bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐EE‐A4‐04: Compartment Modeling Analysis of Cu‐ATSM Dynamic PET Images
Authors: Wang Z , Yuan H , Willett C , Dewhirst M , Yin F
Published: June 2005

Purpose: Copper labeled diacetyl‐bis(N4‐methylthiosemicarbazone) (Cu‐ATSM) has been reported to selectively bind to hypoxic tumor cells. This makes Cu‐ATSM PET a promising modality to image tumor hypoxia. However, intravascular Cu‐ATSM that is not related to hypoxia, can also contribute to the PET signal. The purpose of this study is to use compartment modeling analysis to separate tumor tissue time‐activity Cu‐ATSM signal into intravascular and extravascular components. Method and Materials: A dynamic Cu‐ATSM PET scanning was performed on tumor‐bearing (R3230 mammary adenocarcinoma) rats. The Cu‐ATSM concentration is separated into an intravascular concentration (Cp) with vascular volume fraction (vp) and extravascular concentration (Ce). The transfer between the intra‐ and extra‐vascular compartments is described by rate constant k. The time activity data of Cu‐ATSM were fed into the compartment model. After non‐linear least square (NLLS) fitting of the model, tumor signal was separated into intravascular and extravascular components. Vascular volume fraction vp and rate constant k were also obtained from the fitting. Results: The time courses of the intravascular and extravascular Cu‐ATSM signals were obtained from the NLLS fitting and are shown in figure 1 in the supporting document. The fitted Cu‐ATSM uptake signals match closely with the measured results. The vascular volume fraction obtained from the fitting for three tumors was 2.4%, 2.3% and 2.9%, and the transfer rate from blood to tissue was 0.045, 0.043, and 0.047 (1/minute), respectively. Conclusion: Compartment modeling analysis can effectively remove the intravascular Cu‐ATSM signal from the overall tissue signals, reflecting more accurately the tissue uptake and tumor hypoxia. Tumor vascular volume fraction and Cu‐ATSM transfer rate constant can be obtained from the compartment modeling analysis.
SU‐EE‐A4‐05: Individual Target Volume Definition in NSCLC Using PET
Authors: Zhang B , Mah K , Caldwell C , Danjoux C , Tirona R
Published: June 2005

Purpose: To determine whether quantitatively segmented PET images could be used to identify the volume containing a tumor and its total motion. If possible, PET could provide individualized internal target volumes (ITV) in lung cancer. Method and Materials: A physiological phantom containing background level of Na‐22 was used. Two spheres filled with 0.5 mCi/ml of Na‐22 were used to simulate tumors; each was oscillated within one lung of the phantom with 4 preset motion extents in S/I, A/P, and M/L directions. PET and CT imaging were performed on an integrated PET/CT scanner. A CT‐based GTV was generated using a threshold of −850 HU. A population‐based margin of 15 mm, reflecting both motion and set‐up uncertainties, was added to generate a CT‐based PTV. A PET‐based ITV was defined using a threshold of three standard deviations above normal lung background. A set‐up margin of 7.5 mm was added to PET‐based ITVs to create PTVs. Image‐based PTVs were compared to ideal PTVs. Clinical validation of this methodology was performed on 7 patients with parenchymal lung lesions with the addition of digital fluoroscopy. 18‐FDG was used for patient PET scanning. Results: For the phantom study, PET‐based PTVs were closer to the ideal PTV than those based on CT. While the PET‐based PTVs were approximately half the size of the CT‐based PTVs, in no case would the PET‐based PTVs have resulted in geographical miss. For majority of the patients, PET accurately predicted or slightly over‐predicted the tumor motion extents compared to fluoroscopy; differences were within 2 voxels. Conclusion: Based on the phantom study and initial clinical validation, we have found that quantitatively segmented PET images can provide an accurate individualized ITV that correlates with a tumor and its motion. Conflict of Interest: Research was supported by NCI Canada with funds from Ontario Cancer Society.
SU‐EE‐A4‐06: Longitudinal Correlations in a Small‐Animal PET Studies
Authors: Abbey C , Borowsky A , Gregg J , McGoldrick E , Cardiff R , Cherry S
Published: June 2005

Purpose: One area of interest in the rapidly developing field of small‐animal imaging is preclinical evaluations of cancer therapeutics. It is clear that longitudinal imaging studies reduce the number of animals necessary for such evaluations by following a single cohort over multiple timepoints. However, there is additional benefit to longitudinal data for comparisons between timepoints. Of particular interest in preclinical studies are comparisons between the disease status at the onset of treatment and later timepoints after treatment has been completed. Positive correlations between timepoints add statistical power to tests of differences. In this work, we investigate correlations in quantitative features across timepoints in small‐animal positron emission tomography (PET) images of a mouse model of breast cancer. Method and Materials: We investigate a mammary intraepithelial neoplasia outgrowth (MIN‐O) model in FVB mice. Transplant development in these animals is similar to the neoplastic progression of breast carcinoma from preinvasive ductal carcinoma in situ to invasive carcinoma in humans. A cohort of mice were imaged 5 times on a dedicated small‐animal PET scanner after injection of a commonly used radiotracer (FDG). After reconstruction, quantitative features such as functionally active volume, maximum uptake and total uptake were computed as markers of development. Results: Quantitative features document development of disease in these animals over time. Positive person correlation coefficients ranging over 0.3 and > 0.9 have been observed between timepoints for the extracted features. This leads to substantial gains in statistical power. Conclusion: Features extracted from volumetric PET images in the MIN‐O mouse model correspond with development of disease. Because of the variability in disease progression and proliferation between lesions, there is a considerable statistical advantage to longitudinal studies. Correlations between timepoints measured for this work lead to quantifiable gains in statistical power.
SU‐EE‐A1‐01: Comparison of Monte Carlo and Convolution/Superposition Calculation Methods: Quantification of the Dose Prediction Errors Arising From Tissue Heterogeneities
Authors: Mihaylov I , Lerma F , Siebers J
Published: June 2005

Purpose: To investigate the extent of the dose prediction error (DPE) due to tissue heterogeneities in superposition/convolution (SC) based dose calculations by comparisons with Monte Carlo (MC) calculations for head‐and‐neck IMRT treatment plans. Method and Materials: A retrospective investigation is performed for ten Head‐and‐Neck IMRT patients. Dose calculations are performed with SC and MC algorithms. For both algorithms, the intensity modulation generated by the dynamic multi‐leaf collimator (DMLC) is incorporated into the dose calculation via a transmission matrix generated by determining the ratio of incident and transmitted energy fluence through the DMLC using a MC algorithm. Plans were compared based upon the criteria used during the IMRT optimization: GTV D98, CTV D95, Nodal volume D90, Cord D02, and Parotid D50. As the same transmission matrix is used for both methods and the SC and MC algorithms subsequent dose differences are attributed to handling of the tissue heterogeneities by the SC algorithm. Results: The GTV D98 and CTV D95 local doses agree within ±3.2% for the SC and MC calculations. Differences are within ±1.8% for the D90 of the nodal target volume. The cord and the brainstem D02 doses differ by <±3.5% and <±2.5% of the local dose respectively. The Parotid D50 shows the greatest variations, with local differences up to 5.8%. The observed deviations do not show systematic under‐ or over‐estimate of the dose by SC. Conclusion: When identical transmission matrices are used, the DPE of the SC method, using the MC method as a references, is <±3.2% for the target structures. For the critical structures, DPEs as high as 6% of the local dose were observed, which corresponds to <3% if normalized to the prescription dose. (Supported by NIH‐1R01CA98524)
SU‐EE‐A1‐03: Inhomogeneity Correction in IMRT Beamlets: Significance in Lung Treatments
Authors: Das I , Cheng C , Glatstein E
Published: June 2005

Introduction: To examine the efficacy and accuracy of pencil beam (PB) and collapsed cone convolution (CC) algorithms that are commonly used in IMRT optimization and dose calculation. The magnitude of error is also estimated with measurement for small IMRT beamlets. Method and Materials: The CT scan of a specially designed lung phantom was used in the dose calculations, with and without inhomogeneity correction, for both algorithms. The inhomogeneity correction factor; CF=Di/Dh, where Di and Dh are the doses at the same depth with and without inhomogeneity, respectively, was calculated for 6 MV and 15 MV beams. Small volume ion chamber and Gafchromic films were used for the measurement, with varying depths and field sizes ranging from 1×1 – 10×10 cm2. Dosimetry was also performed with various other detectors to study the accuracy of the dose algorithms in homogenous water phantom. Results: Small volume chambers and diodes provided similar results in homogenous phantom for small fields. The PB algorithm is relatively insensitive to field size whereas collapsed cone is field size dependent. The CF with PB and CC has wide variations (up to 60%) for 6 and 15 MV beams for small fields. As field size increases, the difference decreases. For 10×10 cm2 fields the two algorithms differ by only 4–5%. CF is dependent on the distance of inhomogeneity, field size and beam energy, and the effect is more pronounced for 6 MV than for 15 MV beams. Both ion chamber and Gafchromic films are in better agreement with CC calculation. Conclusion: Significant differences between PB, CC and measurements are noted that disappear for large fields, however, CC should be preferred for IMRT. Faster optimization and calculation hardware should be implemented since CC takes 10 times longer time than PB calculation. Special care is needed for validations of these complex algorithms.
SU‐EE‐A1‐05: Intensity Modulated Radiation Therapy (IMRT) as An Alternative to Adjuvant High Dose Rate (HDR) Brachytherapy in Endometrial Cancer Patients
Authors: Wang S , Smith B , Sutton H , Aydogan B , Mundt A , Roeske J
Published: June 2005

Purpose: To evaluate the role of IMRT as an alternative to HDR brachytherapy for the adjuvant treatment of endometrial cancer patients following surgery. Method and Materials: The CT scans of five patients previously treated with adjuvant HDR were used in this study. All patients were scanned with a vaginal cylinder in place, and HDR planning was performed using the BrachyVision (Varian Medical Systems) software. In all cases, a dose of 700 cGy/fraction was prescribed at a distance of 0.5 cm from the cylinder surface. The same planning CT scans were then used for IMRT planning (Eclipse, Varian Medical Systems). In this paradigm, the vaginal cylinder is a component of a hypothetical immobilization system that would be indexed to the linac treatment table. The goal of IMRT planning was to deliver the prescription dose to the clinical target volume (CTV) while minimizing the volume of rectum and bladder irradiated. Dose volume histograms (DVHs) of the bladder, rectum and CTV were recorded and compared for both HDR and IMRT plans. Results: The mean bladder doses (as a percentage of the prescription dose) were 31.8% and 32.2% (p = 0.93) for the HDR and IMRT plans, respectively. However, in 4 of the 5 plans, IMRT produced lower maximum bladder doses compared to HDR (averages: IMRT = 99.1% vs. HDR = 158.4%). IMRT plans also resulted in lower mean rectal doses (21.6%) than HDR plans (30.9%) (p = 0.01). Moreover, the maximum rectal doses were lower in all IMRT plans compared to the HDR plans (95.1% vs. 165.8%). On average, the minimum dose to CTV was slightly higher using IMRT (97.8% vs. 95.5%). Conclusion: These results suggest than when used in conjunction with a suitable immobilization system, IMRT may provide an alternative to HDR brachytherapy in women with endometrial cancer following hysterectomy.
SU‐FF‐I‐02: Automatic Detection and Sizing of Metastatic Brain Tumors Using 3D Template Matching
Authors: Ambrosini R , Wang P , Victor J , Sobe N , O'Dell W
Published: June 2005

Purpose: The prognosis of patients with brain metastases is generally poor, but is improved with early detection and treatment with stereotactic radiosurgery as performed routinely at our institution. To achieve the earliest possible detection of subclinical lesions requires frequent screenings and use of high resolution volumetric imaging. This results in an ever‐increasing workload for the radiologist, predisposing an increased tendency for reading error, especially for small nodules. We have developed a novel small tumor detection algorithm based on 3D template matching that also quantifies nodule size and hence growth between scanning sessions. Method and Materials: Post‐contrast, coronal, SPGR, T1‐weighted MRI datasets (voxel size 0.43×0.43×2.5 mm) were acquired. Autoextraction of bone and other non‐brain tissue from the brain volumes was accomplished using morphological operations. Spherical tumor appearance models were created to match the expected geometry of the small tumors of interest and accounting for offsets due to the cut of MRI sampling planes. A 3D normalized cross‐correlation coefficient (NCCC) between the brain volume and spherical templates was calculated using a fast frequency domain algorithm. Volumes of nodules were determined using both voxel‐based measurements and by modeling each as an ellipsoid. Results: Spherical templates were optimized for values of the radius, padding, and thresholding parameters. The data collected shows that a 100% tumor detection rate can be achieved with a true positive to false positive ratio of 4.5 with the cerebellum cropped out and 1.25 with the cerebellum present. Growth of the nodules over 11 months was automatically quantified, as well as detection of 1 new lesion. Conclusion: Our results demonstrate that the 3D template‐matching method can be an effective, fast and accurate tool for automated detection of tumors in brain MRIs. Strategic integration of results from multiple templates can further minimize the false positive rate while maintaining a 100% detection rate.
SU‐FF‐I‐05: A Bench‐Top Megavoltage CT (MVCT) Scanner with Cadmium Tungstate‐Photodiode Detectors
Authors: Tu D , Monajemi T , Rickey D , Fallone B , Rathee S
Published: June 2005

Purpose: To design, fabricate and test the data acquisition timing control, precision rotary stage control, and an analog data multiplexer unit for a prototype megavoltage computed tomography (MVCT) detector. To measure the basic detector characteristics such as linearity with dose rate, the pre‐sampled modulation transfer function (MTF), the noise power spectrum (NPS) and the detective quantum efficiency (DQE). Method and Materials: The 80‐element prototype detector array is made with CdWO4 (element size 0.275 × 0.8 × 1 cm3) scintillators and photodiodes placed on an arc with a radius of 110 cm. In addition to designing and fabricating an in‐house data acquisition system (front‐end integrators, data multiplexer unit, and timing control), a precision rotary stage and its control are added to create a third generation MVCT scanner. The data acquisition is synchronized with radiation pulses from a linear accelerator. The response of the detector as a function of dose rate was studied by varying the source to detector distance. A narrow slit beam, at five locations, was used to measure the pre‐sampled MTF. The detector signal in open beam was measured for a number of radiation pulses to use the periodogram method for NPS estimation. Using the measured MTF, NPS, and the photon fluence impinging on the detector, the DQE was calculated. Results: Detector response is linear as a function of dose rate, however, shows a non‐linear component while measuring the attenuation by solid water due to the poly‐energetic spectrum. Therefore, beam‐hardening correction is necessary before MVCT image reconstruction. The MTF at the Nyquist frequency (0.16 mm−1) is approximately 0.48. The zero‐frequency DQE in 6 MV beam at 21% is higher than any experimental MVCT detector. Conclusion: The basic performance of the prototype detector was found to be satisfactory for producing reasonable low contrast resolution in MVCT images with low dose.
SU‐FF‐I‐06: Determination of Optimal KV for Imaging Iodine and Bone in Computed Tomography
Authors: Ellerbusch D , Ranallo F
Published: June 2005

Purpose: To determine the kV that will yield optimal contrast to noise ratio (CNR) at a constant patient dose for iodine/ soft tissue and bone/ soft tissue contrast in head and small body studies. Method and Materials: A head phantom containing water equivalent material and a bone ring to simulate the skull (for head studies) was used to obtain the data. To measure the contrast of iodine to water and bone to water, cylindrical plugs were inserted into the phantom: two plugs contained different dilutions of iodine contrast (Omnipauqe 300mgI/ml), one contained bone equivalent material, and one contained water. This phantom was scanned at kV values ranging from 80 to 140 kV. The contrast was measured as the difference in CT number between the iodine and bone plugs and the water plug. The noise measurements were taken from the water plug. Noise was determined at constant dose (CTDI w), so that the mAs was increased as the kV decreased. Both image noise and image contrast increased as the kV decreased. The relevant parameter for determining optimal kV is the contrast to noise ratio (CNR) at a constant dose as a function of kV. Results: The optimal kV, within the range of 80 to 140 kV, for the imaging of both iodine and bone is 80 kV. Limitations to this kV selection include the possible presence of increased artifacts in bone imaging, and CT scanner limitations in mAs that might not allow low kV with an adequate level of image noise. Conclusion: The common use of 120 to 140 kV in CT scanning may not be optimal for many studies whose primarily objective is the discernment of iodine or bone contrast, such as in brain perfusion studies. The use of lower kV settings may be advantageous in these cases.
SU‐FF‐I‐11: Investigation of a Method to Adjust Non Medical Grade Monitors Without the Use of a Photometer
Authors: Christodoulou E , Kim J , Goodsitt M , Larson S
Published: June 2005

Purpose: Computer monitors with luminance range less than the ACR recommended value of 220 cdm−2 for diagnostic monitors are increasingly being used for the viewing of clinical images. One of the reasons is the increased popularity of Web applications that make clinical images easily accessible from office and home computers. In this study we investigate a quick and easy method for radiologists/clinicians to set‐up the brightness and contrast of such monitors without the use of a photometer. Methods and Material: 17 commonly used flat‐panel desktop monitors were visually optimized for low contrast resolution using the TG18‐BR pattern. Since the monitors' low contrast resolution performance was found to be affected significantly less by the brightness setting than by the contrast setting, we fixed the brightness setting at 75% of maximum brightness and changed the contrast setting to further optimize the low contrast resolution After optimization, the display function of each monitor was compared to the DICOM Gray Scale Display Function (GSDF). After forcing the minimum and the maximum luminance of the monitor to fall on the GSDF we calculated the RMS error between the monitor display function and the GSDF for the 20%, 50% and 90% gray‐scale values of the SMPTE pattern. Results: The mean value of the optimum contrast settings was 39.6% of maximum contrast with standard deviation of 21.8%, and a range of 0% to 63%. The RMS error ranged from 1.9 to 39 with an average of 17. The RMS error was poorly correlated with the contrast setting (r=0.21), 100% luminance (r=0.27) and 0% luminance (r=0.12). Conclusion: Further ROC studies are needed to determine what RMS errors relative to the GSDF are acceptable for viewing images of different types (e.g. CT or chest) on these monitors and whether window and level adjustments can compensate for larger RMS errors.
SU‐FF‐I‐12: Boundary Based Vs. Region‐Based Segmentation Techniques for Breast Lesion Phantoms Produced by Fischer's Full Field Digital Mammography Ultrasound System (FFDMUS): A Novel Tool for Performance Evaluation of LCD's and CRT's
Authors: Suri J , Poolla A , Ye Z , Bilhanan A
Published: June 2005

Purpose: This paper presents a performance evaluation strategy for LCD and CRT display characterization using ultrasound data acquired from Fischer's full field digital mammography and ultrasound system (FFDMUS) prototype. Method and Materials: Lesion segmentation of these ultrasound images acquired through the FFDMUS was performed using two approaches: (a) Gradient Vector Flow (GVF) and (b) Signal‐to‐Noise (SNR). The protocol consisted of FFDMUS ultrasound data acquisition with known X‐ray and ultrasound parameters. The ultrasound ROI images were displayed on LCD and CRT displays, memory grabbed and then segmented using GVF and SNR tools. Note that during the memory grabbing process from the displays, the spatial properties of the displays were ignored. This output was then optimized for partial volume correction, given the ideal boundary. The performance of the segmentation algorithms was evaluated by quantifying the mean error between the ideal boundary and the computer‐estimated boundary. Polyline distance metric (PDM) was used as a ruler. We used the segmentation and error quantification system on LCD and CRT displays. Results: we optimized our segmentation algorithm over 22 ultrasound FFDMUS images. The mean and standard deviation using GVF on LCD/CRT were 0.870 & 0.207/0.900 & 0.244. Correspondingly, the mean and standard deviation using SNR on LCD/CRT were 1.129 & 0.321/1.105 & 0.315. Conclusion: It was observed that both the segmentation strategies are comparable on both LCD's and CRT's for this data set used. Also the GVF performed better than SNR, as it was an interactive methodology.
SU‐FF‐I‐14: New Approaches to Practical CT Dosimetry
Authors: Anderson J , Chason D , Arbique G , Lane T
Published: June 2005

Purpose: To outline the basics of conventional CT radiation dosimetry, to discuss difficulties that new cone‐beam and wide‐area detector geometries present to this conventional dosimetry approach, and to illustrate the practical application of recently proposed dosimetry techniques to both multirow and cone‐beam CT configurations. Method and Materials: Traditional CT radiation dosimetry is reviewed and its limitations in cases in which the radiation field is extended in the axial direction are discussed. Comparison is made between this approach, which is based on the use of the standard 100 mm pencil‐type ion chamber, and a recently proposed technique employing a small “point detector” ion chamber (e.g. an RMI type TDC‐100A with 0.1 ml volume)(RL Dixon, A new look at CT dose measurements: beyond CTDI, Med. Phys. 30, 1272–1280 (2003)). The specific corrections for using the small chamber are demonstrated in the case of full cone‐beam CT performed with rotational angiography equipment (Siemens ARTIS BA neuro‐angiographic room). A complete methodology for performing CT dose measurements with small chambers is presented. Results: Good agreement between the point chamber and pencil chamber methods was demonstrated for conventional CT geometries. Direct measurement in cone‐beam geometry is not possible with the pencil chamber, but can be performed with the point chamber. The estimated patient doses for conventional CTA were compared to those delivered by rotational angiographic equipment performing cone‐beam acquisitions and found to be larger by a factor of between 8 and 25, depending on the specific protocol employed. Conclusion: Modern CT equipment employs geometries that make conventional CT dosimetry inapplicable. The clinical physicist should be aware of this and of the necessity for developing new methods to characterize the radiation dose delivered to the patient.
SU‐FF‐I‐15: Computed Radiography Dose Data Mining and Surveillance as An Ongoing Quality Assurance Improvement Process
Authors: Stewart B , Kanal K , Perdue J
Published: June 2005

Purpose: The purpose of this ongoing quality assurance (QA) project is to use our Picture Archiving and Computing System (PACS) as a data mining tool to surveil the computed radiography (CR) sensitivity number (S‐number). The S‐number provides a good approximation of the average absorbed dose to the imaging plate and can be used as a general indicator of proper CR exposure technique and radiation dose. Method and Materials: Multiple CR systems acquire radiographic exams which are stored on PACS. A data mining program extracts the S‐number information of the CR exams on a monthly basis. The S‐number is approximately defined as S = 200/exposure (mR). A log transform is applied to the S‐number data to normalize the skewed distribution of the S‐number histogram. Data falling outside two SD are discarded to exclude extreme outliers. This data is compared with the previous month's data and initial baseline data to observe if trends are increasing or decreasing with respect to the departmental S‐number goals (bone, spine and extremity exams=200, chest exams and general imaging including abdomen=300; all with ±15% range). The results are presented at monthly QA meetings with radiologists, technologist supervisors, physicists and administrators in attendance. S‐number trends are then used by the technologists to modify radiographic technique charts to reach the S‐number target range. The entire cycle is repeated monthly as an ongoing QA improvement project. Results: The mean S‐numbers for main, trauma and portable radiology exams have increased by 69%, 67% and 46% over the past year respectively, corresponding to an approximate reduction in dose of 32%–41%. As a result of this process, we have adjusted our phototiming systems to reflect the S‐number goals for specific anatomy. Conclusion: This cyclical QA process demonstrates that PACS data can be mined usefully to reduce radiation dose and inter‐exam dose variance.
SU‐FF‐I‐19: Skin Entrance Radiation Dose in An Interventional Radiology Procedure
Authors: Chu R , Thomas G , Maqbool F
Published: June 2005

Purpose: Monitoring of skin entrance radiation exposure in lengthy interventional procedures with X‐ray is recommended because of the potential for skin injury. X‐ray on‐time and dose‐area product (DAP) are readily available real‐time measurements. It would be of interest to study the correlation of these parameters and skin entrance radiation. Method and Materials: Twenty interventional procedures performed through the aortic arch to one or more of its three associated major blood vessels were monitored. Two pieces of GafChromic XR Type R film were placed between the patient and the examination table. An observer recorded the X‐ray on‐time and DAP for each phase of the procedure. Each film was scanned post‐procedure in RBG mode, and then the red component of the image was analyzed for peak skin entrance radiation dose (in air kerma) after proper calibration. All DAP values were corrected according to a calibration with an ion chamber. With the corrected DAP values for the respective phases of a procedure, and the Monte Carlo model used by the National Radiological Protection Board (United Kingdom), the effective dose in a standard man was calculated. Results: For these twenty cases, the mean and standard deviation of were 17.2 ± 6.4 minutes for X‐ray on‐time, 256 ± 65 Gy.cm2 for DAP, 94 ± 34 cGy for peak skin entrance dose in air kerma, and 13.2 ± 3.1 mSv for effective dose. The peak skin entrance dose was correlated to X‐ray on‐time, DAP and effective dose with the coefficients of 0.69, 0.68, and 0.49 respectively. The corresponding r‐values in linear regression analysis were 0.48, 0.46, and 0.24. Conclusion: The poor correlation with DAP and X‐ray on‐time suggests that skin dose should be measured independently. However, peak skin entrance dose would be a poor indicator for effective dose. Determination of the latter requires more detail information.
SU‐FF‐I‐21: Can Prostate CT Contouring Be Improved?
Authors: Narayana V , McLaughlin P , Jackson T , Zelefsky M
Published: June 2005

Purpose: Contouring the prostate on a CT dataset remains a challenge, especially post implant. The prostate apex is not clearly defined on CT. It is difficult to distinguish the bladder neck from the base of the prostate. This study reports the variability in contouring the prostate on CT between individuals and the potential to reach a consensus with training. Method and Materials: Five post permanent prostate implant CT studies scanned using a Picker scanner, 2 mm slice thickness, were open for contouring to participants at an international meeting. Thirty‐nine participants who routinely contoured the prostate contoured all 5 studies using the Variseed software. The volume of the prostate contoured with reference to the standard MR prostate volume is reported. The same five studies were also contoured by 6 experienced radiation oncologist. The participants first received a tutorial on CT contouring techniques. They were provided with 3 test cases to practice and then asked to contour the five studies. Results: The average ratio of the CT to MR prostate volume for 39 participants without the tutorial was 1.09 ± 0.50, 1.68 ± 1.00, 0.92 ± 0.46, 1.12 ± 0.55, and 0.99 ± 0.56, respectively for the five cases. The same average ratio for 6 experienced radiation oncologists with training was 1.02 ± 0.09, 1.52 ± 0.35, 0.85 ± 0.19, 1.16 ± 0.17, and 0.94 ± 0.13, respectively. Conclusion: The average ratio of CT to MR prostate in both studies were comparable. However, the standard deviations for the study with training are small indicating that it is possible to reduce the variability in prostate contouring between individuals. Conflict of Interest: This work was supported by Oncura and Varian Medical Systems, Inc.
SU‐FF‐I‐25: Target Flattener Combinations for Combined Therapy and High Contrast Megavoltage Imaging
Authors: Nishimura K , Svatos M , Zheng Z , Faddegon B
Published: June 2005

Purpose: To optimize target‐flattener design in megavoltage (MV) x‐ray beams for combined therapy and imaging purposes using Monte Carlo methods to quantify the effect of target‐flattener material on treatment and imaging properties. Method and Materials: Carbon, aluminum, stainless steel and tungsten were used in various target‐flattener combinations. The BEAM/EGSnrc Monte Carlo system was used to design flatteners to achieve beam flatness, by the AAPM definition, of under 5% over 20 cm and 40 cm diameter fields. Further simulations were used to determine contrast improvement. Results were compared to experiment for the cases of the conventional tungsten target with stainless steel flattener, a small‐field aluminum flattener, and no flattener. Contrast, contrast‐to‐noise ratio and MTF were measured using a variety of phantoms (aluminum plates, CIRS CT, Pips‐Pro QC‐3). A preliminary experimental investigation of contrast improvement in MV CT was also done, imaging the CIRS and Pips‐Pro phantoms, and the head of RANDO. Results: Measured treatment and imaging properties of the conventional flattener and small‐field aluminum flattener validated the calculation approach. Calculated results demonstrate significant improvements in contrast using low‐atomic‐number targets or flatteners, using smaller flatteners that limit the field diameter to 20 cm, or removing the flattener altogether. The highest contrast is obtained with a carbon‐carbon target‐flattener combination. This combination results in a modest increase in the surface dose. The MV CT scans are visibly improved using the small‐field aluminum flattener in place of the conventional flattener. Conclusion: The Monte Carlo results for low‐Z target and flattener combinations show significant improvement in imaging properties with minimal degradation of treatment properties. Clinical implementation would lead to improved contrast in localization and verification imaging with megavoltage beams. With small‐field flatteners, the dose gradient outside the flattened region could be compensated with IMRT. Conflict of Interest: This work is partially supported by Siemens Oncology Systems.
SU‐FF‐I‐31: An Improved Method for Susceptibility Correction of MR Spectroscopic Images
Authors: Blechinger J , Hearshen D , Peck D , Bower L
Published: June 2005

Purpose: Multivoxel spectroscopic imaging usually requires a correction for magnetic field differences between voxels. The correction enables a narrower frequency range for integration to produce the metabolic image, increasing the signal to noise ratio of the image. One method employs a single reference peak common to spectra in all voxels, such as n‐acetylaspartate, NAA. This works well in all but tumor cases where NAA is not present. A manual search must be done to find and correct the spectra in those voxels by referring to the creatine or choline peaks. This is rather tedious so a method of using multiple reference peaks was developed. If the pattern of the reference peaks is recognized, it can be used to correct for the magnetic field, automatically. Method and Materials: Data was acquired with the sequence from the NIH on 1.5T and 3T magnets from GE Healthcare. The sequence includes water saturation and outer volume suppression and allows for 4 slices to be acquired with a 32×32 matrix yielding a voxel size of 0.9 cc. The analysis was performed on Eigentool software with spectroscopy analysis code CSX. The reference peaks are defined by with a window and a maximum. The pattern of space between the reference peaks is compared to that of peaks larger than a second threshold. The pattern is allowed to shift up to one quarter of the span between the reference peaks. Results: The technique increases the speed of the analysis by decreasing the number of voxels that need to be checked manually from 100 or more to just the perimeter, perhaps 25, where the outer volume suppression may have missed some fat. Conclusion: Improving the analysis of MRSI can improve patient care by speeding up the time to report the results to the referring physician.
SU‐FF‐I‐38: Mask‐Based vs. Reverse Engineering‐Based Strategies for Skin‐Line Enhancement in Low Contrast Projection Mammograms
Authors: Suri J , Bilhanan A , Sun Y
Published: June 2005

Purpose: This paper presents two new strategies for skin‐line enhancement in mammograms based on brightness preserving bi‐histogram equalization (BBHE) [1] framework during window and level process. Method and Materials: Image enhancement is performed using two different strategies based on BBHE framework: (A) masked‐based strategy, and (B) reverse engineering approach. In the first approach, the image is divided into two regions: skin‐line zone mask and the rest of the breast region. The skin‐line zone mask is computed by subtracting the binary images obtained using two different threshold techniques: whole breast region threshold using Ojala's method [2] and stroma breast region threshold using Otsu's method [3]. The BBHE is then applied in this masked zone and the remaining breast region, thereby boosting the skin‐line zone of the mammograms. The second approach uses the reverse engineering technique where the enhancement is started in the reverse direction from skin‐line towards the parenchyma. The bands are taken from the outer region of the breast moving inward. This method is implemented by performing BBHE on a significant band (say 50 pixels wide) on the image and replacing only a small band (say 10 pixels wide) by the enhanced BBHE band. This is repeated until the whole image was enhanced. This method performs very well on mammograms with very low contrast in the skin‐line zone. Results: Both techniques demonstrated a considerable boosting in the skin‐line zone, which was the goal of the enhancement process. The lesion conspicuity is improved and skin‐line edges are well seen during window level. The algorithm has been tested on 15 MIAS mammograms. Conclusion: Both implemented methods show enhancement in the skin‐line region. We are currently testing its robustness on other mammogram databases.
SU‐FF‐I‐39: A Computer Simulation Platform for the Optimization of Breast Tomosynthesis System
Authors: Zhou J , Zhao B , Zhao W
Published: June 2005

Purpose: In breast tomosynthesis there are tradeoffs between optimization of resolution, noise and acquisition speed with a given glandular dose. Our purpose is to provide a simulation platform to investigate any plausible configuration for a tomosynthesis system, and find an optimal combination of these parameters. Method and Materials: Simulated projections of a slanted thin tungsten wire placed in different object planes are modified according to a detector's MTF (binned or not binned). In addition, the focal spot blur (FSB), which depends on the location of the wire, the system geometry, the source‐detector movement speed and exposure time, is also incorporated into the projections. Then a maximum likelihood (ML) algorithm is used for 3D reconstruction. The in‐plane and in‐depth MTF were determined. To evaluate the noise performance, simulated noiseless projections of calcification and tumor in uniform breast tissue were modified with real detector's NPS and for a given detector noise and dose. The signal to noise ratio (SNR) of the reconstructed images is calculated with different configurations, e.g. view number and angle, pixel binning and FSB. Results: The FSB is determined by the exposure time of each view at a fixed gantry travel speed. For SID = 65cm and exposure time ≤ 80ms per view, the 2×2 binning causes more degradation for the in‐plane resolution than the FSB and reconstruction blur. The in‐depth resolution can be improved by increasing the number of views and the span of view angle. However the SNR will be degraded because with the lower exposure per view (total dose constant), the detector performance is degraded by electronic noise. Conclusion: Many design parameters need to be considered for optimizing a tomosynthesis system. We provide a simulation platform to predict system performance with different configurations in advance. It will be helpful for practical implementation of breast tomosynthesis.
SU‐FF‐I‐42: Imaging Technique in Estimating Lung Shunting of Yttrium‐90 Microspheres
Authors: Luo J , Rao P , Zimmer M , Polis M , Mistretta M , Spies S
Published: June 2005

Purpose: This study was to evaluate lung shunting from Tc99m MAA and Y90 imaging, and its effect on treatment planning. Y90 Microspheres (Therasphere, MDS Nordion) have been used for the treatment of unresectable hepatocellular carcinoma (HCC). Tc99m MAA imaging is utilized to assess pulmonary shunting which will affect treatment dose. Standard shunting compares the ratios of activity in the liver and lungs. Method and Materials: Twenty five patients were randomly selected to examine shunting ratios. Eight studies required the redrawing of RoIs to correct the variance in geometric mean. Actual activity was determined following treatment planning guidelines based on standard and measured shunting. Y‐90 imaging of patients was also investigated for radionuclide distribution. Results: Inadequate RoIs were identified in 8 patients, which yielded up to 5% (mean 0.79%, STD 1.76%) difference (p=0.90) in lung shunting. The treatment dose showed 5.29% (mean 0.74%, STD 2.21%) deviation (p=0.91) caused by the ratios. It was further compared with standard ratios of 4% for none‐HCC and 7% for HCC. Difference in the treatment doses from corrected ratios and the standard was: mean 9.01%, STD 19.7%, p=0.19 for the 4% and mean 5.18%, STD 19.0%, p=0.55 for the 7%. Y‐90 patients images did not provide activity distribution in lungs when there was high shunting based on Tc99m MAA imaging, but demonstrated Y‐90 activity in liver. Conclusion: Tc99m MAA imaging is important in treatment planning to avoid error from lung shunting. RoIs should be accurate and consistent to reduce error in treatment dose. Y‐90 imaging depends on scatter characteristic of tissue and does not yield appropriate shunting images with Yttrium‐90.
SU‐FF‐I‐52: Quantitative Assessment of Physical Characteristics of Laser and CCD Film Digitizers in PACS Applications
Authors: Kang W , Han D , Jang B , Kim J , Yang K , Jung H , Yoo S , Kim H
Published: June 2005

Purpose: We quantitatively assessed the spatial resolution, contrast, and image uniformity of the laser and CCD film digitizers in PACS applications for our Hospital. Method and Materials: The modulation transfer function(MTF) was measured by using the created chessboard‐pattern test film to obtain the edge spread function(ESF) for both of horizontal and vertical scanning direction. The line spread function(LSF) was obtained from the ESF results. A step wedge test film was created in order to evaluate the contrast characteristics. Optical densities(ODs) for each step‐wedge region were measured using calibrated densitometer(x‐rite, USA). Those values were grouped with the corresponding film OD values. To measure the accuracy of pixel value distribution in proportion to the distance from center of the film, we also created the uniformity test film which was quartered with different OD values for each quarter. All test films were digitized using both LASER (Model 2905, Array Corp.,Japan) and CCD‐based unit (SEDAS Media Film Scanner, Kodak, Japan). Results: Spatial resolutions of the laser digitizer for both horizontal and vertical directions were 4.06±0.32cycles/mm and 4.24±0.20cycles/mm, respectively. However, those of the CCD digitizer were 2.06±0.33cycles/mm and 2.06±0.19cycles/mm at 10% of MTF. No differences in resolution were found with respect to location on the film. Contrast results were determined by means of useful OD range. Those values for the laser and CCD digitizer were 0.2∼2.8, 0.8∼2.8., respectively. The image uniformities of laser digitizer were 99.9, 99.4, 97.9, and 82.7%, where the corresponding ODs of the quarter were 0.2,0.7,1.4,and 3.1,respectively. However, those were 94.4,75.6,62.9,and 53.7% in CCD digitizer. Conclusion: In conclusion, laser digitizer can provide relatively higher resolution, wider useful OD range, and especially better image uniformity. Besides, because relatively low image uniformity of CCD digitizer may be caused by distribution of brightness of backlight, additional study for this aspect is necessary in further study. This study was supported by grant of the Korea Health 21 R&D Project, Ministry of Health&Welfare, Republic of Korea. (02‐PJ3‐PG6‐EV08‐0001).
SU‐FF‐J‐57: Digital Tomosynthesis for Verification of Radiation Therapy Positioning: Preliminary Results From a Kilovoltage On‐Board Imaging System
Authors: Godfrey D , Oldham M , Dobbins J , Yin F
Published: June 2005

Purpose: This study introduces a new radiation therapy target localization technique using online digital tomosynthesis (DTS), a method for reconstructing 3‐D slices from 2‐D projection data acquired with limited source motion. By separating the visualization of overlapping structure, DTS is expected to improve the visualization of anatomy compared with 2‐D planar radiographic imaging techniques, and may therefore yield more accurate target localization during radiation therapy set‐up. Method and Materials: We simulated treatment planning and setup of an anthropomorphic chest phantom. A treatment isocenter was marked in CT images. The phantom was then aligned for treatment on a Varian 21EX equipped with an on‐board‐imager (OBI), attached to the gantry orthogonal to the megavoltage treatment axis. Once aligned, 2‐D image projections were acquired over 200 degrees and coronal and sagittal DTS planes were reconstructed through the treatment isocenter from projection sub‐sets spanning 40°. Comparison of DTS images with corresponding planes from the CT data, as well as lateral and postero‐anterior (PA) planar radiographs, yielded estimations of set‐up error. Results: Sagittal and coronal DTS slices improved the visibility of anatomy when compared with planar radiograph equivalents, improving estimation of the set‐up error. Registration of sagittal and coronal DTS reconstructions with corresponding planes through the isocenter in the CT data was found to be feasible for estimating set‐up error. Preliminary determination of the set‐up accuracy of our clinical procedure was determined to be within 1mm for the phantom study presented here. Conclusion: Tomosynthesis has been demonstrated on a commercially available medical accelerator, and may be practical for improving patient set‐up when full cone‐beam‐CT is not required. DTS significantly improves the visibility of soft‐tissue detail that is obscured by overlying anatomy in radiographs and portal images. Additional benefits include a reduction in dose, acquisition and reconstruction time, and easier data handling compared with full cone‐beam‐CT.
SU‐FF‐J‐63: Improved Dose Accuracy for On‐Line Adaptive Radiation Therapy Using Deformable Dose Registration
Authors: Siebers J , Murphy M , Fix M
Published: June 2005

Purpose: The time available for dose evaluation in daily on‐line adaptive radiotherapy scenarios necessitates the use of fast correction‐based algorithms such as pencil beam (PB) algorithms, but precludes the use of accurate Monte Carlo (MC) algorithms. This study proposes to improve PB dose accuracy by utilizing deformable image registration techniques in a process called deformable dose registration (DDR): MC results on a deformed patient anatomy are approximated based on an MC calculation on a reference anatomy and the deformation field of the PB calculations between the reference and current anatomies. Method and Materials: A 5×5 cm2 6‐MV AP beam incident upon a thoracic CT image set I0 (x) was computed with both PB and MC dose‐calculation algorithms resulting in and . A thoracic case was chosen because of known inaccuracies in the radiological path‐length correction of PBs for lung heterogeneities. The same treatment beam was then computed on a deformed data set, , to obtain and . Treating and as images, the (Discrete Cosine Transform) DDR operator was determined that transformed to . was then transformed to using (∧ indicates an estimated dose distribution). Dose distributions were compared to determine if or better predicts based upon isodose contours, dose differences, distance‐to‐agreement, and gamma‐analysis. Results: Isodoses for better predicted than those from . The mean dose difference for is zero, while for it is ∼−‐3%. Using a 3%, 3 mm criteria, 70% of agreed with with γ < 1.0, while 92% of had γ < 1.0 indicating that is a better predictor of than . Conclusion: Using DDR techniques with fast PB results to estimate a more accurate algorithm's dose improves overall dose accuracy compared with using the fast PB algorithm alone. Such techniques may be useful in on‐line adaptive radiotherapy scenarios where dose accuracy is required, but dose calculation time is limited. (Work supported by NIH‐R01‐CA98524)