bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐I‐37: An Adaptive Simultaneous Algebraic Reconstruction Technique
Authors: Zhang L , Lu W , Yin F , Zhang Y
Published: July 2007

Purpose: To improve the computational efficiency of Algebraic Reconstruction Technique (ART), and suppress the “stripping” artifacts due to ART like ray‐by‐ray update, especially in cone‐beam reconstruction. Method and Materials: Inspired by Adaptive ART (AART) and Simultaneous ART (SART), a new ART, the Adaptive Simultaneous ART (ASART), which combines multi‐level scheme (MLS) data‐access scheme, data‐driven contribution weighting, and SART like updating, is proposed. When the CT system is modeled as Wv = p, ASART can be mathematically expressed as:
urn:x-wiley:00942405:media:mp0414:mp0414-math-0001 where λ is.0 the relaxation factor that is typically chosen within the interval (0.0, 1.0] and the initial value are uniformly set to be a nonzero value. This method combines the advantages of SART and AART: the feature of SART, simultaneous correction image update in each view, is introduced into AART. In ASART, the reconstructed object is updated view‐by‐view, rather than ray‐by‐ray, and all views are accessed according to MLS. In general, the computation burden for ASART is less than that of SART. Results: For quality evaluation, we adopt a 3D extension of the Shepp‐Logan phantom, in which the least value variance is only 0.5% of the maximal value of the model, in our experiments. It is observed that ASART always achieves higher correlation coefficient (CC) than MLS‐SART does. Actually, 1‐iteration ASART produces much higher CC than 10‐iteration MLS‐SART does in our experiments. We have also applied the proposed approach on real dataset reconstruction. Fine image details are fairly visible in the slices obtained by our approach when only 96 limited numbers of projections are used. Conclusion: A new image reconstruction technique inspired by AART and SART is proposed in this work. Although the convergence has not been proved mathematically, this approach always performs well in our experiments. Both quantitative and visual analyses have shown that promising computational efficiency and better reconstructed image have been achieved.
SU‐FF‐I‐42: Making Hanging Protocols Work in a Clinical Setting
Authors: Jones A
Published: July 2007

Purpose: The radiologists at our institution prefer to read bone surveys in a specific order. The specific order allows them to read studies more quickly, and easily perform comparisons between contralateral body parts (e.g. right and left humerus). However, we have four generations of DR equipment from a particular manufacturer, and the DICOM header information for DX objects is inconsistent amongst the systems. Therefore, a hanging protocol was developed to facilitate the hanging of bone survey images in the proper order. Materials and methods: Our PACS system (iSite, Stentor) allows the use of hanging protocols. These protocols use matching series rules to establish hanging orders. Matching series rules were used where DICOM header information was present (i.e. not in a hidden/private field) and consistent. Also, technologists were provided with a schematic detailing the order in which specific images had to be acquired to result in the correct hanging order where matching series rules could not be used. Results: A successful hanging protocol was created using a combination of PACS tools and technologist instruction. The resulting protocol maximized patient comfort, minimized patient movement between table and wall detectors, and was simple enough to ensure a high rate of compliance from technologists. In addition, we provided tools to technologists and supervisors to view their studies in the order it would hang when opened for reading, and to correct studies (via presentation states) where patient safety or comfort required an exception to be made or where a mistake was made by the technologist. Hanging protocols for CR objects were also created. Conclusions: Creation of useful hanging protocols is still possible even when limitations are presented by DICOM header structure and content.
SU‐FF‐I‐58: A Software Toolkit for Multi‐Image Registration and Segmentation in IGRT and ART
Authors: Foskey M , Gash A , Han Q , Tracton G , Joshi S , Pizer S , Chaney E
Published: July 2007

Purpose: Extracting information from images for image‐guided and adaptive radiation therapy usually involves segmentation and/or registration with a reference image. The purpose of this research was to develop and make freely available a software toolkit for research use that combines several registration and segmentation methods and is applicable to problems involving multiple sequential images. Method and Materials: Two automatic approaches have been integrated with standard interactive methods. One automatic approach solves PDEs describing visco‐elastic flow to register a set of target images with a reference image. Segmentations can then be transferred from the reference image to target images via corresponding deformation fields. The second method segments images via Bayesian posterior optimization of a 3D deformable shape model called an m‐rep. User efficiency has been improved by the ability to queue, view, work with, and compare multiple images and segmentations during a single session. The software was developed in C++ and runs on Windows and Linux. Results: The GUI, including a window with panes for standard orthogonal 2D views linked to a second 3D window, preserves a common look and feel for all three approaches. A set of treatment images of the same patient initially are rigidly registered to a reference image. The images are then segmented by the methods of choice. Unsatisfactory automatic results are edited with conventional methods. Registered images and segmentations are output in DICOM RT format. Conclusion: The toolkit combines multiple approaches for image registration and segmentation in a system specifically designed to support research on IGRT and ART. A cost‐free license to download and use the software is available at http://planunc.radonc.unc.edu.

Research supported by NCI/NCRR R01 RR 01861501.
SU‐FF‐I‐60: Delineation of Synovial Tissue in MR Images of the Knee for Patient Specific Dosimetry Planning of Radionuclide Synovectomy
Authors: Jaiswal A , Mawko G , Cada M
Published: July 2007

Purpose: Delineation of synovial tissue in MR images of the knee for feasibility in patient specific dosimetry planning of radionuclide synovectomy. Method and Materials: A semi automated method based on marker controlled watershed was developed to delineate the synovial tissue in MR images of the knee. Markers were calculated using gray reconstruction algorithm. Segmented regions were extracted interactively by using a graphical user interface. Images used for testing were T1‐weighted spin echo (TR 800, TE 20), post contrast enhanced, acquired using 1.5 Tesla MR Units (Siemens, Magnetron) and polarized knee coil. Image slices were of 0.625mm ×0.625mm in size and 3mm in thickness. Only one patient's data was used. Various performance metrics were determined for evaluating the method. Results: Results obtained from the semi automated method were compared with the manual results. Maximum overlap ratio of 86.3 % was achieved between the manually delineated and semi automatically delineated synovial tissue regions. Mean percentage error of 19% in the surface area of synovial tissue was recorded. Conclusion: This study indicates that developed method has more robustness and reproducibility as compared to the manual method. For future work this method can be applied to other patients data, pre contrast enhanced images for volume calculation of the synovial tissue and also to individualize radionuclide synovectomy treatments.
SU‐FF‐I‐71: Measurement of the 2‐D Modulation Transfer Function for Screen‐Film Magnification Mammography
Authors: Maalej N , Asuni G , Al‐Dhukair A , Naqvi A
Published: July 2007

Purpose: High resolution and contrast are very important for the detection of micro‐ calcifications and tumor masses in mammography screening. A very good measure of contrast versus resolution is the Modulation Transfer Function (MTF). In this study, we performed the measurement of the 2‐dimensional (2‐D) point spread function (PSP) and determined the 2‐D MTF for regular and magnification screen film mammography. Method and Materials: The experimental set up consists of the mammography machine, a pinhole camera mounted on test stand and the screen‐film cassette. The pinhole camera has circular aperture (10 μm diameter) in a lead disk. The pinhole camera was carefully aligned with the vertical line under the x‐ray tube focal spot. We used a Molybdenum anode/ Molybdenum filter x‐ray tube with a nominal focal spot size of 0.3 mm. We exposed the film‐screen using 30 kVp and 10 mAs exposure settings. The exposed films were processed and scanned using a transmission scanner with 4,800 × 4,800 dpi resolution to obtain the PSF. The PSF was processed with 2‐D Fourier transform to obtain the 2‐D MTF. Results: The obtained PSF was a double Gaussian function of space at high magnification (2.5) and was closer to a single Gaussian at low magnification (1.15). The spatial resolution in the image plane in all directions was observed to decrease with increasing magnification. The image resolution was focal spot limited as expected. However, the variation of limiting resolution with magnification did not exactly fit the theoretical expectation. Conclusion: We have successfully measured the 2‐D PSF and the 2‐D MTF for a screen film mammography in regular and magnification modes. While magnification provides a magnified view of a small part of the breast it has a lower limiting resolution due to the focal spot blurring and may compromise the detection of micro calcifications.
SU‐FF‐I‐74: A Modulation Transfer Function Comparison of Dual‐Screen CR Systems
Authors: Cheong S‐K , Cai Y C , Chu J C H , Kriz R
Published: July 2007

Purpose: The goal of this study is to measure MTF of two dual‐screen CR systems, and to explain the correlation between their system resolution and the physical properties of phosphor screens. Method and Materials: Modulation transfer function (MTF) is commonly used method to characterize the performance of an imaging system. The well‐established edge method is used to quantify the MTF of digital radiographic systems. We use a sharply polished edge slanted with respect to sampling detector grid, which allows measurement of oversampled edge function profiles. The focus of this study is on the comparison of the presampled MTFs obtained for different thicknesses of phosphor screens and pixel sizes. MTFs were measured with both diagnostic and 6 MV x‐rays. The storage phosphors used in this study were two commercially available CR plates: Kodak EC‐L fast and Kodak EC‐L regular cassettes. Results: The scan times per pixel for both high (0.171 mm) and low (0.342 mm) resolution are much shorter than 558 μs of the dominant luminescence lifetime for , used in this study. Consequently, the spatial resolution of KODAK 2000RT CR system is lower in the scan direction than in the moving direction due to the afterglow effect. A comparison of the MTFs with Kodak EC‐L fast and regular cassettes indicates that the spatial resolution of dual‐screen CR systems does not depend on the total thickness of phosphor screens but is determined by the thickness of the thicker phosphor screen in the dual‐screen CR system. Conclusion: MTFs in laser scan direction roll off faster than in phosphor transport direction with KODAK 2000RT CR system. The resolution is related to the thickness of individual phosphors layers.
SU‐FF‐I‐76: Slot Scan Imaging Versus Anti‐Scatter Grid Method in Digital Chest Imaging‐ a 4‐AFC Study
Authors: Lai C , Shaw C , Liu X , Altunbas M , Chen L , Wang T , Han T
Published: July 2007

Purpose: To investigate and compare the anti‐scatter grid and slot scanning methods for their effects on the observers' performance in digital chest imaging. Materials and Methods: Anthropomorphic chest phantom was imaged with an a‐Si/a‐Se flat‐panel based digital radiography system. The system was operated in both the slot scanning and full‐field modes. An anti‐scatter grid was used. Imaging technique was 120 kVp and 0.15 to 16 mAs for both modes. After that, the grid was removed and same imaging technique was applied to acquire phantom images for both modes. 1‐cm diameter computer‐simulated nodule with a nominal peak contrast ratio of 5% was used to generate simulated nodules at hilum and sub‐diaphragm locations by applying SPR values for all images. 4‐AFC experiment was conducted to measure the ratio of correct observations as a function of the exposure level for various imaging conditions and locations. 24 sets of four‐512×512 images were generated for each exposure level, resulting in generating 192 sets for each imaging condition and location. These images were displayed randomly on a review workstation. The ratios of correct observations versus exposure levels were computed for various imaging conditions and locations. Result: With low exposure, the observers' performance improved with the exposure level but reached the maximum at ∼4 mAs for all techniques. At the hilum location, slot scan imaging without grid performed the best, followed by full‐field imaging without grid. The use of an anti‐scatter grid in both full‐field and slot scan modes seemed to degrade the performance significantly. Conclusion: Improvement with the exposure level has been observed for all imaging techniques. However, the observers' performance reached the maximum at different rates depending on the nodule location and techniques.

(This work was supported in part by a research grant EB000117 from the NIH‐NIBIB and a research grant CA104759 from the NIH‐NCI).
SU‐FF‐I‐77: Relationship of Uncertainty in Pixel Intensity to Apparent Diffusion Coefficient Calculation
Authors: Vijayakumar N , Ewell L
Published: July 2007

Purpose: To estimate how variations in pixel uncertainty can affect calculations of Apparent Diffusion Coefficients (ADCs) used in therapy evaluation. Methods and Materials: ADCs are calculated for a Region of Interest (ROI) using Diffusion Weighted Magnetic Resonance Imaging (DWMRI). Uncertainties in pixel intensities, e.g. due to noise, are simulated by increasing or decreasing pixel intensities by ± 50% from their nominal value. The large value (50%) of variation allows trends to be observed more easily. The resulting modified DWMRI images are then used to calculate ADC for ROIs, and the variation of the ADC as a function of position and/or slice number and/or ROI size is then observed. We have analyzed DWMRI scans for a number of patients. Results: Positive increases in pixel intensity result in lower ADC values and we hence observe the largest relative variation with this change. For the nominal ∼300mm2 ROI, with a +50% increase in pixel intensity, we see a maximum relative change of roughly a factor of six going from left to right (as the ROI crosses the ventricles) compared with a factor of three for the nominal pixel intensity. Similar changes were observed for inferior — superior positions (slice number). We see minimal or no variation in ADC Values as the area of the ROI is varied from 150 mm2 to 600 mm2. Conclusion: Positive variations in pixel uncertainty result in the largest variation of ADCs and have the most effect in the region which has low average pixel intensity. This behavior is due to low Signal to Noise Ratio (SNR) in that region.
SU‐FF‐I‐78: Evaluating the Effect of Dielectric Resonance On Image Uniformity at 1.5T and 3T in An ACR MRI Phantom Filled with Mineral Oil and Silicone Fluid
Authors: Hatab M , Goerner F , Clarke G
Published: July 2007

Purpose: The use of oil‐based phantoms instead of water‐based ones is known to be a more suitable method of assessing image uniformity of high field magnets. This study aims to investigate the appropriateness of using oil or silicone in the ACR phantom for routine quality control for both 1.5T and 3T MRI systems paying particular attention to the dielectric resonance effect. Methods and Materials: A prototype ACR phantom which was used to help develop the existing ACR MRI phantom was filled with three different materials and scanned in both a 1.5T and 3T magnets using the recommended ACR T1 sequence. The first material was the standard phantom water‐based liquid, the second material was mineral oil and the third was a silicone fluid. Percent image uniformity (PIU) as well as low and high contrast resolutions were assessed for all three filling liquids at both fields. Results: For the standard MRI phantom solution, the PIU was calculated to be 95% at 1.5 T and 80% at 3T. The same phantom filled with mineral oil produced a PIU of 99% on the 1.5 T and 95% on the 3T magnet. There was a marked decrease in SNR in going from standard aqueous solution to mineral oil, but this did not seem to affect the high contrast resolution or the low contrast detectability at either field. Results for the silicone fluid will also be presented. Conclusions: Central brightening artifacts are often seen as high signal intensity in the center of the imaged object and have caused problems with the PIU analysis of the water‐based ACR phantom on 3T systems. Filling the phantom with a material that has a lower dielectric value than water such as mineral oil or silicone provides images which are more uniform and tends to improve the artifactual lower PIU measurements.
SU‐FF‐I‐82: Noise Cancellation and Onset Detection of Verbal Responses During Functional Magnetic Resonance Imaging
Authors: Sen A , Parrish T
Published: July 2007

A method for scanner noise cancellation and detection of verbal responses during an fMRI experiment is presented. In recent fMRI experiments overt responses have been used to monitor the subject's response and the timing used in the statistical analysis.. Due to the presence of scanner noise, the subject's speech can be difficult to understand. Data were collected on a 3T scanner during EPI acquisition. A template of the scanner noise is created during the period of scanning that is used to allow the signal to reach equilibrium. For each TR intervals, correlation of the template is used to optimize the subtraction by a shift of +/− 5 pixels. A median filter (1×5) is used to remove spurious noise spikes resulting from an incomplete subtraction. Finally, a threshold is applied defined as 2 standard deviations above the baseline, to identify the verbal responses. The time position of each verbal response is obtained with respect to an initial setting.

The result is an audio stream that is nearly free of scanner noise with a reduction in noise by 15 dB. The subject's voice is detectable. A spreadsheet of verbal response onsets is also created for use during analysis to improve the statistical model. Future implementation is aimed at having a real‐time version to monitor the subject during any form of imaging to provide additional levels of safety. The experimental data is sampled at a rate of 25000 samples/second. Figure 1, shows pictures of scanner signals, before and after the processing of an event related trial. Figure 2, shows the scanner signal before processing in one TR segment. Figure 3 shows the power spectrum plot of the audio signals, before and after processing. The result shows that it is possible to reduce the scanner noise by 15 db using this technique.
SU‐FF‐J‐12: Respiratory Training Using Audio Visual Bio‐Feedback
Authors: Venkat R Batta , Keall P , Sawant A , George R
Published: July 2007

Purpose: To investigate the effectiveness of a novel respiratory training tool based on audio‐visual biofeedback for 4D CT image acquisition and dynamic tumor tracking during radiation therapy. Method and Materials: During radiation therapy it is important that a patient follows the same breathing pattern throughout the treatment. However, in practice, such regularity is very difficult to achieve. Our hypothesis is that, by training a patient to breathe according to a representative breathing pattern constructed from the patient's own free breathing samples, it is possible to achieve significantly higher regularity and reproducibility in the real time breathing pattern. Initially for each subject, the real‐time position samples for free breathing are acquired using a real‐time position monitoring system. After collecting a sufficiently large number of free breathing samples, a representative breathing pattern is constructed by estimating the average of the Fourier series coefficients corresponding to each breathing cycle. The patient is then instructed to follow the representative breathing pattern as closely as possible. The new method of respiratory training was tested on four volunteers (non‐patients). For each volunteer, the data for free and trained breathing was analyzed to calculate the RMS error of period and displacement with respect to representative waveform. Results: The average of RMS errors in time period and displacement for trained breathing was 2.32 seconds and 4.32 cm respectively. Similarly, average of RMS errors for free breathing was found to be 3.27 seconds and 7.9 cm. The reduction in the errors from free breathing to trained breathing was approximately 30 percent in time period and 45 percent in displacement. Conclusion: This tool provides valuable insights into identifying respiratory training methods that are customized for each subject. Further analysis of this methodology will be performed by developing alternate user interfaces and investigating the data from a larger set of volunteers.
SU‐FF‐J‐20: A Decision Strategy for Re‐Optimization in Adaptive Radiotherapy
Authors: Chen M , Lu W , Chen Q , Ruchala K , Olivera G
Published: July 2007

Purpose: Discrepancy between the delivered and the planned dose, hereafter referred to as dose discrepancy, occurs in every fraction due to patient or setup variation from the initial plan. Re‐optimization is a necessary step in adaptive radiotherapy to correct for the cumulated dose discrepancy from previous fractions. However, re‐optimization is very time consuming. The number of times it can be applied is limited. In this work, we propose a simple strategy to determine the best time to re‐optimize based on some statistical assumption on dose discrepancy. Method: Dose discrepancies of single fractions are modeled as independent random variables with known probability distributions. We assume that re‐optimization can be performed only once for the whole treatment course and the correction amount generated by re‐optimization to be applied for all remaining fractions can not exceed a given bound. Under this simplified conditions, we propose a decision criterion for re‐optimization based on the expected squared cumulated dose discrepancy, which are built inductively from the one‐fraction case. Results: Assuming that the probability distribution of dose discrepancy is Gaussian, we calculate, for each fraction, both upper and lower threshold of cumulated dose discrepancy for re‐optimization. For cumulated dose discrepancy within the upper and lower threshold, re‐optimization should be postponed. The calculated thresholds are close to two lines with slopes c,μ and,(c+μ), where c is the correction bound and μ is the systematic dose discrepancy. The result of the retrospective study using simulated data agrees well with our theoretical calculation. Conclusions: This study provides a guideline for determining whether re‐optimization should be done given the cumulated dose discrepancy and the number of remaining fractions. Our inductive approach can also be extended to cases when multiple re‐optimizations are allowed.
SU‐FF‐J‐21: A Comparison of a Point Based Tool with An Image Overlay Tool for Fiducial Based Setup
Authors: Balter P , Lindsay P , Kudchadker R , Nelson C , Briere T , Vedam S , Komaki R , Mohan R
Published: July 2007

Purpose: To compare interactive image overlay tools for fiducial based setup with a point based system. Method and Materials: A single implanted fiducial was used for localization. Gated kVp images were acquired for daily setup; if a shift was made, a 2nd set of images were acquired subsequent to the shift. Shifts were determined using both a commercial software package designed for point matching (ISOLOC, CIVCO, Kalona, IA) and also by dragging the projection of the fiducial contour over the image of the fiducial using tools integrated into the treatment delivery console(4DTC, Varian, Palo Alto, CA). Data was collected for 29 shifts on 15 different days. Results: The mean magnitude of the initial shifts were 1.5, 5.7, and 1.5 mm and the means of the differences between the shifts were 0.2, 1.1 and 0.8 mm in the lateral, cranial‐caudal, and AP directions respectively. On many days there was a discrepancy of 1–2 mm between the AP and lateral gated kVp X‐rays. The interactive tools allowed the user to compromise between the two projections, while the automatic system forced a compromise. The interactive tools also displayed a projection of the tumor allowing validation of the position of the fiducial with respect to the bulk tumor. The interactive tools were quicker to use and automatically applied the shifts; these tools are somewhat limited by the accuracy of the contouring of the fiducials. Conclusion: Both the interactive tools and the automatic system are practical for daily setup of patients with fiducials, but the integration into the console, the speed of localization, and most importantly the ability to correlate the fiducials with radioopaque anatomy make the interactive tools superior.
SU‐FF‐J‐29: Preliminary Experimental Study for Tumor Position Tracking During Radiotherapy Using Positron Emission Markers
Authors: Xu T , deKemp R , Wassenaar R , Chamberland M
Published: July 2007

Purpose: To experimentally evaluate the feasibility of tumor position tracking using positron emission markers for external beam radiation therapy. Method and Materials: Clinical PET imaging is known to be limited by its low spatial resolution of approximately 4–10 mm. However, if the geometry of the source is known, the position of the sources can be determined with sub‐millimeter accuracy. We propose to apply this concept for real‐time tumor position tracking during radiotherapy. For pulmonary and abdominal tumors, delivering accurate radiation therapy is limited by the motion of the tumor as the patient breathes. By implanting positron emission markers into tumor, and using pairs of position‐sensitive detectors to track the resulting annihilation gamma rays, the position of the tumor can be tracked in real‐time with high accuracy. Positron emission based technique will deliver a lower radiation dose to normal tissue than x‐ray fluoroscopy, and the smaller size of the positron emission markers reduces risk to the patient during implantation. The concept and simulation study has been previously published (T. Xu et.al, Med. Phys. 33(7) p2598). In this feasibility study, the technique was evaluated using a clinical PET system (CTI ECAT). A Ge‐68 Linear source was used to simulate a point source in 2D slices during conventional 2D acquisition. The Ge‐68 source was put at 3 locations and the data were combined to simulate multiple (3) markers. Results: Three point sources were successfully localized using proposed technique. The localization precision ranges from 4 mm down to 0.2 mm when the number of coincident events used increases from 100 to 4100. The precession reaches 0.77 mm with only about 200 events from three point sources. Conclusion: The study has shown that multiple positron emission markers can be localized with sub‐millimeter precision, which is sufficient for tumor localization during radiotherapy.
SU‐FF‐J‐30: Simultaneous Use of An Implanted Fiducial System and An Endorectal Balloon for the Treatment of Prostate Cancer
Authors: Munley M , Marshall D , Hampton C
Published: July 2007

Purpose: To report on our initial experience of using an on‐line implanted fiducial system simultaneously with an endorectal balloon to treat patients with prostate cancer. Method and Materials: Patients had three fiducial seeds implanted in their prostate prior to radiotherapy treatment planning. Treatment was given in the prone position with an endorectal balloon inflated to 60 cc and a full bladder. Patients were initially positioned with the aid of lasers/tattoos and an immobilization cradle. Open‐field radiation electronic portal images were then taken in the treatment position and compared to reference images prior to each fraction of treatment. The intermarker distances (IMDs) between the three implanted seeds were examined to gain insight on prostate deformation and seed migration for this treatment strategy. The IMDs for the initial three fractions were averaged for each seed pair to serve as our references. For subsequent fractions, the differences in IMDs between measured and reference values were computed. Our data were also compared to similar previously reported studies. Results: We have analyzed the IMDs of 13 patients treated with implanted fiducials and an endorectal balloon. A total of 349 alignments were evaluable and thus, 1047 IMDs were calculated for this set of patients. The mean absolute IMD difference for all samples was 0.86±0.88 mm, while the largest single IMD difference was 8.9 mm. For individual patients, the ranges of mean absolute IMD differences for a given seed pair and corresponding standard deviations were 0.32–1.85 mm and 0.22–1.66 mm, respectively. The maximum absolute IMD difference for individual patients ranged from 1.2–8.9 mm. Conclusions: We have simultaneously implemented an on‐line implanted fiducial system and an endorectal balloon during prostate cancer radiotherapy. The degree of deformation of the prostate gland during treatment has been examined. This study may help predict the potential dosimetric consequences due to prostate motion/deformation.
SU‐FF‐J‐32: A Feasibility Study of Image‐Guided Non‐Invasive Single‐Fraction Stereotactic Radiosurgery Using the 2D2D Match of An On‐Board Imaging System
Authors: Chang J , O'Meara W , Mechalakos J , Yamada Y , Lovelock D , Lymberis S , Amols H
Published: July 2007

Purpose: To investigate the feasibility of image‐guided non‐invasive single‐fraction stereotactic radiosurgery (SRS) using the 2D2D match of a kilo‐voltage on‐board imager (kVOBI). Method and Materials: An institutional‐approved prospective protocol was developed to evaluate the accuracy of frameless SRS over our current invasive system. Each participating patient was immobilized with a thermoplastic mask covering the face and shoulders. Anterior‐posterior and lateral digitally reconstructed radiographs (DRRs) were generated based on the treatment isocenter identified on the planning CT scan. The patient was then transferred to the treatment room and setup by manually aligning an orthogonal pair of kVOBI projection images with the corresponding DRRs. The patient remained in the treatment position for 20 minutes to simulate a mock SRS treatment. Two cone‐beam CT (CBCT) scans, acquired at the beginning and end of the procedure, were fused with the simulation CT scan to determine the setup accuracy and cumulative intra‐fraction movement. For comparison, the setup accuracy was also measured for the same patient in an invasive SRS frame. Results: Three patients were successfully recruited and studied to date. The setup accuracy (distance between the center of the first CBCT scan and planning isocenter) was 2.25±0.67 mm (mean ± one standard deviation). The cumulative intra‐fractional movement was 1.91±0.30 mm, mainly in the superior‐inferior direction (1.79±0.45 mm). The total setup error at the end of treatment (the second CBCT scan) was 3.89±0.09 mm. The setup accuracy of invasive SRS frame was superior (1.63±1.39 mm) in comparison to the mask system. Conclusion: The setup accuracy of two‐dimensional kVOBI was insufficient for single‐fraction SRS. Volumetric CBCT scanning should be used instead for frameless SRS setup. The observed cumulative intra‐fractional was significant for the mask system and should be monitored and corrected using a realtime position feedback device.
SU‐FF‐J‐36: Dosimetric Evaluation of MV Portal Imaging Methods for Localization of the Prostate During 3D Conformal Radiotherapy
Authors: Watchman C , Urcadez E , Tanyi J , Dougherty S
Published: July 2007

This study was done to determine the dosimetric consequences to the PTV and rectum of different portal image guided methods to localize prostate patients with gold markers during 3D conformal radiotherapy. Three treatment plans were generated for five patients illustrative of three treatment scenarios A) a 6‐field treatment (RL/LL/LAO/LPO/RAO/RPO) where weekly portal image dose was ignored, B) the same plan as scenario A that included daily portal dose was cumulated for an initial and verification images and C) treatment plan for a 7‐field method (AP/RL/LL/LAO/LPO/RAO/RPO) that included using 6 MU from the AP and RL treatment fields to generate positioning images. Dosimetry from each of these was compared for dose distributions, max and average dose to the PTV and rectum. Comparisons of the scenario A to B indicated mean dose differences on the order of 10% to the PTV with the former being greater. Average rectal doses were comparable between the two plans but hot spots were (∼10% greater) seen with the inclusion of portal dose. In contrast, the 7‐field plan demonstrated comparable dosimetry to the plan for scenario A. Differences were on the order of <1% for the PTV and ⩽2.5% to the rectum due to differences in the number of beams, beam orientations and beam weighting. Inclusion of the dose accumulated from daily portal imaging can significantly increase the dose to the patient and should be accounted for. Positioning using daily MV portal images can be done using a 7‐field treatment plan where an AP and a LAT field with 6 MU can result in treatments that are dosimetrically comparable to a traditional six field treatment.
SU‐FF‐J‐37: Automatic Optical Tracking System Calibration for Radiation Therapy
Authors: Bootsma G , Sie F , Moseley D , Siewerdsen J , Jaffray D
Published: July 2007

Purpose: Optical tracking systems provide high‐resolution real‐time positioning data. To provide clinically beneficial data in a radiation therapy context the optical tracking system's coordinate system must be registered to the isocentric coordinate system of the treatment delivery room. Current systems use a rigid phantom aligned relative to the isocenter, often using in‐room lasers. An algorithm has been developed which allows the automatic registration to the isocentric coordinate system using a calibration phantom and cone‐beam CT (CBCT). Methods and Materials: A custom calibration phantom with passive infrared reflective markers was designed for use in conjunction with the Polaris, an IR emitting stereoscopic camera (NDI, Waterloo). The phantom was placed on the treatment couch of a linear accelerator (Elekta Synergy) within the field‐of‐view of the kV source and CBCT acquired. The reconstructed volume was imported into custom in‐house software. The four reflective markers on the phantom were automatically localized inside the volume using a novel template matching algorithm. The software also retrieved the coordinates of these same markers from the unregistered camera. Using the two point sets, a rigid transformation was computed using a least squares fit, allowing the camera's coordinate system to be calibrated to the isocentric CBCT coordinate system. After calibration five reflective markers were placed on the treatment couch and their positions captured using three methods: infrared camera, CBCT, and orthogonal EPIDs. The 3D marker positions in each reference frame were then analyzed. Results: The error between the infrared camera and CBCT, infrared camera and orthogonal EPIDs, and CBCT and orthogonal EPIDs for the marker positions was 1.93, 1.81, and 1.31mm(RMS), respectively. Conclusion: Calibration errors are within the precision requirements for radiation therapy patient positioning aids (<2mm). By automating the procedure the subjectivity is reduced and the reproducibility is increased.
SU‐FF‐J‐43: Use of Kilovoltage Cone Beam CT (kV‐CBCT) for Hypofractionated Image‐Guided Radiation Therapy (HF‐IGRT) of Lung Tumors
Authors: Della Biancia C , Guan Y , Yorke E , Chang J , Rosenzweig K , O'Meara W , Amols H
Published: July 2007

Purpose: We retrospectively studied geometric and dosimetric differences between bony (vertebral body‐based) and soft tissue (GTV‐based) registrations of kilovoltage cone‐beam CT (CBCT) scans for setup and intra‐fraction motion assessment of lung tumor patients receiving hypofractionated image‐guided radiation therapy (HF‐IGRT). Method and Materials: kV‐CBCT scans were acquired before and after HF‐IGRT treatment for ten patients with lung tumors. Pre‐treatment CBCT was registered with planning CT using GTV‐based and bony registrations to determine the treatment isocenter. Isocenter positions and tumor and normal tissue DVHs were compared for the two registration types. Intra‐fraction motion of vertebral bodies and GTV during the approximately half‐hour treatment was determined from pre‐ and post‐treatment CBCTs acquired at the same isocenter. Normal tissue doses were evaluated. Results: The average ±1 SD differences (mm) between isocenter position determined by bony and GTV registrations of planning CT with pre‐treatment CBCT are 1.8±4.2 (left‐right), 0.5±5.7 (ant‐post), 0.6±3.6 (sup‐inf), and 6.4±4.5 (3‐D magnitude). For 6 patients, the distance between the GTV and bony registration isocenters exceeded 5 mm. For the clinical margins used (1 cm GTV‐PTV), coverage and most normal tissue DVHs were minimally affected by registration type except for maximum bronchus dose in one patient that increased by 15 Gy. For 7 patients, GTV and vertebral intrafraction motion determined from the pre‐ and post‐treatment CBCTs, was similar. The average difference was 2.3±1.6 mm with a maximum in one patient of 5 mm. Except for one maximum bronchus dose increase of 18 Gy, normal tissue dose changes were small. Conclusion: Isocenter positions determined by bony and GTV registration can differ by more than 5 mm. This can affect normal tissue doses and, for reduced margins, target coverage. For target dose delivery, GTV‐based registrations are more accurate. Difference in intra‐fraction GTV and vertebral motion is often, but not always, within 3 mm.
SU‐FF‐J‐52: A Quantitative Assessment of the Improvement in Treatment Setup Accuracy with IGRT in TomoTherapy
Authors: Bichay T , Meadows J , Tran H , Nash A , Chen C
Published: July 2007

Purpose: Image guided radiation therapy (IGRT) is becoming the standard of practice for many treatment sites. Our purpose in this study was to quantify the improvement in setup accuracy with the use of IGRT in TomoTherapy. We have analyzed shifts in the X,Y,Z directions for patients undergoing daily IGRT and treatment with a TomoTherapy Hi‐Art unit. Total vector shifts were also calculated. Four distinct patient groups were analyzed: cranial, head and neck, prostate with implanted fiducials, and prostatectomy patients. Method and Materials: Megavoltage computed tomography (MVCT) was carried out at each treatment fraction. The MVCT was fused to the planning KVCT and the resultant X,Y,Z offsets determined. A total of 1,303 X,Y,Z measurements from 48 patients were collected for this study. The data is presented separately for each of the four groups. Results: Prostate patients with implanted gold markers had the largest vector shifts with a mean of 9.0 mm. The magnitude of this vector was largely due to vertical shifts (Z direction) with a mean of 7.1 mm. Prostatectomy patients were set up based on bone fusion and had an average vector shift of 7.8 mm, while head and neck and cranial patients had an average shift of 5.0 mm and 4.7 mm respectively. Data for the displacement in each of the X,Y,Z directions is also presented. The variation in shifts between different patients within a group was significant and varied by at least a factor of four. Conclusion: This study demonstrates quantitatively the potential improvement in radiotherapy accuracy with the use of IGRT in TomoTherapy. Corrections in setup in the Z (vertical) direction account for the largest contribution to the vectors calculated. The use of extremely high dose gradients in IMRT has made patient positioning accuracy even more critical than in previous modalities.
SU‐FF‐J‐58: Clinical Evaluation Using Digital Tomosynthesis for Positioning Verification of Breath‐Hold Liver Treatment
Authors: Fuller J , Wu Q , Godfrey D , Zhang J , Wang Z , Yoo S , Yin F
Published: July 2007

Purpose: To demonstrate clinical feasibility of generating digital tomosynthesis (DTS) in a single breath‐hold (BH) period compared to multiple BH periods for CBCT acquisition and to examine on‐board BH‐DTS as an efficient alternative to BH‐CBCT for target localization of breath‐hold liver treatment. Methods & Materials: 3 patients receiving 3D conformal or IMRT treatments to the liver were retrospectively studied. Reference DTS images (RDTS) were generated using the BH planning CT and BH‐DTS images were reconstructed using the projection images acquired with BH‐CBCT. Matching between on‐board image set and reference image set was performed by (1) aligning bony anatomy near isocenter and (2) aligning target soft tissue using all image sets. Localization variations were calculated as the relative couch shifts in the vertical, longitudinal and lateral directions, as well as the relative couch rotations in pitch, yaw, and roll directions. Results: 10 – 40 degrees DTS images can be acquired within 1 single BH. Localization accuracy is in the range of 0.2 cm and 1.0 degree using the coronal‐view DTSs and is in the range of 0.35 cm and 1.6 degree using the for sagittal view DTS. The localization accuracy is comparable either using bony anatomy or using soft tissue. Conclusion: Rapid (< 10 sec.) BH‐DTS is more efficient than BH‐CBCT (> 5 min.) for daily 3D on‐board image guidance and localization of liver under breath‐hold radiation therapy.

Partially supported by research grant from Varian Medical Systems.
SU‐FF‐J‐129: Implementation and Special Considerations for Dedicated PET/CT Simulation in Radiation Oncology
Authors: Kearns WT , Bourland JD , Hinson WH , Hampton CJ , Munley MT
Published: July 2007

Purpose: Our radiation oncology department has implemented PET/CT simulation having performed over 125 procedures in the past year. Dedicated PET/CT simulator eliminates the need to fuse outside PET studies and provides scans in the treatment position. However, PET/CT brings special challenges that must be managed to ensure image quality, spatial accuracy, efficient process flow, accurate target definition, and radiation safety. Materials/Methods: In January 2005 our department began providing F‐18 FDG PET/CT simulations on a GE Discovery ST hybrid scanner and GE Advantage Sim software (GE Healthcare, Waukesha WI). Patients were immobilized on a flat table insert, injected, scanned, and had isocenters placed. Phantom studies were performed to ensure spatial accuracy and image quality of the automated fusion software. Studies included measurement of displacement of table height due to patient weight. Due to the time spent adjacent to the patient and the expected high exposure rates, process flow was modified in order to reduce staff exposure. Results/Discussion: Our department was able to confirm spatial accuracy of the automated fusion via phantom studies to meet manufacturer specifications. However, we did reveal a significant table deflection of up to 10mm from the external lasers to the inside bore of the CT scanner which caused a change in scan protocol. Contouring window levels were studied with similar phantoms to determine appropriate settings. Process flow was aided by the hiring of an experienced, certified nuclear medicine technologist to assist the radiation therapists. Additionally, we implemented the process of immobilizing the patient prior to injection to reduce staff exposure. We determined in a separate study dose rates of up to 94μSv/hr at 15 cm from the patient. Conclusion: Dedicated PET/CT simulation in radiation oncology departments is a useful modality, but can add to time and complexity to the simulation workflow.
SU‐FF‐J‐131: The Effect of Respiratory Motion On the GTV Contoured with PET Image
Authors: Yin Yong
Published: July 2007

Purpose To evaluate the effect of respiratory motion on the GTV contoured with PET image, using a 2D respiratory motion phantom system. Methods Twenty‐eight kinds of respiratory motions were simulated using a respiratory motion phantom system. The phantom was scanned by PET‐CT machine under different motion conditions, then the PET images were obtained. The GTV was contoured using PET images. Results The GTV under static condition (GTV 0) was 7.90±0.21cm3. The GTV with motion frequencies of 16 per minute, 18 per minute and 20 per minute were 11.56±2.62cm3 (GTV16), 12.51±3.57cm3 (GTV18) and 11.86±3.27cm3 (GTV20), respectively. The differences among GTV0, GTV16, GTV18 and GTV20 were significant (all P<0.01). The GTV with motion amplitudes of 1.0cm, 1.5cm and 2.0cm on z axis were 11.44±3.68cm3 (GTVz−1.0), 11.64±3.47cm3 (GTVz−1.5) and 12.83±2.02cm3 (GTVz−2.0), respectively. The GTV with motion amplitudes of 0.5cm, 1.0cm and 1.5cm on x axis were 9.68±2.32cm3 (GTVx−0.5), 14.41±3.19cm3 (GTVx−1.0) and 11.83±1.92cm3 (GTVx−1.5) respectively. The differences of GTV on z axis and x axis were significant (p<0.01). Conclusions The GTV contoured with PET image will be severely effected by respiratory motion which will impact on radiation treatment planning. The gating technique should be used in order to decrease this kind of effect when the GTV was contoured with PET image.
SU‐FF‐P‐05: Five Year‐Report On a Web‐Based Interactive Dosimetry Training Tool
Authors: Keall P , Kaylor S , McCune D , Boyer A
Published: July 2007

Purpose: To address the critical shortage of medical dosimetrists in radiation oncology, an NCI‐funded web‐based ‘Dosimetry Training Tool’ education program was developed. The aim of this work was to present the end of funding period findings. Method and Materials: A dedicated group of volunteer medical physics and medical dosimetry experts developed high quality educational material enhanced by the interactive capabilities offered through web‐based learning. Educational rigor was provided by frequent interaction between the developers and a psychometrician and internet education specialist. During the development of the program, tests were performed to evaluate and revise the program direction using selected sites. Pre‐ and post module quizzes are taken by the students to quantify the educational benefit of the learning tool. An online user feedback tool is available for content and/or quiz queries. Results: Twenty‐four modules were developed, from Fundamentals of the Medical Management of Cancer (module 1), external beam and brachytherapy treatment planning, to Basic Math Skills for Dosimetry (module 24). Each module contains between 3 and 26 sessions. Over 1100 users, including over 800 students have used the dosimetry training tool, with a steady increase in the number of users throughout the program development. Mentors and students are predominantly from the US, however, other countries with approved mentors and active students are Afghanistan, Australia, Canada, China, Greenland, Hong Kong, Ireland, Israel, Pakistan, Singapore, Taiwan, and Thailand. Increases in pre‐ and post‐quiz scores range from 2 to 35% with a mean of 15% improvement. Conclusion: A successful web‐based dosimetry training tool has been developed and is in use by over 800 students. The use of the developed web‐based interactive educational design approach could be extended to augment and facilitate the development of medical physics graduate programs, medical physics residencies and other allied health care professional education.