bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐DD‐A4‐04: Micro Angiographic and Fluoroscopic Real‐Time Image Data Handling Using Parallel Coding Techniques in LabVIEW
Authors: Keleshis C , Ionita C , Bednarek DR , Hoffmann K , Verevkin A , Rudin S
Published: July 2008

Purpose: Multicore programming coding techniques have been designed to meet the high‐speed requirements of a High‐Sensitivity, Micro Angiographic‐Fluoroscope (HSMAF) detector for 30 fps acquisition, image‐processing, display, and rapid frame transfer of high‐resolution, region‐of‐interest (ROI) images. Method and Materials: The HSMAF detector was built by our group using a CsI(Tl) phosphor, a light image intensifier, and a fiber‐optic taper coupled to a charge‐coupled device (CCD) camera which provides real‐time 12 bit, 1k × 1k images capable of greater than 10 lp/mm resolution. A graphical user interface (GUI) was developed to control the system and enable real‐time acquisition, image‐processing, display, and rapid storage of high‐resolution images. To accommodate all these processes working in real‐time, parallel coding methods, such as instruction pipelining and task parallelism, were designed and used to take advantage of the available multicore processors (dual and quad cores). Results: The parallel coding techniques of the GUI can handle radiographic procedures that require on‐the‐fly image processing at 30fps such as Roadmapping, Digital‐Subtraction‐Acquisition (DSA), and rotational DSA. On a 2.4 GHz dual processor a high resolution image is acquired, processed and stored in less than 30ms. Recursive temporal filtering, as well as gain correction can be added to the above procedures and still maintain the required high frame rates when a quad‐core processor is used. Moreover, the overall system design offers virtually unlimited memory for acquisition and huge, expandable storage capacity. Conclusion: The ability of high frame‐rate acquisition, image processing and display for this unique high‐resolution detector along with the user friendly implementation of the interface should provide angiographers and interventionalists with a new capability for visualizing details of small vessels and endovascular devices such as stents. Such capability should enable more accurate diagnoses and image guided interventions. (Support from NIH Grants R01NS43924, R01EB002873 and Toshiba Medical Systems Corporation).
SU‐EE‐A1‐01: Acceleration of Tomotherapy Treatment Delivery by Increasing Pitch and Decreasing Modulation
Authors: Woch K , Soisson E , Westerly D , Kapatoes J , Olivera G
Published: July 2008

Purpose: To determine the feasibility of reducing Tomotherapy treatment delivery time by planning with increased pitch and reduced modulation factor (MF). Method and Materials: Twelve patients with Tomotherapy treatment sites (head/neck, prostate, prostate/nodes, lung) and fraction size of 1.8–2.5 Gy originally planned with a low pitch (< 0.3) and fast gantry period (< 20 s) were replanned. The first replan increased the pitch to 0.43 and used the original MF (MF0). If the first replan was acceptable and the gantry period increased, the patient was replanned again with pitch = 0.43 and a lower MF to reduce treatment time. This was repeated until the plan (DVH) became unacceptable or the gantry period reached its minimum (15 s). If the first replan was not satisfactory or if the gantry period did not increase, the MF was increased by 0.5 to improve the plan and to test if the treatment time was still reduced. Results: For all patients, we were able to produce a DVH comparable to the original DVH using pitch = 0.43 and MF0. When comparing the original DVH to the accelerated plan DVH that most closely matched it, treatment times were reduced by 13–66%. Comparing these accelerated plans to the original plans showed the PTV median dose increase 0.4±0.5 Gy, insignificant changes in target coverage and homogeneity index, an average change in critical structure median dose of −0.8±1.3 Gy, and a maximum critical structure median dose increase of 1.3 Gy. Conclusion: Faster treatment times can be achieved by planning with increased pitch and reduced modulation. Treatments planned with pitch = 0.43 and MF0 showed little or no plan degradation and most had faster treatment times. Further reduction in treatment time was possible by reducing the MF. Conflict of Interest: Some of the authors have financial interest in TomoTherapy, Inc.
SU‐EE‐A1‐02: Image Guided Hypofractionated IMRT for Multiple Intracranial Metastases — An Alternative to Arc‐Based SRS
Authors: Wang L , Paskalev K , Feigenberg S , Fan J , Buyyounouski M , Lally B , Price R , Ma C
Published: July 2008

Purpose: Stereotactic radiosurgery (SRS) uses an invasive head‐frame and involves long treatment times when multiple isocenter plans are treated, which becomes intolerable for some patients. This study evaluates intensity‐modulated radiotherapy (IMRT) for treating multiple (⩾4) intracranial tumors in comparison to arc‐based SRS. Method and Materials: This study involved 3 patients treated with image‐guided hypofractionated IMRT (Eclipse) and 3 treated with SRS using arc therapy (XKnifeRT). There were 28 intracranial lesions in total with planning target volumes (PTVs) ranging from 0.195cc to 5.64cc. For this study, 3 IMRT patients were re‐planned for arc therapy, while 3 SRS patients were re‐planned for PTVs (=GTVs+2mm) for both IMRT and arc therapy. By keeping the minimum surface dose of the PTVs the same between the IMRT and arc plans, we have compared maximum doses and PITV (the ratio between the volume of Prescribed Isodoseline and the Target Volume) for the two methods. We also compared the doses received by 10%, 20% and 50% of the whole brain, as well as the maximum doses to the critical structures (eyes and brainstem). Results: The average maximum doses to the 28 targets were 125.85%+/− 18.4% for arc plans and 115.2%+/−4.6% for IMRT plans. The average PITVs were 2.65+/−1.22 and 1.93+/−0.52 for the arc and IMRT plans, respectively. For critical structures, average doses received by 10%, 20% and 50% of the brains, as well as the maximum doses to other structures, were higher for IMRT plans. However, the treatment time for IMRT is significantly reduced (e.g. 15 min) compared to that for multiple isocenter SRS (up to hours). Conclusion: IMRT plans appeared to achieve comparable conformality compared to arc based SRS. This provides a good alternative for poor performance status patients. However, further study needs to be conducted to ensure the PITV calculation accuracy for small targets.
SU‐EE‐A1‐04: Dual Focus Collimator Design Studies For Temporally Precise IMRT Delivery
Authors: Kolsky K , Antolak J , Molloy J
Published: July 2008

Purpose: Increasing the temporal precision of IMRT delivery is hampered by current mechanical limitations. We are studying the feasibility of a novel system that would electronically modulate a radiation beam and deliver a time dependent IMRT beam by incorporating pencil beam scanning with a dual focus collimator. This design requires a sharply focused photon pencil beam (FWHM ∼ 1 cm at 100 cm SSD), comparable to beams achievable with current LINAC technology. Collimator specifics were investigated using Monte Carlo (MC) techniques to evaluate the capability of producing photon pencil beams. Method and Materials: The BEAMnrc code was used to develop a geometry incorporating a novel 200 hexagon channel tungsten collimator. Simulations were performed varying collimator thickness, size, and spacing of the channels. Dose in water phantoms was calculated at depth of 10 cm using DOSXYZ. Similar MLC generated pencil beams were measured at equivalent depth using Computed Radiography (CR). Script files were written in MATLAB® to calculate peak output, FWHM, and off‐axis dose/dmax ratios. Results: Pencil beam FWHM and output decreased with increasing collimator thickness (2 cm collimator: FWHM = 1.5 cm, 9 cm collimator: FWHM = 0.6 cm), keeping all other factors constant, and compared favorably to the MLC pencil beam FWHM of 0.9 cm. Off‐axis dose leakage ratios decreased 20% between 2 and 9 cm thickness. These ratios also decreased 20% with increasing hexagon spacing (0.25 – 0.75 mm). An 8‐cm collimated (0.5 mm channel spacing, 0.43 mm radius) pencil beam (FWHM = 1.1 cm) matched closely the MLC pencil beam. Conclusion: A dual focus collimator was designed using Monte Carlo modeling to produce photon pencil beams comparing favorably with current LINAC technology. Future work will focus on comparing theoretical isodose distributions to those of our clinical IMRT system. Conflict of Interest: Research sponsored in part by Varian.
SU‐EE‐A1‐06: A Real‐Time Dynamic‐MLC Control Algorithm for Delivering IMRT to Targets Exhibiting 2D Rigid Motion in the Beam's Eye View
Authors: McMahon R , Papiez L , Berbeco R , Nishioka S , Shirato H
Published: July 2008

Purpose: We have developed a real‐time MLC control algorithm that allows for delivery of dynamic‐MLC (DMLC) IMRT to targets exhibiting 2D rigid motion in the beam's eye view (BEV). Method and Materials: The control algorithm consists of two components: 1) Construction of baseline DMLC leaf trajectories, and 2) real‐time control loop. The synchronized baseline leaf trajectories are constructed using target motion data that is collected prior to delivery. Only target motion that is aligned with leaf travel is included in this step. To account for target motion in the BEV that is not aligned with leaf travel, we have implemented a real‐time leaf‐pair switching mechanism, which allows the MLC to track motion along this axis in discrete increments of the leaf width. Using patient data, 36 target trajectories were constructed. One of these trajectories was used to construct the baseline leaf trajectories, and the others were used to simulate a 35 fraction IMRT treatment. Errors were analyzed using difference maps and a distance‐to‐agreement analysis. Results: The results indicate that 2D tracking resulted in deliveries that were superior to both no tracking and 1D tracking. A 160ms system lag time produced errors that were approximately equal those that resulted from ignoring one component of motion altogether. Additional results show that the algorithm's performance is very insensitive to the level of agreement between the target motion collected prior to delivery, and the motion observed during delivery. Conclusion: Over the course of a fractionated IMRT treatment, the MLC tracking algorithm is able to accurately compensate for 2D rigid target motion in the BEV. The performance of the algorithm is insensitive to the difference between the target motion measured during planning and the motion that actually occurs during delivery.
SU‐EE‐A2‐03: Establishing a Trade‐Off Between Number of Beams and Plan Quality in Robotic Radiosurgery
Authors: Schlaefer A , Blanck O
Published: July 2008

Purpose: To study the potential trade‐off between the number of beams and the plan quality in robotic radiosurgery. Specifically, to assess, whether the number of beams can be reduced by repeating the series of optimization steps on a subset of substantially weighted beams. Method and Materials: We use a linear programming formulation of the planning problem, where objective terms are matched by corresponding constraints. The optimization is decomposed into a series of steps. When a plan with acceptable quality has been obtained, the activation time of the beams is studied. Beams with an activation time below a threshold are removed from the plan. We then compare the effect of (A) rescaling the weight of the remaining beams to obtain at least 98% of the previous coverage, and (B) to re‐optimize the beam weights by applying the series of optimization steps to the reduced set of beams. The methods are applied to three clinical cases, a spinal lesion, a head and neck tumor, and a prostate case. Results: We removed up to 17.6%, 52.3%, and 28.4% of the beams for the spinal, the head and neck, and the prostate case, respectively, while retaining the plan quality with reoptimization. In contrast, rescaling changed the dose distribution substantially and the plan quality metrics degraded to an unacceptable level. Conclusion: Removing low weighted beams can reduce the number of active beams, and hence the overall treatment time. Reoptimization using the original series of optimization steps leads to better plan quality compared with rescaling. The potential to reduce the number of beams while retaining plan quality depends on the clinical case, and the fraction of beams that is removed. Conflict of Interest: Research partially sponsored by Accuray Inc.
SU‐EE‐A3‐01: 4D Locally Adaptive Radiation Delivery Using Integrated In‐Room MRI and DMLC Tracking
Authors: Sawant A , Kondaji S , Keall P
Published: July 2008

Purpose: The ideal IGRT‐based delivery to manage intrafraction motion has two requirements: complete spatio‐temporal knowledge of the anatomy, and real‐time beam adaptation corresponding to motion‐induced anatomical changes. Toward this goal, we investigate an integrated strategy combining two powerful techniques — online image‐guidance using fast cine‐MR imaging (4D‐MRI) and real‐time, locally adaptive delivery using dynamic multileaf collimator (DMLC)‐based tracking. Method and Materials: Image SNR and, therefore, field strength (Bo) requirements for an integrated MRI+Linac for the task of radiotherapy guidance were investigated. Using multisection, multiphase steady‐state free precession (SSFP) and spoiled gradient recall (SPGR) sequences, 3D volumes (1.4s/volume) and 2D coronal slices (0.5s/slice) of a volunteer's thoracic region were acquired with a 1.5T MRI. For each set, a region of interest encompassing the diaphragm was segmented and trajectories of superior‐inferior and left‐right motion were computed for voxels within. In order to simulate real‐time imaging with lower field strength MRI+Linacs, the SNR for each set was progressively degraded and corresponding motion trajectories recalculated. 4D locally‐adaptive IMRT was implemented using a DMLC tracking algorithm which adapts the beam aperture(s) in real‐time using 3D position information from an independent monitoring system. The aforementioned trajectories were programmed into a high‐resolution 3D‐programmable motion platform and geometric accuracy of DMLC tracking was measured. Results: The SSFP‐acquired 2D and 3D images yielded adequate SNR for registration, while the SPGR sequence yielded faster acquisition but poorer SNR. For SSFP images, even with a factor‐of‐six SNR reduction (corresponding to Bo ∼0.2T), no significant changes were observed in estimated motion trajectories. Finally, sub‐millimeter tracking accuracy was observed for these traces for simultaneous target motion in the S‐I and left‐right directions. Conclusion: These initial studies provide valuable insights into design requirements of integrated MRI+Linac systems and indicate that 4D‐MRI combined with DMLC tracking represents a highly promising approach for intrafraction motion management.
SU‐GG‐I‐04: Grid‐Computing for Optimization of CAD
Authors: Jamieson A , Giger M , Wilde M , Pesce L , Foster I
Published: July 2008

Purpose: Pilot study to utilize large scale parallel grid computing to harness the nationwide cluster infrastructure for optimization of medical image analysis parameters. Method and Materials: A previously developed CAD scheme for mass lesions in mammography was ported onto the grid computing environment by wrapping the algorithm code with the virtual data language (VDL). The CAD scheme was then configured into a parallelizable workflow by the grid‐software. The workflows were executed using two test clusters (in Santa Monica, CA and Chicago, IL) consisting of over 220 dual‐CPU nodes combined. Using the grid‐environment workflow, parameter sweeps were conducted for lesion segmentation settings based on radial‐gradient‐index (RGI) methods. Specifically, the Gaussian width (GW) used in initially filtering lesion images for segmentation was varied by increments of 1 mm from 1 to 60 mm. For each GW sweep the entire 850 biopsy‐proven mass lesion database (411 benign, 439 malignant) was analyzed. In each, 29 different mathematical descriptor features were calculated, followed by feature selection and merging with linear discriminate analysis. Diagnostic performance was estimated by ROC analysis by calculating AUC (from PROPROC) values based on both individual features alone, and merged. For merged classifiers, AUC values were found using round‐robin case‐by‐case removal and replacement. Results: Computation jobs requiring over 30 CPU hours on a single lab computer were completed in approximately 35 minutes in this preliminary study. Merged AUC values increased from 0.50 (std.err.=0.018) at GW of 1mm with, to 0.81 (std.err.=0.015) at 10mm GW, with relative plateaus across the rest of the parameter space to 60mm. Conclusion: The parameter space sweep in GW identified trends in individual feature performance as well as merged results. Large scale, computationally intensive image analysis can be carried out in a timely fashion, feasible for expedited experimental discovery, as well as for more thorough future statistical analysis.
SU‐GG‐I‐20: Dynamic Volume CT: Technical Aspects and Image Quality of the Aquilion ONE
Authors: Boedeker K , Mather R
Published: July 2008

Purpose: In order to cover entire organs, multislice CT requires helical acquisition. This need for table motion in multislice CT causes image volumes acquired for whole organ motion and perfusion studies to lack temporal uniformity. Dynamic volume CT mitigates this limitation by providing the ability to acquire an entire organ with isotropic resolution in a single gantry rotation with no table movement. The purpose of this study is to examine the technical aspects of the Aquilion ONE, the first dynamic volume CT scanner, and the effect on image quality versus a standard 64‐slice system. Method and Materials: An Aquilion ONE with a detector configuration of 320× 0.5mm channels is examined and compared to an Aquilion 64 with a 64×0.5mm detector configuration. Studies performed include low contrast resolution, high contrast resolution, uniformity, slice sensitivity profile, and CT number accuracy. These studies were performed using a CATPHAN 500. Results: The technical challenges associated with dynamic volume, such as cone beam reconstruction, and their physics implications, such as image clipping, will be presented. It will be shown that low contrast, high contrast, slice sensitivity profile, and CT number accuracy are equivalent to a standard 64‐slice system. Some differences in uniformity were found and will be discussed. Conclusion: Dynamic volume CT allows clinicians to visualize contrast flow, motion dynamics, and entire volumes at a single instant in time while maintaining the image quality found on current systems. Dynamic volume CT promises to transform the way medicine approaches stroke patients, myocardial perfusion studies, and imaging of other moving body parts such as the lung and joints.
SU‐GG‐I‐21: Image Reconstruction From Sparse Data in Breast CT
Authors: Bian J , Yang K , Packard N , Sidky E , Boone J , Pan X
Published: July 2008

Purpose: Because breast CT acquires projection data at a large number of views and involves no breast compression, the radiation dose involved may be significant. In this study, we investigate image reconstruction from projections acquired at a small number of views in breast CT, thus potentially reducing the radiation dose to the patient. Method and Materials: A clinical trial has been carried out at UC‐Davis using their breast CT scanner. Circular cone beam projections are acquired at 500 views over 360 degrees for each patient. Based on compressed sensing approach, we have developed an algorithm for image reconstruction from sparse data, which involves the minimization of the total variation (TV) of the underlying image function subject to the data condition. We have applied the TV‐based algorithm to reconstruct breast images from patient data acquired in the clinical trial studies. The reconstructed images are compared to those reconstructed by the FDK algorithm. Results: Image reconstruction was performed using both TV and FDK algorithms for patient data sets acquired only at 50 views and 100 views. The results suggest that images obtained with the former are superior to that obtained with the latter. Images were also reconstructed by the FDK algorithm from the full data sets containing 500 views, which are regarded as the gold standard in this study. A comparison shows that the TV reconstructions from sparse data can reveal most of the details that are observed in the FDK reconstruction from full data. Conclusion: An initial comparative study suggests that the TV reconstructions from sparse data can reveal most of the details of a patient breast. A potentially significant implication is that the TV‐based algorithm may lead to a reduction of radiation dose in breast CT imaging.
SU‐GG‐I‐31: Comparison of Breast‐Centered and Volume‐Of‐Interest (VOI)‐Centered VOI Cone Beam CT Techniques — Dose and Scatter Considerations with Monte Carlo Simulation
Authors: Chen L , Lai C , Han T , Liu X , Shen Y , Wang T , Shaw C
Published: July 2008

Purpose: To evaluate and compare dose saving and scatter reduction properties of VOI‐centered and breast‐centered approaches to VOI cone beam CT with Monte Carlo simulation. Method and Materials: To implement the VOI scanning technique, a mask with an opening is inserted between the x‐ray source and the patient to deliver higher exposures inside the VOI and lower exposures outside the VOI during the scan. There are two approaches to implement this technique. One is to center the breast with the rotation axis and move the VOI mask to track the VOI. The other is to center the VOI with the rotation axis, thus keeping the VOI mask fixed during the scan. A cylindrical breast model with a VOI close to the breast boundary was constructed to evaluate and compare the two approaches with Geant4 based Monte Carlo simulation. Dose distribution in the breast and scatter‐to‐primary ratios (SPRs) at the detector input were evaluated and compared to those estimated for full field cone beam CT. Results: Both VOI scanning techniques significantly reduce the radiation doses and scatter intensities both inside and outside the VOI. However, dose saving with the breast‐centered approach was approximately twice as much as that with the VOI‐centered approach both inside and outside the VOI. SPRs inside the VOI were similar for the two approaches and varied little with rotation degree. Conclusion: The breast‐centered scan appears to be the preferred approach to VOI cone beam CT because it resulted in substantially better dose saving while similar scatter reduction as compared to the VOI centered approach. Effort to implement this technique is underway to demonstrate this technique and to validate the simulation results.

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‐GG‐I‐35: Geometric Accuracy of High Contrast Region Visualization On 4D X‐Ray CT Imaging Using Sinogram Binning
Authors: Rosu M , Weiss E , Wiesmeyer M , Brady A , Williamson J
Published: July 2008

Purpose: To assess geometric errors in delineating high‐contrast structures from 4DCT‐acquired images undergoing simulated motion of various amplitudes. The broader goal is to formulate margin‐design guidelines that account for imperfections in 4D target imaging for a range of tumor sizes and motion amplitudes. Method and Materials: Three spherical objects with different diameters were placed on a moving platform adjusted to provide sinusoidal, one‐dimensional motions of various excursions (range: 0.5–4 cm) along the longitudinal axis of a Philips Brilliance scanner. Repeated scans were performed for three pitch values (0.15, 0.11, 0.075). Sinogram data were sorted into 10 different breathing phase bins. In addition, time‐averaged and maximum intensity projection (MIP) image sets were reconstructed. Data analysis included qualitative inspection of the shape of scanned objects, comparisons of contoured volumes for the static and moving targets, and centroid motion assessment. Results: The accuracy of reconstructed objects generally improves with decreasing amplitude and pitch. For large excursions and phases intermediate between exhale and inhale, large deviations from the spherical shape are observed; amplitude and volume deviations are as large as 10 mm and 30%. The observed centroid excursion is always less than the actual bin midpoint excursion. Smaller pitch does not always guarantee better results. The MIP centroid lines up closely with the centroid from time‐averaged datasets, but its actual position is underestimated by 3–4 mm as well. There is a tendency for deviations to be larger for datasets reconstructed during inhalation. Conclusion: The accuracy of 4D‐acquired datasets depends on motion characteristics and protocol acquisition parameters. The evaluation of the associated uncertainties is necessary for a more accurate margin design during treatment planning when either one or multiple 4D‐derived datasets are used for treatment planning. More studies are required to investigate the clinical significance of such errors.

Supported in part by NIH P01 CA116602.
SU‐GG‐I‐38: A Study On the Accuracy of MIP for Irregular Target Motion
Authors: Park K , Huang L
Published: July 2008

Purpose: For the treatment of lung cancer, internal target volume (ITV) is frequently determined utilizing Maximum Intensity Projection (MIP) images generated by 4DCT. In order to check the accuracy of MIP for various target motion, especially for targets moving irregularly, we performed phantom studies using programmable dynamic lung phantom. Method and Materials: House built programmable lung phantom, with cylindrical (2.5cm(D) × 2cm(H)) and cubic (2.5cm(W) × 2.5cm(L) × 1cm(H)) acrylic targets, was utilized to simulate regular and irregular sinusoidal type target motions in superior‐inferior direction. Moving targets were scanned with Philips 4DCT with bellow system in helical mode. For each scan we obtained 10 reconstructed phase images and composite MIP images. Scan parameters such as pitch (0.082) and gantry rotation time (0.5 sec/rotation) were chosen as recommended by the vendor in order to minimize motion artifacts. Obtained images were imported into Pinnacle 8.0 treatment planning system for image analysis. Results: For all regular, periodic target motions with constant ranges (10mm and 15mm, appropriately) and period (4sec), ranges of measured MIP along superior‐inferior direction were accurate. For example, the MIP spanned 36–37mm for target motion of 10mm amplitude while the expected value was 35mm. For irregular target motion with various combinations of amplitudes (10mm and 20mm) but with the same period (4sec), the MIP spanned 38–40mm while the expected value was 45mm. The measured range of motion by MIP turned out to systematically underestimate the range of irregular target motion when amplitudes were varying. We associate these discrepancies with the fact that current reconstruction algorithms of commercial 4DCT are based on phase binning. Conclusion: According to our phantom measurement, MIP reflects the range of target motion accurately for regular target motion while it generally underestimates the range of target motion when the motion is irregular, exhibiting variation in amplitude.
SU‐GG‐I‐40: Scatter Profiles for a 16‐Slice CT Scanner with Cylindrical and Anthropomorphic Head and Body Phantoms
Authors: Hatab M , Goerner F , Al‐Senan R
Published: July 2008

Purpose: We sought to validate the stray radiation dose maps provided by CT manufacturers and to investigate the effects of varying phantom composition and shape on these scatter profiles especially as they pertain to shielding requirements. Method and Materials: The standard CT dosimetry cylindrical body phantom was used to validate the published results by the manufacturer. The technique factors used were: 8 × 3 mm detector configuration, 140 kVp, 400mA, 2 second rotation time, and 350 mm FOV. A 150 cc ion chamber at isocenter height and always facing isocenter was used to measure the secondary radiation. The chamber was clamped to a rolling cart and was moved in 50 cm increments around isocenter to cover a grid of 3 m × 4 m. This was repeated for the standard CT dosimetry head phantom, an anthropomorphic head phantom, and an anthropomorphic chest and pelvis phantoms. Results: There was poor agreement between the nominal data obtained for the standard CT dosimetry body phantom and that supplied by the manufacturer especially on the cranial side of the gantry. There was considerable difference between the results from standard CT dosimetry body phantom and the anthropomorphic pelvis phantom, both in magnitude (40% higher on average) and shape of the isodose contour plots. In addition, comparisons between anthropomorphic head and the standard CT dosimetry head phantom will be presented as isodose contour plots in the horizontal plane 100 cm from the floor. Conclusion: There were differences in the scatter magnitude between the manufacturer supplied values and those measured. However, as this information is often used in barrier shielding calculations, these differences were not significant enough to alter shielding requirements for barriers 1.5 meters or further away from isocenter. The manufacturer values tended to be somewhat higher and thus more conservative than those measured.
SU‐GG‐I‐44: Real‐Time Dose Measurements of Automatic Tube Current Modulation in Multislice CT
Authors: Tsai HY , Chang YC , Tyan YS
Published: July 2008

Purpose: To estimate real‐time doses which are controlled by automatic tube current modulation (ATCM) in multidetector computed tomography (MDCT), and to verify the dose decrease with the prediction by software. Method and Materials: Brilliance 40 MDCT scanner (Philips) provides five ATCM methods. Those are automatic current selection (ACS), xy‐plane dose modulation (D‐DOM), z‐axial dose modulation (Z‐DOM), ACS combined D‐DOM, and ACS combined Z‐DOM. Real‐time doses were measured by two CT pencil‐type detectors operating with a Barracuda (RTI‐e) electrometer connected to a PC running the software oRTIgo2002 (RTI‐e). One detector is DCT10 CTDI ion chamber (RTI‐e) with 100 mm sensitive length. The other is CT‐SD16 CT slice detector (RTI‐e) with 160 mm sensitive length. Several geometric phantoms, which are circular, oval, and elliptic cylinders with 15 cm height, were fabricated to simulate body shapes and to verify the xy‐plane dose modulation. An Apollo phantom was also fabricated to verify the z‐axial dose modulation. Results: For circular cylindrical phantoms with 16–24 cm diameter, doses decreased 28–69% for ACS, 28–67% for ACS combined D‐DOM, and 24–66% for ACS combined Z‐DOM. But dose increased 13–20% for 32 cm diameter. For oval and elliptic cylindrical phantoms, doses decreased 17–27% for ACS, 15–40% for D‐DOM, 31–39% for ACS combined D‐DOM, and 15–28% for ACS combined Z‐DOM. D‐DOM and Z‐DOM real‐time dose variation curves were similar for circular cylindrical phantoms. However, real‐time dose variation curves got closed along with increasing diameter. For oval and elliptic cylindrical phantoms, ACS and ACS combined Z‐DOM real‐time dose variations were resembling. But Z‐DOM real‐time dose variations were remarkable for the Apollo phantom. Conclusion: The methods established by this study could investigate the real‐time dose variations. Using ATCM techniques in MDCT scanning could decrease patient doses. However, it needs to pay more attention to use ATCM techniques for obese patients.
SU‐GG‐I‐45: Dose Trends in Tube‐Current Modulated Multi‐Detector CT Imaging
Authors: Fisher R , Hintenlang D , Winslow J , Moloney W
Published: July 2008

Purpose: The purpose of this work was to compare clinically relevant point dose measurements in both homogenous geometric and anthropomorphic phantoms in order to compare the effects of MDCT tube‐current modulation on the dose distributions in each. These dose measurements were compared to corresponding CTDIvol measurements to determine this metric's effectiveness in describing clinical scan doses in MDCT. Method and Materials: A fiber optic coupled dosimeter system was utilized with both a homogenous elliptical phantom and an anthropomorphic phantom incorporating accurate anatomical features scaled to represent ICRP reference man. Point dose measurements were taken at various points in both phantoms using routine abdominal scan techniques. Both modulated and fixed tube‐current scans were performed, and the resulting data was used to create an isodose map for each phantom. CTDI measurements were taken using the same scan techniques, and the resulting CTDIvol was compared to the doses measured using the elliptical and anthropomorphic phantoms. Results: Tube‐current modulated scans produced an average point dose reduction of 7.6% in a homogeneous elliptical phantom. This reduction was accompanied by a more uniform dose distribution across the transverse slice, with the most reduction apparent across the minor elliptical axis. The average point dose reduction was slightly less in the anthropomorphic phantom, where tube modulation resulted in an average dose reduction of 4.5% and a similar improvement in dose uniformity. CTDIvol was found to underestimate the average point dose measured from the anthropomorphic phantom, with measured doses being 90% higher than the predicted CTDIvol. Conclusion: Tube‐current modulation was found to reduce both the average dose and the dose variation for an individual slice in both a homogeneous geometric phantom and a heterogeneous anthropomorphic phantom. CTDIvol was found to be a poor predictor of organ doses in MDCT.
SU‐GG‐I‐58: GafChromic EBT Film for Cone‐Beam CT Dose Measurement — Preliminary Study
Authors: Li T , Fountain L , Duffy E
Published: July 2008

Purpose: To find a new method for Cone‐Beam CT dose measurement. Method and Materials: EBT‐1417 films (Lot: 47171‐02I, ISP) were irradiated on a Varian 21EX Linac (VMS) using 6 MV photon beams to the following doses: 2, 4, 6, 8, 10, 12, 16, 20, 30, 50, 80, and 100 cGy to construct a dose calibration curve. A NIST traceable ion chamber was inserted in the phantom to check for Linac output consistency during film irradiation process. The time error of Linac was measured to be less than 0.005 MU. These films were scanned with Vidar VXR‐16 (Vidar Systems Corporation) after 2 hours post exposure to guarantee full development. The CBCT irradiated EBT films were also scanned using Vidar scanner in the similar way and were analyzed by RIT113 software. The Vidar scanner had been calibrated with NIST provided step wedge (SN L4592). The Acuity simulator (VMS) was used for CBCT measurement. The standard full fan with bowtie filter was used. The EBT‐1417 film was sandwiched in the center of two solid water slabs, and was placed at the central axis plane of the simulator. To increase the EBT film response, three CBCT scans were delivered to the same region of interest. Results: The CBCT dose on the central axis level in a slab phantom was about 5.3 cGy after three Cone‐Beam CT scans. A single scan would have given about 1.8 cGy. Three dimension dose map showed relatively uniform distribution throughout the plane. Conclusion: We utilized an attractive feature of EBT film, e.g. minimal energy dependence from keV to MeV range, for CBCT dose measurement. Preliminary results showed that EBT film is a potentially promising solid‐state dosimeter for measuring dose in CBCT. Evaluation of sensitivity and uniformity for EBT film response at low dose levels is under way.
SU‐GG‐I‐60: Effective Dose to Patients Undergoing Radiostereometric Analysis of the Lumbar Spine
Authors: Greene‐Donnelly K , Ogden K , Ordway N , Roskopf M , Calabrese J
Published: July 2008

Purpose: To determine the effective dose of patients undergoing radiostereometric analysis (RSA) of the lumbar spine. Method and Materials: 12 patients with total disk replacement prosthetic devices in the lumbar spine participated in an IRB approved study to follow the sagittal and coronal range of motion using RSA. Image pairs were obtained at 6 weeks, and then 3, 6, 12, 18 and 24 months. Five image pairs were acquired at each visit (neutral, flexion, extension, and left and right lateral bend). Radiographic techniques were recorded for all acquired images. Patient mass was used to estimate abdominal AP thickness. Tube output and half value layers were measured at the appropriate tube accelerating potentials. This information was used with the image geometry to calculate the entrance kerma‐area product (KAP) incident on the patients. The KAP and patient thickness were then used to estimate the energy imparted to the patients and the resulting effective dose. Results: The average technique used was 141 kVp and 11.6 mAs. The mean effective dose per image pair was 0.304 mSv, and the mean per visit (5 image pairs) was 1.52 mSv with a standard deviation of 0.7 mSv. The average for the entire two year study was approximately 9.1 mSv. This compares very favorably with the value of 18 mSv reported in the 2000 UNSCEAR report for a single diagnostic lumbar spine study. Conclusion: Image quality requirements for RSA are not the same as for general diagnostic imaging. The use of high kV techniques that would result in unacceptable low contrast images for general diagnostic purposes are adequate for visualizing fiducial beads used in RSA. Low doses allow for the acquisition of multiple image sets to detect motion of prosthetic devices with total effective doses that are much lower than a typical diagnostic lumbar spine examination.
SU‐GG‐I‐61: Is It Safe? A Look at Exposures in the Shadow of MDCT Scanner Gantries
Authors: Jones A
Published: July 2008

Purpose: Computed tomography (CT) is used quite frequently as an imaging tool during interventional radiology (IR) procedures. Interventional radiologists at our institution often stand adjacent to the gantry of the CT scanner while scanning in “biopsy” mode, as it is commonly thought that the shadow of the gantry is the safest place to be if one remains in the room during CT scanning. An investigation was performed to more closely investigate the radiation dose to persons standing in the shadow of the gantry. Method and Materials: OSL area monitors were used to gather long‐term dose data at various points outside the CT gantry. Measurements were performed on 16 and 64 slice scanners used in the IR department. Results: Dose rates varied substantially within the shadow of the CT scanner gantry for both the 16 slice and 64 slice scanners. Compared to the value in the center of the gantry shadow, doses measured halfway between the center and edge of the gantry towards the “foot” side were 34.8 and 17.0 times higher for the 16 slice and 64 slice scanners, respectively. Similarly measured doses towards the “head” side were 4.2 and 3.4 times higher than dose levels in the center of the shadow for the 16 slice and 64 slice scanners, respectively. The ratio of foot side to head side doses was 8.2 and 5.0 for the 16 slice and 64 slice scanners, respectively. Conclusion: Asymmetric distribution of hardware within the gantry can lead to steep dose gradients along the table axis in the shadow of modern CT gantries. It was found that the dose to someone standing in the shadow of a CT gantry can vary by as much as a factor of 35 based on position within the shadow.
SU‐GG‐I‐62: The Relationship Between Half Value Layer and CTDI for Multidetector CT (MDCT)
Authors: Turner A , Angel E , Zhang D , DeMarco J , Cagnon C , McNitt‐Gray M
Published: July 2008

Purpose: CTDI is a common measurement for MDCT, but Half Value Layer (HVL) is not routinely measured. The purpose of this study was to determine the relationship between these two measured values for different scanners at different beam energies, specifically to determine if HVL alone is an adequate predictor for CTDI values. Method and Materials: CTDI measurements (CTDI100, periphery, CTDI 100, center and CTDIw) were performed using the 32 cm diameter (body) phantom on MDCT scanners from three different manufacturers, using similar collimation settings. CTDI values were reported on a normalized (per mAs) basis. The HVL was obtained using a static (nonrotating) tube. CTDI and HVL were measured for each available beam energy and bowtie filter (for body scanning) for each system. Results: Normalized CTDIw values ranged from .019 to .134 mGy/mAs across all scanners, kVps and bowtie filters with a mean of .071 mGy/mAs. HVLs ranged from 4.5 to 9.7 mmAl across scanners, kVps and bowtie filters with a mean of 7.3 mmAl. For a given kVp (e.g. 120 kVp) the normalized CTDIw ranged from .065 to .096 mGy/ mAs with an average of .081, while the HVLs ranged from 6.6 to 8.6 mm Al with a mean of 7.9 mmAl. In general, for a given kVp, the systems with lower HVL tended to have higher CTDIw values. Conclusion: There is significant variation in normalized CTDIw values and HVL values across scanners and even bowtie filters within a scanner. However, higher HVL values yield lower CTDIw values. Thus, for a given scanner and bowtie filter selection, there does seem to be a relationship between HVL and CTDIw, but these latter values can also be influenced by other factors such as filtration not accounted for by HVL (filtration in bowtie not through the central ray) as well as beam collimation.
SU‐GG‐I‐73: Investigation of the Relationship Between the Contrast‐Detail Figure of Merit IQFinv and Three Characteristic Parameters of the Contrast‐Detail Curve
Authors: Christodoulou E , Goodsitt M , Larson S
Published: July 2008

Purpose: To investigate the relationship between the figure of merit IQFinv that is estimated by the CDRAD Analyzer software as an overall descriptor of the contrast‐detail characteristics of a radiographic image of the CDRAD phantom, and the fitted contrast‐detail curve parameters: limiting object size (object diameter below which the threshold contrast must be increased by more than a pre‐set value for the object to be detectable), limiting threshold contrast (the threshold contrast of the limiting object size), and large object threshold contrast (the threshold contrast of the object with the largest diameter). Method and Materials: We analyzed CDRAD phantom images acquired with four different digital radiographic detectors using x‐ray beams with HVL of 7.1 and 10.2 mm Al for each detector, and five different radiographic exposures for each beam quality. The IQFinv and a scatter plot of the contrast‐detail curve were generated for each image. These plots where best‐fitted with S functions, and the contrast‐detail curve parameters were determined from these functions. Results: For a large range of IQFinv (i.e. ∼7 to ∼2) the limiting object size and the limiting threshold contrast generally increase (in this case, from ∼0.5 to ∼1.4 mm and ∼0.1 to ∼0.7% respectively) as IQFinv decreases. For smaller ranges of the IQFinv (i.e. 6.0–8.0 or 3.0–5.0) this relationship for both parameters appears significantly weaker, considering the pool of images from all four detectors. This may be due to the uncertainty in the IQFinv estimate, the selection of the pre‐set value in the determination of the limiting object size, and the fitting parameters of the contrast‐detail curves. The relationship between IQFinv and large object threshold contrast is less pronounced. Conclusion: IQFinv becomes a more accurate descriptor/comparator of the contrast‐detail characteristics of digital imaging systems if it is combined with the proposed fitted contrast‐detail curve parameters.
SU‐GG‐I‐79: Effective Doses to Pediatric Cystic Fibrosis Patients Undergoing Chest CT Examinations
Authors: Frey G , Fordham L , Huda W
Published: July 2008

Purpose: To compare radiation doses to five year old pediatric patients with Cystic Fibrosis (CF) undergoing chest CT examinations at five North American imaging centers. Method and Materials: A questionnaire was sent to five facilities participating in a CF research study (Chapel Hill NC; Washington WA; St Louis Mo; Denver Co; Toronto ON) to obtain their protocols for chest CT examinations on a five year old child with Cystic Fibrosis. The ImPACT CT dose calculator was used to determine adult effective doses for techniques used at each facility (i.e., kV/mAs/pitch). Adult effective doses were scaled to those for five year olds to account for differences in scan length, patient size and energy imparted. Results: The five facilities used four different models of CT scanner from two vendors. CT techniques for five year old patients with CF were generally 120 kV, 60 mAs, and an average pitch ratio of ∼ 1.2. Adult scan lengths were 30 cm whereas those for 5 year olds were 15 cm. Adults weigh 70 kg compared to 18.5 kg for a 5 year old. For a single 360 ° x‐ray tube rotation, energy absorbed in the chest region of a five year old is only 55% of that for an adult. Three facilities had effective doses of ∼ 2.4 mSv, whereas two facilities had lower doses of ∼1.25 mSv. The main reasons for the lower doses were the use of lower x‐ray technique (i.e., 30 mAs) or a lower x‐ray tube voltage (i.e., 100 kV). Conclusion: Effective doses to 5 year old CF patients can be obtained by scaling adult effective doses, and average to 2 mSv per patient examination.
SU‐GG‐I‐80: Preliminary Evaluation of the QCkV‐1 Phantom and CyberKnife® Digital Flat Panel Detector (FPD) Imager Response
Authors: Purwar A
Published: July 2008

Purpose: To evaluate the applicability of the QCkV‐1 phantom (Standard Imaging) for trending analysis of the FPD imagers of CyberKnife® Robotic Radiosurgery System (Accuray Incorporated) and to study their response over a period of time and under different conditions. Method and Materials: Images of the QCkV‐1 phantom were acquired on different CyberKnife systems over several months to study trends as well as reproducibility. X‐ray settings like kVp were varied to simulate x‐ray generator drift to see if this can be detected. These images were analyzed using Standard Imaging's PIPSpro software package to obtain the Relative Modulation Transfer Function (RTMF) and Contrast‐to‐Noise Ratio (CNR). Results: After performing the PIPSpro image analysis we obtained values for f30 and f50 (f50 is defined as the critical spatial frequency for which the response is 50% of the maximum RTMF) as well as CNR. Imaging tests of the CyberKnife FPDs show consistency over a period of several months. Changes in x‐ray kVp show up in measured quantities like the RMTF and CNR. Conclusion: Although QCkV‐1 was originally designed for FPD systems that are quite different from the CyberKnife imagers, its trending analysis can be a useful tool for early detection of imager issues. We are investigating the relationship between these low‐level measurements and overall performance of the system, which is used for tracking tumors and patient motion rather than diagnostic radiology. This will require longer term monitoring and correlating these measurements with actual tracking performance.