bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐J‐94: Feasibility Study On the Efficacy of Dual Energy Cine Imaging in Radiation Therapy for Lung Cancer
Authors: Baydush A , Godfrey D , Segars W
Published: July 2008

Purpose: Modern IMRT plans have necessitated improved image localization techniques. In the lungs, internal target volumes (ITVs) are often generated from 4DCT images; however, the patient must be properly localized daily for this to work effectively. In this simulation study, we investigate the efficacy of dual energy cine (DEC) imaging in radiation therapy (RT). Method and Materials: An advanced 4D NURBS (nonuniform rational b‐splines) based Cardiac‐Torso (NCAT) phantom, which includes a detailed whole‐body anatomy of organs including the lungs, airway tree, heart, and vessels, was used for this study. This model allows for the insertion of a lung nodule of any size, shape, contrast, and location. The NCAT phantom also incorporates realistic 4D modeling of periodic cardiac and respiratory motion. The NCAT includes an x‐ray projection algorithm that can accurately generate x‐ray images in 4D. This algorithm was used to generate cine images of the chest with an embedded lung nodule. Images were generated using spectra of 80 and 120 kV. Dual energy subtraction was performed on these two sets of cine images to remove the overlying bony anatomy. The resulting images were visually examined to determine if the lung nodule motion could be better visualized in the DEC images then in the 120 kV images. Results: The removal of the overlying bony anatomy of the chest allowed the DEC images to demonstrate superior visualization of the temporo‐spatial motion of the nodule. Conclusion: This feasibility study demonstrates that DEC imaging may provide increased visualization of lung nodules for RT treatment. Daily DEC imaging would allow for proper treatment portal placement for thoracic plans using ITVs and IMRT. Additionally, this technique shows much promise to be used in conjunction with dynamic adaptive radiation therapy, where nodule tracking is a necessity.
SU‐GG‐J‐101: IGRT Prostate: Analysis of the Effect of Body Size On Setup Error
Authors: Jiang R , Osei E , Barnett R
Published: July 2008

Purpose: Daily MV EPI for localization of prostate implanted with gold seeds provided data for analysis of setup error and organ motion for 118 patients. Simultaneous time‐course trends of prostate motion and setup error were analyzed fraction‐to‐fraction for 20 patients. The correlations of setup error and organ motion, setup error and body size, bladder and rectum filling and organ motion were evaluated. Method and Materials: Setup error was determined from bony anatomy mismatch between the EPI and the DRR fraction‐to‐fraction, while the organ motion was determined from the gold seed displacement relative to bony anatomy. The data are the original setup error before positional corrections were applied. Results: A Gaussian probability density function is reasonable for modeling geometric uncertainties. Prostate motion occurred independently from bony anatomy displacement. Setup error is more pronounced in the AP direction and correlates with body size. For the 10 patients with setup error larger than 5mm, the correlation coefficient between the AP setup error and AP separation is 0.82. The larger body size leads to larger AP setup error. For prostate AP motion, SD decreased with increasing bladder volume in CT scan. The correlation coefficient of SD of prostate AP motion with bladder volume is −0.67. While SD of prostate AP motion increased with increasing rectal volume in CT scan. The correlation coefficient of SD of prostate AP motion with rectal volume is 0.60 because patients were CT scanned and treated with full bladder and empty rectum. Conclusion: A Gaussian PDF is reasonable for modeling geometric uncertainties. There is a correlation of patient size and magnitude of setup error where, the larger a patients body, the larger the potential setup error. Prostate motion occurred independently from bony anatomy displacement during treatment, and correlated with bladder and rectal filling.
SU‐GG‐J‐104: Image‐Guided Intervention Based On Registration Between C‐Arm Projection and Cone‐Beam Reprojection of Reconstructed Volume
Authors: Chen Z
Published: July 2008

Purpose: To provide an image‐guided manipulation of the catheter introduction during intervention procedure by registering the C‐arm projection image with the cone‐beam reprojection image of a reconstructed volume that was generated previously by a volume CT (64‐slice CT or flat‐panel‐ based cone‐beam CT). Method and Materials First, reconstruct a volume for the interventional region by volume CT scanning and reconstruction, i.e., generate an angiographic volume; Second, perform volume segmentation to segment 3D blood vessels; Third, capture the C‐arm projection image during catheter introduction; Fourth, calculate the cone‐beam reprojection image on the angiographic volume, and adjust the reprojection parameters based on the matching or coregistration with the C‐arm image; Finally, perform 3D display of the segmented vessels where vessel segments are colored as indications of the catheter position. Results: The angiographic volume for the interventional region is reconstructed from a 64‐slice CT scanner or from a cone‐beam CT scanner. The volume segmentation is based on voxel value and vessel tree structure knowledge. The 2D image registration between the C‐arm image and the cone‐beam reprojection image of the angiographic volume requires a trial‐and‐error process by adjusting the reprojection geometric settings. The 3D vessels are displayed by fast isosurface or volume rendering. Conclusion: By reprojecting a reconstructed angiographic volume and co‐registering the projection image with the C‐arm projection image, the catheter in the 3D blood vessels can be visualized by 3D rendering, which provides a 3D intuitive image‐based guidance for the intervention procedure.
SU‐GG‐J‐105: Image‐Guided Thermal Ablation in Bone Using Dynamic Chemical Shift Imaging
Authors: Taylor BA , Shetty A , Elliott AM , Springer AC , Hwang KP , Hazle JD , Stafford RJ
Published: July 2008

Purpose: To investigate the use of a novel dynamic chemical shift imaging technique for guiding image‐guided thermal therapy delivery in bone ex vivo. Method and Materials: Interstitial laser applicators (980‐nm) were placed into the yellow marrow of freshly excised canine femur under MR‐guidance. A fluoroptic probe was inserted 0.5 cm from the laser source in order to provide an absolute measurement of temperature. Image acquisition was performed using a multiple gradient‐echo at 1.5T and a super‐resolution spectral processing algorithm was used to calculate the PRF of water and lipid. A six‐pixel ROI near the fluoroptic probe was created and the PRF of water and lipid were measured as a function of temperature to calculate the temperature sensitivity coefficient (TSC). Another bone was used to perform an external laser ablation. This was performed at 3.0T to demonstrate the use at higher fields even in the presence of gradient power constraints. Temperature maps were created using lipid as an internal reference for susceptibility and field drift correction. Results: The TSC of water was measured to be . The lipid showed low correlation and sensitivity to temperature with a TSC of . Interestingly, the TSC of the difference between water and lipid was which is consistent to findings in lipid‐water based phantom calibrations. Conclusion: We've demonstrated the ability of monitoring temperature changes in bone marrow which would be a great benefit in using image‐guided thermal therapies for treatment of primary and metastatic bone neoplasms. The technique possesses the ability to monitor the water PRF separate from the lipid, which alleviates the problem of lipid contamination in PRF temperature mapping with no time or SNR penalty. In addition, use of the lipid signal can potentially be exploited as an internal reference to correct for field‐drift or susceptibility errors in temperature estimation.
SU‐GG‐J‐109: Inhomogeneities of Intratumoral FDG Uptake in Human Colon Adenocarcinoma HT29 Tumor Model
Authors: Pugachev A , Sun X , Carlin S , Humm J
Published: July 2008

Purpose: It has been shown previously that in rat prostate carcinoma tumor R3327‐AT the highest uptake of 18‐FDG in tumors was observed in the areas of hypoxia rather than the areas of increased blood flow or active cell proliferation. In the present study we investigated the pattern of intratumoral FDG uptake in human colon adenocarcinoma cell line HT29. Method and Materials: Three nude rats were inoculated with HT29 cells. When the tumors reached 25mm in diameter, the animals were injected with 18‐FDG, pimonidazole, and bromodeoxyuridine (BrdU). 1hr later injection animals were injected with Hoechst33342 and sacrificed. Tumors were immediately dissected, frozen and sectioned. One section from each tumor was placed onto a phosphor plate for autoradiography. The images of the fluorescence produced by Hoechst33342 and by fluorescent antibodies raised against pimonidazole and BrdU were acquired from the adjacent sections and co‐registered. Results: All tumors in the study had extensive necrosis well intermixed with viable tumor tissue. Typically, hypoxia was forming bands about 100μm wide at the interface between viable tissue and necrosis. Analysis of the autoradiography data demonstrated associations between 18F‐FDG uptake and all of the markers studied. However, when analysis is done on the viable tumor tissue only by carefully masking out the necrotic areas, 0FDG uptake was positively correlated with staining intensity of pimonidazole and negatively correlated with Hoechst and BrdU. Conclusion: In larger tumors with complicated morphology it is necrotic fraction that plays crucial role in forming FDG uptake variations rather than any of the microenvironmental parameters considered. However, in the viable tumor tissue FDG uptake was positively correlated with staining intensity of pimonidazole and negatively correlated with Hoechst and BrdU, thus demonstrating association of increased FDG uptake with hypoxia.
SU‐GG‐J‐114: Intrafraction Set‐Up Variability in SBRT Patients Monitored by IR Optical Localizer and KV X‐Ray Images
Authors: Spadea M , Tagaste B , Riboldi M , Baroni G , Garibaldi C , Catalano G , Orecchia R , Pedotti A
Published: July 2008

Purpose: To investigate intrafraction setup variability in high precision stereotactic body radiotherapy (SBRT) by means of integrated infra‐red optical localization and stereoscopic kV X‐ray imaging. Method and Materials: We analyzed data coming from 24 patients treated with SBRT. Patient setup was realized through the ExacTrac X‐ray 6D system (BrainLAB, Germany), consisting of 2 infra‐red TV cameras for external fiducial localization and 2 couples of X‐ray source‐detectors for image registration. Before irradiation, patients were pre‐aligned relying on optical marker localization. Subsequently, patient position was refined through the automatic matching of X‐ray images to digitally reconstructed radiographs (DRR, 3 mm CT slice thickeness), providing 6 corrective parameters that were automatically applied using a robotic couch. The 3D position of the external configuration of control points was detected and stored before (PREmk) and after (POSTmk) the irradiation fraction. A final set of stereoscopic images was acquired and registered to DRR at the end of the treatment, relying on bony anatomy, thus obtaining 6 verification parameters (VP_post). Patient intrafraction motion was evaluated by comparing PREmk with POSTmk (optical measurement). Moreover VP_post parameters were applied to POSTmk thus defining a new configuration of control points (POSTmk‐Xray) that was compared to PREmk (X‐ray measurement). Results: According to the optical measurement, intrafraction motion measured on external fiducials was 0.61±0.53 mm (median±quartile). The X‐ray measurement overestimated intrafraction motion up to 2.05±1.8 mm. The latero‐lateral direction resulted more sensitive to residual errors in X‐ray measurement (0.34±2.88 mm, mean±std). Conclusion: Intrafraction motion, as monitored by the optical system, is not significant. When relying on X‐ray imaging registration, larger motion may be measured because of inherent limitations in DRR cranio‐caudal resolution and digital X‐ray image noise. Such results lead to further questions in assessing the accuracy of X‐ray based setup when integration with optical patient localization is not taken into account.
SU‐GG‐J‐130: Monte Carlo Simulation of Elekta XVI Cone Beam System and Dose Distribution in CTDI Phantom
Authors: Feng W , Deng J , Chi Y , Drake D , Bakalyar D , Yan D
Published: July 2008

Purpose: (1) To validate a Monte Carlo model for kV cone beam CT simulations. (2) To determine whether a bow‐shaped radial dose distribution with equal weighting can be applicable for cone beam CT. Method and Materials: A BEAMnrcMP Monte Carlo package has been employed and modified to simulate the Elekta XVI system operated at 120 kVp with collimator M20 and bowtie filter F1. Percentage Depth Dose (PDD) has been measured with PTW Farmer and Roos chambers in a CNMC water tank as well as a GAMMEX Solid Water phantom at 100cm SSD with 10cm backscatter. Dose profile at depth of 1cm has been measured with a Wellhofer IC‐10 chamber in Solid Water. Sample dose calculation is performed on a standard CDTI phantom aligned at Linac isocenter. Results: The simulated PDD curve agrees very well with both Farmer and Roos chamber measurements in water, but differ slightly with the Farmer chamber measurement in solid water at large depths and build‐up region. This is due to the higher attenuation of solid water in kV range and the loss of scatter equilibrium at phantom surface. Excellent agreement has been shown between the measured dose profile and the Monte Carlo simulations along both in‐plane and cross‐plane directions. The CTDI calculations have indicated that equal weighting on both the center and the periphery can result in errors of −1.1% while unequal standard weighting (1/3 for center and 2/3 for periphery) can result in errors of up to 8.1%. Conclusion: Our Monte Carlo model has been validated by various measurements to simulate the kV cone beams from the Elekta XVI system. A bow‐shape radial profile in CDTI phantom results in equal weightings for volumetric average dose calculations using only center and peripheral CTDI measurements. Investigation on patient dose deposition due to kV CBCT is in progress.
SU‐GG‐J‐133: MR Guided Focused Ultrasound (MRgFU) for Cance Therapy
Authors: Chen L , Mu Z , Hachem P , Konski A , Freedman G , Pollack A , Ma C
Published: July 2008

Purpose: The purpose of this work was to commission and to evaluate the role of MR guided high intensity focused ultrasound (MRgHIFU) in cancer therapy in ex vivo and in vivo. Method and Materials: An InSightec ExAblate 2000 HIFU system with a 1.5T GE MR scanner (MRgHIFU) is approved by FDA for the treatment of uterus fibroids clinically and being investigated in our department for treating bone metastases, prostate and breast cancers under local IRB approval. The phased array transducer is housed in a sealed bath and connected to a motion system. The focal region is cigar shaped, about 2mm in diameter and 10mm in focal length. Extensive experiments have been carried out on phantoms and excised tissues to determine optimal ultrasound parameters including the acoustic power output, frequency and exposure duration. We also performed in vivo studies on feasibility of enhancement of drug delivery for both chemotherapy and gene therapy using an animal model. Both MR T2‐weight MR image and proton resonance frequency shift MR images were used for treatment planning and monitoring the effect of the treatment in real time. Results: Phantom studies demonstrated that MRgHIFU could provide adequate temperature elevation for tissue ablation; acoustic power >10W leading to temperature elevation (ΔT) > 7 °C. At a lower acoustic power (5 W) we could keep ΔT < 4 °C, which is adequate for drug enhancement. The results were served for animal studies. Tissue damage was achieved at predetermined region in excised tissue through MR real‐time guidance. Our preliminary results showed increased drug concentrations in MRgHIFU treated mice than the control group. Conclusion: MRgHIFU may have a great potential as a safe, noninvasive treatment modality for cancer therapy including tumor ablation, enhancement of drug livery and boost treatment for hypoxic tumors in combination with radiotherapy.
SU‐GG‐J‐135: Nanoparticle Transport Study for Drug Delivery in Diagnostic & Therapeutic Oncology
Authors: Boddu S , Loyalka S , Rangaraj D
Published: July 2008

Purpose: To study the fundamental transport properties (diffusion) of nanoparticles in tumor and surrounding normal tissue for several geometries and several volumetric nanoparticles. Method and Materials: Diffusion is the dominant mode of interstitial transport for small solutes, and when the driving force for convection is diminished, it may be the dominant or at least a significant mechanism for the transport of macromolecules. Computation of transport of nanoparticles using the Fluid Dynamics program Fluent® 6.2 with the use of user defined functions made it possible to study diffusion in arbitrary geometries. Fluent computations for time dependent particle distribution for four different cases of volumetric nanoparticle sources were performed for model geometries, and tissue/tumor properties and results for arbitrary scalar (φ) value (e.g. mass concentration, particle concentration, etc.) were analyzed. Different volumetric sources that we have considered are (1) constant, (2) no source, (3) an arbitrary function of space and time, and (4) as an arbitrary function of space. For the several model cases, we have also verified Fluent results against analytical results. Results: The computations are carried over a 6 hour diffusion time period in the tissue‐tumor geometry. Computational results for particle distributions in the model are sampled for every 30 minutes and volume integral of φ are plotted for tissue and tumor volumes. Volume integrals of φ in normal tissue volumes and tumors for the four cases of sources gave an estimate of the amount of φ absorbed in the tumor volumes. Conclusion: These results appear consistent with expectations, and the computational model thus appears appropriate for future explorations/verifications. The study of transport property of the nanoparticles using Fluent has provided insight into the distribution of the nanoparticles. This would allow us to explore variety of different nanoparticles like gold, gadolinium, tungsten etc for diagnostic and therapeutic oncology.
SU‐GG‐J‐138: New Weighted Maximum Intensity Projection (MIP) Images for Assessing Tumor Motion in the Thorax Without a Respiratory Surrogate
Authors: Pan T , Chang J , Riegel A , Ahmad M , Sun X , Luo D
Published: July 2008

Purpose: MIP image is effective for encompassing the tumor motion except in the area where the tumor is near the diaphragm. This is due to the fact that the tumor and the diaphragm may occupy the same space at two different times in respiration. We developed a new weighted MIP image to eliminate this constraint and advanced the application of cine CT imaging for assessing the tumor motion without a respiratory surrogate. Method and Materials: We selected three patient studies from the conventional cine‐CT based 4D‐CT imaging on a GE 8‐slice CT. These three patients each had a lung tumor near the diaphragm, and their MIP images were compromised by the diaphragm obscuring the tumor. We first identified the obscured region of 2 to 6 cm for weighted MIP processing. In each cine acquisition of 2 cm coverage, we identified one image of 2.5 mm thickness corresponding to the end‐inspiration (EI) phase, associated with the least diaphragm or the largest lung region in the image. Selection of one image automatically groups in the other 7 images acquired at the same time from the 8‐slice CT, reducing the selection time. We then submitted the selected images of EI phase along with the cine CT images outside the obscured region for MIP processing, resulting in a new weighted MIP image that shows good contrast for encompassing tumor motion. Results: The contrast of tumor in MIP was improved with weighted MIP for all three patients when the tumor in near the diaphragm. Conclusion: A new weighted MIP has been designed to further advance the application of cine CT imaging for assessing tumor motion without a respiratory surrogate when the tumor is near the diaphragm.
SU‐GG‐J‐143: Performance Optimization of the Integrated Acquisition Mode of the Varian AS500‐II EPID and Investigation for Measurement of Enhanced Dynamic Wedge
Authors: Al kattar Z , Foulquier J , Touboul E
Published: July 2008

Purpose: To better understand the image acquisition operation of an EPID and to evaluate the dosimeter properties in treatments with enhanced dynamic wedges. Method and Materials: The Work presented rests on the study of the Varian EPID: aS500‐II and the Image Acquisition system IAS3. We are interested in integrated image acquisition mode not synchronized to the accelerator beam pulses. We investigated the influence of the Frame Cycle Time “FCT” parameter on the gray level, the speed of acquisition and the noise in the image, according to the energy of the X‐ray beams (6 and 15 MV) and the Clinac 2100 C/D dose rate. We also studied the performances, stability and the reproducibility of the EPID aS500‐II in measurements of the wedge factors of the fields with enhanced dynamic wedges. Results: In this mode, only one parameter the “FCT” influences the pixel value. The pixel value is directly proportional to this parameter. When the FCT ⩾ 55ms, the speed of acquisition is inversely proportional to this parameter. The noise lies between 0.2% and 0.5%. We determined a rule to avoid saturation. EPID measurements were found to exhibit a dependence on the wedge direction and EPID position. An empirical correction function was developed to correct the wedge profiles. Due the reproducibility of the EPID measured EDW factors the device is highly suited in this mode of acquisition to regular measurement of EDW. Conclusion: The choice of the acquisition parameters is essential for the complete detection of radiations and especially to use this detector as a dosimeter.
SU‐GG‐J‐153: Prolonged Discrimination of Target Structures in CT and MR‐Guided Therapies Using a Novel Contrast Agent
Authors: Zheng J , Allen C , Jaffray D
Published: July 2008

Purpose: To evaluate the performance of a liposome‐based contrast agent in allowing for persistent discrimination of target and disease structures (tumor, invaded lymph nodes) using CT and MR imaging in tumor‐bearing rabbits following a single intravenous administration. Method and Materials: Five New Zealand White rabbits bearing VX2 sarcoma in their left lateral quadriceps received a single i.v. dose of liposomes (80 nm) encapsulating 250 μg/g of iodine in the form of iohexol and 15 μg/g of gadolinium in the form of gadoteridol. They were CT (80 kVp, 200 mA) and MR (3D FSPGR, TR/TE=9.8/4.3) imaged at 1 hour and 1, 2, 3, 5, 7, 10 and 14 days post contrast administration. Semi‐automated contouring using MicroView v2.2 allowed for generation of volumes of interest consisting of kidneys, spleen, liver, tumor and the contralateral muscle, which were subsequently used for data analysis. Results: Co‐localized accumulation and clearance of the liposome contrast agent is visually detected over a two‐week period in both CT and MR. In the tumor volumes, the mean HU increased following the administration of the contrast agent peaking at 3 days post‐injection, while the mean HU measured on the controlateral muscle volumes remained steady. Furthermore, the distribution of the liposome agent is highly heterogeneous within the tumor volume. For a representative rabbit at three days post‐injection, 29.6% of the tumor voxels measured between 115 and 290 HU. This liposome agent also proved to be able to target invaded lymph nodes (as confirmed by pathology). Specifically, 9 out of 10 iliac nodes from the 5 rabbits were enhanced. Conclusion: These investigations demonstrated the ability of nano‐sized liposomes encapsulating iohexol and gadoteridol to allow for persistent discrimination of disease structures and their potential for use in CT and MR‐guided therapies.
SU‐GG‐J‐155: Quantifying Interfractional Prostate Motion and Deformation Based On Daily KVCT to Determine Selection Criteria for Adaptive Correction Schemes
Authors: Peng C , Ahunbay E , Li X
Published: July 2008

Purpose: To quantitatively characterize interfractional prostate motion and deformation using daily kVCT to determine the frequencies of different adaptive corrections and the selection criteria. Method and Materials: Daily kVCT images for 20 prostate cancer patients treated with CT‐guided repositioning using a linac and CT‐on‐Rails combo (CTVision, Siemens) were analyzed. The prostate, rectum and bladder were delineated for a total of 486 sets of CT images. The daily organ contours were compared to the planning contours after bony anatomy registration. Several quantities, including center of mass (COM), Dice's coefficient (DC), maximum overlapping rate (MOR), were calculated for each of the structures and were used to characterize the prostate motion and deformation and to indicate the need of performing an adaptive correction strategy. Results: The daily prostate motion and deformation were mainly due to the daily variations in the volumes of the rectums and bladders. The largest differences in daily volumes was 650% for rectum and 820% for bladder. The mean prostate DC is 69.7±13.8% (1SD). In 76% of all cases, DC is lower than 80%. In 57% of all cases, MOR is greater than 85%; 39% is between 70% and 85%; only 4% is below 70%. These, combined with dosimetric data from a separate study, indicate that, on average, the current standard repositioning and the simple correction schemes (such as aperture morphing) are adequate for approximately 60% and 35% of fractions, respectively. The full‐scope replanning is required for approximately 5% of fractions. Criteria in terms of several daily anatomic parameters were suggested. Conclusion: Adaptive correction schemes for prostate interfractional changes may be selected based on anatomic quantities such as COM, DC and MOR as determined from the CT of the day. Specific criteria were suggested. Conflict of Interest: This work is supported partially by MCW Cancer Center Fotsch Foundation.
SU‐GG‐J‐156: Quantitative Analysis of Onboard SPECT Imaging Using Compact Gamma Cameras
Authors: Roper J , Bowsher J , Yin F
Published: July 2008

Purpose: Single photon emission computed tomography (SPECT) imaging on‐board radiation therapy machines may enhance radiation therapy. Use of a light‐weight, compact detector would be desirable because of maneuverability, yet is challenged by truncation and consequently reconstruction artifacts. We hypothesize that, for a sizeable volume surrounding the tumor target, and with properly chosen detector trajectories, compact detectors can provide image quality that is comparable to that of full‐size SPECT detectors. Method and Materials: On‐board SPECT imaging was computer simulated for detectors with active surface widths of 21.2 and 40.0 cm. Detector trajectories were selected such that the common volume encompassed an 8‐cm‐diameter ROI surrounding each tumor in the torso of a NCAT phantom. For deep tumors, two common volumes — interior and partially exterior — were investigated. Radiotracer distribution was modeled for 99mTc‐Sestamibi. Noise‐free and noisy projection images were generated with an analytical simulator that models non‐uniform attenuation, collimator & detector efficiency, and spatially‐varying spatial resolution. Images were reconstructed by OSEM. In reconstructed images, root mean square error and recovered tumor activity were analyzed as a function of detector width and detector trajectory. Results: Image truncation reduced overall image quality. For example, RMS error over an entire noise‐free image slice was 18 – 35% worse with the 21‐cm‐wide detector versus the larger detector. However, for regions within the common volume for both detector widths, RMS errors differed by less that 2%. Similar results were observed for noisy images. Moreover, the recovered fraction of tumor activity was comparable, except for when the smaller‐detector common volume was interior — the recovered activity was reduced by 11%. Conclusion: Preliminary results show that an 8‐cm‐diameter ROI can be reconstructed using 21 or 40‐cm‐wide detectors with comparable RMS errors and recovered tumor activities, supporting the proposal that on‐board target localization could be accomplished using compact SPECT detectors.
SU‐GG‐J‐158: Application of Computed Radiography in Small Animal Imaging: X‐Ray Contrast Agents
Authors: Maghsoodpour A , Keyes G
Published: July 2008

Purpose: X‐ray contrast agents play an important role in small animal imaging studies, e.g. tracking tumor growth without sacrificing animals. This multiphase study evaluates the performance of a computed radiography (CR) system for detecting iodinated contrast agent in tumors, using x‐ray exposures at energies below the iodine K‐edge. Method and Materials: The CR system is characterized by measuring MTF and NPS. Polychromatic x‐ray spectra are modeled for different available kVps, and the mean energy for each kVp is determined. Contrast from a theoretical model is calculated for a range of mean x‐ray energies. A microtitration multi‐well plate filled with mixtures of contrast agent and water is imaged to study the contrast sensitivity of the CR system. Each row contains a specified concentration, while each column represents a fixed volume (or corresponding thickness). CR images are acquired and the contrast of each well is measured and compared to a theoretical model. Next, a special PMMA phantom is designed to compare the measured CR contrast to contrast measured using a micro‐CT, as a reference. Finally, several mice with implanted tumors are injected with different volumes of contrast agent and imaged by CR. Results: Initial results show measured contrast is consistent with the theoretical model. A Chi‐Square goodness‐of‐fitness test as a function of x‐ray energy indicates the best fit between measured and theoretical contrasts is consistent with the mean energy estimates from the polychromatic beam model. A few tumor vessels are visible on mouse images. Conclusion: Wide dynamic range, fast throughput, low radiation level and low cost are the potential advantages of CR imaging. Further studies are in progress to monitor the progression of tumors. CR imaging potentially offers a complementary procedure for small animal studies using micro‐CT when acquiring the complete three‐dimensional data is not necessary or time‐efficient.
SU‐GG‐J‐163: Radiotherapy Response Assessment Using Deformed Serial 18F‐FDG PET/CT
Authors: Cannon B , Zhang L , Mawlawi O , Schwartz D , Moeller B , Dong L
Published: July 2008

Purpose: To assess the ability of SUV measured on serial PET/CT to differentiate radiotherapy (RT) responders from non‐responders. Method and Materials: Between November 2005 and August 2007, 88 eligible patients with AJCC stage III‐IVb HNSCC were enrolled in an IRB approved protocol to receive serial PET/CT imaging studies prior to and following RT. Analysis of similar anatomic volumes on temporally separated images was facilitated with a deformable image registration technique to map pre‐ and post‐RT CT images to a reference image set, namely the RT planning CT images. The resulting deformable transformations were applied to the pre‐ and post‐RT PET images, thereby aligning both PET data sets to the RT planning CT images. SUV reduction factors were created from pre‐ and post‐RT SUV ratios and calculated for RT contours and fixed thresholds of the maximum signal intensity on PET images. Variations in pre‐ and post‐RT PET/CT scanner model and uptake duration were controlled to eliminate possible confounding factors for intrapatient analysis. Results: Cross correlation of patients whose serial PET/CT images were collected with the same scanner model and with uptake duration differences ⩽ 15 min reduced the useable number of patients drastically from 88 to 10. For the controlled patient cohort, the average SUV reduction factor for responders (N = 7) vs. non‐responders (N = 3) calculated for the GTV contour was (1.4 ± 1.6) and (1.0 ± 1.7), respectively. For all contours (N = 4), nonparametric testing revealed [P > 0.05]. Conclusion: The average SUV reduction factor was not able to significantly differentiate responders and non‐responders in all contours studied. The large reduction in useable patients following strict data set control may be an important cautionary note for future studies investigating serial PET/CT for treatment response monitoring.

Research sponsored by Varian Medical Systems.
SU‐GG‐J‐166: Reduction of Motion Artifacts Occurring at the Lung/diaphragm Interface Using 4D‐CT Attenuation Correction On 4D‐PET Scans: Implications for Radiation Therapy Planning
Authors: Killoran J , Mamede M , Park S , Ionascu  , Gerbaudo V , Berbeco R
Published: July 2008

Purpose: For PET/CT the fast CT acquisition time can lead to errors in attenuation correction, particularly at the lung/diaphragm interface. Gated 4D‐PET can reduce motion artifacts, though it is not always attenuation corrected with a similarly acquired 4D‐CT. We performed phantom studies specifically designed to evaluate 4D‐PET images using three different methods for attenuation correction: a single 3D‐CT (3D‐CTAC), an averaged 4D‐CT (CINE‐CTAC), and a fully phase matched 4D‐CT (4D‐CTAC). Method and Materials: A phantom was designed with two density regions corresponding to diaphragm and lung. An 8ml vial loaded with FDG was used to represent a lung tumor and background FDG was also added with an 8:1 ratio. Imaging was performed with a GE Discovery DVCT‐PET/CT scanner. Periodic motion of 2 cm amplitude was used and the image data was reconstructed into 10 phase bins over the motion cycle. Image data was analyzed using a GE image processing workstation and in‐house developed software. Values of activity within the target for each relative phase were corrected for decay and compared to those derived from a 3D PET scan with no motion present (3D‐STATIC). Results: Activity values derived from 4D‐CTAC corrected PET images are generally closer to 3D‐STATIC images with no motion present. Mean activity over the known target volume over the motion cycle, normalized to the activity for 3D‐STATIC, was 93%, 101% and 98% for 3D‐CTAC, CINE‐CTAC and 4D‐CTAC images respectively with corresponding standard deviations of 6%, 10% and 3%. Conclusion: Compared to other attenuation correction methods, 4D‐CTAC corrected 4D‐PET images correspond more closely on average to similar 3D‐STATIC images. Using CINE‐CTAC for correction resulted in mean activity values slightly closer to 3D‐STATIC, but with much greater variation over the motion cycle. We believe these results have implications for the use of 4D‐PET imaging for radiation therapy target definition.
SU‐GG‐J‐168: Respiratory‐Gated Radiation Therapy for the Liver: A 5‐Patient Study
Authors: Briere TM , Krishnan S , Balter P , Nelson C , Starkschall G , Gillin MT , Beddar AS
Published: July 2008

Purpose: To investigate the feasibility and accuracy of using a combination of internal and external fiducials for respiratory‐gated image‐guided radiotherapy of liver tumors with commercially‐available systems. Method and Materials: Five patients were enrolled in the study. Patients were treated on either a 2100EX or Trilogy linear accelerator (Varian Medical Systems). Respiration was tracked and the beam was gated using the RPM system (Varian). Radio‐opaque fiducials implanted adjacent to the liver tumor were used for daily online set‐up using non‐simultaneous orthogonal electronic portal or kV images and ISOLOC software (MedTec). The threshold for couch shifts was 2 mm, while the respiratory gate was set at 1 mm. The accuracy of respiratory‐gated treatment using an external fiducial was verified offline using cine mode images acquired during treatment. Results: The range of tumor motion was between 8.0 mm and 44.3 mm in the supero‐inferior (SI) direction, which is the dominant direction of motion due to respiration. For all patients, interfractional variation, a measure of set‐up uncertainty, was 0.3 ± 2.3 mm (1σ) in the SI direction. The intrafractional variation, a measure of the precision of gating, was found to be ±1.0 mm (1σ). The average duty cycle varied between 18% and 28%. Conclusion: Respiratory gating with either EPID or kV imaging using readily available and affordable infrastructural elements can provide accurate, reproducible, and verifiable means to deliver precision radiotherapy to liver tumors. Daily analysis of the cine images is an effective way to verify that the treatment was delivered as planned and we strongly recommended it.
SU‐GG‐J‐169: Setup Errors Using Daily CT for Image Guided Extracranial Stereotactic Body Radiation Therapy
Authors: Wu J , Fuss M , D'Souza W
Published: July 2008

Purpose: To estimate setup errors using daily CT for image guided extracranial stereotactic body radiation therapy (SBRT). Method and Materials: Five patients undergoing SBRT of lung cancers were retrospectively considered. Prior to each treatment, patients were re‐scanned in the simulation room. These CT images, named control CT (CCT), were registered with the planning CT to calculate daily offsets from the initial marker‐based setup. This was done in two steps: first, bony structure based rigid registration was performed, which mimicked patient setup using fiducial markers; second, deformable registration was performed which would capture daily tumor shifts with respect to bony structures. After registration tumor contours were mapped from the simulation CT to CCT using the translation fields obtained from both rigid and deformable registrations. The center of mass of both mapped contours was calculated. Their difference would be the offset to be applied to the patients after patients being aligned using fiducial markers. To estimate the accuracy of CCT based patient setup, after marker‐based patient setup in the treatment room, each patient was scanned again using CBCT. The CBCT image was also registered to the planning CT using the same two step registration. Similarly, CBCT based patient offset was also calculated. Finally the difference between these two offsets was calculated for each patient. Results: The mean of the absolute offset difference was on average 1.8±1.5 mm, 1.0±0.8 mm and 2.3±1.8 mm in the left‐right (LR), anterior‐posterior (AP) and superior‐inferior (SI) directions respectively. The corresponding p‐values between these two alignment methods were 0.07, 0.76, and 0.89 in the LR, AP and SI directions respectively. Conclusion: Patient alignment using daily CT agreed well with the alignment using CBCT. The difference was statistically indistinguishable. Alignment using daily CT provides a solution for image guided radiation therapy on facilities without the on‐board imaging capability.
SU‐GG‐J‐172: Static and Dynamic Tracking Accuracy of a Novel Radioactive Tracking Technology for Target Localization and Real Time Tracking in Radiation Therapy
Authors: Shchory T , Schifter D , Lichtman R , Neustadter D , Corn B
Published: July 2008

Purpose: In radiation therapy there is a need to accurately know the location of the target in real time. A novel radioactive tracking technology is being developed to answer this need. The technology consists of a radioactive non‐migrating implanted fiducial marker and a linac mounted tracking device. This study measured the static and dynamic accuracy of the new tracking technology in a clinical radiation therapy environment. Method and Materials: The tracking device was installed on an Elekta Synergy® linac gantry. The radioactive marker was located in a tissue equivalent phantom. Actual marker location was measured using a Microscribe G2 coordinate measuring machine (CMM) arm (certified spatial accuracy of 0.38 mm). The marker was attached to the tip of the CMM arm and its location was measured simultaneously by the CMM and the tracking system. Static accuracy was measured at multiple locations covering a 12cm cube centered at the linac iso‐center. The measurements were repeated at multiple gantry angles. Dynamic accuracy was measured with the marker located inside a breathing phantom. Results: The mean localization error for the static source was less than 0.7mm throughout the tested region at all measured gantry angles. The mean real time tracking error for the dynamic source within the breathing phantom was less than 1mm. Conclusion: The novel radioactive tracking technology has the potential to be useful in accurate target localization and real time monitoring for radiation therapy. Conflict of Interest: Research sponsored by Navotek Medical Ltd.
SU‐GG‐J‐191: Use of Megavoltage Fluoroscopy and Cone‐Beam CT for On‐Line Verification During 4D/gated Delivery
Authors: Tai A , Christensen J , Gore E , Khamene A , Boettger T , Li XA
Published: July 2008

Purpose: On‐line real‐time monitoring of tumor motion is essential for 4D/gated radiation delivery based a surrogate signal because the correlation between the surrogate signal and tumor locations on the treatment day may change from that on the simulation day. The purpose of this study is to develop tools to establish a real‐time correlation between the surrogate signal and tumor motion by registering on‐line megavoltage fluoroscopy (MVF) and/or cone‐beam CT with the planning images. Method and Materials: Both MVF and cone‐beam CT were acquired using a flat panel detector installed on a Siemens Linac using 6MV photon beams for phantoms with moving structures and for thoracic cancer patients. A frame‐grabber of 7 frames per minute was used to capture the MVF movie. The cone‐beam projection images consist of 200 frames corresponding to 200 gantry angles. The acquired images were synchronized with the breathing signal from a pressure sensor (Anzai Inc.). A previously developed software, RTReg4D, was used to register acquired images with planning DRRs from 4DCT. Results: The software can effectively and accurately register MVF images with time‐sequenced DRRs. For the registration with the cone beam projection images, the software fails at some gantry angles and manual registration is needed to correct these false registrations. These registration results can establish a real‐time correlation between the Anzai surrogate signals and tumor motion. This correlation would update the correlation established during the planning process for subsequent treatment delivery using either gating or 4D tracking. If gated delivery is used, the gating window may be adjusted based on the real‐time correlation. Conclusion: MV fluoroscopy and/or cone‐beam CT acquired before treatment delivery can be used to establish a real‐time correlation between surrogate signal and tumor location for 4D/gated treatment delivery. Conflict of Interest: This work is sponsored in part by Siemens OCS.
SU‐GG‐J‐198: Phantom Evaluation of Implanted Coil Localization Accuracy of the BrainLab ExacTrac Gating System and 4DCT
Authors: Matney J , Parker B , Neck D , Henkelmann G , Rosen I
Published: July 2008

Purpose: The purpose of this study was to evaluate the accuracy of measured target motion using 4DCT scanning and BrainLab ExacTrac (ET) Gating system for gated therapy. Motions of an implantable coil as a function of respiratory phase were compared from the two systems to the known motion for a commercial gating phantom. Method and Materials: A Quasar respiratory motion phantom containing an implantable coil as a surrogate target was used. Phantom motion was sinusoidal with a 4‐second period and amplitudes of 5–25 mm. 4DCT datasets were sorted in 10 distinct respiratory phases, reconstructed, and imported into the Pinnacle TPS. Coil endpoints were identified on each phase‐sorted CT datasets to measure coil distortion. To compare coil localization accuracy, both systems imaged the implanted coil at the same respiratory phases and measured overall relative coil displacement as a function of respiratory phase. Results: Coil length errors measured on the 4DCT were <0.8 mm at end inhale/exhale phases, but 8.1 mm at mid‐inhalation. Maximum localization error from the expected position for all motion profiles was 5.5 mm for both coil tips in 4DCT. but only 0.8 mm for the ET Gating system. Even at the greatest coil velocity, ExacTrac coil localization agrees with calculated coil motion within 1 mm. 4DCT showed problems resolving a coil during large respiratory‐induced velocities, but accurately resolved the coil length within 1 mm of actual coil length at end expiration/inhalation. Conclusion: 4DCT can provide accurate representation of the phantom at end‐respiration for treatment planning. ExacTrac can accurately localize the coil to determine target motion over all phases. Good agreement of the techniques will allow minimization of internal motion margins in gated radiotherapy. Conflict of Interest: This work was supported in part by a research agreement with BrainLab, Inc.
SU‐GG‐T‐04: Dosimetry of Curvilinear Brachytherapy Sources Using TG‐43U1 Formalism
Authors: Aryal P , Johnson E , Meigooni A
Published: July 2008

Purpose: TG‐43U1 recommendation for dosimetric characteristics of brachytherapy sources with active length of <1 cm does not include the possibility of source deformation during the clinical procedure. However, this assumption may not be valid for elongated (active length > 1 cm) sources. In this project, the impact of the source curvature on its dose distribution will be evaluated for elongated Pd‐103 sources. Method and Materials: The MCNP5 Monte Carlo simulation code has been used to calculate the dose profiles around for Pd‐103 sources with active length >1 cm. The calculated dose profiles for various curvatures have been compared to the values from a straight line source with the same active length. The dose calculation points are considered every 0.5 cm from each other and 0.5 cm away from the inner surface of the curvilinear source. Results: The results of the dose rates inside and outside of a 5 cm long RadioCoil™ Pd‐103 source as a function of distance from the center of the source have been compared with line source of same length. It is found that, at the mid level of the source, the dose rate is 50% higher in inner dose calculation points and 10 % less in outer points as compared to dose rate from a line source geometry. However, at 2.5 cm distance from the middle of the source, dose rate for inner point is only about 30% of the straight line source. Conclusion: Dose calculations for elongated curvilinear sources have been evaluated which was not introduced in TG‐43 dose calculation algorithms. The results of these investigations indicate that the degree of the curvature should be considered to achieve accurate dose calculations in a clinical practice.