bluuebunny/crossref_metadata_2025 huggingface dataset:
Lateral Bifurcation Behavior of a Four-Axle Railway Passenger Car
Authors: Gao Xuejun , Li Yinghui , Gao Qing
Published: April 2010

We investigate the kinematics and dynamics of a high-speed four-axle railway passenger car, which has 17 degrees of freedom, considering the lateral motion, roll and yaw angles of the car body and the bogie frame, and the lateral motion and yaw angle of the four wheelsets. The creep forces and the flange forces between the oscillating wheels and the rails are main nonlinearities and can be estimated by the Vermeulen–Johnson creep force laws and a piecewise linear function, respectively. The dynamical equations for the motion of the vehicle running with constant speed along an ideal, rigid, straight, and perfect track are formulated, and the lateral bifurcation behavior of the vehicle system is investigated numerically. The results indicate that both stable and unstable orbits are obtained, and the linear and nonlinear critical speeds are determined as well. Several kinds of dynamical behaviors, such as stationary equilibrium point, symmetric or asymmetric periodic oscillations, and symmetric or asymmetric chaotic motions, are found and described in great detail within the investigated speed range.
Force field experiments of an epitaxial superstructure of 3,4,9,10-perylenetetra-carboxylic-dianhydride on Ag(111)
Authors: Braun Daniel-Alexander , Langewisch Gernot , Fuchs Harald , Schirmeisen André
Published: April 2010

A new epitaxial superstructure of 3,4,9,10-perylenetetra-carboxylic-dianhydride adsorbed on Ag(111) is presented. The wirelike structure is analyzed with topographic images obtained by noncontact atomic force microscopy. The stacking of the molecules in the superstructure deviates strongly from the usual herringbone structure of the molecules. Additional force field spectroscopy experiments performed on the wire structure reveal that parts of the structure undergo mechanical relaxations in the presence of the tip. Furthermore, the dissipated energy between tip and molecules during the deformation process is derived.
SU‐AA‐BRD‐02: Licensure and the Practicing Medical Physicist: AAPM Licensure Regulations Guidance Document
Authors: Pizzutiello R
Published: April 2010

AAPM has made a significant commitment of priorities and resources to advance licensure in the 46 states that do not presently license medical physicists. Pending federal legislation may motivate States to implement licensure on a short timetable.

The AAPM Licensure Regulations Guidance Document is among the significant steps in this effort completed by the Joint Medical Physics Licensure Sub‐Committee (JMPLSC). This document was created modeled after the licensure laws in Texas, New York and Florida.

This session will review the big picture of how licensure is accomplished, and how licensure will affect the practicing medical physicist. Key provisions of the Guidance document will be presented with an emphasis on practical implementation issues.
SU‐AA‐BRD‐03: A New “CARE” and a New Focus
Authors: Fairobent L
Published: April 2010

As you are aware we have a new administration and a new congress and health care reform is a priority of both. On July 15, 2008 the Medicare Improvements for Patients and Providers Act of 2008 (MIPPA) was enacted making changes to the Medicare program. There has been a lot of confusion over MIPPA and how it relates to the goals we have for the “CARE” legislation (which stands for Consistency, Accuracy, Responsibility, and Excellence in Medical Imaging and Radiation Therapy (CARE) Act of 2009”). Questions have been raised do we still need to pursue the CARE legislation. This session will review the relationship between MIPPA, proposed CARE legislation and the overall AAPM and ACMP efforts to efforts to ensure that medical physics is performed by Qualified Medical Physicists.

Learning Objectives:

1. To review the provisions of the Medicare Improvements for Patients and Providers Act of 2008 (MIPPA).

2. To discuss the between MIPPA and the proposed “Consistency, Accuracy, Responsibility, and Excellence in Medical Imaging and Radiation Therapy (CARE) Act of 2009.”

3. To review the overall AAPM and ACMP efforts to ensure that medical physics is performed by Qualified Medical Physicists.
SU‐DD‐A1‐02: Incorporating Prior Knowledge Into the Segment Optimization in Segment‐Modulated Arc Therapy
Authors: Ma Y , Xing L
Published: April 2010

Purpose: Recently, various stochastic algorithms have been applied to the segment modulated arc therapy (SMART) inverse planning. Most, if not all, algorithms are brute force trial‐and‐error search in nature without inclusion of a priori knowledge for segment position and shape. The purpose of this work is to provide an effective way to speed up the SMART planning process by incorporating dosimetric knowledge of the system into the segment shaping. Methods: The SMART inverse planning was performed in two steps. First, the maximum intensity map (MIM) was evaluated for each beam. The intensity of MIM is defined as the maximum intensity without violating the threshold dose of the organ‐at‐risks (OARs) located on the path of the beamlet. Based on MIM, a probabilistic map (MP) model was properly established which describes the probability for a beamlet to be open (=1) or close (=0). A rule of thumb is that a beamlet traversing sensitive OARs (which is bad) tends to have smaller chance to open and vice versa. Second, a SMART inverse planning was performed based on simulated annealing method. In each step, MP serves as a likelihood function for the trial change of a segment. With this likelihood, a bad segment tends to be rejected without spending valuable CPU‐time to calculate the dose distribution and vice versa. Results: The proposed method was tested on a prostate case. A comparison of a prostate SMART planning with and without prior knowledge indicated that the computational efficiency was increased by a factor of ∼4. Besides, it is observed better sparing of OARs is also achieved by using MIM‐guidance. Conclusion: MIM information provides useful priors for the selection of potentially good segment shape and position and greatly facilitates the search for a set of optimal segments for SMART.
SU‐DD‐A1‐04: TomoTherapy Dose Painting
Authors: Lu W , Chen M , Ruchala K , Olivera G
Published: April 2010

Purpose: Dose painting, or heterogeneous dose prescription is desired in many situations including re‐optimization in ART to fix hot/cold spots from previous deliveries, and dose boosting based on theragnostic imaging. With minimal modification of the current TomoTherapySM planning workflow, we developed a simple scheme and studied the feasibility of dose painting in TomoTherapySM treatment planning. Method and Materials: Optimization of TomoTherapySM treatments is driven by a DVH‐based objective function and user relies on DVHs to evaluate plan quality. Given an arbitrary prescribed dose distribution, we introduce a “complimentary‐dose”, which is the difference between a (homogeneous) “reference prescription” and the “heterogeneous prescribed distribution”. During each optimization iteration, the “complimentary‐dose” is added back to the “calculated‐dose” for DVH‐based objective function evaluation. The DVH shows “optimized‐dose”, which is the summation of “complimentary‐dose” and “calculated‐dose”. The ideal DVH is still a vertical line through the reference point. All DVH constraints for tumors and OARs are employed as in regular optimization. A similar method could be used for re‐optimization in ART to fix previous errors as identified in a prior dose. Results: We used phantom studies to evaluate the feasibility of dose painting in TomoTherapySM treatment planning. Various discrete and continuous prescribed dose distributions were tested. Dose profiles and effective DVHs are used to evaluate the results. For boosting discrete regions, the results show that TomoTherapy® technology is able to resolve boost regions as small as 1 cm in diameter. Concave and convex continuous prescribed dose distribution, with gradient up to 20%/cm, can be well achieved via TomoTherapySM dose painting. Conclusions: We developed and studied dose painting in TomoTherapySM treatment planning. Phantom studies show that TomoTherapy® is an ideal modality for dose painting. Dose boosting or hot/cold spots fixing region as small as 1 cm and dose painting with gradient up to 20%/cm, is achievable.
SU‐DD‐A2‐02: Monte Carlo Design of An Internally‐Shielded Peripheral Breast Brachytherapy Applicator
Authors: Yang Y , Rivard M
Published: April 2010

Purpose: The AccuBoost® breast brachytherapy system applies HDR irradiation under mammographic image guidance. The round‐ and D‐type applicators have been developed and are in clinical use. However, it is possible to improve upon the resultant dose distributions through introduction of an internal shield for sparing the skin. The design of this internal shield has been optimized using Monte Carlo methods to retain tumor dose uniformity while minimizing skin dose. Materials and Methods: Dose distributions in breast tissue from a round applicator (60 mm internal diameter) were obtained by varying the dimensions of the tungsten‐alloy internal shield. Specifically, the superior diameter and inferior diameter of the shield were varied and generally took the shape of a truncated cone. Dimensions were chosen for cone foci at tissue depths, d, of 0, 2, 5, and 10mm with field edges −1, 0, and +1mm from the source dwell plane. The MCNP5 radiation transport code was used for calculating breast dose throughout a cylindrical phantom R=15cm radius and H=8cm high. Results: Cone design 7 was determined to be the best design. This design had relatively uniform skin dose distribution and relatively good retained tumor dose. Average skin dose was about 70% of the maximum dose, which was improved by about 27%. Average skin dose was reduced by more than 44% compared to that of an applicator without a cone. The maximum reduction in skin dose was 92%, which was typically outside the applicator aperture. In the mean time, average tumor dose at 30 mm depth was only about 5% lower than that of applicator without a cone. Conclusions: Significant improvements in critical structure dose can be obtained through introduction of an internal shield, with design optimization using Monte Carlo methods.
SU‐DD‐A3‐01: Swallowing‐Induced Target Motion and Dosimetric Impact for Head and Neck Cancer Radiotherapy as Assessed by Dynamic MRI
Authors: Paulson E , Bradley J , Ahunbay E , Wang D , Li X
Published: April 2010

Purpose: Deglutition (i.e., swallowing) results in dynamic changes in the geometry of aerodigestive tract anatomy, which may affect the doses delivered to targets and critical structures in head and neck cancer radiotherapy. The purpose of this study was to determine (1) whether MRI could be used to capture the motion of swallowing, (2) the geometrical variation induced by deglutition, and (3) the dosimetric impact of deglutition on head and neck cancer radiotherapy. Method and Materials: Five patients with aerodigestive tract cancer were imaged in treatment position on a 3.0T Siemens Verio scanner. Two time series of single‐slice sagittal images were acquired using a 2D FLASH sequence (6.667 frames/sec with and 3.257 frames/sec without parallel imaging). Swallowing frequency and duration were determined from time series data and motion was assessed using contours of gross tumor volumes (GTV) drawn during one swallowing event. Using each patient's IMRT plan and swallowing frequency and duration results, dosimetric impact was assessed by worst‐case scenario of the GTV moving completely out of the treatment field during deglutition. Results: Deglutition was non‐periodic, with frequency and duration ranging from 2.89–24.18 mHz and 3.86–6.10 sec. Dynamic changes in GTV position, size, and shape resulted from deglutition, ranging from 0–28.36mm and 0–60% change in area of GTV projection. Deglutition resulted in a 1.4–14.3% reduction in dose delivered to GTV. Conclusion: MRI is able to capture the motion of swallowing with or without the use of parallel imaging. Deglutition is non‐periodic, and results in dynamic changes in GTV position, size, and shape. The overall impact of deglutition on dose delivery for head and neck cancer, although generally insignificant, can be non‐negligible for patients with extremely high swallowing frequency and long duration.

Conflict of Interest: Partially supported by Siemens Healthcare and the MCW Cancer Center Meinerz Fellowship.
SU‐DD‐A4‐02: Potential Improvement of PET Imaging Quantitative Accuracy with An External Reference Source
Authors: Song C , Jaskowiak C , Pyzalski R , Jeraj R
Published: April 2010

Purpose: PET has been increasingly used to assess therapeutic response. As PET suffers from many inaccuracies, it might be difficult to distinguish between actual treatment response and acquisition error. The purpose of this study was to investigate the accuracy improvement of PET imaging with an external reference source. Method and Materials: A reference source was scanned in two different PET/CT scanners: GE Discovery LS (DLS) and GE Discovery VCT (DVCT). The reference source was scanned at various distances from the center of bore and at a fixed position near a scatter phantom filled with . In addition, the reference source was scanned next to patients over the period of two years. A series of scans was performed for each patient. All PET images were reconstructed using 2D‐OSEM. A cylindrical region of interest on PET was automatically segmented. Results: The measured activity was found to be inversely proportional to the distance from the center of the bore. The activity decreased by 0.95 ± 0.09 % and 0.78 ± 0.19 % per cm for DLS and DVCT respectively. The measured activity was also found to be related to activity concentration of the phantom. Within each series of patient scans, the position of the reference source varied by 1.1 ± 0.8 (SD) cm leading to 1.0 % variation in activity. However, the observed inter‐scan variation of activity was 7.0 ± 6.4 %, which cannot be explained solely by the distance effect. Conclusion: The observed inter‐scan variation for the same patients was greater than that solely due to displacement of the reference indicating a significant intra‐scan variation at different time points. The on‐going phantom studies will determine quantitative accuracy of PET imaging, providing a standardized imaging procedure.
SU‐DD‐A4‐03: Regional Atrophy in Alzheimer's Disease Measured by Voxel Based Morphometry Compare with PET and MRI
Authors: Juh R , Suh T , Kim S
Published: April 2010

Purpose: Voxel based morphometry (VBM) has been increasingly applied to investigate differences in brain morphology between a group of patients and control subjects. VBM permits comparison of gray matter (GM) volume at voxel‐level from the entire brain, thus is an efficient method for assessing regional differences. The purpose of this study was to assess the regional GM volume loss measured by VBM in Alzheimer's disease (AD) compared to controls, and to measure hippocampal volume using manually delineated volumetry and compare the results to VBM findings. Method and Materials: Twenty‐three AD (mean age 70 ± 8y; m/f= 7/16, Mini‐Mental State Exam [MMSE]= 22.2) and 20 cognitively normal elderly control subjects (mean age 69 ± 4y; m/f= 10/10) were included in this study. The 20 sets of images were first normalized and create the probability maps for segmentation. Normalized hippocampal volume to the intracranial volume was compared between AD and control groups. Results: The AD group had a lower GM %, and a higher CSF% compared to controls. The hippocampal volume of AD patients was significantly lower than that of controls (P<0.001). The region includes parahippocampal gyrus, cingulate, insula, frontal lobe and middle temporal complex. Despite the high significance in manual ROI analysis, hippocampus was not revealed in the VBM. Conclusions: We found that the hippocampal volume in AD was significantly smaller than in controls using ROI‐based volumetry. However, although our VBM results demonstrated that AD patients had a significant atrophy in middle temporal lobe, parahippocampus and insula, the hippocampus was not revealed. While VBM can be applied to assess global atrophy efficiently, manual volumetry is needed to study irregularly‐shaped subcortical structures.
SU‐EE‐A2‐03: Motion‐Weighted Dose‐Volume Histogram: A More Meaningful and Practical Four‐Dimensional Planning and Evaluation Method
Authors: Zhang G , Feygelman V , Stevens C , Dilling T
Published: April 2010

Purpose: 4D‐CT is frequently utilized by radiation oncologists to delineate a tumor and account for its motion. Current methods to generate the PTV do not fully utilize the 4D image data. After expanding from ITV to PTV, the 4D information is partially lost as the specific volume occupied by a tumor in any given respiratory phase is no longer apparent. Therefore, the planning process is the same as in 3D static planning. The 4D dosimetry introduced here uses a different method to delineate PTV (called “IPTV” in this work), which carries all of the 4D information into the planning process. This motion‐weighted IPTV allows generation of motion‐weighted DVH's. Method and Materials: Our new method expands the GTV to a CTV and PTV on each individual respiratory phase and makes a union of all the PTV's to create the IPTV. Different sub‐volumes of the IPTV are assigned different importance in treatment planning. Volumes occupied by PTV throughout the entire respiratory cycle receive higher dosimetric priority than those occupied by PTV only a fraction of the time. Coordinates of the center‐of‐mass of each PTV volume are used to calculate a motion vector for each phase. These motion vectors are used for motion‐weighted dose calculation based upon the 3D dose distribution. Motion‐weighted DVH's are generated from the motion‐weighted dose. The same process can be applied to normal structures. Results: Motion‐weighted dose distribution differs from 3D dose distribution for both target volumes and normal structures. Reducing coverage to volumes of high PTV occupancy worsens the DVH more than reducing coverage to regions of low occupancy. Conclusions: By altering the current ITV to PTV expansion method and weighting the dose with motion, 4D dosimetry can be realized with current planning systems and used to improve treatment plans and generate more realistic DVH's of mobile structures.
SU‐EE‐A3‐03: Radiation Induced Effects in An 8.5 MHz Magnetic Resonance Imaging Coil
Authors: Burke B , Rathee S , Fallone B
Published: April 2010

Purpose: Few research groups are involved in integrating magnetic resonance imaging (MRI) with a linear accelerator in order to obtain real‐time MRI images during the treatment beam‐on. Therefore, the radio frequency (RF) coils used in MRI will be irradiated during this real‐time image guided radiotherapy. The radiation effects on RF coils include instantaneous induced currents and long term radiation damage to components. These effects are potential obstacles facing linac‐MRI integration. This work measures and characterizes the instantaneous effect of pulsed radiation on MRI coils. Method and Materials: A CAT Solenoid coil was placed inside an RF cage, to remove RF noise, and connected to a current amplifier. The amplifier output was sent through RF filters to the RF cage exterior and then to an oscilloscope. The cage was placed in the pulsed beam of a linac and the current induced by pulsed radiation was measured by the oscilloscope; the waveforms were then transferred to a PC and power spectral density was calculated. Results: The RF cage was very effective in eliminating the extraneous RF noise from the radiation induced signal. The induced signal is only present when the radiation beam is on and incident upon the coil. The power spectrum of the induced current indicates that most of the power is contained below 1 MHz, but there is signal is present at the coil resonance frequency (8.5 MHz). The induced current a) occurs mainly in the copper winding, b) is reduced if buildup material is placed on the coil and c) increases linearly with the dose rate. Conclusion: Radiation induced current is present in MRI coils, but its impact on imaging is yet to be determined. This, along with magnetic field impact on induced current will be examined using the functioning 0.2 Tesla linac‐MR prototype.
SU‐EE‐A4‐04: Evaluation of Two Optical Systems for Respiratory Sensing in 4DCT
Authors: Spadea M , Baroni G , Sharp G
Published: April 2010

Purpose:. The purpose of this study is to assess the temporal and reconstruction accuracy of two different optical systems for respiratory motion detection for 4DCT. Materials and methods: A clinical CT scanner, run in cine mode, was used with two optical devices, the Gate CT®, (Vision RT, London, UK) and the RPM® (Varian, Palo Alto, CA), to detect respiratory motion. A radiation detector, GM‐10 (Blackcat, Westminster, MD), triggers the Xray on/off to Gate CT system, while the RPM is directly synchronized with the CT scanner through an electronic connection. Two phantoms were imaged: the first phantom translated a rigid plate along the antero‐posterior direction, and was used to assess the temporal synchronization of each optical system with the CT scanner. The second phantom consisted of 4 spheres that translated 3cm peak‐to‐peak in the superior inferior direction, used to assess the rebinned images created by Gate CT and RPM. Results: Calibration assessment showed a nearly perfect synchronization with the scanner for both the RPM and Gate CT systems, thus demonstrating the good performance of the radiation detector. Results for the volume rebinding test showed a variations in volumes for the 3D reconstruction of up to 15% for Gate CT and up to 12% for RPM. The mean of the standard deviations errors were 11% and 9% respectively. Errors are mainly due to phase detection inaccuracies and to the large motion of the phantom. Conclusions: This feasibility study assessed the consistency of our two optical systems in synchronizing the respiratory signal with the image acquisition. A new patient protocol based on both RPM and GateCT will be soon started.
SU‐FF‐P‐01: Conducting a SWOT Analysis ‐ A Useful Framework for Medical Physics Strategic Planning
Authors: Sternick E , Curran B
Published: April 2010

Purpose: To describe the use of SWOT (Strengths, Weaknesses, Opportunities, Threats) Analysis for medical physics strategic planning. Method and Materials: An organizational profile review of a department's medical physics staff serves as an essential preamble to the SWOT Analysis methodology. The intent of the profile study is to define important components of the work environment including: purpose, mission, vision, values, reporting relationships, workforce relationships, vendor relationships, regulatory environment and productivity tracking. A four‐quadrant SWOT matrix that is consistent with the results of the profile study is created to identify Strengths, Weaknesses, Opportunities and Threats to be used by the medical physics team as an aid in the design of appropriate action items that will lead to successful strategic outcomes. Strengths are organizational characteristics that contribute positively to achieving the defined objectives. Weaknesses are organizational characteristics that are detrimental to achieving the defined objectives. Opportunities are external factors that will assist with achieving the defined objectives. Threats are external factors that could hinder achieving the defined objectives. Results: This methodology facilitates the implementation of specific medical physics operational objectives by utilizing team‐based “brainstorming” techniques that focus on carefully targeted initiatives. Conclusion: SWOT Analysis is a well‐ established management planning tool that has been employed advantageously by diverse industries, including health care, for many years. It is a useful system also for providing medical physicists with a structured, systematic approach in the pursuit of performance excellence.
SU‐FF‐I‐04: Quantitative 3D Analysis of Stenosis Rate for Carotid Artery On CT Angiograms
Authors: Hara T , Shiraishi J , Fukuoka D , Wu T , Basiouny H , Doi K
Published: April 2010

Purpose: The diagnosis of arteriosclerosis is often based on the estimated quantities of carotid plaque. Computed tomography angiography (CTA) is an established examination method for depicting faint plaque and calcifications along the carotid vessel wall, although ultrasound imaging and magnetic resonance angiography also have been employed for this purpose. Our aim in this study was to develop a computerized method for quantifying carotid plaque and determining the stenosis rate by 3D analysis of the composition of the plaque volume. Method and Materials: Our scheme consisted of the following steps: 1) Manual drawing of the outlines of the vessel wall by an experienced physician, 2) quantitation of the vessel wall thickness, 3) volume measurements of a plaque by use of thresholding and shape analysis, 4) determination of the stenosis rate based on the volume ratio of blood flow to vessel caliber, and 5) 3D visualization of the vessel and plaque. The composition of plaques was classified into three categories based on the range of CT values as an initial estimate, i.e., lipid (−100 HU to 50 HU), hemorrhage (50 HU to 180HU), and calcification (500HU +). Shape analysis methods using a region growing technique were applied for segmentation of isolated regions such as calcifications. Results: We employed 70 CTA cases to determine the stenosis rate and to visualize the plaque composition. The results indicated that the visualization was very useful for understanding of the spatial composition of plaques and confirming the location of the stenosis relative to the vessel wall. Conclusion: The quantitative results obtained with the computerized scheme for characterization of carotid plaques on CTA would be useful for evaluation of the effect of treatment with minimally and non‐invasive vascular procedures.
SU‐FF‐I‐08: Ramping and Overscanning Contributions to Patient Dose in Helical CT
Authors: Tien C , Winslow J , Hintenlang D
Published: April 2010

Purpose: In helical computed tomography (CT) scans, slices adjacent to the clinical volume of interest, known as z overscanning lengths, are acquired for reconstruction. Additionally, CT machines undergo a transient power state, known as tube ramping, to reach full power. This investigation will characterize the dependence of tube ramping time and z overscanning length on pitch, rotation time, beam collimation, and reconstruction slice width. These relationships will be utilized to determine the contributions to patient dose. Methods and Materials: A real‐time fiber optic coupled dosimetry system with 10 ms temporal resolution is interfaced with three organic scintillators with 0.157 mm3 volumes. A Siemens Somatom Sensation 16 multislice helical CT scanner is used for the study with pitches varying from 0.5 to 1.5; rotation speeds between 0.5 and 1.5 seconds per rotation; reconstructed slice widths of 2.0 to 10.0 mm; and beam collimation of either 12 or 24 mm. One dosimeter remains stationary while two dosimeters are translated through the beam to provide real‐time profiles of the x‐ray field. Results: The ramping time was found to be independent of pitch and represented 0.5% of the total scan time. The z overscanning length was found to be monotonically increasing with pitch and represents anywhere from 14.3% to 35.9% of the total scan length. Conclusions: While ramping time remained constant, it has been demonstrated that z overscanning length is heavily dependent upon pitch — a high pitch added 7.1 cm to a 20.3 cm clinical scan length. Both z overscanning and ramping time must be taken into consideration when planning and managing patient dose. The effect of rotation time, beam collimation, and reconstruction slice width on ramping time and z overscanning length will be investigated in future work.
SU‐FF‐I‐09: Quantitative Image Quality Assessment of High‐Dose CT Images Simulated by Averaging Multiple Low‐Dose CT Images for Prospective CT Dose Reduction Studies
Authors: Hulme K , Kappadath S
Published: April 2010

Purpose: To quantify image quality differences between the average of n low‐dose images and a single high‐dose image of equivalent effective dose. Method and Materials: An electron density phantom (CIRS) was scanned on a 16‐slice CT scanner 25 times each at 12, 24, 48, 72, and 144 mAs (130 kVp, 5 mm slices, standard‐body filter). Low‐mAs scans were averaged to simulate 25 realizations of 9 high‐mAs scans: 24mAs=2×12mAs, 48mAs=2×24mAs=4×12mAs, 72mAs=3×24mAs=6×12mAs, 144mAs=2×72mAs=3×48mAs=6×24mAs=12×12mAs. Mean and standard deviation (SD) were calculated for 18 ROIs over a range of materials (−790 to 235 HU) on matched pairs of simulated and acquired images. The Welch's t‐test was used to evaluate differences in mean and SD between images. Similar experiments were performed on a Catphan® and anthropomorphic‐body phantom (ATOM, CIRS). Catphan images were visually scored for spatial and low‐contrast resolution. Profiles through selected ATOM images from the head, shoulder, and thorax were compared. Results: For every simulation, the average (range) difference in mean CT number between simulated and acquired images over all ROIs was <1 HU (−0.1±0.4 to 0.7±1.1 HU); no statistically significant difference was observed for any one material (p⩾0.27). For every simulation, the average (range) relative difference in SD over all ROIs was ⩽4% (−4.0% ±4.9% to 3.6%±3.1%); no statistically significant difference was observed for any one material (p⩾0.56). Spatial resolution of simulated images was ± 1 lp/cm of acquired images and low‐contrast resolution was ± 1 disc at all contrast levels. ATOM images profiles showed excellent agreement in all slices. Conclusion: Image quality of the average of n low‐mAs CT images is equivalent to a high‐mAs (nxlow‐mAs) image for the dose range studied; suggesting prospective CT dose‐reduction studies may be feasible using multiple low‐dose CT image acquisitions in place of the single high‐dose diagnostic scan.
SU‐FF‐I‐13: Organ Doses From Cone‐Beam CT in Radiation Therapy
Authors: Hyer D , Hintenlang D
Published: April 2010

Purpose: Daily use of cone‐beam computed tomography (CBCT) for patient position verification can lead to a substantial dose to a large volume of normal tissue outside of the planned target volume. The purpose of this work is to quantify this dose for the two kilovoltage CBCT systems currently available on medical linear accelerators, namely the X‐ray Volumetric Imager (XVI®, Elekta Oncology Systems) and the On‐Board Imager (OBI®, Varian Medical Systems). Method and Materials: An adult male anthropomorphic phantom was constructed from three tissue equivalent materials representing lung, bone, and soft tissue. To perform dose measurements within the phantom, a new fiber optic coupled (FOC) dosimeter was also developed and characterized. A total of three clinically relevant scan sites were investigated for each machine: head and neck, chest, and pelvis. For each scan site, the dose to a total of 25 organs was measured based on recommendations by the International Commission on Radiological Protection (ICRP) Publication 103 for the evaluation of effective dose. Results: The dose to organs inside the CBCT scan volume was found to be as high as 30 mGy. Due to the large field‐of‐view (FOV) of CBCT and associated radiation scatter, a substantial dose to organs outside of the scan volume was also observed and in some cases this dose was nearly 50% of the dose to organs inside of the scan volume. Conclusions: Results indicate that daily CBCT imaging in a high fraction therapy regimen can result in a substantial dose to organs well outside the planned target volume and should be taken into consideration during the treatment planning and delivery process.
SU‐FF‐I‐19: Mega‐Voltage Cone‐Beam Computed Tomography Image Quality: Effects of Scan Length and Monitor Units Per Projection
Authors: Gayou O , Akpati H
Published: April 2010

Purpose: To present a quantitative evaluation of the impact of scan length, monitor unit (MU)/projection, and total MU on the image quality in mega‐voltage cone‐beam computed tomography (MV‐CBCT). We present results of a systematic comparison of contrast‐to‐noise ratio and modulation transfer function obtained for 9 varying acquisition protocols with the MVision system (Siemens Medical Solutions, Concord, CA). Method and Materials: Image quality is characterized by contrast, noise and spatial resolution. Utilizing the manufacturer.s image quality phantom, we obtained sets of images from 9 different acquisition protocols of varying scan length, MU/projection, and total MU. The images are analyzed in terms of contrast‐to‐noise ratio (CNR) and modulation transfer function (MTF), which quantifies spatial resolution. Results: The CNR data suggest that the image contrast is not enhanced by increasing the MU/projection beyond 0.0675, but rather may be diminished. However, for comparable MU/projection the CNR is reduced from 7.25 to 4.8 by lowering the total MU from 15 to 8. For the same MU/projection the CNR is slightly better for the 360° scan compared to the 200° scan. On the other hand, the MTF analysis shows that neither the scan length, nor the sampling rate, nor the total MU have an effect on spatial resolution. Furthermore, the MTF analysis indicates that objects of spatial frequency larger than 0.3 line pair/mm cannot be resolved adequately with current MV‐CBCT imaging irrespective of the scanning protocol utilized. Conclusion: The study shows that spatial resolution is not affected by acquisition or reconstruction parameters in MV‐CBCT. However, the system is optimally used in terms of contrast‐to‐noise ratio with the default setting of 1 projection every degree. Conflict of Interest: This research was partially supported by Siemens Medical Solutions.
SU‐FF‐I‐21: Dose Variation with Breast Density in Cone Beam Breast CT‐ a Monte Carlo Simulation Study
Authors: Yi Y , Han T , Lai C , Chen L , Liu X , Shen Y , Zhong Y , Ge S , Shaw C
Published: April 2010

Purpose: By using Monte Carlo (MC) dose calculation to investigate the variation of radiation dose with the breast density (tissue composition) in cone beam breast CT, both globally and on a voxel‐by‐voxel basis. Method and Materials: To simulate cone beam breast CT imaging, we first used Rep78 to build an x‐ray spectrum for an x‐ray tube with tungsten target and a HVL of 4.08mm Al. A collimator was defined in BEAMnrc and used to form a half‐cone beam for pendant geometry used in cone beam breast CT. For validation, we compared MC dose calculations with ionization chamber measurements at 4 different locations inside the 11 cm diameter, 12 cm high cylindrical phantom under the same imaging conditions. After normalizing for the iso‐center dose, the deviations were within 3.7%. 3 cone beam CT images were first corrected and filtered to minimize the cupping artifacts and then filtered to reduce the noise level. The processed images were then segmented using threshold method to separate the dense tissue from the adipose tissue. The segmented image sets were binned into a 100×100×80 image sets with a pixel size of 1mm for MC calculation. DOSXYZnrc was used to track 1×109 incident photons distributed over 300 projection images over 360°. The resulting radiation dose was tallied for each voxel and averaged over all voxels in the breast. Results: Results from MC calculations indicated that radiation dose was significantly higher in dense tissue structures and lower in the adipose tissue. The regions of higher dose were found to match the 3D dense tissue structures. The average breast dose was found to linearly vary with the breast density computed from the breast CT data. Conclusion: Our MC study has shown a close relationship between the radiation dose and the breast density both globally and on a voxel‐by‐voxel basis.
SU‐FF‐I‐23: Full‐Scan Versus Half‐Scan in Cone Beam Breast CT ‐ a Quantitative Comparison
Authors: Chen L , Lai C , Zhong Y , Ge S , Han T , Liu X , Shen Y , Yi Y , You Z , Wang T , Shaw C
Published: April 2010

Purpose: To evaluate and compare half‐scan and full scan techniques for cone beam breast CT in terms of CT number, radiation dose distribution and CNR. Method and Materials: CT number comparison: A 11 cm diameter breast phantom, made of a stack of glandular and fat tissue, was analytically modeled to evaluate the difference of CT numbers reconstructed from Feldkamp algorithm based half and full scan reconstruction. Radiation dose distribution: An 11 cm diameter cylindrical breast model was constructed to evaluate the dose distribution with Geant4 based Monte Carlo simulation. CNR evaluation: An 11 cm diameter polycarbonate cylinder was imaged to simulate breast imaging. Five holes of the same size (5 mm in diameter) were drilled at different radial distance from the phantom center. The phantom, filled with iodine solution, was imaged with an aSi/CsI flat panel detector based cone beam CT scanner. Iodine CNRs were measured for different half‐scan coverage selection. Results: It has been found that the CT numbers reconstructed from half‐scan were close to those from full‐scan. The radiation doses in the half‐scan coverage can be twice than those out the coverage as the radial distance increasing. The CNRs for different half‐scan coverage were approximately identical. Conclusion: Our results show that the reconstructed data from half‐scan are comparable to that from full‐scan. The radiation doses are low for the positions out the half‐scan coverage. The CNRs vary little with half‐scan coverage. Acknowledgement: This work was supported in part by grants CA104759 and CA124585 from NIH‐NCI, a grant EB00117 from NIH‐NIBIB, and a subcontract from NIST‐ATP.
SU‐FF‐I‐24: Scan Time and Patient Dose for Thoracic Imaging in Neonates and Small Children Using Axial Volumetric 320‐Detector Row CT Compared to Helical 64‐, 32‐, and 16‐ Detector Row CT Acquisitions
Authors: Kroft L , Roelofs J , Geleijns J
Published: April 2010

Purpose: To evaluate scan time and patient dose for axial cone beam thoracic imaging in neonates and small children by phantom study with a 320‐detector row computed tomography (CT) scanner compared to helical multi‐detector row CT (MDCT) acquisitions. Method and Materials: Acquisition parameters that yield similar image quality were derived for standard thoracic scan protocols with volumetric 320‐MDCT and with helical 64‐, 32‐ and 16‐MDCT. The weighted CT dose index (CTDI300w) was derived from measurements with a 300 mm long CT pencil ionization chamber (CT‐110, Applied Engineering Inc., Japan) in an extended 350 mm long CT dose head phantom (diameter 160 mm). Dose length product (DLP, mGy⋅cm) was derived from the measured CTDI300w. Scan ranges of 80 mm, 120 mm, and 160 mm were considered. The paired t‐test was used to determine statistical differences in radiation exposure between the scan modes. Results: Scan time was 0.35s (one full rotation) for 320‐MDCT acquisitions; scan times varied between 1.9s and 8.3s for helical acquisitions (respectively 80 mm helical 64‐MDCT and 160 mm helical 16‐MDCT). Patient radiation dose savings varying between 18% and 40% were achieved with volumetric scanning as compared to helical scanning. Mean dose saving for 320‐MDCT versus 64‐MDCT was 25% (p < 0.001); versus 32‐MDCT was 28% (p< 0.001), and versus 16‐MDCT was 33% (p < 0.001). The smaller the selected scan range was; the higher the achieved dose reductions were. A clinical case wil be presented. A 4‐weeks‐old 3.5 kg male patient was scanned with axial volumetric 320‐MDCT. The dose length product (DLP) was 16.6 mGy⋅cm (based on CTDI300w), estimated effective dose was 0.65 mSv. Conclusion: Axial thoracic CT of neonates and small children with volumetric 320‐MDCT can be performed 5 to 24 times faster compared to helical scanning and saves between 18% and 40% in patient dose.
SU‐FF‐I‐27: Can a Flat Panel Cone Beam CT Imager Pass the American College of Radiology CT Accreditation Requirements for Head Scans?
Authors: Shapiro E , Star‐Lack J , Sun M , Tognina C
Published: April 2010

Purpose: To evaluate the performance of a flat panel cone‐beam CT system with the American College of Radiology (ACR) CT Accreditation Program. Methods and Materials: A bench‐top flat panel (FP) cone‐beam CT system using the Varian Medical Systems 4030CB panel and G424/B130 x‐ray tube with a rotating stage were used. The FP was operated in the dynamic gain mode with a frame rate of 15 fps and a scan time of 42 seconds and 625 views. The source and detector geometry were such that a full‐fan head size 25 cm field‐of‐view was reconstructed. The Gammex Inc. 464 ACR accreditation phantom and ACT automated evaluation software were used to form an unbiased pass/fail determination of the ACR head scan criteria. Standard CTDI dosimetry measurements were performed with a 16 cm diameter PMMA phantom and Victoreen 660 survey meter with 10 cm ionization chamber. Results: The ACR phantom has 4 sections, which are to evaluate a number of performance criteria. The scans were performed at a measured CTDI100 of 45 mGy absorbed dose in air. These results are from the first attempt at using the ACR phantom on the FP CBCT system. The image quality was sufficient to pass the majority of the criteria, but failed to pass the CT number accuracy by 1 HU on the acrylic sample and by 1–2 HU on the CT number uniformity test. Conclusion: The results indicate that the CT number accuracy and uniformity are areas that can be improved with better software beam hardening and scatter corrections. Also these scans were taken without an anti scatter grid, which if used should improve CT number uniformity. Therefore, there are significant indications that we can pass all categories of the ACR head accreditation tests. Additional test are then to be performed on a C‐arm based system.
SU‐FF‐I‐28: Effects of Voxel Size On Visibility of Microcalcifications in Cone Beam Breast CT
Authors: Shen Y , Chen L , Zhong Y , Ge S , Han T , Yi Y , You Z , Liu X , Lai C , Wang T , Shaw C
Published: April 2010

Purpose: To investigate the effects of voxel size on the visibility of simulated microcalcifications (MCs) in cone bream breast CT. Method and materials: Calcium carbonate grains (ranging from 140–150 to 200–212 μm), were used to simulate MCs. 25 MCs from same size group were arranged into a 5 × 5 cluster and embedded at the center of a 15 mm diameter paraffin rod. Rods with MCs from various size groups were constructed and scanned with a bench top experimental CBCT system. A CCD detector (C4742‐56‐12ER, Hamamatsu Photonics K.K) operated in 2×2 binning mode was used to acquire 300 projection images with a pixel size of 48 μm over 360°. Imaging geometry was configured with a magnification factor of 1.16 to result in a voxel size of 42 μm to match the spatial resolution limit. The acquired images were further binned into image sets of larger pixels (96, 144, 192, 240 and 288 μm). The image sets were then reconstructed with Feldkamp's backprojection algorithm using a ramp filter. The reconstructed image sets were reviewed by 6 readers independently. The visibility, computed as the ratio of visible MCs and averaged over all readers, was plotted as the function of voxel size to quantify the effects of voxel size on the visibility of MCs. Results: Based on the visibility versus voxel size plot, 90% visibility was achieved for 200 – 212, 180 – 200, 160 – 180, 150 – 160 and 140 – 150 μm calcifications at a voxel size of 249, 249, 206, 166 and 125 μm, respectively. The visibility versus voxel size plot may be used to determine the minimum pixel size required to achieve a specific visibility level for MCs of certain sizes. Conclusions: We have demonstrated that the minimum voxel size required to achieve a specific visibility level decreased with the MC size.
SU‐FF‐I‐31: A Novel Application of MRI‐Polymer Gel Dosimeter for Measurement of CTDI On X‐Ray 64 Slices CT Scanner
Authors: Riyahi‐Alam N , Karimiafshar L , Ay M , Pourfallah T Alahvirdi , Allahverdi M
Published: April 2010

The purpose of this study is to measure the Computed Tomography Dose Index (CTDI) of GE multi‐slice CT scanner(64‐slice) using polymer gel dosimetry based on MRI imaging (MRPD). CTDI is the sum of point doses along the central axis and estimates the average patient dose during CT scanning.

For measuring CTDI, after designing and fabricating the phantom and preparing MAGIC‐gel, MRI imaging using 1.5 T Siemens MRI scanner was performed with imaging parameters of ST=2mm, NEX=1, TE=20–640 ms and TR=2000 ms. CTDI was measured with a 100 mm ion chamber (CTDI100) and also MAGIC gel with MRPD method for 10 mm and 40 mm CT scan nominal width.

With measuring CTDI100 for 10 mm and 40 mm nominal slice width of multi‐slice scanner with the use of both ion chamber and MAGIC gel, the results showed that ion chamber underestimates CTDI100 by 28.71% and 14.03% compared to gel respectively for 10 mm and 40 mm.

It was concluded from this study that gel dosimeters have the capability to measure CTDI in wide beams of multi‐slice CT scanners whereas 100 mm standard ion chamber due to its limited length is not reliable even for 10 mm beam width. In addition, due to 3 dimensional nature of gel dosimetry, by using MAGIC polymer gel it is possible to obtain a lot of important information from the mentioned profiles such as the actual slice thickness and z axis geometric efficiency. In addition to the stated parameters, the percent of the total homogeneity and partial homogeneity in the slice plane can be obtained only from the gel dosimetry. The results of this study show that MAGIC polymer gel based on MRI can be used as a supplementary method in measuring conventional ion chambers dosimetry especially in measurements of more than 2 mm slice width.
SU‐FF‐I‐32: Profile and Exposure Measurements in Axial and Helical Multi‐Slice Computed Tomography
Authors: Tchou P , Rong X , Cody D
Published: April 2010

Purpose: To investigate why organ doses for helical computed tomography (CT) scans were found to be up to 25% less than similar axial scans. The organ dose measurements were performed previously using thermoluminescent point dosimeters (TLD) in a pediatric phantom. Method and Materials: Tension rods were placed across the bore of the CT scanners, flanking the scan region, in order to support measurement devices without relying on the patient table which moves during helical scans. Under this configuration, the table was kept out of the scan region for all measurements. Beam profile measurements were made for 20mm and 40mm beam configurations using computed radiography (CR) plates and software to compute the FWHM of the profile. Exposure measurements were made with a 10cm pencil ion chamber in a 16cm head phantom, similar to standard CTDI measurements. These measurements were made for multiple 64‐channel CT scanners in both axial and helical modes. For the exposure measurements, multiple scan parameters were varied including kVp, focal spot size, field of view, rotation time, exposure time, and pitch. Differences between axial and helical measurement results were compared. Results: Differences in FWHM values for the beam width measurements between axial and helical scan modes were found to be less than 1%. The normalized exposure values between axial and helical scans were found to be less than 1% in general. The only exceptions were caused by differing focal spot sizes and rotation times of less than 1 second, for which the difference was up to 2.5%, but still well within the manufacturer's tolerance. Conclusion: There were no substantial differences between axial and helical scans for the radiation profiles and exposure parameters we examined. Therefore, we conclude that the explanation for the axial/helical point dose differences must lie elsewhere. One possibility might be patient table mechanic.