ∼ 3 to 5 iterations for most points in both the simulated and experimental images. For the 1 cm diameter sphere, the contrast recovery improved from 12 % to 36 % and from 21% to 55 % for the simulated and the experimental data respectively. For the larger spheres the recovery coefficients were increased to above 68% and 80%. No increase in variance was observed except for few voxels neighboring strong activity gradients and inside the largest spheres. Testing the method using patient images indicated potential for increasing the visibility of small lesions within a non‐uniform background. Conclusion: Regularized iterative deconvolution with variance control based on local topology and on estimated image noise is a promising approach for partial volume effect corrections in PET.
TH‐C‐351‐09: Partial Volume Correction of PET‐Imaged Tumor Heterogeneity Using Expectation Maximization
Authors: Barbee D , Flynn R , Holden J , Jeraj R
Published: July 2008

Purpose: Due to the limited spatial resolution of PET imaging, small objects experience partial volume effects which impact the quantification and spatial distribution of imaged tumor heterogeneities. This study examines the ability of an iterative partial volume correction (PVC) method to restore imaged heterogeneity to an object heterogeneity map using expectation maximization. Method and Materials: Treating PET as a linear system, images obtained through the convolution of a true object's radioactivity distribution and the system's point spread function (PSF) may be used to uncover the true object's activity distribution. The presented method uses iterative expectation maximization with the measured system PSF to determine the true object activity distribution. The three‐dimensional spatially dependent PSF was obtained by Gaussian fitting point objects imaged on a Discovery LS PET/CT scanner radially in single plane. The technique was tested on dual‐tracer heterogeneity phantoms using spheres of 10 and 15 mm diameter as both hot and cold heterogeneities relative to the phantoms' uniform tumor activity. The method was also applied to clinical studies to observe the impact of quantitative changes. Results: The observed PVC showed dependencies on heterogeneity size and contrast with surrounding regions. This PVC technique successfully recovered phantom heterogeneities hotter than uniform tumor activity, but experienced difficulty with cold heterogeneity. Quantitative image accuracy was restored as heterogeneities experienced shifts of 25 and 35% for diameters of 15 and 10 mm, respectively. Using changes in the image correction matrix proved a successful stopping criteria for determining the optimal number of iterations for PVC in phantoms. Changes as large as ±20% were frequently observed in patient heterogeneities. Conclusion: The expectation maximization PVC method successfully recovers tumor heterogeneity lost through PET imaging. Inclusion of PET information into treatment planning or treatment assessment would greatly benefit from the quantitative accuracy gains shown in this PVC method.
TH‐C‐332‐01: Low Dose Flat‐Panel Cone‐Beam CT and Tomosynthesis for Interventional Guidance Via Prior Image Constrained Compressed Sensing (PICCS)
Authors: Nett B , Tang J , Leng S , Aagaard‐Kienitz B , Chen GH
Published: July 2008

Purpose: Intra‐operative three dimensional imaging via FP‐CBCT (flat‐panel cone‐beam computed tomography) offers high spatial resolution and the ability to image low contrast structures such as soft‐tissue. However, repeated FP‐CBCT scanning requires irradiation of the patient for each subsequent acquisition. The aim of this work is to significantly reduce the delivered dose for monitoring and verification scanning, by using a planning scan to constrain the reconstruction. Method and Materials: An extension to compressed sensing (CS) has recently been proposed wherein a prior image is utilized as a constraint in the image reconstruction procedure (i.e. Prior Image Constrained Compressed Sensing — PICCS). The PICCS framework was used here on a clinical neuro‐interventional C‐arm system. Geometric calibration was incorporated into the algorithm through measured projection matrices of a known phantom. Results: The clinical task of placing a needle into a target was simulated with phantom and cadaver experiments. A full range of tomographic angles was explored from 10 degrees to 200 degrees. In the phantom experiments the delivered dose used for the reconstruction was twenty times less than the planning image. In the cadaver experiments PICCS images were reconstructed with a dose reduction factor of ten. The needle was well visualized in the tomosynthetic planes (e.g. coronal planes for a PA arc) for all acquisitions and the PICCS algorithm enabled improved reconstruction of the background anatomy compared with CS and standard FBP. Conclusion: The PICCS algorithm enabled reconstruction of the needle introduced from few views, while maintaining the background anatomy. If a tomosynthesis acquisition is chosen the orientation of the arc with respect to the object of interest is no less important than with standard image reconstruction. Experimental data indicates that a significant undersampling is acceptable (e.g. an order of magnitude dose savings) when using the PICCS reconstruction algorithm.
TH‐C‐342‐01: Image Display, Processing and Analysis (CAD)
Authors: Krupinski E
Published: July 2008

Medical imaging is rapidly expanding in the manner in which images are acquired and thus the manner in which they are displayed has also become a very important issue. The presentations in this session will discuss some of the issues associated with three important links in the imaging chain with respect to the display of radiographic images: Image Display, Processing and Analysis (CAD). In each area the key to success is to develop ways to present image data to the human observer in the most efficient and informative manner, taking into account the perceptual and cognitive capabilities of the human observer. The ultimate goal is to facilitate the decision‐making process and enhance patient care — improving the radiologist's ability to render correct diagnoses with a minimum of errors. Another important consideration is how Image Display, Processing and Analysis (CAD) tools affect workflow. Radiologists are being faced with an ever increasing number of images to interpret overall and within a given case. To the extent possible, these tools should make the interpretation process more efficient rather than prolong the process.

The three presentations will focus on the state‐of‐the‐art in Image Display, Processing and Analysis (CAD). Specific imaging applications will be discussed, but the underlying principles extend to medical imaging applications in general.

Educational Objectives:

1. Understand the role of the display in the interpretation process and why optimization is important.

2. Understand how image processing or the rendering of image data in new ways can improve the radiologists' interpretation process.

3. Understand the basic nature of CAD and the various ways it is being used (e.g., detection and discrimination) to improve diagnostic accuracy of radiologists.
TH‐C‐352‐04: Acceptance Testing, Commissioning, Data Entry, and QA for Brachytherapy Treatment Planning Systems
Authors: Rivard MJ
Published: July 2008

Clinical medical physicists are compelled to concern with accuracy of brachytherapy treatment planning systems as the basis for treatment delivery. The role of the medical physicist in brachytherapy is key — close interactions with physicians are needed, and often a radiation therapist may not be present. In comparison to external beam, dose gradients are steeper, record‐and‐verify is not typically used, and treatment fraction dose is usually higher. Thus, the importance of our input. The role of brachytherapy for cancer treatment has expanded in recent years. Many of these new modalities push the limits of the conventional brachytherapy treatment planning dose calculation algorithm. A solid understanding of these systems and their clinical role is crucial towards ensuring success. This tenet holds true for both the newer modalities and the more established brachytherapy procedures.

This continuing education lecture will provide a quasi‐chronological overview of the resources and actions required of a clinical medical physicist

Educational Objectives:

1. Acceptance Testing and Commissioning recommendations.

2. Data Entry of brachytherapy dosimetry parameters based on AAPM‐, manufacturer‐, and user‐provided data.

3. Quality Assurance, including startup and on‐going efforts, towards ensuring a safe and accurate environment.
TH‐D‐350‐03: The Benefits of Integrating the Healthcare Enterprise (IHE) Efforts for the Radiation Oncology Physicist
Authors: Curran B
Published: July 2008

Purpose: An issue for the practicing clinical physicist is the integration of computer systems in support of radiation therapy. Standards such as DICOM and HL7 exist, however, applications in the process apply these standards differently, resulting in unreliable exchanges of data at points in the imaging, planning, and delivery of treatment. Solving this problem requires the support of users, vendors, and professional societies to achieve a global solution and allow ‘best‐of‐breed’ selection of applications. Method and Materials: IHE (Integrating the Healthcare Enterprise) is an effort started by RSNA and HIMSS. Its goal is improving the integration of information systems in support of clinical care. IHE‐RO (IHE Radiation Oncology) is an effort supported by ASTRO, AAPM, other societies, and vendors aimed at identifying issues of computer integration and developing solutions. Meetings were held to identify bottlenecks in the treatment process. Use cases were written and an “Integration Profile” was developed for the exchange of CT, Region‐of‐interest, treatment plan, and 3D dose calculation data among different vendors. Vendors then tested their product implementations using test tools developed in support of the effort, 2 rounds of testing (informal and formal), and a public demonstration. Results: In the first two rounds of testing a number of incompatible interpretations of DICOM protocols were identified. At the formal Connectathon, manufacturers were able to prove compliance with the Integration Profile for applications that included RT‐Archive, CT‐Simulation, Treatment Planning, and Dose Display. Conclusion: IHE‐RO is an effort that is beneficial to the practicing medical physicist. It provides a venue for controlled and demonstrable testing of multi‐application compatibility. It reduces the effort required in selection and integration of new systems into clinical practice by providing a reference of proven integration. The improved robustness of application‐to‐application information transfer results in reduced quality assurance requirements of such interfaces.
SU‐GG‐J‐54: Comparison of Head and Neck Localization with Portal Imaging and Megavoltage Cone‐Beam Computed Tomography
Authors: Gayou O , Parda D , Miften M
Published: July 2008

Purpose: To compare portal imaging (PI) and mega‐voltage cone‐beam CT (MV‐CBCT) for head and neck (HN) cancer patient localization. Method and Materials: The treatment couch shifts were recorded for 30 HN cancer patients localized weekly using anterior‐posterior and right‐lateral portal images, and for 11 patients localized using MV‐CBCT, either daily (n=4) or twice weekly (n=7). A total of 214 and 184 shifts were obtained for PI and MV‐CBCT, respectively, in the left‐right (LR), superior‐inferior (SI) and anterior‐posterior (AP) directions, along with the magnitude of the 3D shifts. The percentage of shifts that are equal to 0 in any direction, that is no treatment couch correction was applied in that direction, was also compared for the two techniques. Results: The average MV‐CBCT and PI shifts were −0.9±3.9 and 0.0±2.2 mm, respectively, in the LR direction, −0.2±2.4 and −0.1±3.5 mm in the SI direction, −1.0±4.2 and −0.2±2.6 mm in the AP direction. The average 3D shifts were 5.2±3.6 mm and 2.2±4.3 mm for MV‐CBCT and PI, respectively. The proportion of 0 mm shifts for MV‐CBCT and PI was 55% and 88%, respectively, in the LR direction, 71% and 81% in the SI direction, 49% and 90% in the AP direction. Conclusion: The three‐dimensional nature of the MV‐CBCT localization method offers a greater ability to detect small shifts and helps reach a compromise between the 3 translational treatment couch shifts that can be applied and the 12 degrees of freedom corresponding to translational and rotational movements of the head and/or neck, independently. This greater accuracy of MV‐CBCT allows to reduce CTV‐to‐PTV margins, therefore potentially improving the therapeutic ratio. Research partially supported by Siemens Medical Solutions.
SU‐GG‐J‐57: Comparison of the Residual Error in Treatment Set‐Up Using Different Imaging Modalities: A Phantom Study
Authors: McNiven A , Chin CL , Vandermeer AD , Moseley D
Published: July 2008

Purpose: To assess the accuracy of three different imaging modalities (orthogonal pairs of 2D‐kV or MV images and kV cone‐beam CT (CBCT)) for image guided radiation therapy (IGRT) for four clinical treatment scenarios. Method and Materials: The accuracy of IGRT was investigated using four anatomical phantoms, each representing a specific clinical site and treatment set‐up strategy. Bony alignment was used as a surrogate for tumour location and set‐up accuracy for pelvic, head and neck and thorax phantoms, while implanted fiducials were the alignment target of a second pelvic phantom. Each phantom was subjected to the IGRT process currently used at this institution. For each imaging modality, the phantoms were set‐up on the treatment couch and imaged. These images were aligned to the reference images and a couch translation was applied to correct for the set‐up error. Verification images were then obtained to determine the residual error, which is an indication of IGRT accuracy. Results: All three image modalities resulted in a low average residual error (<1mm), with the residual error represented by the mean 3D displacement vector. The 3D CBCT resulted in the lowest overall residual error (0.35mm) as compared to the 2D MV imaging (0.7mm) and 2D kV imaging (0.5mm). This advantage, however, is site specific, and the use of volumetric imaging had the largest impact on IGRT strategies relying on bony alignment to the skull or thorax. For example, the volumetric information helped reduce the residual error to 0.24mm for the skull, compared to 1.04 and 0.63mm for the MV and kV portal imaging based techniques, respectively. Conclusion: CBCT imaging provided the lowest residual error for set‐up correction, but the magnitude of the advantage was site‐specific. More sophisticated or clinically time‐consuming techniques would be best suited to treatment sites for which they would provide the most benefit.
SU‐GG‐J‐58: Computed Radiography in Radiation Oncology: A Study of Cassettes and Technique
Authors: Liu R , Willis C , Tailor R , Vicic M , Prado K
Published: July 2008

Purpose: This study was conducted to compare commercially available computed radiography (CR) systems and to determine the effect on image quality of cassettes and Monitor Units (MU) used for portal imaging. Method and Materials: The quality of CR portal images was assessed using a “Las Vegas”hyphen;type contrast‐detail (CD) phantom. The 6MV beam from a linear accelerator (Varian 2100), collimated to phantom dimensions, irradiated the phantom in contact with the cassette using 1–6 MU. The commercial CR systems evaluated were: the Carbon XL (FujiFilm USA, Stanford, CT) with Fuji portal imaging cassettes, and the Kodak 2000RT (Carestream, Rochester, NY) with two types of portal imaging cassettes, Kodak Lightweight (KLW) and Oncology (KONC). Images were analyzed using ImageJ (National Institutes of Health, USA). Five observers scored images under identical viewing conditions. Average number of features detected and standard deviation were used to assess image quality. Head and chest images of an anthropomorphic phantom (Computerized Imaging Reference Systems, Inc., Norfolk, VA) were acquired with cassettes under the couch to correlate with clinical imaging. Results: The total number of objects detected increased with MU: 22% for KLW, and 17% for KONC (1–6 MU), and 9% for Fuji (1–5 MU, saturation occurred at 6 MU). Fuji had better contrast detectability for all features at all MU; 19% more objects were detected. No difference was observed between KLW and KONC cassettes. Fuji produced anthropomorphic‐phantom images with better contrast. Increasing MU improves image quality, but high inter‐observer variability made differences difficult to resolve at 2 MU and above. Conclusion: Although all systems produced adequate portal images, the Fuji system performed best with the CD phantom and with anthropomorphic phantoms. Fuji's advantage can be attributed to digital image processing and better system DQE. We found 2–3 MU was adequate to get acceptable contrast for portal images.
SU‐GG‐J‐59: Computerized Gating of Breathing Pattern for Synchronized Delivery of Radiation
Authors: Lam K , Balter J
Published: July 2008

Purpose: To evaluate the stability of a device that accepts inputs from a spirometer in gating the breathing cycle to synchronize the breath hold state with the generation of radiation for treatment delivery or imaging. Method and Materials: We have constructed a Gated Breath Synchronizer (GBS) consisting of a data acquisition module with USB interface to a computer. The module has A/D input channels to acquire flow and other signals from a spirometer. It has a 16 bit digital I/O for controlling a breathing valve solenoid, connection to a panic button, and interfacing with the radiation generating device. We have developed software to monitor the lung volume and accept a target breath hold lung volume. It adjusts the timing and duration of the breath hold to coach the patient to reach the target breath hold lung volume gradually in a regular breathing pattern. We are also developing a simulated patient in software with relevant characteristics in pulmonary physiology for testing the system. The simulated patient has a 0.5 liter tidal volume, increases the depth of breathing after breath hold, has an inspiration reserve volume (IRV) of 3.5 liters and sets the panic switch after prolonged breath hold. We have evaluated the transition of the system from a restful breathing state to a steady state of regular breathing with breath hold for target breath hold lung volumes at 0.05 liters and 0.5 to 4.5 liters in 0.5 liter steps above functional residual capacity. Results: Stable breathing patterns with acceptable breath hold lengths were achieved in all cases except for when the coached breathing state approached the IRV, in which case the simulator properly activated the panic switch. Conclusion: The GBS system showed stable response in adjusting the patient from restful breathing to regular breathing with breath hold. Supported by NIHPO1CA59827.
Poster — Thurs Eve‐40: The potential of using SPECT ventilation information with IMRT for functional lung avoidance in radiotherapy of non small cell lung cancer
Authors: Munawar I , Yaremko B , Craig J , Chen J , Oliver M , Gaede S , Rodrigues G , Yu E , Reid R , Leung E , Wong E
Published: July 2008

We have investigated the feasibility of using ventilation scans obtained from single photon emission computed tomography (SPECT) in intensity‐modulated radiation therapy (IMRT) planning in lung cancer radiotherapy to avoid well functioning lung. We fused SPECT ventilation scans acquired at GE Hawkeye SPECT‐CT of ten stage‐III lung radiotherapy patients with planning CT in treatment planning system (Pinnacle v8.0, Philips Medical Systems). We automatically segment out 50% and 70% ventilated volumes. For each patient, we generated IMRT plans using nine equally spaced beams with and without avoiding well ventilated volume. They were compared with three beam IMRT plans with beam directions chosen to minimize the mean dose to the ventilated lung volumes, while keeping cord dose below tolerance and dose uniformity in the target. The plans generated using functional lung avoidance information reduces the doses to the functioning lung. With both IMRT avoidance plans, we could not obtain better functional avoidance or lower V‐20Gy (volume receiving 20Gy or more) for total lung when the planning target volume (PTV) was surrounded by functional lung volumes. We were able to achieve better ventilated lung avoidance and lower total lung V‐20Gy when the PTV is close to, but not surrounded by functioning lung volumes. For patients with the PTV that is far from 50% and 70% functional lung volumes, three‐field IMRT spare the ventilated lung as well as nine‐field IMRT ventilation avoidance plan, with a lower total lung V20‐Gy.
Sci‐Fri AM: YIS‐01: Comprehensive MR distortion correction: Phantom validation and in‐vivo application
Authors: Baldwin LN , Wachowicz K , Fallone BG
Published: July 2008

MR images provide excellent diagnostic information; however, their treatment planning utility is limited due to geometric uncertainties from both system and patient related sources. Despite this concern, interest in developing MR‐based treatment planning protocols is on the rise because of the ease with which clinically relevant structures can be identified in MR. Here we present our systematic approach to quantifying both machine (gradient non‐linearity and B0 inhomogeneity) and patient (susceptibility and chemical shift) distortions. Gradient non‐linearities were previously measured using a 3D grid phantom while the remaining types of distortion were measured using a double gradient echo scan to obtain a B0 distortion map specific to each object/patient. Distortion measurement and correction were validated on phantoms and then implemented on a volunteer. B0 inhomogeneity and susceptibility distortions were simulated by offsetting the x2‐y2 shims; maximum absolute distortion was reduced from 5.4 mm to 1.0 mm and mean (± standard deviation) was reduced from 1.7 ± 1.4 mm to 0.4 ± 0.2 mm. Chemical shift distortion was qualitatively evaluated using a phantom containing fat and water inserts; displacement of the fat signal was much improved following distortion correction. Intensity correction was validated using a uniformity phantom and undistorted image profiles were compared to distorted image profiles and to profiles corrected for geometric and geometric/intensity distortion; the need for intensity correction was clearly demonstrated. Once all types of distortion correction were validated on phantoms, the technique was implemented on a volunteer brain image. Both GE and multi‐shot EPI images were corrected.
Sci‐Fri AM: YIS‐04: Scatter correction of cone beam optical computed tomography for polymer gel dosimetry
Authors: Holmes O , Olding T , Schreiner LJ
Published: July 2008

Optical computed tomography (OptCT) may become the preferred scanning method for gel dosimetry dose validations, due to its high sensitivity and relatively low cost. Cone beam computed tomography (CBCT) arrangements are advantageous because of reduced scan time. However, CBCT arrangements are more sensitive to errors associated with scatter than other CT configurations. Unfortunately in polymer gel dosimetry this problem is amplified as the primary mode of beam attenuation is through scatter. Thus, managing and reducing the effects of scatter remains an important challenge for cone beam OptCT. In this work we examine two schemes for reducing the effects of scatter in the Vista cone beam OptCT system. First, we employed a pair of anti‐scatter polarizing planes to reduce the magnitude of stray light reaching the camera. Secondly, we implemented a beam stop array (BSA) sampling method ‐which has been successful in correcting for scatter in X‐ray CBCT‐ to obtain scatter field measurements that are subtracted from CT projections removing veiling glare. While both implementations reduced scatter related artifacts, the BSA technique yielded greater improvement without obvious image degradation. Comparative studies between absorbing dye standards and colloidal scattering standards with the same spectrophotometric optical attenuation revealed that application of the BSA technique nullified OptCT measurement disagreements between scattering and absorbing systems. When the BSA scatter correction technique was applied to polymer gel dosimetry 3%3mm agreement rose from 79.2% to 99.82%. These findings underscore the strength of the BSA sampling technique and its utility in cone beam OptCT.
Sci‐Fri AM: YIS‐05: A new guidance device for lateral‐approach stereotactic breast biopsy
Authors: Ma K , Bax J , Kornecki A , Mundt Y , Fenster A
Published: July 2008

Stereotactic breast biopsy (SBB) is the gold standard for noninvasive breast cancer diagnosis. Current systems rely on one of two methods for needle insertion: a top‐approach (from above the breast compression plate) or a lateral‐approach (parallel to the compression plate). While the top‐approach is more commonly used, it is not feasible in patients with thin breasts (less than 2.5 cm thickness after compression), or with superficial lesions. We present a novel design of lateral guidance support for SBB, which addresses these limitations of the top‐approach, and provides improvements over existing lateral support hardware. This device incorporates spherical linkages to allow two degrees of rotational freedom in the needle trajectory for increased targeting flexibility, as well as an adjustable rigid needle support to minimize needle deflection within the tissue. Needle placement error in SBB experiments is compared using both the new lateral guidance device and a commercial lateral guidance device in agar phantoms. The effect of elevation angle on needle placement accuracy using the new lateral guidance device is also assessed. Finally, a biopsy accuracy experiment is presented using a certified SBB phantom to compare the new design and the commercial lateral guidance device. In these experiments, SBB performed using the new lateral guidance device results in improved needle placement error and biopsy accuracy, while increasing targeting flexibility and maintaining procedural workflow.
Sci‐Fri AM: YIS‐06: On‐line adaptive radiation therapy based on the intra‐fractional digital tomosynthesis images
Authors: Mestrovic A , Nichol A , Clark B , Otto K
Published: July 2008

Purpose: To investigate the feasibility of performing on‐line adaptive radiation therapy (ART) based on the intra‐fractional digital tomosynthesis (DTS) images. Method and Materials: Intra‐fractional DTS images were reconstructed as the gantry rotated between treatment positions. An edge detection algorithm was used to automatically segment the DTS images as the gantry arrived at each treatment position. The original treatment plan was then re‐optimized for the most recent DTS image contours and dose was delivered from each treatment position based on the newly re‐optimized plan. Plan re‐optimization was performed using modified direct aperture optimization (DAO). To test our system, a model representing typical prostate, bladder and rectum anatomy was generated. First, a treatment plan based on this original anatomy was created using our DAO system. To simulate prostate deformations, three clinically relevant deformations (small, medium and large) were modeled by systematically deforming the original anatomy. The ability of our approach to adapt the original treatment plan and account for the anatomy deformations was investigated. Results: Based on the dose‐volume constraints from the RTOG 0415 prostate protocol, the original treatment plan would have been clinically unacceptable for all three deformations. Using our approach to on‐line ART, the original treatment plan was successfully adapted to arrive at a clinically acceptable plan for all three anatomy deformations. Conclusion: We have shown that performing on‐line ART based on intra‐fractional DTS images is feasible. The advantages are reduced treatment time and the ability to detect and account for patient motion during the treatment fraction.