bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐I‐81: Gamma Camera Guided Permanent Breast 103Pd Seed Implantation
Authors: Ravi A , Caldwell C , Keller B , Pignol J
Published: July 2006

Objective: To assess whether a proposed SPECT device could address the requirements of resolving distributions of permanent breast brachytherapy seeds following implantation; while maintaining an acceptable imaging time to allow for correction of misplaced seeds. Method: Monte Carlo simulations of a cadmium zinc telluride crystal‐based gamma camera were used to assess whether the detection of 22 keV photons emitted from the seeds was feasible. A hexagonal parallel hole collimator, hole length 38 mm, diameter 1.2 mm with 0.2 mm septa was modeled. The design of the gamma camera device was evaluated on two phantom models. The first model consisted of a simple representation of the clinical problem by simulating the breast as 8 cm diameter sphere of breast tissue containing a central, 1cm cubic distribution of 8 seeds. The second simulation presented a more accurate depiction of the clinical problem, where the breast model was based on the pre‐implant CT scan of a typical breast brachytherapy patient and the activity was simulated from the patient's corresponding treatment plan. Results: The spherical phantom yielded promising results after 24 s of imaging time, where the maximum error between the center of mass of the seeds in the reconstructed image and the simulated seed location was 1.02 mm. The results from the clinically accurate simulation revealed that individual seeds could not be identified from the reconstructed images after 2 minutes of imaging. However, the strands of seeds, arranged in each needle were localized to a maximum error of 1.9 mm. Conclusion: The online gamma‐camera approach to imaging the seeds is feasible for simple seed distributions. Additional improvements to the collimator design and the gamma camera orbit are required before the gamma camera device will be able to distinguish each seed in an implanted seed distribution.
SU‐FF‐I‐87: High Frequency Ultrasound To Monitor Murine Orthotopic Bladder Cancer Model : An Alternative To Magnetic Resonance Imaging
Authors: Shetty A , Stafford R , Esparza‐Coss E , Andtbacka R , Brown G , Black P , Metwalli A , McConkey D , Dinney C , Hazle J
Published: July 2006

Purpose: The study of human bladder cancer is often performed using subcutaneous xenograft models. But, a more relevant model is the orthotopic approach where tumors are grown in their native host environment. Studying the growth kinetics of these intraabdominal tumors is much more difficult as they are not accessible for caliper measurements. The purpose of this study is to demonstrate the feasibility of high frequency ultrasound (US) imaging as an efficient and time saving alternative to magnetic resonance (MR) in longitudinal monitoring of an orthotopic bladder cancer model. Method and Materials: Eleven athymic nude mice underwent orthotopic injection of 10 6 253‐J B‐V cells into their bladder walls. MR imaging was performed weekly on a 4.7 T small animal MR scanner (Bruker Biospin). Axial T1 weighted spin‐echo and T2 weighted fast spin‐echo acquisitions (TR: 700ms, TE: 8.5ms, FOV: 4.0cm × 3.0cm, Matrix:256 × 192,duration:45–50 minutes) were performed. 3D US data (step size:0.25mm, range:12mm, duration:5–10 minutes) was collected using a Vevo 660 (Visualsonics) system operating at 40 MHz. Tumor size at necropsy was measured with a caliper, and volume calculated with the formula , where a, b, c are the tumor dimensions. Results: The MR volume measurements were made from the fused T1 and T2 images, as done in previous experiments. Two independent observers made the MR and US measurements. There was very good correlation between the MR and 3D US volume measurements with Pearson's correlation coefficient of 0.987 (p<0.05). The correlation between the US volume and the specimen measurements was 0.793 (p<0.05). Conclusion: High frequency ultrasound can effectively monitor murine intraabdominal tumor growth. It is a cheaper and faster modality than CT and MR. Extensions of this technology in the future could include orthotopic injections under US guidance, Power Doppler and harmonic imaging with microbubbles for evaluation of tumor vascularity.
SU‐FF‐I‐88: The Small Animal Radiation Research Platform: Benchtop Cone‐Beam CT
Authors: Ford E , Kennedy C , McNutt T , Armour E , Iordachita I , Kazanzides P , Wong J
Published: July 2006

Purpose: We are constructing a benchtop small‐animal radiation research platform to deliver focused, conformal radiation for translational research. An x‐ray tube is employed for both irradiation and cone‐beam CT imaging. This paper reports on the design and initial results of an integrated cone‐beam CT sub‐system to provide image guidance prior to radiation treatment delivery. Materials and Methods: The design of the platform necessitates cone‐beam acquisition with a unique geometry in which projection images are acquired as the animal is rotated about an anterior‐to‐posterior axis. In these prototype experiments, images of a euthanized mouse were acquired (1 image per degree for 360°) using a phosphor‐mirror‐coupled CCD camera and with the x‐ray tube operating at 80 kVp. We perform cone‐beam CT reconstruction via the filtered back‐projection algorithm of Feldkamp et al. Results: This system produces high‐quality CT reconstructions with isotropic resolution and minimal artifacts. Soft‐tissue contrast is easily visualized. Reconstruction time is approximately 3 minutes. The acquisition requires approximately 22 cGy dose to isocenter. Work is ongoing to reduce the dose with the use of a higher DQE flat‐panel imager, to optimize imaging parameters using the constant voltage x‐ray beam, and to automate acquisition and reconstruction. Conclusions: High quality CT reconstructions are possible with our prototype small animal system. In conjunction with robotic motion stages, the novel acquisition geometry enables the construction of a benchtop system in which the x‐ray tube is used for both on‐line CT acquisition and radiation delivery.
SU‐FF‐I‐89: Performance Evaluation of a Unique Transrectal Ultrasound System
Authors: Wood R
Published: July 2006

Purpose: To present a performance evaluation for a unique transrectal ultrasound probe for use in prostate seed implants. The ultrasound probe transducer moves inside the probe case while the case remains stationary. This allows imaging in different planes without moving the prostate. Sagittal and transverse plane imaging is available. Electronic longitudinal stepping and sagittal plane rotation of the transducer replaces manual/mechanical movement. Method and Materials: The ultrasound probe evaluated was the TargetScan® System from Envisioneering Medical Products (St. Louis, MO). Proper alignment of the needle template and software grid was verified, as well as electronic stepper position accuracy. Image quality was evaluated using a Multipurpose Tissue/Cyst Ultrasound Phantom (Nuclear Associates Model 84‐317). Tests included, maximum scanning depth, axial distance calibration accuracy, spatial resolution, high scatter resolution, low scatter resolution, superficial low scatter resolution, and dead zone region limit. All tests were performed with the probe immersed in a water medium. Both axial and sagittal scanning modes were tested. Results: Needle template/software grid coincidence (axial mode) was within 2mm, with most measurements being less than 1 mm. Longitudinal stepper accuracy was within 1mm. The following results apply to both sagittal and transverse scanning modes. Maximum scanning depth was approximately 60 mm in the medium. Axial distance accuracy was within 1 mm. Spatial resolution was 2mm axial, 3mm lateral. The 4 mm high and low scatter targets could be resolved. The 2 mm low scatter superficial targets could be resolved at the 2.2 cm and 4.4 cm depths for both sagittal and transverse modes. The dead zone limit was 2mm for both sagittal and transverse modes. Conclusion: The TargetScan® System has high image quality and transducer placement accuracy which makes it suitable for both diagnostic scanning as well as image guided prostate brachytherapy.
SU‐FF‐I‐90: Brain Phantom for Validation of Low Frequency Ultrasound Heating Divices
Authors: Martinez J , Jarosz B
Published: July 2006

Ultrasound thermal therapy of the brain may emerge as an independent modality of treating radioresistant tumours. Prior to clinical use, the heating technologies must be accurately evaluated either in animal models or in brain phantoms. In this paper, a gel phantom based on bovine powder gelatin in ethanediol is proposed. A heuristic method was used to determine an accurate percentage of powder gelatin in ethanediol. In our phantom, at 10.54 % of gelatin in ethanediol the following physical properties were obtained: density of 1040 kg/m3 ± 1.0 % at 24 °C; acoustic speed of 1540 m/s ± 0.8%; the amplitude attenuation coefficients of (61 ± 2), (113 ± 4) and (175 ± 5) dB/m at 1, 1.6 and 2.25 MHz, respectively. The average thermal conductivity in the gel was (0.532 ± 0.054) W/m/K at 24°C. The sources of uncertainties in determination of acoustic and thermal properties of the gel are discussed. Both the thermal and acoustic properties of our phantom correspond closely to those reported for brain in the literature. The concentration of the gelatin in the solvent is similar to protein content in the brain, thus suggesting that the protein concentration is of primary importance in tissue phantom preparation.
SU‐FF‐I‐92: A Computerized Automated Segmentation Methodology for the Recognition of Vessels From in Vivo Acquired DSA Images
Authors: Kagadis G , Spyridonos P , Mihailidis D , Daskalakis A , Katsanos K , Diamantopoulos A , Karnabatidis D , Siablis D , Cavouras D , Nikiforidis G
Published: July 2006

Purpose: In vivo dynamic visualization, recognition and quantification of microvascular networks represent a methodological requirement of both therapeutic angiogenesis and tumor anti‐angiogenesis basic research and clinical studies. The purpose of our study was to develop an automated computerized tool for the segmentation of in vivo acquired DSA images. Method and Materials: We applied the scale space structural tensor in order to delineate blood vessels. The concept of structural tensor has been extensively investigated and may allow for analysis of local structures, as well as their strength and orientation in local neighborhood pixels. We optimised the image processing software on the basis of the structural tensor concept, and tested the software on a series of DSA images of collateral vessels in the established in‐vivo model of chronic rabbit hindlimb ischemia. Firstly, the image is smoothed by a sigma standard deviation 2D Gaussian. Sigma is a free parameter, which controls the scale of the extracted vessels. Finally, the accuracy of vessel recognition was evaluated by direct comparison with the analysis of an expert vascular radiologist, who was considered a priori as the “gold standard”. Results: The result was a fully automated tool developed in Matlab that can be used to process images as a batch process without any user intervention. Microvessels' recognition sensitivity depended on the value of the sigma parameter. The segmentation performance of the software was tested in the recognition of collateral vessels in digital DSA images of ischemic rabbit hindlimbs. The proposed software was highly successful in delineating vessels of all sizes with an accuracy score varying between 77.24% and 82.12%. Conclusion: The proposed method is automatic, robust and escapes human subjectivity. It is a promising new tool for analyzing macro‐ and micro‐vessels in DSA images acquired for either experimental or clinical use.
SU‐FF‐I‐95: The Use of Deformable Registration Model to Improve Visibility of the Lesion in Gated PET Images
Authors: Pevsner A , Erdi Y , Nemeh S , Davis B , Joshi S , Yorke E , Rosenzweig K , Humm J , Larson S , Ling C , Mageras G
Published: July 2006

Purpose: Gated PET images from a respiration‐correlated 4D PET/CT protocol potentially provide more accurate definition of tumor compared to motion averaged non‐gated PET images. However, gated PET images have reduced event statistics in each phase bin, due the shorter acquisition time relative to the clinical study. We have previously demonstrated that a deformable registration algorithm can accurately model changes in lung lesion position from CT images obtained at different respiration phases. The purpose of this study was to evaluate method of deformable image registration to improve the visibility of lung tumors in gated PET Methods and Materials: The data for two patients were acquired on a PET/CT scanner using a respiration‐correlated PET/CT protocol, which yielded CT and PET images at different phases of the patient's respiratory cycle. For each patient PET and CT data were sorted in 8 bins. Application of a deformable CT‐to‐CT registration algorithm produced a set of 7 deformation fields that mapped the CT images at different phase bins onto a reference CT phase (end inspiration). The set of deformation fields was then applied to deform the gated PET images to the reference phase. The deformed PET images were summed with the PET image at the reference phase to produce a single PET image. Results: We have examined T/B ratio in the images by drawing ROIs in the lesion and in the vicinity of the lesion. The most noticeable changes in visibility of lesion were observed in the periphery of the tumor. In two patients the T/B ratio in the summed warped image sets improved by 80% and 21% in periphery, 31% and 16% in the center of the tumor relative to single gated image. Conclusion: Deformable registration can be used to improve T/B ratio and the visibility of lesions in gated PET data.
SU‐FF‐I‐96: Automatic Registration of EPI and DRR Images for Treatment Planning and Delivery Verification
Authors: Liu J , Drzymala R , Bradley J
Published: July 2006

Purpose: To automatically register electronic portal images (EPIs) and digitally reconstructed radiographs (DRRs) for the verification of treatment planning and delivery based on Average Intensity Projection (AIP) imaging. Method and Materials: AIP 4D CT images are obtained by averaging 4D CT images acquired for lung tumors using multi‐slice CT simulation. The AIP images are used to represent tumor motion during treatment planning and delivery in extracranial stereotactic radiotherapy (ESRT). Planning DRR images are created for each treatment field. Cine EPIs are collected for each treatment field. The apertures are segmented from EPIs by thresholding, and then used to register the EPIs and the associated DRRs. The segmented EPIs are enhanced to highlight the tumor area. Then enhanced EPIs and DRRs are fused together in the aperture to produce a fusion movie. Cine EPIs are averaged to produce an average EPI. The tumor movement in each EPI is enhanced by subtracting the average EPI from the original Cine EPI. A sequence of tumor movement images is sorted to form a subtraction movie. Results: The registration procedure is performed automatically without user supervision. Fusion movies show the target motion against the static background of DRR, providing a visual perception of the moving anatomy around the target. Subtraction movies show clearly the track of the target motion inside the aperture. Periodic displacement of the tumor reflects respiratory movement. The size, deviation, and deformation of the tumor can be observed. Conclusions: This technology will benefit the verification of treatment planning and delivery, the evaluation of the patient set up, and the visual inspection of the tumor movement during ESRT. Conflict of Interest: Part of this work was funded by Elekta, Inc., Norcross GA.
SU‐FF‐I‐97: Fuzzy Segmentation of Brain Tissue and Optimum Number of Clusters: Application to Quantitative Assessment of Arterial Spin Labeling Perfusion Maps
Authors: Maleki N , Roberts T
Published: July 2006

Purpose: To perform brain tissue segmentation using Fuzzy C‐means (FCM) clustering and find the optimum number of clusters for application in brain perfusion quantification employing Flow‐sensitive Alternating Inversion Recovery (FAIR) arterial spin labeling technique. Method and Materials: For this study a single‐shot spin‐echo EPI‐FAIR imaging sequence was employed. Imaging was performed using FAIR inversion times of 300, 450, 600, 800, 1000 and 1200. Other imaging parameters were 64×64 matrix, TE/TR=20/2000, 8‐channel phased array head coil, and 40 consecutive selective and non‐selective inversion recovery (IR) image pairs of healthy volunteers (n=5) were acquired. A FCM algorithm was developed and implemented for clustering the IR images. Also another algorithm was developed to determine the optimum number of clusters based on validity indices proposed in the literature including Partition Index (PI), Separation Index (SI), Beni's Index (BI) and Dunn's Index (DI). Results: Optimum TI value for best segmentation results turned out to be TI=800msec. The optimum number of clusters for quantitative analysis of perfusion maps was found to be 6. The measure for the goodness of the clusters was based on a combination of the meaningfulness of the generated clusters and the value of validity indices mentioned above. With 6 clusters, a cluster of grey matter would appear with more tissue homogeneity and less partial volume effect which would result 20–25% increase in average measured signal in that whole segment which would lead to a higher SNR for more robust quantification of perfusion in that area. Partial volume effect seems to be more problematic at grey matter and CSF border Conclusion: FCM is a powerful method for the purpose of brain segmentation since fuzziness could be considered as a measure to account for partial volume effect present in the brain images specially at lower resolutions used for perfusion imaging.
SU‐FF‐I‐98: Segmentation of CT Image Using Fast‐Marching and Active‐Contour
Authors: Chen Q , Lu W , Ruchala K , Olivera G
Published: July 2006

Purpose: To reduce the workload of manual contouring by developing a semiautomatic method that can successfully perform segmentation of liver, kidney, bladder, lung, and trachea. Method and Materials: A Canny edge detector was used to extract edges. The obtained edge image was used by a gradient vector flow (GVF) snake algorithm to deform an initial surface onto the edge. For the GVF snake to work, the initial surface has to be reasonably close to the edge. This problem was solved by using a fast marching algorithm on the Canny edge image. Several measures were adopted to prevent the initial surface to leak through the places where the edge was broken. Results: This segmentation method was tested on clinical CT images and found to be very successful in liver, kidney, bladder, lung, and trachea. There are cases when the organ to be segmented contacted with other organs and there is no image contrast observed between them. Small error may exist in those areas. Those errors can be easily identified and corrected by some simple human interactions. Conclusions: Our study has shown that the algorithm we developed can successfully perform CT image segmentation of several important structures. This algorithm can greatly reduce the workload of contouring the patient.
SU‐FF‐J‐01: 3‐D Computed Rotational Angiography for Radiotherapy Planning for Cerebral Arteriovenous Malformations: Comparison of Tomotherapy and Non‐Coplanar Dynamic Arcs
Authors: Hyde D , Bauman G , Batchelar D , Taylor J , Lownie S , Holdsworth D W
Published: July 2006

Purpose: Three‐dimensional Computed Rotational Angiography (CRA) provides high quality images of the complex anatomical structure of cerebral arteriovenous malformations (AVMs). The objective of this research is to combine CRA, as an alternative to bi‐plane angiography for target definition, with innovative radiotherapy techniques for stereotactic radiation therapy. This preliminary treatment planning study investigates the utility of Helical Tomotherapy, as compared to multiple non‐coplanar dynamic arcs using a conventional linear accelerator (linac). Materials and Methods: A Siemens Axiom scanner was used to acquire CRA images for this treatment planning study. Non‐coplanar dynamic arc treatments were planned using Theraplan Plus. These plans were designed for delivery on a conventional linac (Varian 2100 EX) equipped with a multileaf collimator (5 mm leaf width at isocentre). The same images and regions of interest were used to generate plans for helical tomotherapy delivery (TomoTherapy Inc., Hi‐Art II). Tomotherapy is a dedicated intensity modulated radiation therapy system that delivers a narrow fan‐beam, modulated by binary multileaf collimators (6.25 mm leaf width at isocentre). Results: The CRA images have an isotropic voxel spacing of less than 0.38 mm, with a signal‐difference‐to‐noise‐ratio greater than 20:1. These high quality images facilitated the delineation of the complex target volume for treatment planning. Each of the treatment planning techniques offered specific advantages. Multiple non‐coplanar arc plans generated a lower integral dose to the surrounding healthy tissue (a 12 Gy isodose volume of 40 vs. 100 cm3 for presented sample patient). Tomotherapy inverse‐planning provided a more homogeneous dose distribution over the target volume (homogeneity index of 1.006 vs. 1.087), as well as better avoidance of critical structures (maximum brain stem dose of 8.2 vs. 13.2 Gy). Conclusion: Tomotherapy presents an alternative to forward planning with non‐coplanar arcs. Moreover, the megavoltage CT imaging capabilities of Tomotherapy could provide frameless, stereotactic localization for AVM radiotherapy.
SU‐FF‐J‐03: 4DCT‐Based Study of Lung Tumor Motion Reproducibility
Authors: Michalski D , Sontag M , Li F , Andrade R , Uslene I , Brandner E , Heron D , Yue N , Huq M
Published: July 2006

Purpose: To investigate the reproducibility of lung tumors motions and their characteristics during the course of the treatment. Materials and Methods: Two 4DCT scans were obtained at an interval of about three weeks with a GE‐scanner and Varian's RPM System under free breathing for 13 patients. Each respiration cycle had 10 phases. 14 GTVs and 10 lungs in all phases were contoured. Geometrical characteristics of these structures were obtained with Eclipse TPS for the motion reproducibility analysis. Results: The GTVs of the initial scans ranged from 2.0cc to 280.5cc with a median of 50.3cc. Their median relative change in the second scan was a 28% decrease. The 3D extent of the respiration‐induced motion of the GTVs' centroids in the first scan ranged from 0.34cm to 1.78cm with a median of 0.90cm. For the second scan it was 0.13cm, 1.99cm, and 0.89cm, respectively. The largest motion was in a projection on a sagittal plane. The overall displacements of the GTVs' edges exhibited same trend. These motion tracks from two scans overlapped along DICOM directions. The median change of phase 50 lung volumes in both scans relative to the tidal volume at the first scan was −12% for ipsilateral and −11% for contralateral lungs. The median tidal volume change between scans relative to the first scan volume was 8% for ipsilateral and 4% for contralateral lungs. Conclusion: Most of the patients results show reproducible patterns of motion. The hysteresis of the motion varies between scans. This might be due to GTV changes during the treatment. A large and anisotropic shape change perturbs the initial motion trajectory, however general patterns appear repetitive. The respiratory changes of lung volumes were similar. They are not indicative of the GTVs motion reproducibility.
SU‐FF‐J‐07: A Low‐Z Target with No Flattener and Reduced Energy for Improved Contrast in Megavoltage Cone‐Beam CT
Authors: Faddegon B , Ghelmansarai F , Bani‐Hashemi A
Published: July 2006

Purpose: To improve contrast in MV cone‐beam CT using a low‐Z target (LZT). Method and Materials: A high‐Z tungsten target (HZT) at 6 MV and low‐Z carbon targets of different thicknesses were used with no flattener. The maximum energy was used with LZT while eliminating primary electron leakage into the monitor chamber. Output and dose distributions were measured. Images were acquired at 7 frames/sec with a 1024×1024 400‐micrometer pixel flat panel detector with 1mm Cu build‐up and a Lanex fast scintillator. Phantoms were QC‐3V, a contrast/spatial resolution phantom, a sheep head and a cadaver. Results: Beam energy was 3.5±0.5 MV and 4.5±0.5 MV for the 1.016 cm and 1.35 cm carbon targets, respectively. The higher energy was more stable with higher output: 0.299 cGy/sec compared to 0.084 cGy/sec. Surface dose was 80%. Field diameter at isocenter was limited to 36 cm by the electron monitor, when present. Computed contrast‐to‐noise ratio (CNR) for the contrast‐spatial resolution phantom for LZT was 3.5 times that of HZT at 10 cGy. Computed CNR for HZT for the 2D QC‐3V phantom images is 24 and for LZT is 100 with dose per projection of 0.035cGy. The f50 of LZT is 0.41 lp/mm. Adaptive noise filtering with a kernel of 8×8 increased the CNR by a factor of 2.4 without degrading resolution. Preliminary cone beam images with the low Z target show remarkable bone contrast and indicate improved soft tissue contrast. Conclusion: A stable 4.5 MV beam was produced on a standard treatment linac equipped with a carbon target, showing improved CNR over images taken with the treatment target and sufficient output for cone‐beam CT. A direct comparison to images taken with the carbon and tungsten targets on the same cadaver, expected to show an improvement in soft tissue contrast, will be available at the meeting.
SU‐FF‐J‐08: A Novel Method for Image‐Guided Verification of SBRT with An EPID in Cine Mode
Authors: Berbeco R , Ionascu D , Hacker F , Lobo J , Mamon H
Published: July 2006

Purpose: The adoption of stereotactic radiosurgical techniques for extra‐cranial treatment sites is predicated on a high accuracy and precision of tumor localization before and during each treatment. We introduce a novel method for monitoring the tumor location while the treatment beam is on by using a conventional electronic portal‐imaging device (EPID). Method and Materials: In our clinic, we are currently treating some liver patients under a Phase‐I IRB‐approved extra‐cranial radiosurgery protocol. Prior to treatment planning, multiple (n > 2) gold fiducial markers are implanted on the periphery of the tumor. At the time of treatment, the patient is placed in a stereotactic body frame with abdominal compression. After the set‐up orthogonal portal images are taken, the EPID is left in its acquisition position. When employed during treatment, the EPID, in cine mode, collects the exit radiation and produces a sequence of images for each field. By the end of treatment, a collection of images will be available in PortalVision for review. For advanced analysis and quantification, the images are exported and evaluated off‐line. Results: Given the length of hypofractionated treatments (due to the high dose delivered), we are able to acquire as many as 78 images for each field. The implanted gold markers are visible in the images even before processing. We use an in‐house program for calculating the location of the seeds and their relative distance to the planned location (as defined by the DRRs). Conclusion: We have developed an algorithm for quickly assessing target localization using implanted gold markers as surrogates. Not only is this information used to verify the treatment, but it may also be used in the future to adapt the treatment either for subsequent fields or remaining fractions. Conflict of Interest: This work was partially supported by a grant from Varian Medical Systems, Inc.
SU‐FF‐J‐09: A Novel Non‐Rigid Image Registration Algorithm for Radiation Therapy Using P‐Element Based Biomechanical Model (PBM)
Authors: Xia J , Samant S
Published: July 2006

Purpose: Daily pre‐treatment volumetric imaging can be acquired with onboard CT or MR simulator. This imaging can be used for adaptive radiotherapy (ART) provided deformations occur on time scales >15–30 min. A necessary component of ART is automatic, fast and robust deformable registration. An algorithm using p‐element based biomechanical model (PMB) is presented. Its performance is compared with published algorithms. Method and Materials: PBM achieves successful registration using a coarse mesh by “automatic adaptivity”, whereby convergence is achieved by iteratively increasing the order of the polynomial used for fitting without necessarily requiring mesh refinement (i.e. distance scaling of mesh element), resulting in linear scaling in computation time. A conventional biomechanical model (BM), which utilizes second order polynomial, requires mesh refinement at each iteration for convergence, resulting in an exponential scaling in computation time. For intra‐modal deformations, the performance of PBM was compared with Demons method (DM) for T1‐weighted MR and CT using simulated transformations and clinical data. Results: DM resulted in certain anatomical structures either missing or misplaced since it assumes that pixel intensity does not change between the target and reference images for the same structure. PBM and BM provided similar results in terms of faithful structural connectivity and accuracy, and were superior to DM. The number of p‐elements in PBM was 360, much less than the 1616 elements in BM, allowing for automatic mesh generation to be more robust for PBM. Furthermore, mesh refinement was necessary in BM in order to achieve convergence. The computation time for PBM was 15% less than BM, and 100% more than DM. Conclusion: PBM provides a superior accuracy compared to DM. It has accuracy comparable to BM but with reduced computation time.
SU‐FF‐J‐11: A Novel Use of a Real‐Time Tumor Positioning System in Reducing Cone Beam CT Artifacts
Authors: Parikh P , Santanam L , Hubenschmidt J , Malinowski K , Lechleiter K , Chaudhari A , Dimmer S , Mayse M , Bradley J , Low D
Published: July 2006

Purpose: The Calypso® Medical 4D Localization system is capable of tracking real‐time dynamic motion without ionizing radiation. A limitation of any fiducial based system is the inability to visualize surrounding tissues. Cone beam CT (CBCT) of moving objects results in image blurring due to long acquisition times. We investigated the use of the Calypso® 4D localization system to improve motion artifacts obtained from the Varian Trilogy CBCT. Materials and Methods:. A research Calypso® 4D tracking system was installed in a Varian Trilogy vault. A rectangular phantom with implanted transponders was attached to an internally‐developed 4D stage. A CBCT was obtained while moving the phantom under the Calypso® measurement array using a patient tumor derived trajectory. The projection images were obtained and shifted using the corresponding Calypso® transponder positioning information and then reconstructed into CBCT images. This process was repeated for a dog with transponders implanted in the lung as part of an IRB‐approved study. Results: The Calypso® based image shifts caused the radiographic projection of the transponders remained stable in sinogram space. CBCT images from the shifted sinogram exhibited reduced image motion artifacts. Without artifact reduction, the transponders were visualized as multiple streaks and the surface of the phantom was heavily deformed. With artifact reduction, the transponders were accurately localized, and the deformation was removed. The dog's breathing cycle made qualitative image motion artifact reduction review difficult. Quantitative analysis of the reconstructed CT numbers showed sharper gradients through the transponders, indicating that the shifting process had improved the image quality. Conclusions: Use of a wireless electromagnetic implanted transponder system for motion correction of CBCT is possible. This preliminary sinogram shifting technique was very effective for non‐deforming objects. Further work will increase the synergy between real‐time tracking systems and volumetric imaging.

This work was supported by Calypso® Medical Technologies.
SU‐FF‐J‐14: A Simulation Program for Cyberknife Treatment Setup
Authors: Xia F , Recalde N
Published: July 2006

Purpose: During the setup of Cyberknife patients with extracranial tumors, it is always a challenge to tell the angles of misalignment (roll, yaw and pitch) from the two digital reconstructed radiographs (DRRs) and the radiographs from two X‐ray cameras. Most of the cases, software handles the problem, but in some cases, software fails, it is because of fiducial migration or not enough fiducials to give 6D information (fiducial), or fiducial motion due to tumor motion (synchrony), or the angles are too large for the software to handle (skeletal structure tracking). When this happens, the operator needs to make the right decision fast, in order to shorten the setup time and to deliver the correct dose to the tumor. We decided to write a program to help people in this situation. This program can generate DRRs before and after each transformation. It will be a great learning tool; new users can practice how to set up a patient from a random starting position; we can't practice the setup on a live patient. Experienced users can use it to study setup, learn how the positions of different structures change relative to different rotations. Method and Materials: Java programming was chosen to build the software. The DRRs were reconstructed from a series of CT images according to Cyberknife X‐ray sources and screens configuration. Results: A graphic user interface (GUI) with two DRRs will be presented to the user, user can choose to translate and rotate the patient, two more DRRs will be generated; and a CT slice will also show up on the GUI. The user can identify the features that have the most change in each transformation. Conclusions: This program works as expected. It also demonstrates to the medical physics community that we can easily write programs to manipulate images.
SU‐FF‐J‐15: A Study of Some Immobilization Techniques by Using An On Board Imaging System
Authors: Xue T , Jackson A , Kearney K
Published: July 2006

Purpose: To study the effectiveness of a head and neck immobilization system and a prostate immobilization technique by using an on board imaging system. Method and Materials: For head and neck, the immobilization system includes standard head rests, MEDTEC base plate and standard thermoplastic masks. For prostate, the MEDTEC HipFix system is used. All patients are in supine position. For head and neck, the daily setup is straight forward. For prostate, our Therapists developed a routine to set up patients. Varian Eclipse treatment computer system is used to generate the setup field DRR from 3 mm CT scan. Varian CL21EX with On Board Imaging (OBI) is used to setup the patient. KV or MV portal images of a lateral and an anterior or posterior setup fields are taken, and then align with corresponding DRR by using bony structures. The OBI software gives the couch shifts in vertical, lateral and longitudinal directions. The 3D (or vector) shifts are calculated from the three orthogonal shifts. Results: About 900 prostate setups and 300 head and neck setups have been studied. For 52% of prostate setups and 32% of head and neck setups, the 3D couch shifts are 3 mm or less. For 82% of prostate setups and 60% of head and neck setups, the 3D couch shifts are 5 mm or less. Conclusion: This study shows that the prostate immobilization technique gives very good reproducibility, and the head and neck immobilization is not as good. We will try to improve our head and neck immobilization method for IMRT purpose.
SU‐FF‐J‐17: Accuracy and Dosimetric Advantage of Target Localization Using Stereoscopic Image‐Guided Radiotherapy for Lung Cancer Treatment
Authors: Ding M , Stuhr K , Newman F , Johnson T , Kavanagh B
Published: July 2006

Purpose: We analyzed the accuracy of stereoscopic image‐guided radiotherapy (S‐IGRT) with the ExacTrac® system (BrainLAB AG, Heimstetten, Germany), and demonstrated the dosimetric advantage for lung cancer treatment. Methods: The accuracy of target localization using the ExacTrac system was analyzed by re‐scanning ten patients immobilized in the Vac‐loc bag with BB tags put on the isocenter marks determined by the ExacTrac system. The re‐scanned CT data from each patient was fused and compared to the isocenter locations on the original CT used for the treatment planning. The Active Breathing Coordinator™ (Elekta, Norcross, GA) was employed to minimize the breathing motion effect on S‐IGRT. The dosimetric advantage of S‐IGRT was demonstrated by comparing the normal lung volume receiving 15%, 30% and 50% of the prescription dose (V15%, V30% and V50%) between the plans with smaller margins in the S‐IGRT and those with normal margins in the conventional radiotherapy for the ten patients. Results: The average isocenter shifts using S‐IGRT were within 3.4 ±1.7mm in the lateral, 3.6±1.9mm in the anterior/posterior, and 2.2±3.2mm in the superior/inferior directions. The added margins around the CTV to create the PTV were chosen to be 10mm in the superior/inferior and 5mm in radial direction for the lung cancer treatment planning in S‐IGRT. For the ten patients with CTV volume from 8.3cm3 to 43.4cm3 and lung volume from 2736cm3 to 3640cm3, the averages of V15%, V30% and V50% were 17.4%, 9.8%, 5.9% for the S‐IGRT plans, and 33.4%, 18.2%, 12.8% for the conventional radiotherapy plans with 2cm margins in the all directions. Conclusion: The S‐IGRT with the ExacTrac system provided highly accurate tumor localization. The margins from CTV to PTV in S‐IGRT treatment planning could be reduced significantly due to the accurate target localization which will reduce the lung volume receiving doses in the medium and low ranges.
SU‐FF‐J‐18: Adaptive IMRT Using Cone‐Beam CT: A Case Study On Patients with Bulky Head and Neck Tumors
Authors: Ding G , Duggan D , Coffey C , Hallahan D , Deeley M
Published: July 2006

Purpose: The objective of this work is to demonstrate the feasibility and efficacy of acquiring on‐board Cone‐Beam CT (CBCT) volume images for adaptive radiotherapy (ART) and image‐guided‐radiotherapy (IGRT) for patients with bulky head and neck tumors treated with IMRT. Method and Materials: The quality of the CBCT volume images acquired on the treatment table was evaluated by measuring the spatial accuracy, contrast, resolution, and the curve for converting CT number to electron density. A patient planning CT volume images were acquired before treatment and at mid‐course. CBCT volume images were acquired weekly during treatment. To cover the IMRT fields, two CBCT acquisitions were combined into one volume image using in‐house software. PTV and organ contours were copied from the pretreatment CT volume to the CBCT volume and adjusted as necessary. The IMRT plan was applied to the CBCT volume and dose‐volume histograms were calculated for the adjusted PTV and spinal cord. The CBCT images were used for patient treatment verifications and dose calculations for ART. Results: Significant changes in the skin contours and PTV contours were seen on patients with bulky HNC after as few as five treatments. The dosimetric consequences were also significant. Adapting the IMRT plan to the changes in patient anatomy by re‐optimizing on the CBCT volume was found to be feasible. For patients whose Head and Neck cancer was not bulky, there were no significant changes in setup or anatomy. Conclusion: It is feasible to acquire weekly CBCT images on the treatment table for analyzing significant changes in anatomy and determine dosimetric consequences of those changes. The CBCT can be used to obtain the accumulative target dose and to modify treatment plans without performing additional planning CT. The CBCT is shown to be a very effective tool for ART for IMRT treatment.
SU‐FF‐J‐24: An Optical Flow Based Motion Tracking Method Using Fluoroscopic Video
Authors: Xu Q , Hamilton R , Jiang S
Published: July 2006

Purpose: To present an optical flow‐based method for tracking tumor motion and propose a noninvasive respiratory detection method using fluoroscopic video. Method and Materials: Fluoroscopic video of a patient is acquired. Only one frame is selected as the reference frame and objects in this frame are manually segmented. The motion of a segmented object is found by computing the average optical flow of pixels within the object. Optical flow provides a two‐dimensional motion vector for the displacement of pixels between two frames. The object is moved between frames by moving all pixels by the average velocity vector. Then the position of the object in the new frame is adjusted by applying a template matching algorithm. The algorithm moves the object over a search range of +/− 2 pixels. The object is placed at the position having the maximum correlation coefficient (CC) between the pixels in the original and new frames. This procedure is repeated to advance the object from frame to frame. Results:The outlines of tracked objects are viewed superimposed on the fluoroscopic videos. The outlines follow the general motion of the objects without drifting away for the approximately 30 seconds (300 images) and 8 respiratory cycles of a typical video. Objects that do not significantly deform are well tracked. The boundaries of objects that deform are not well described by the tracked outlines, however, the centroid motion of the objects is. The analysis yields the mean displacement of objects. As the distance an object moves away from the reference position increases, the CC decreases. A plot of the CC vs frame shows a sinusoidal curve with the breathing period as does the displacement plot, but with reversed phase. Conclusion: The mean motions of objects in fluoroscopic video are well tracked. The displacement and respiratory signal are also obtained.
SU‐FF‐J‐29: Assessment of Patient Setup Variations with a Commercial On‐Board Imaging System: Is There a Benefit to the Patient?
Authors: Ku L , Olden M , Shaddock S , Forster K
Published: July 2006

Purpose: Kilovoltage imaging with a commercial on‐board imager (OBI) has been implemented in our treatment room for image‐guided radiation therapy (IGRT). It holds great potential to improve treatment accuracy by reducing the setup errors. However, performing patient setup with OBI costs extra time and effort. Thus, it is important to demonstrate which patient will benefit from this new technique. We have assessed patient setup variations and its dosimetric effect. Method and Materials: We perform daily OBI setup on the prostate, head‐and‐neck (H&N), and central‐nerve‐system (CNS) IMRT patients. Our setup procedure: (1) Patients were aligned to their skin marks. (2) Orthogonal kV images were acquired with OBI. (3) Setup corrections were made by registering the kV images with DRR's based on bony landmark (H&N and CNS patients) or fiducial markers (prostate patients). Shifts larger than PTV margins were verified with MV portal imaging. Setup data from 2 CNS, 9 H&N, and 10 prostate patients were analyzed. For H&N and CNS patients, dose redistributions that incorporate each day's actual shifts were calculated by rigid‐body translation. Results: (1) H&N and CNS patients: the random setup variations (standard deviation of the daily data) are 0.15cm, 0.32cm and 0.42cm in LR, AP, and SI direction. The systematic setup variations (the average) are 0.5cm. The largest shift is 1.2cm. (2) Prostate patients: average interfractional variations are 0.26 cm (LR), 0.24 (SI) and 0.39 cm (AP). (3) Dose redistribution in the postplans demonstrated that OBI setup corrections typically don't modify the CTV coverage but frequently affect sparing of the critical organs. Conclusion: Our random setup variations were found to be smaller than the PTV margin (5mm). With OBI setup corrections, we can further reduce the PTV margin safely. Our postplans have shown that OBI setup corrections can dramatically improve sparing of the normal structures.
SU‐FF‐J‐30: Automatic Determination of Required Adjustment in Patient Setup for Radiation Therapy
Authors: Kassaee A , Bloch P , Khamene A , Stripp D
Published: July 2006

Purpose: To automatically determine the required adjustment for radiotherapy patient setup from two electronic portal images and rapidly calculated digitally reconstructed radiographs (DRR's) from the CT dataset acquired during CT‐simulation. Method and Materials: An amorphous silicon EPID (OPTIVUE, Siemens) was used to obtain setup portal images on patients receiving radiotherapy treatment at various anatomical sites. Two orthogonal portal images or a pair of portals with minimum of 12 degree parallax were acquired. A CT dataset obtained during CT‐simulation was used in an algorithm that calculated DRR's in approximately 80 ms. An iterative procedure compared the generated DRR with the acquired portal image using as the initial position the treatment plan isocenter and gantry angles. The minimum deviation between the generated DRR's and the acquired portal images was obtained using various similarity measures. The output from the registration algorithm gave the required patient setup adjustment with 6 degrees of freedom (3 couch translation shifts, and 3 rotational shifts) Results: The alignment of the acquired portals images with the generated DRR's were evaluated by a radiation oncologist for 37 patients (74 portal images). The agreement between generated DRR's and acquired portal images were within 2 mm in 73 of the 74 images analyzed. The largest deviation was approximately 5mm. The calculated translational shift from planned isocenter was between 1 mm and 7 mm. Rotational shifts were usually less than 2 degrees. Conclusion: A robust and intensity‐based software was evaluated for automatic patient positioning based on DRRs and portal images. The software shows agreement to within 2 mm as compared to evaluations performed by a human observer for various anatomical sites. The software also provides rotational shifts which are difficult to be determined by a human observer in cases where the magnitude is small.
SU‐FF‐J‐31: Breath‐Hold Cone‐Beam CT for Patient Setup in Stereotactic Body Radiation Therapy for Lung Tumors
Authors: Duggan D , Ding G , Coffey C , Lu B
Published: July 2006

Purpose: To investigate the feasibility of using breath‐hold cone‐beam CT (CBCT) on the treatment table to set up patients for stereotactic body radiation therapy (SBRT) for lung tumors. Method and Materials: After observing the motion of the patient's lung tumor by fluoroscopy, each patient was taught to hold his or her breath for 35 to 45 seconds. If negligible motion was observed during breath‐hold fluoroscopy, a planning CT was obtained during a single breath‐hold with a CT‐simulator. This breath‐hold planning CT was used to design a radiation treatment plan with 7–9 static, noncoplanar beams in accordance with a Radiation Therapy Oncology Group SBRT protocol. A CBCT acquired on the treatment table in three breath‐holds was used to set up each patient. A single breath‐hold was used for the acquisition of each kilovoltage radiograph and portal image and the delivery of each treatment beam. Results: The CBCT setup technique was found to be more reliable than using orthogonal kilovoltage radiographs on the treatment table because the tumor could always be seen in the CBCT images, but not always in the radiographs. For some patients, registering the setup image with the planning CT using only bony anatomy, the only practical method with orthogonal radiographs, would make the setup inaccurate. The time required for CBCT setup was acceptable. Conclusion: For setting up SBRT treatments of lung tumors, a breath‐hold CBCT on the treatment table is feasible and more reliable than using orthogonal radiographs. For some patients, the CBCT setup is more accurate because the tumor can always be seen in the CBCT images and registering images with bony anatomy alone may not place the isocenter in the center of the tumor.