bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐I‐93: Comparison of Seven Similarity Measures for Intensity‐Based 3D/3D Image Registrations On CBCT
Authors: Kim J , Hammoud R , Li S , Lord B , Patel S H , Pradhan D , Movsas B
Published: July 2006

Purpose: The goal of this study is to evaluate seven similarity measure functions for an intensity‐based rigid‐body 3D/3D image registration. The registration method was specifically designed to localize prostates on cone‐beam CT (CBCT) images, acquired for the use of daily patient setup, accomplished by maximizing the similarity from the corresponding simulation CT in an iterative fashion. Methods and Materials: Registrations were conducted with seven different similarity measure functions (NCC‐normalized cross‐correlation, EOD‐entropy of difference, MI‐mutual information, CR‐correlation ratio, GC‐gradient correlation, GD‐gradient difference, and PI‐pattern intensity), three different transformations (translation only, translation plus couch rotation, and translation plus three rotations), and two preprocessing methods (window‐leveling and histogram equalization). For accuracy and robustness estimation, prostate calcifications were identified on the images from four prostate patients (4 simulation CTs + 27 CBCTs), and the average calcification distances (errors) were measured after registrations. Each registration was marked as “converged” if it had less than 5 mm error, and the average distance was used as an accuracy index. Results: In general the histogram equalization and higher degree of transformation freedom improved the accuracy. The only exception was NCC, which performed better without histogram equalization. In the order of better performance, we found the convergence rate and accuracy were (96%, 1.7±1.0mm) for GC, (96%, 1.8±1.0mm) for GD, (96%, 1.8±1.0mm) for PI, (93%, 2.0±1.0mm) for NCC, (81%, 2.9mm) for CR, (78%,2.5mm) for MI, (44%, 2.1mm) for EOD. Conclusions: Among the seven similarity measure functions, registrations utilizing GC, GD, and PI showed the least prostate localization error on daily CBCT images. Such 3D‐3D image registration will be critical in order to make the future use of CBCT more objective, efficient, and accurate.
SU‐FF‐I‐94: Intensity‐Based 3D/3D Image Registration for Prostate Localization On CBCT Images
Authors: Kim J , Hammoud R , Li S , Lord B , Patel S , Pradhan D , Movsas B
Published: July 2006

Purpose: We have developed an intensity‐based 3D/3D image registration program for automatic prostate localization on CBCT images. The main application of this program will be the online and offline analysis of CBCT images for daily image guided radiation therapy. Methods and materials: The program provides with two different ways of defining region of interests (ROI); rectangular ROI and irregular ROI. The rectangular ROI is generally defined around the pelvic bone for bone matching, and the irregular ROI is around prostate and seminal vesicle for prostate matching. The ROIs are defined on the simulation CT images, and the volumes within which are registered with daily CBCT images. Registration is accomplished by maximizing the similarity within the ROIs. Uphill simplex method is utilized for the maximization, and it stops when the number of iteration reaches a preset threshold, or when the simplex shrinks to a preset simplex radius. Then, the users verify the registration result in three different overlay views, and the treatment machine correction shifts are calculated from the verified registration. Results: As a similarity function, mutual information provided very robust and accurate registrations for the pelvic bone registration. In one of our preliminary studies, the prostate registrations with gradient correlation, gradient difference, and pattern intensity showed 1.7±1.0mm average error, estimated from calcification mismatches. The registrations were also compared with the average manual registrations conducted by four clinicians. The isocenter difference in each dimension was around 1.0±0.7mm. The execution time, except the ROI definition and image loading, was around 7 seconds for each pelvic bone and prostate registration on a 1.8 MHz PC. Conclusions: Further thorough experiments are due, but the preliminary results indicated that the newly developed program may be able to provide accurate, robust, and fast online and offline CBCT analysis for image guided radiation therapy.
SU‐FF‐I‐99: Implementation and Evaluation of Automatic Contour Propagation in 4DCT of Lung
Authors: Boldea V , Sharp G , Jiang S , Choi N , Ginestet C , Carrie C , Sarrut D
Published: July 2006

Purpose: To implement and evaluate automatic contour propagation in 4DCT of lung Method and Material: 4DCT of lung cancer patients was acquired and GTV contoured in each of 10 respiratory phases. Demons‐based deformable registration was performed to find the volumetric mapping from the exhale reference phase to each other phase. Contours were propagated using volumetric methods. Usually, the GTV is contoured on one reference phase (end‐exhale for example) of the 4D‐CT which is copied and edited on the others phases. This is a very important, but time consuming task that is inconvenient for every day clinical use. Using a deformation field computed between 4D‐CT phases could accelerate the contouring process. The reference GTV contour would be deformed from one phase to another and the clinician would have to do only small adjustments. The contouring time spent would be significantly reduced. The question is if deformable registration could be used as a semi‐automatic contouring tool. We compared differences between GTV reported with and without deformation from one 4D‐CT phases to another. Three metrics were used to assess the quality of the contour propagation: the volume intersection and two volume differences. Results: Volume intersections between manual and automatic contouring were generally between about 85 and 90 per cent, while volume differences were generally between 5 and 15 per cent. Differences between manual and automatic results were correlated with the variability of manual GTV volumes delineation between phases. Conclusions: Deformable registration is a viable option for contour propagation, and may be used to assist the clinician in defining the GTV for large 4DCT data sets. Conflict of Interest: This research was supported by Elekta Oncology Systems and Varian Medical Systems.
SU‐FF‐I‐100: Investigate Between the Voxel Based Morphometry and Region of Interest Study in Alzheimer's Disease
Authors: Juh R , Su M , Lee C , Suh T , Nalcioglu O
Published: July 2006

Purpose: Voxel based morphometry (VBM) has been increasingly applied to investigate differences in brain morphology between a group of patients and control subjects. VBM permits comparison of gray matter (GM) volume at voxel‐level from the entire brain, thus is an efficient method for assessing regional differences. The purpose of this study was to assess the regional GM volume loss measured by VBM in Alzheimer's disease (AD) compared to controls, and to measure hippocampal volume using manually delineated volumetry and compare the results to VBM findings. Method and Materials: Twenty‐three AD (mean age 70 ± 8y; m/f= 7/16, Mini‐Mental State Exam [MMSE]= 22.2) and 20 cognitively normal elderly control subjects (mean age 69 ± 4y; m/f= 10/10) were included in this study. The 20 sets of images were first normalized and create the probability maps for segmentation. Normalized hippocampal volume to the intracranial volume was compared between AD and control groups. Results: The AD group had a lower GM %, and a higher CSF% compared to controls. The total intracranial volumes analyzed using SPM and our own ROITOOL program were very close (p<0.0001). The hippocampal volume of AD patients was significantly lower than that of controls (P<0.001). The region includes parahippocampal gyrus, cingulate, insula, frontal lobe and middle temporal complex. Despite the high significance in manual ROI analysis, hippocampus was not revealed in the VBM. Conclusions: We found that the hippocampal volume in AD was significantly smaller than in controls using ROI‐based volumetry. However, although our VBM results demonstrated that AD patients had a significant atrophy in middle temporal lobe, parahippocampus and insula, the hippocampus was not revealed. While VBM can be applied to assess global atrophy efficiently, manual volumetry is needed to study irregularly‐shaped subcortical structures.
SU‐FF‐J‐02: 3D Target Localization Using Cone‐Beam CT for Head and Neck IMRT Patients
Authors: Wu Q
Published: July 2006

Purpose: To evaluate clinical effectiveness of target localization using cone‐beam CT (CBCT) for H&N IMRT treatment. Method and Materials: All H&N patients treated with an IRB approved protocol were imaged on the first day of treatment and weekly thereafter with Varian On‐Board Imager. After the patient was aligned with skin markers, 2D kilovoltage portal images were acquired and compared to the planning DRRs for set‐up corrections (2D‐based correction). Then, CBCT images were acquired and registered with the planning CT by matching both soft tissue and bony landmarks, which generated the 3D‐based corrections. The difference between two correction measurements yielded the treatment isocenter variation using the 3D/3D matching method. Dose distributions with different isocenter deviations were re‐constructed on the planning CT. The treatment DVHs of PTVs and critical structures were compared with those in the original plan. Results: A total of 12 CBCT were analyzed for 3 patients during their first 4‐weeks of treatment. Compared to set‐up variations, anatomical shrinkage/deformation was negligible. The mean isocenter deviations after 2D‐based corrections were 1.1mm in AP direction (max 3.0mm), 2.6mm in lateral direction (max 5.0mm), and 3.8mm in SI direction (max 6.0mm). For the worst isocenter deviation, the reconstructed mean PTV dose was reduced by 3.6% from the planned mean value. For two patients, the mean brainstem dose increased from 33% to 49.5% and from 36.9% to 66.8%, respectively, in worst cases after 2D‐based correction. Other critical structures that received significantly higher doses were cord (max dose changed from 41.8% to 64%), eye (mean dose changed from 37.5% to 83.9%) and parotid (mean dose changed from 58% to 72.5%). Conclusion: For H&N IMRT treatment, CBCT image‐guidance improves localization accuracy compared to 2D‐based technique and should be the method of choice for target localization when tight margins are applied.

Partially supported by Varian research grant.
SU‐FF‐J‐04: A Computerized Method for Peak and Valley Detection in Respiratory Waveforms Without Flow Measurement
Authors: Lu W , Nystrom M , Parikh P , Fooshee D , Hubenschmidt J , Bradley J , Low D
Published: July 2006

Purpose: To develop a computerized method for reliable peak (end inspiration) and valley (end expiration) detection in respiratory waveforms for gated radiotherapy and 4D CT. Method and Materials: A computerized method for peak (end inspiration) and valley (end expiration) detection in respiratory waveforms without flow measurement is described. The respiratory period T was estimated by applying a Fast Fourier Transform. The intercepts of the respiratory waveform with a moving average curve were determined with an averaging width of 2T. Peaks and valleys were defined respectively as the maximum and minimum between pairs of interwoven intercepts. While this method worked well the majority of the time, both automatic corrections and manual user interventions were employed to correct errors and adjust the results. Results: The method was implemented in MATLAB on a PC with a 3.0 GHz Pentium IV CPU and 2.0 GB RAM. On average, the respiratory waveform was 575.3 s long and contained a total of 307 peaks and valleys. For each patient, 99% of all peaks and valleys were correctly located by the automatic algorithm in 2.8 s. Only three (1%) points required manual user adjustment. A user spent 66.8 s for reviewing, and manually adding or deleting points. For nine of the 20 patients, all peaks and valleys were automatically detected. The high efficiency of the automatic algorithm is clear. Conclusion: The results demonstrated that this method was reliable and efficient for peak detection in respirator waveforms with noise and large variations in baseline level, amplitude and period.
SU‐FF‐J‐05: A Deformable Phantom for Dynamic Modeling in Radiation Therapy
Authors: Kashani R , Balter J , Lam K , Litzenberg D
Published: July 2006

Purpose: The vast array of research projects aimed at measuring and managing intra‐fraction motion in treatment planning and delivery demand sufficient quantitative means of verification. While analytic models and patient data are useful, a reproducible, compartmented, mechanical phantom is critical to proper commissioning and use of new systems for physiological motion management. In this study we evaluated the reproducibility of a deformable lung phantom for various simulated breathing states. Methods and Materials: A diagnostic thoracic phantom was modified for this purpose. The abdominal cavity insert was removed, and an extension of the existing lung insert was created using high density foam. To mimic lung density, the foam insert was infused with iodine. Tumor‐simulating inserts of varying density and size were inserted and fixed to the foam at different positions. A programmable actuator‐driven diaphragm was created to compress/decompress the foam according to an arbitrary breathing profile. Repeat CT scans of the phantom at different diaphragm positions were acquired and the locations of the tumor‐simulating inserts were measured. Results: The phantom has been demonstrated to produce compression as well as reproducible breathing states. All tumor positions are reproducible to within 1.5mm (with a maximum of 3.5mm deviation for the most inferior large tumor) over multiple repeat scans at the same simulated breathing state. Compressions of over 60% of the foam insert have been demonstrated, with propagation of motion ranging from 95% of the actuator motion at the diaphragm to about 20% near the “apex” (the interface with the existing lung insert). Hounsfield units equivalent to the relative attenuation of lung (∼20% of water) were achieved in the uncompressed foam. Conclusion: This phantom is simple, efficient, and viable. Experiments in quantitative dynamic modeling of breathing‐induced deformations are underway using this system.
SU‐FF‐J‐10: A Novel Signal‐Processing Strategy for in Vivo Ultrasonic Imaging of Brachytherapy Seeds
Authors: Mamou J , Feleppa E J , Wuu C‐S
Published: July 2006

Purpose: Brachytherapy is proving to be a well‐accepted means of treating prostate cancer. Unfortunately, implantation using needles inserted transperineally causes gland movement, and the resulting distortion may cause seed misplacement and dosimetry errors. Our approach employs novel methods of digitally processing ultrasound echo signals to markedly improve ultrasonic imaging of seeds during the implantation procedure. This approach will enable the radiation oncologist to determine where all implanted seeds are located and to make additional implantations to correct for dosimetry errors cause by misplaced seeds.

Method and Materials: Our signal‐processing strategy uses singular spectrum analysis (SSA) and shows promise for ultrasonically detecting and imaging radioactive seeds implanted in the prostate. This SSA‐based strategy utilizes pairs of eigenvalues derived from the autocorrelation matrix of envelope‐detected radiofrequency echo signals to identify seed‐specific signal repetitions. The power spectrum associated with a repetition signal is computed to derive a P‐value indicative of the likelihood of the presence of a seed at the location of that repetitive signal. P‐values throughout each scan plane are then color‐coded and superimposed on the corresponding conventional grayscale ultrasound images. These new ultrasound images are thus readily usable by clinicians to locate seeds. Results: Simulations assessing performance as a function of different levels of white and speckle noise and in the presence of signals at repetition periods not associated with seeds; experiments in an ideal scattering environment; and in vitro experiments using seeds implanted in beef were conducted and led to encouraging results. Simulations showed robustness to noise (signal‐to‐noise ratio < 25 dB) and in vitro experiments allowed for seed detection and imaging. Conclusion: Overall, our SSA‐based strategy shows encouraging potential for seed detection and imaging in the operating room. Clinical implementation of this methodology would be straightforward because it uses enveloped‐detected signals directly available from clinical scanners.
SU‐FF‐J‐12: A Phantom Study to Compare 2D Electronic Portal Imaging with 3D KV Cone‐Beam Imaging
Authors: Nawaz A O , Houser C , Bednarz G , Dicker A , Galvin J
Published: July 2006

Purpose: To compare patient positioning using a 2D Electronic Portal Imaging Device (EPID) with a 3D registration technique that uses a kV Cone Beam (CB) device. Introduction: The Elekta kV CB device represents a significant advancement in on‐line imaging for patient positioning and structure delineation. There exists an obvious interest in studying the robustness of this new technology. The phantom‐based study reported here compares the cone‐beam imaging capability with conventional EPID 2D imaging and registration. Additionally, a technique was developed to generate digitally reconstructed portal images (DRPIs) from the CBCT and compare them to EPID images. Materials and Methods: A Rando anthropomorphic phantom had surgical screws placed in the pelvic region. A treatment isocenter was selected in the pelvic region of the CT dataset of the phantom. The phantom was initially positioned using the CB volume imaging capability. Known shifts of the phantom were introduced and the phantom was repositioned using the CB. The CB corrections were compared to the corrections obtained using the internal fiducials and EPID imaging. Additionally, the EPID‐based positioning was mimicked by simulating the 2D imaging using the 3D CB data set. The digitally reconstructed images (DRR) were generated from the CBCT set and used as DRPIs. They were compared to both the diagnostic CT DRR's and the EPID images. Results: and Conclusion: The CB and EPID shifts were well correlated as determined by linear regression analysis. The correlation between the DRPIs and the EPIDs was even higher using the same analysis. However, on the shift‐by‐shift basis the CB was more accurate than the EPID: it gave more accurate shift determination than the EPID for approximately 90% test shifts. The DRPIs had the advantage over the CB 2Dimages because they included the treatment isocenter, field edges and distance scale.
SU‐FF‐J‐13: A Simple Method to Calibrate Stereo‐Vision System In Image‐Guided Radiotherapy
Authors: Liu D , Li S
Published: July 2006

Purpose: To calibrate a 3D stereovision system (or 3D camera in short) with complex planning and treatment systems to implement a 3D image‐guided radiotherapy system. Method and Materials: A calibration template with a printed grid is used to correlate the treatment machine coordinate system to the 3D camera image coordinate system. The calibration template is carefully placed on the top of the treatment machine table and precisely aligned with the corresponding machine axes. A 3D surface image of the template is captured by a 3D camera mounted on the ceiling of treatment room. Nine points of the 3D surface image are manually digitized and used to calibrate two coordinate systems. Two algorithm, analytical method and multi‐points registration method are conducted to find the transformation parameters. The analytical method only needs 3 points to find a rigid transformation between two coordinate systems. Trigged by least‐squares approximation, the multi‐points method uses 9 points to find an optimum rigid transformation between two coordinate systems. Results: Results from a set of experiments demonstrated that both methods can provide acceptable accuracy (<1‐mm) for the image‐guided radiotherapy. Ideally, all points of the template surface transformed from the calibration should be in the O‐XY plane but due to image nose and calibration uncertainty, large error (up to 2 mm) can be introduced by the analytical method. In contrast, for the same template image, the multiple‐point registration approach provided image transformation with the maximum error in the template plane less than 1.0 mm under the noisy circumstance. Conclusions: Both methods can be used for accurate image system calibration. However, the multiple‐point registration method yields more reliable results than that of the analytical method. Both methods are simple and the calibration can be conducted weekly with the QA of radiotherapy systems.
SU‐FF‐J‐16: A Tool for Off‐Line Review of 3D Target Verification and Localization with Cone‐Beam Computed Tomography
Authors: Wu Q , Yan H , Yin F , Yoo S , Das S , Willett C
Published: July 2006

Purpose: To implement a clinical tool for off‐line review of Cone‐Beam Computed Tomography (CBCT) based 3D target verification and localization. Methods and Materials: An in‐house 3D target localization and verification tool is being developed to allow physicians and physicists to review daily treatment target off‐line. The system provides quick initial target verification via user selected landmark points. An automatic gray‐scale registration technique provides fine‐tuning of the 3D target localization. It also allows the preference of soft‐tissue weighted vs. bony landmark weighted registration. A rigid body 3D‐image registration method, using a combination of correlation coefficient and mutual information measurements, has been developed. The registration algorithm uses a downhill simplex optimization technique to search for the best match of the two image sets. This study evaluates the efficacy and accuracy of the system. First, each CBCT and CT pair is manually registered by a human expert. Then these CBCT are input to the software to be registered with the planning CT. The comparison of the computer calculated 3D correction against the manual alignment evaluates the accuracy of the system. Results: 5 CBCT sets of prostate cancer patients are tested. The registration is bone weighted to simulate actual treatment target position. For all cases, the bone structures are well superimposed on the fused images. However, part of the prostate and rectum shown certain degree of mismatch due to different rectal fillings between CBCTs and CTs. Overall registration accuracy is as accurate as 1 mm and 1 degree for bone structures. Conclusion: An off‐line 3D target localization review tool was implemented. For prostate cases, its accuracy is acceptable for clinical use. Further implementation of the tool to other disease sites and evaluation of soft tissue vs. bone based target localization is underway.

Partially supported by a Varian research grant.
SU‐FF‐J‐19: Adaptive Radiation Therapy Using Helical Tomotherapy
Authors: Meeks S , Manon R , Kupelian P , Langen K , Lu W , Chen Q , Haimerl J , Ruchala K , Olivera G
Published: July 2006

Purpose: To describe and illustrate the processes required for adaptive radiotherapy (ART) with a helical tomotherapy system. Method and Materials: ART is a radiation treatment process where the subsequent delivery can be modified using a systematic feedback of the geometric and dosimetric information in the previous fractions. The first step in the process is CT guidance to achieve soft tissue localization. Dose recalculation is used to determine the dose delivered on a daily basis. Deformable image registration is required to place the daily image set, and hence regions of interest, in a common coordinate system. The total doses delivered are accumulated, and the treatment is evaluated relative to the original treatment plan. If significant deficiencies are noted in the dose delivery, plan re‐optimization can be performed to compensate for these deficiencies and make the treatment delivery more closely match the intent of the original treatment plan. Results: Prostate and head and neck cases have been used as clinical examples to test this adaptive strategy. Plan re‐optimization can maintain plan quality with no major degradation in most cases if two or three re‐optimizations are performed during the course of the treatment. Conclusions: ART provides a powerful tool to improve the delivery of radiotherapy, especially in situations where there is significant deformation of anatomy during a course of radiotherapy. In addition, it provides a powerful tool to retrospectively or prospectively examine the doses received by regions of interest, and hence, more accurately define tolerance doses for normal anatomy and curative doses for tumors. Conflict of Interest: Several of the authors are employees of TomoTherapy, Inc., and portions of this research have been funded by TomoTherapy, Inc.
SU‐FF‐J‐20: An Evaluation of User Variability for Image‐Guided Radiation Therapy (IGRT) Shift Determination
Authors: Wolfe M , Patel R , Jenkins T , Mota H , Sibata C , Allison R
Published: July 2006

Purpose: To evaluate the Image‐Guided (IGRT) shift variability calculated by different users using the same patient data and same IGRT process. Method and Materials: IGRT was performed using the Siemens Primatom. This system consists of a Siemens Primus Linear Accelerator and a Siemens Emotion diagnostic CT on rails. Patients have a daily, pretreatment CT scan taken that is transferred to the Siemens Coherence Workstation where the daily CT is fused with the original treatment planning CT. The fusion is performed so that the daily internal organ or critical structure position can be determined and the organ/structure can be aligned to give the same position relative to the isocenter that was determined from the treatment plan. A shift in the x, y and z directions are made to facilitate this alignment. Four users retrospectively calculated the shifts required for an IGRT patient using the same CT data set and the same IGRT process. The treatment area for the patient was the prostate gland and a total of 39 daily shifts were performed. Results: The maximum variation on any one day was 0.90cm in the right/left direction, 1.10cm in the superior/inferior direction and 0.93cm in the anterior/posterior direction. The averages of the maximum daily variations were 0.39cm, 0.54cm and 0.55cm respectively. Conclusion: There are multiple systems that will perform IGRT but the advantage to using CT‐on‐rails systems is the high soft tissue resolution you get from the diagnostic CT sets. The higher resolution allows the user much more information that can be included in the shift evaluation. Our results show the user variability to be acceptable but when implementing this type of IGRT, user variability must be considered.
SU‐FF‐J‐21: An External‐Marker Based Non‐Respiratory Body Motion Monitoring System
Authors: Jin J , Ajlouni M , Ryu S , Chen Q , Li S , Movsas B
Published: July 2006

The development of new technologies has leaded a trend of tighter target margin and longer treatment procedures in the new era of image‐guided radiotherapy. This prompts a concern of potential body motion of a patient during the treatment, especially for stereotactic body radiosurgery. The purpose of this study is to develop a technique to monitor the non‐respiratory motion of a patient, separated from the relatively large respiratory motion. BrainLab ExacTrac system is used as the platform for the study. Multiple infrared external markers are placed on a patient's chest and abdominal surfaces. The position of each marker is monitored with two infrared cameras. The motion signal of each marker, which is the mixture of respiratory and non‐respiratory motions, is recorded. The markers on the chest surface show much smaller, but correlated respiratory signals than those on the abdominal surface. The non‐respiratory component can be derived from the motion signal at the chest surface subtracting the respiratory component represented by the motion signal at the abdominal surface. A computer program has been written to calculate the two motion components in real‐time and was retrospectively tested in patients enrolled in a 4D‐gated‐CT protocol. Total of 24 patients were tested. The duration of recorded motion signals ranged from 10 to 25 minutes for different patients. The extracted non‐respiratory motion signal showed reduced respiratory ripples of less than 0.5 mm for most of the patients, with the maximal ripple of about 1.2 mm. It also showed slow‐drifts as well as some sharp spikes or irregular fluctuations. The slow‐drifts were <1.5mm for 8 patients, >1.5mm and <2.5mm for 6 patients, >2.5mm and <3.5mm for 5 patients, and >3.5mm for 3 patients with maximal drift of 6.5mm. This result suggests that monitoring non‐respiratory motion during treatment might be necessary.
SU‐FF‐J‐22: An Image Based Statistical Shape Model and Its Application in Radiotherapy Margin Design
Authors: Zhou S , Yan H , Wang Z , Yoo S , Das S , Yin F , Anscher M , Marks L
Published: July 2006

Purpose: A novel imaging based model is proposed to describe the stochastic nature of the shape and location of a volume of interest (VOI). Based on the VOIs in sequential patient images, the model can predict the probability that a specific point will belong to the VOI. An application of the model is in customized radiotherapy margin design. Methods: N sequential patient images taken on‐board or online contain all VOI information immediately before or during the treatment sessions. Typically these images are already registered in the radiation device coordinates, a signed distance transform (SDT) will be applied to the VOI boundary in each image to generate a distance map d(r⃗). The sign of d(r⃗) indicates whether the point r⃗ is inside (negative) or outside (positive) the VOI. The VOI shape/location random variation around its mean will propagate through SDT into d(r⃗). It is reasonable to assume that d(r⃗) is Gaussian and its measured values are independent from each other. Consequently, obeys Student's t‐distribution, with N − 1 degrees of freedom. Here d̄(r⃗) μ(r⃗), and s(r⃗) are the sample mean, the expected mean, and sample variance of d(r⃗). By definition of level‐set theory, before any more measurement, a point belongs to the expected VOI if and only if μ(r⃗) ⩽ 0. The probability that a point x⃗ belongs to the VOI can be estimated by . When the VOI is clinical tumor volume (CTV) we can use to design our radiation field margin after a cut‐off coverage probability p is specified. All points in space with are included as part of the expected CTV. Thus we effectively generated a planning tumor volume (PTV). Conclusion: The model has been tested on real clinical cases. The results show that it is robust and easy to use. The customized probability/imaging based non‐uniform margin obtained through this model should be extremely useful in image guided radiation treatment.
SU‐FF‐J‐23: An Image‐Intensity Modification Method to Deal with Non‐Correspondence Problem in Deformable Image Registration of the Gaseous Rectum
Authors: Gao S , Zhang L , Wang H , de Crevoisier R , Kuban D , Mohan R , Dong L
Published: July 2006

Purpose: The goal of this study is to develop an image intensity modification method together with the intensity based deformable registration algorithm for auto‐segmentation of the rectum on daily CT images. In CT‐guided prostate cancer radiotherapy, the planning CT image may contain an empty rectum while there may exist bowel gases in the rectum on any given treatment day (daily CT). The intensity based image registration algorithms alone were insufficient to produce the correct spatial transformations for all objects, especially for the rectum since there was no one‐to‐one correspondence in the gaseous region. Material and Methods: In this study, we proposed a diffusion‐based deformable image registration algorithm combined with an automatic intensity modification method that introduces artificial gas pockets in the planning CT based on prior knowledge of the previously contoured rectum. This will allow for the establishment of correspondence between the two CT images. A multi‐grid method was used for solving the nonlinear partial differential equation for the displacement field, and this displacement field was used to map the manual rectum contours from the planning CT to the daily CT. 30 CT images with the largest bowel gas fillings from 15 prostate cancer patients were chosen to test the algorithm. Results: The intensity modification technique is demonstrated to be effective in correctly delineating the daily rectum. Compared with the deformable image registration method without rectum image modification, the average volume overlap index was improved from 50.6% to 71.2%. This was visually verified by overlaying the segmented contours onto the daily CT images. Conclusion: We developed an effective auto‐segmentation technique for rectum using a deformable image registration algorithm combined with an image intensity modification method. The approach is fully automatic and capable of handling the special non‐correspondence problem in CT images of prostate cancer patients.
SU‐FF‐J‐25: An Optimized Dose‐Based Patient Alignment Method for On‐Line Adaptive Radiotherapy
Authors: Pan Y , Lu W , Ruchala K , Chen M , Chen Q , Kupelian P , Langen K , Meeks S , Olivera G
Published: July 2006

Purpose: To develop an on‐line patient alignment procedure that fully utilizes the CT guidance and dose verification feasibility in image guided radiotherapy. The new patient position is selected to optimize the plan that is evaluated using the daily contours created based on deformable image registration. Method and Materials: Before a treatment fraction is delivered, a CT image of the patient in the treatment position is obtained. The couch is adjusted to match the planning CT image via on‐line image guidance. Verification dose is calculated using this daily image. A deformable registration between the planning image and the daily image is performed and the ROIs are automatically re‐contoured on the daily image. The daily dose is mapped back to the planning frame and then accumulated with the previous fraction dose. The new patient position is chosen via a procedure that optimizes the plan evaluated using the daily ROIs. The whole procedure entails the sequential execution of the following tasks: daily CT, CT‐guided patient setup, deformable registration and automatic re‐contouring, deformation of dose back to reference CT, dose‐based patient position optimization, and plan evaluation using cumulative and daily doses. Results: The new couch alignment procedure was validated on clinical prostate cancer data that includes a planning CT image and 17 fraction CT images (256×256×47) with resolution of 0.1875×0.1875×0.3cm3. The whole procedure was completed in a few minutes. The DVH results indicated improved sparing of the sensitive structures and better target coverage. Conclusion: The new dose‐based patient alignment procedure is an advancement to the image guidance alignment alone. Notable improvement in delivery dose can be achieved for certain types of treatment sites such as prostate cancer where the inter‐faction positions of target relative to sensitive structures are not well correlated with the positions of rigid structures and are difficult to predict.
SU‐FF‐J‐26: Analysis of 10,327 Pre‐Treatment Ultrasound Localizations for 387 Prostate Cancer Patients Treated with Conformal 3D External Beam Radiation Therapy
Authors: Parker W , Poli E , Patrocinio H , Souhami L , Campos L Lucente , Podgorsak E
Published: July 2006

Introduction: Daily 2D ultrasound‐based target localization is routinely used for the patient setup in treatment of localized prostate cancer with external beam radiation therapy. A statistical analysis of a large data set can provide insight into target margin definition. Methods and Materials: Data from 387 patients treated between 2001 and the end of 2005 was retrospectively analyzed. Every patient in the study received daily pretreatment localization resulting in a total of 10,327 localizations, each comprising an isocenter shift in 3 directions: anterior‐posterior (AP), right‐left (RL), and superior‐inferior (SI). The mean shift for each direction for each patient was computed from daily treatment records, and a mean of the means was used in the analysis. The standard deviations (SD) for each direction were also computed for each patient and averaged. The data was statistically verified for normality. The mean shifts represent systematic uncertainties in the patient setup, and the SD represent the random variations. Results and discussion: The mean distances required for shifting the target to the required position were 6.1 mm posterior (4.4 mm SD), 2.1 mm superior (4.5 mm SD), and 0.5 mm right (3.6 mm SD). The 6.1 mm shift posterior is indicative of a non‐negligible systematic uncertainty. There are several sources of this uncertainty, the major one being the difference in patient setup and procedures between the CT simulation and the treatment room. Conclusion: Our study has revealed systematic inter‐treatment uncertainties. The results support the use of up to a 15 mm PTV margin to encompass the CTV for 95% of our sample, if the ultrasound localization system were not used.
SU‐FF‐J‐27: Analytical Quality Assurance Criteria For CT‐MRI Mutual Information Image Fusion
Authors: Hanley J , Rebo I , Barbiere J , Ingenito A
Published: July 2006

Purpose: To use point‐based error metrics as an analytical criterion for CT‐MRI mutual information (MI) image fusion. Method and Materials: A commercially available MI algorithm was used to fuse CT and MRI image sets for 5 patients. Three corresponding anatomical landmarks were manually identified on CT and MRI to initialize the fusion algorithm. All landmarks, designated A(CT) and A(MRI), were identified by a single expert user. A program was developed to extract the CT and MRI point coordinates, scaling factors and homogenous transformation matrix M from the commercial system. The parameters were used to calculate the “ideal” MRI coordinates, A'(MRI) = M*A(CT), that analytically always produce zero documented error by the manufacturer's software. The difference between the ideal calculated A'(MRI) and the user indicated MRI data set A(MRI) was then analyzed in terms of standard point‐based error metrics, Fiducial Localization Error (FLE) and Fiducial Registration Error (FRE). The program also performs the inverse transformation, A'(CT) = M‐1*A(MRI), into CT space for a similar error analysis. Results: The FLE was determined, by statistical analysis in the form of the repeated digitization of the anatomical landmarks by the same expert user, to be 0.6mm (+/− 1 pixel). The range of FRE for the 5 patients was 2.2 mm to 2.5 mm. Visual inspection of the MRI points transformed into CT space clearly indicated that the fusion error was as much as 20% of the cone diameter for small treatment cones and therefore clinically significant. Conclusion: FREs as large as 2.5 mm are dosimetrically significant given that typical dose gradients in stereotactic radiosurgery are 10%/mm. In addition to being representative of the performance of the MI fusion, FRE should be considered when determining clinical target margins for stereotactic target delineation.
SU‐FF‐J‐34: Can Functional Imaging Be Used to Individualize Adaptive Radiation Therapy for Non‐Small Cell Lung Cancer?
Authors: kong f , Frey K , Gross M , Feng M , Fernando S , Kessler M , Chetty I , Ten Haken R , McShan D , Normolle D , Tatro D , Hayman J , Kalemkerian G , Lawrence T , Eisbruch A
Published: July 2006

Background/purpose: To determine the changes in tumor and lung function during the course of radiation and their potentials in adaptive radiation therapy for non‐small cell lung cancer (NSCLC). Materials/Methods: FDG‐PET‐CT and Ventilation/perfusion (V/Q) SPECT were acquired prior to and after the delivery of 45 Gy during the course of radiation in 15 patients with NSCLC. Tumor activity was measured by relative standard uptake value (RSUV). V/Q SPECT was evaluated blindly by radiobiologist, through comparing to healthy normal controls. Results: After 45 Gy radiation, the mean RSUV decreased from 4.6±1.9 to 2.1±1.0 for primary tumors (p<0.0001) and from 3.2+1.3 to 1.7+0.5 for nodal diseases (p=0.0008). Mean reduction in PET tumor volume was 78% (67–100%). There was 28% (4/15) and 0% (0/15) complete responders on PET and CT, respectively. Three patients achieved a complete CT response at 3 month follow‐up, all of them were PET complete responders at 45 Gy. Boosting after 45 Gy, normal tissue complication probability (NTCP) could be reduced by 50%, V20 by 28%, and mean lung dose by 29% while keeping the total dose constant. Keeping the NTCP constant, dose could be escalated by 50%. Lung functional mapping also changed remarkably at 45 Gy during radiation. Fifteen of 15 patients had V/Q defects at or adjacent to tumor on the baseline SPECT, while 14/15 patients had at least one defect located remotely from tumor. For those defects located adjacent to tumor, 79% improved remarkably, while only 7.9% of the others had notable change (p<0.001). Lung NTCP adjusted by V/Q SPECT obtained during radiation was significantly different from those generated from the pretreatment V/Q SPECT and simulating CT. Conclusions: Tumor and lung functional imaging during the course of radiation may provide useful information for adaptive radiation therapy in patients with NSCLC.
SU‐FF‐J‐36: Commissioning of a Six‐Degree‐Of‐Freedom Robotic Patient Positioning System in a Proton Gantry
Authors: Allgower C , Farr J , Mascia A , Schreuder A , Hsi W
Published: July 2006

Purpose: To report on commissioning of a robotic patient positioning system with six degrees of freedom and three digital radiographic panels in a gantry for proton radiotherapy. Method and Materials: A new proton gantry with a robotic patient positioner was commissioned in early 2006. The patient positioning “couch” is a Motoman UP200 industrial robot with six degrees of freedom. Image‐guided patient positioning is done with three digital radiographic panels and the DIPS software system. DIPS is in use elsewhere, but this was the first time it is used with three X‐Ray sources and panels instead of one or two. The beamline and gantry‐90 panels are mounted on retractable arms, and an additional gantry‐axis panel swings down from above the patient and does not rotate with the gantry. We believe this was the first time an industrial robot was used for patient positioning in a proton gantry. The presentation includes in overview commissioning methods, which involve theodolites, room lasers, and testing with phantoms. Results: The patient positioning system meets tight clinical specifications demanded for proton radiotherapy. It is capable of correcting patient position in all six degrees of freedom, namely position in X/Y/Z, pitch, roll, and rotation about the vertical. The first patient treatment with this system will have taken place shortly prior to the 2006 AAPM meeting. Conclusion: This patient positioning system is unique, and provides greater degrees of freedom to adjust patient position than conventional ones. It is early to judge its clinical performance just as it comes online, but we are optimistic about the outcome.
SU‐FF‐J‐37: Comparison Between CT‐Based and Ultrasound‐Based Localization for Prostate Patients
Authors: Paskalev K , Feigenberg S , McNeeley S , Horwitz E , Price R , Wang L , Konski A , Ma C , Pollack A
Published: July 2006

Purpose: Prostate cancer is often treated with intensity‐modulated radiation therapy (IMRT) that provides very steep dose fall‐off outside of the target volume and therefore requires precise alignment. In this report, we compare ultrasound (U/S) and CT localization, and evaluate the uncertainties of the two modalities. Method and Materials: A total of 19 prostate patients (275 alignments) were included in the study. The prostate was localized with the BAT U/S system (Nomos, Cranberry, PA). CT scans were performed with the Primatom CT‐on‐Rails system (Siemens, Concord, CA). The two alignment techniques were identical: the simulation contours of the prostate, proximal seminal vesicles, bladder, and rectum were aligned with a pre‐treatment image. The random uncertainty of the CT system was estimated based on intra‐user variability, and a simple mathematical model of the motion of radio‐opaque markers. Then the random error of the ultrasound alone was calculated. Results: The systematic differences between (U/S) and CT alignments were (in mm): 0.3 (lateral), 0.4 (AP) and 0.3 (longitudinal). The random differences between the two modalities (one standard deviation) were (in mm): 2.2 (lateral), 2.2 (AP) and 2.4 (longitudinal). The estimated ranges of random uncertainties of the CT alignments (one standard deviation) were (in mm): 0.9 to 1.2 (lateral), 0.7 to 1 (AP), and 1.2 to 1.5 (longitudinal). Based on these results, the calculated ranges of random uncertainties of the U/S alignments were (in mm): 1.8 to 2.0 (lateral), 2.0 to 2.1 (AP), and 1.9 to 2.1 (longitudinal). Conclusion: There was a strong correlation between the extent of prostate inter‐fraction alignments using ultrasound and CT. The localization of the prostate had a total uncertainty (two standard deviations) of 2 to 3 mm when using the Primatom CT‐on‐Rails and around 4 mm when using the BAT system.
SU‐FF‐J‐38: Comparison of Different Image‐Guided Setups for Radiotherapy of Prostate Cancer
Authors: Feng Y , Yi B , Patel S , Kwok Y , Yu C
Published: July 2006

Purpose: To compare different methods of image‐guided daily setup for prostate cancer treatment. Method and Materials: 10 CTs were acquired on non‐consecutive treatment days for 20 patients receiving radiation therapy of their prostate cancer under an IRB approved protocol. One physician contoured the prostate, rectum and bladder for all scans. 3 different patient setup methods were compared dosimetrically: 1) laser‐skin mark alignment; 2) 2D bony landmark alignment; and 3) prostate center‐of‐mass alignment. A commercial planning system (Panther, Prowess, Inc.) based on the Direct Aperture Optimization was used for the initial and subsequent planning and analysis. For each patient, the original plan using the first CT set was copied to the subsequent 9 CT sets in 3 different ways based on the setup methods. Dose distributions and DVHs were compared using simple averaging of 9 samples. Results: So far we have completed the analyses for 6 patients. Average patient shifts needed after laser alignment were: Left‐Right(Lt‐Rt): 0.37±0.27cm, Superior‐Inferior(Sup‐Inf): 0.33±0.25cm and AP‐PA: 0.08±0.09cm with bony landmark‐based alignments. The shifts based on the center of mass were: Lt‐Rt: 0.4±0.29cm, Sup‐Inf: 0.08±0.11cm and AP‐PA: 0.2±0.21cm. Three measures were used for the comparisons: 1)PTV getting the prescription dose of 75.6Gy; 2) rectal volume getting 60Gy; and 3) bladder volume getting 65Gy. These measures averaged 100%, 13.2% and 16.6% in the original plans. With lasers alignment, these measured changed to 88%, 17.0% and 20.7% respectively. With 2D bony landmark alignment, these three measures were 90.3%, 20.9%and 24.8% respectively. With volumetric image guidance, they were 93.0%, 16.6%, and 17.8% respectively. Conclusion: Significant plan degradations by reducing target coverage (up to 12%) and increasing normal tissues dose were observed with conventional skin mark‐based alignment. Daily bony landmark‐based setup only improved marginally. Rigid‐body volumetric alignment of the PTV showed the least degradation of the original plan.