bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐C‐330A‐05: Segmentation of Radioactive Seed in 3D Ultrasound Images for Intraoperative LDR Prostate Brachytherapy
Authors: Wei Z , Fenster A
Published: July 2006

Purpose: Develop and evaluate an algorithm to automatically localize implanted radioactive seeds in 3D ultrasound images for dynamic intraoperative low dose rate (LDR) brachytherapy procedures, in which all phases of the procedure are performed in one session to deal with variability in the current prostate brachytherapy. Method and Materials: Intraoperative seed segmentation in 3D TRUS images is achieved by performing a subtraction of the image before the needle has been inserted, and the image after the seeds have been implanted. The seeds are searched through a thresholding operation in a “local” space determined by the needle position and orientation information, which are obtained from a needle segmentation algorithm. To test this approach, 3D TRUS images of the agar and chicken tissue phantoms were obtained. Within these phantoms, dummy seeds were implanted. The seed locations determined by the seed segmentation algorithm were compared with those obtained from a volumetric cone‐beam flat‐panel micro‐CT scanner and human observers. Results: Evaluation of the algorithm showed that, the rms error in determining the seed locations using the seed segmentation algorithm was 0.98mm in agar phantoms, and 1.02mm in chicken phantoms. In both agar and chicken phantoms, 100% of the implanted seeds were correctly identified using the seed segmentation algorithm. Conclusions: The seed segmentation algorithm is insensitive to different materials, as the errors of the algorithm are almost the same in agar and chicken phantoms. This work indicates the potential to achieve an intraoperative post‐implant dosimetry. Integration of this algorithm into a clinical brachytherapy system is now ongoing and clinical testing with patients will take place in the near future.
WE‐C‐330A‐08: An Efficient Morphometric Skull Atlas for Image Guided Radiotherapy
Authors: Barbiere J , Tuna M , Rebo I , Hanley J
Published: July 2006

Purpose: We describe an efficient method to extract the outer skull features from CT transaxial slices for use in IGRT. Method and Materials: A Bezier curve B(t) was fit to four sections of the outer skull on CT slices at 0.3cm spacing. B(t) is a parametric equation defined by two anchor points (A1,A2) and two control points (C1,C2) such that for 0⩽t⩽1. The parameter t is sampled to create a sequence of points at 0.3cm interval. The atlas consists of all the Bezier points and can be transformed by rotation R and translation T such that . Thirty‐two points on the anterior‐posterior and right‐lateral Portal Images are digitized for analytical computation of setup error. The position and orientation (i.e. pose) of the atlas with the minimum Hausdorff Distance (HD) between the PI points and the outer projected atlas contour determines the homogenous transformation. Results: Manual draw‐by‐wire technique can take up to 15 minutes per slice. The total time is reduced by 50% for similar size patients in nearly identical positions. The overall accuracy was determined to be 0.15 cm. A semi‐automatic technique with improved accuracy of 0.1 cm was investigated using simulated annealing. An automatic algorithm using monochromatic bit maps with edge detection was also evaluated. For 30 CT slices, the complete atlas is defined by only 360 points. Setup error for a clinical case was measured and the effects of pure rotation mimicking translation quantified. Conclusion: We have demonstrated that a series of four piecewise continuous Bezier curve segments can accurately extract the outer skull feature from a CT transaxial scan. A patient specific atlas can be quickly morphed from the generic atlas. The atlas has been shown to be clinically useful for 3D analysis of setup error and theoretical quantitative analysis of pure rotation.
WE‐C‐330A‐10: Brightness‐Based Methods for Correcting Beam‐Former Sound Speeds
Authors: Al‐Sadah J , Zagzebski J
Published: July 2006

Purpose: The speed of sound (SOS) varies among patients and spatially within a patient. Differences between the SOS assumed in the beam former and that of tissue defocuses B‐mode images. A global effective SOS value can be chosen to maximize image quality. This study investigates brightness based methods for SOS corrections. Method and Materials: The beam former assumed SOS in a Siemens Antares machine was varied while imaging two phantoms having different SOS's (ATS539‐1440m/s and RMI403‐1540m/s). Three methods were used to quantify resultant image quality changes: visual inspection, zeroth order statistics over a region of interest (ROI) and axial/lateral variation of echo signals arising from discrete reflectors. Peak brightness (PB), mean brightness (MB) and mean of brightness squared (MBS) were measured. Results: Visual inspection showed image sharpness improvement at an appropriate SOS. The optimal SOS values correlate with phantom specifications, but are lower (30–70m/s). Operating conditions affect the optimal SOS. The brightness varies partially due to the fractional overlap of the transmission/reception focal zones, drifting apart with depth.

MBS over a ROI proved superior to MB in distinguishing an optimal SOS. Both measures suffered drift problems with SOS for ROI's far from the transmit focus. Including structures in the ROI affects the ability to generate an SOS peak.

The lateral extent of a bright spot/glint selected either visually or by a simple search, varies with the assumed SOS. PB and MBS of line signals showed a peak around the optimal SOS. Axial signals are more robust. The maxima at glints result in minima for neighboring axial lines demonstrating good focusing. Conclusions: Visual inspection and glint analysis yield consistent SOS's that improve image quality. SOS accuracy for diagnostic use is limited due to effects of operating conditions of the machine and needs further investigation.
WE‐C‐330D‐02: Image Science and CAD: In Pursuit of a Fundamental Theoretical Basis for CAD Development
Authors: Nishikawa R
Published: July 2006

Computer‐aided diagnosis is still a very immature field, with very little theoretical framework upon which it is based. This is a major limitation in both developing systems and in evaluating them in a meaningful way. It is clear that in the future CAD will play a greater role in radiology, both as secondary reader and as a primary reader. The current clinical implementation of CAD is as second reader to radiologists. This will shift to CAD being used by a physician assistant and CAD as the primary reader and the radiologist as the secondary reader. Ultimately, CAD will be the only reader, at least for a subset of cases.

However, to increase the development and adoption of new CAD systems, the field needs a better fundamental foundation. This foundation will come from several areas. First, as we gain a better understanding of human observers, we can use this information not only to develop more accurate CAD algorithms, but also importantly, to design CAD systems that can be integrated into the radiologists' workflow more fully. Second, models of CAD techniques need to be developed. In analogy to modeling ideal observers and human observers, much can be gained from modeling CAD schemes. Third, a thorough understanding of the interaction between the image and the CAD technique is needed. For example, if the shape of the NEQ curve of the image receptor changes, can we predict how the performance of the CAD technique will change.

Medical imaging technology is rapidly changing. The current paradigm for developing CAD systems — try different techniques on hundreds of images — cannot keep pace with these changes, especially as new imaging systems are developed, where clinical images are scarce. Our goal should be to develop the field to the stage where it will be possible to model the imaging system's characteristics and then, guided by models of human observer performance, select from an array of image processing, artificial intelligence and pattern recognition techniques a group of techniques that will produce the optimum CAD system.

This talk will present my vision for the future of CAD and what is necessary for the field to make rapid progress.

Educational Objectives:

1. Discuss future roles of CAD as both a secondary and the primary reader.

2. Explain the fundamental limitations of CAD development.

3. Discuss one possible approach to overcoming the limitations in the future.
WE‐C‐ValA‐03: The Use of CT Density Changes at Internal Tissue Interfaces to Monitor Respiratory Induced Lung Tumor Motion
Authors: Gaede S , Carnes G , Yu E , Van Dyk J , Battista J , Lee T
Published: July 2006

Purpose: To describe a non‐invasive method to monitor the motion of internal organs affected by respiration without using external markers or spirometry, to apply the method to construct 4D‐CT datasets, to test the correlation with external markers, and to calculate any time shift between the datasets.

Method and Materials: Ten lung cancer patients were CT scanned with a General Electric Fast 4‐Slice CT scanner operating in ciné mode. An external signal was also acquired simultaneously using the Real‐Time Position Management (RPM) Respiratory Gating System (Varian Medical Systems). We retrospectively reconstructed the raw CT data to obtain consecutive 0.5s reconstructions at 0.1s intervals to increase image sampling. We defined regions of interest containing tissue interfaces that move due to breathing on each axial slice and measured the mean CT number as a function of respiratory phase. We constructed 4D‐CT data sets by retrospectively sorting each image set based on the respiratory phase determined by the mean CT number curve. The external marker and tumor motion were directly correlated using the sample coefficient of determination, r2. Any time shift between the two data sets was calculated by shifting the tumor motion curve until r2 was maximized. Results: Only three of the ten patients showed correlation higher than r2=0.80 between tumor motion and external marker position. However, after taking into account time shifts (ranging between 0s and 0.4s) between the two data sets, all ten patients showed correlation better than r2=0.8. Conclusions: 4D‐CT acquisition using an internal method improves the temporal registration of CT images affected by respiratory motion without the need for external markers or spirometry. A non‐invasive method to directly correlate the motion of external markers and internal organs can be used to help guide decisions regarding the validity of the RPM system for respiratory gated radiotherapy on a patient‐specific basis.
WE‐C‐ValA‐05: Comparison of Thermocouple and Spirometer for Monitoring Patient Breathing
Authors: Ha J , Yi B , Yu C
Published: July 2006

Purpose: To show the feasibility of using a thermocouple for monitoring patient breathing and to compare its breathing signal with that of a spirometer. Method and Materials: A mask covering the nose‐and‐mouth region was used to channel the subject's breath to a K‐type thermocouple (TC) and a spirometer. Two different placements of the TC were studied: either it was inserted through a side hole of a plexiglass tube connecting the mask and spirometer or in the oxygen inlet of the mask. This setup allowed simultaneous readings of the temperature and air volume in synchrony. The temperature change is a response to the amount of heat deposited to or taken away from the TC junction. Both signals were collected at the sampling rate of 100 KHz using a data acquisition board. The acquisition program was written in LabWindows. Results: The TC temperature and measured air volume are found to be highly correlated at the two locations. When placed in the oxygen inlet away from the direct inhale/exhale air streams, the sensing temperature shows a cubic dependence on the flow rate. When placed in the plexiglass tube where it was more directly exposed to the inhale air, the temperature exhibits some hysteresis on the flow rate. At both locations, the temperature signals show no drift for 10 minutes of breathing. Conclusions: The proposed TC system can be used as an external surrogate to monitor patient breathing at both TC locations. It has the advantages of spirometry in that it directly responds to the lung air flow. The setup is very easy and has no setup error. However, it does not have the drift problem that plagues spirometry. It is also relatively inexpensive. All these qualities make it attractive and suitable for respiratory gating or tracking to deliver external beam radiation therapy.
WE‐C‐ValA‐06: Characterizing and Modeling Patient Respiratory Patterns for Radiation Therapy
Authors: Repp J , Lu W , Hubenschmidt J , Parikh P , Mutic S , Bradley J , Low D
Published: July 2006

Purpose: Lung tumor breathing motion is a function of both the breathing depth (tidal volume) and breathing rate (airflow). Treatment planning for lung tumors will require a patient‐specific tumor motion model. An understanding of the patient's typical breathing cycle will be critical to accurate treatment planning predictions for linear‐accelerator gating or tracking. This work examines patient‐breathing characteristics to determine the patterns and stability of the breathing cycle. Method and Materials: A total of 34 patients (with and without lung cancer) were scanned with a previously described 4DCT protocol under synchronized tidal breathing monitoring. We examined the scatter plot of air flow against tidal volume for the entire scan session. A 2D histogram was then generated by calculating the frequency of data points falling into each tidal volume‐airflow window. The 2D histogram depicted the probability that the patient breathed at certain tidal volume and air flow window. We evaluated the breathing consistency of the three patients with multiple scans. Results: There was no significant differences in the breathing period (P=0.11) or in the peak‐to‐peak amplitude (P=0.22) between patients with lung cancers and patients with upper‐abdomen cancers. The 2D histogram revealed two different breathing patterns: patients who spent more time breathing at the end of exhalation (20 patients), exhibiting a characteristic volume‐flow curve, and patients who spent the majority of time inhaling and exhaling (14 patients). The latter patients did not spend any appreciable amount of time between successive breaths. For the three patients with two sessions, the mean frequency difference between corresponding tidal volume‐airflow windows was <0.3%. Conclusion: We characterized patient breathing by examining the tidal volume‐airflow plot and histogram. The results showed two different breathing patterns suggesting that not all patients are appropriate for gated radiotherapy. All three patients showed high consistency in two scan sessions.

Supported by NIH R01CA96679.
WE‐C‐ValB‐04: Magnetic Resonance Spectroscopy Detects Metabolic Changes Upon Chemotherapy of Human Non‐Hodgkin's Lymphoma Xenografts
Authors: Lee S , Huang M , Nelson D , Pickup S , Poptani H , Delikatny E , Glickson J
Published: July 2006

A preliminary multi‐institutional study has recently demonstrated that ratios of the hosphomonoesters, phosphoethanolamine plus phosphocholine, to NTP of human non‐Hodgkin's lymphoma (NHL) easured by 31P MRS before initiation of therapy can identify about 2/3 of the patients who will not exhibit a complete local clinical response. These patients should be encouraged to undergo more aggressive alternative therapy, which entails some risk of mortality but also offers hope of response, remission or cure. However, the limited sensitivity of 31P MRS limits its application mostly to large, superficial tumors. We have, therefore, been developing much more sensitive 1H MRS and MRI methods to examine smaller tumors. Here we report studies of mouse xenografts of the most common form of human NHL and the only form that exhibits cures (in about 1/3 of the patients) — diffuse large B‐cell lymphoma (DLCL2). In vivo 1H MRS using a selective multiple quantum coherence pulse sequence (Sel‐MQC) detected decreases of lactate and total choline in DLCL2 tumors treated with three cycles of CHOP (cyclophospamide, doxorubicin, vincristine, prednisone) chemotherapy with Bryostatin added to suppress expression of the mdr1 gene. Single voxel localized spectroscopy (STEAM) detected decreases in choline and lactate/lipid that accompanied response. These changes correlated decreases in phosphomonesters detected by 31P MRS with tumor growth delay. In vivo data were correlated with data on tumor extracts. Our data suggest that 1H MRS may provide a very sensitive method for detecting early response of human NHL to chemotherapy; 1H MRI studies of response are in progress.
WE‐C‐224C‐02: Preliminary Analysis of ProQura, a Multi‐Institutional Database of Prostate Brachytherapy Dosimetry
Authors: Allen Z , Grimm P , Merrick G , Butler W , Chaudhry U , Mazza A
Published: July 2006

Purpose: To analyze the ProQura database in terms of patient implant sequence number for each institution to determine evidence for a dosimetric learning curve. Materials and Methods: In the ProQura database there are 4,614 patients with postimplant dosimetry implanted at 56 institutions between June 1999 and September 2005. The the mean preimplant prostate volume was 34.5 ± 10.7 cm3, and the mean and median days between implant and postimplant CT scan was 30.4 ± 14.0 and 30 days, respectively. I‐125 seeds were used in 3,071 patients, and Pd‐103 seeds were used in 1,543 patients. Results: The mean V100 was 88.9% ± 8.6% volume and the mean D90 was 101.9% ± 15.1% of the prescribed dose. When analyzed in terms of patient sequence number within each institution, the mean V100 for the first 10 patients was 87.3% ± 9.6% volume, while for the second 10‐patient cohort for each institution, the mean V100 was 88.6% ± 10.1% volume (p = 0.036). Similarly, the mean D90 for the first 10 patients was 98.9% ± 16.8% prescribed dose, while for the second cohort of ten patients the mean D90 was 102.2% ± 16.1% of prescribed dose (p = 0.001). There was little further change in V100 or D90 for subsequent 10 patient institutional groupings of patient sequence numbers. Therefore, the first cohort had a significantly lower V100 and D90 than all subsequent cohorts. The mean monotherapy seed activity per prostate volume was 0.94 ± 0.19 mCi/cm3 for I‐125 and was 4.51 ± 0.94 mCi/cm3 for Pd‐103. The specific monotherapy seed activity fluctuated between cohorts but reached a nadir in the seventh cohort at 0.92 ± 0.18 mCi/cm3 for I‐125 and 4.33 ± 0.87 mCi/cm3 for Pd‐103. Conclusion: Dosimetric quality parameters V100 and D90 improve with experience and approach a plateau after 20 – 30 patients.
WE‐C‐224C‐06: Influence of Air Gap On Dosimetric Characteristics of Uniform and Composite Clinical 90Y Plaques for Dural Irradiation
Authors: Folkert M , Mauceri T , Munro J , Chen G
Published: July 2006

Purpose: A semi‐cylindrical polycarbonate plaque incorporating a 90Y foil has been developed and used to irradiate the dura in 14 spinal tumor patients. It has been hypothesized that inadequate fitting of the irradiator plaque to the dural surface could adversely affect the area of therapeutic dose delivery at the 90% level. A differentially‐loaded composite treatment plaque has been designed to ameliorate potential air gap effects and maximize therapeutic dose delivery. Method and Materials: Two clinical plaque designs were evaluated, including a “standard” plaque containing a single foil of uniform activity, and a “composite” plaque containing a differentially‐loaded 90Y source created by placing a single activated square foil under an activated foil frame of the same outer dimensions in a titanium shell. Two dosimetry phantoms surrounded by a layer of radiochromic film (GafChromic HS) were constructed with radii approximating a perfect fit (matched to inner plaque radius) and a gap fit (80% of inner plaque radius) and irradiated with the two plaques. Results: Analysis of the irradiated film demonstrated that the effective treatment width to 90% of the plaque along the arc in the standard plaque is 65.8% when fitted and 58.1% in the presence of a gap; for the composite plaque, the corresponding treatment widths to 90% are 88.6% when fitted and 69.4% in the presence of a gap. Thus, in the presence of a gap the composite plaque delivers dose at the 90% level to a 19.6% greater arc width than the standard plaque with a gap, and 5.5% greater arc width than a perfectly fitted standard plaque. Conclusion: Differentially‐loaded composite 90Y plaques deliver therapeutic dose to a substantially larger treatment area than standard plaques currently used, and completely resolve treatment area to the 90% level potentially lost to inadequate fit with standard plaques.
WE‐C‐224C‐08: Pre‐Clinical Evaluation of the New Xoft‐AxxentTM Electronic Brachytherapy System
Authors: Turian J , Bernard D , Hu Z , Dickler A , Chu J
Published: July 2006

Purpose: To evaluate the preclinical functionality of the new Xoft‐Axxent™ Electronic Brachytherapy System intended for partial breast irradiation treatment. Methods and Materials: The EB system consisting of: controller, X‐ray source catheter, and the balloon applicator was tested for: graphical user interface functionality, X‐ray generator parameters stability, beam output constancy, source position accuracy, timer accuracy, end effects, and dose distribution versus Ir‐192 source. The safety features and the adequacy of the proposed shielding also have been tested. The system's log files which record the kVp, beam and filament currents were used to make inferences about the stability of the X‐ray generator. Output constancy, timer accuracy, and end effects were measured using a PTW‐34013 ion chamber and phantom. The dosimetric characteristics of the source obtained in a manner consistent with TG‐43U protocol were entered into Plato™‐TPS to compute the dose distributions. Source position verification was performed using manufacturer supplied procedures. Source step size accuracy was independently verified using external markers. The effect of transit time on dose distributions was simulated using low steps and dwell times for the transit positions. Results: The GUI was found to be functional for its intended purposes. The parameters of the X‐ray generator were found to have variations of <0.5%(1σ). Output for single source was constant within 0.7% and for multiple sources 1.6% over the duration of the testing. Source position accuracy was <1.0mm. The timer error and linearity were −2.0s and 0.32%, respectively. Dose distributions show higher inhomogeneities towards the proximal end compared with Ir‐192 distribution. All safety features were found to be operational. Conclusion: During preclinical evaluation the system was found to perform as expected. Minor revisions were proposed and should be integrated in the clinical system.
WE‐C‐224A‐01: Peter Wootton: A Personal and Professional Remembrance
Authors: Kalet I
Published: July 2006

Peter Wootton was a legendary figure in the field of medical physics. He is known for early work on the foundations of dosimetry, for pioneering neutron therapy, for establishing regional medical physics services in the Pacific Northwest, and for many years leading the medical physics training program at the University of Washington. The American Association of Physicists in Medicine (AAPM) was incorporated in 1965, with Peter as a member of the initial Board of Directors, and signer of the organization's articles of incorporation. He also served a term as AAPM President in 1978. Under his leadership, in the early 1980's the University of Washington acquired, installed and operated what was then the most sophisticated neutron therapy facility in the entire world. This facility, still in service over 20 years later, continues to be state of the art. Peter was a superb teacher, and left a legacy of many M.S., Ph.D. and postdoctoral trainees, of which the author is one. His kind and wise spirit is greatly missed and remembered with awe and appreciation.

Educational Objectives:

1. Understand the role of Peter Wootton in the development of the field of medical physics.
WE‐D‐330A‐03: PO2 Measurements in Animal Tumors Using An Image‐Guided Robotic System
Authors: Chang J , Wen B , Kazanzides P , Zanzonico P , Finn R , Ling C
Published: July 2006

Purpose: To develop and evaluate an image‐guided robotic system for measuring pO2 in animal tumors. Method and Materials: The robot consists of an X‐Y horizontal platform holding the rodent bed, a dual‐axis vertical arm for positioning the measurement probe and cannula, and fiducial markers for registering the coordinates of the imaging and robotic systems. Anesthesized and immobilized tumor‐bearing rats are injected with the hypoxia tracer 18F‐FMISO and imaged in the rodent bed using an animal PET scanner. The reconstructed PET images are then uploaded into the robot computer, the rodent bed affixed to the X‐Y platform, and the coordinates of the robot and PET registered. Based on the tumor hypoxia image displayed on the robot computer, motion of the robotic X‐Y platform and vertical arm are coordinated to guide the positioning and percutaneous insertion of a probe (OxyLite‐Optronix) to measure pO2 at various locations in the tumor. The pO2 readings (cps/voxel) are then compared to the respective image intensity of the measurement points. Results: The registration accuracy between the robot and image coordinate system was better than 0.2mm. Although the 18F‐FMISO in the bladder produced characteristic starburst artifacts in the surrounding, low‐intensity regions, we successfully measured the pO2 for three tracks. The 18F‐FMISO image voxel values were found to be inversely correlated with the intra‐tumoral pO2 of the three tracks with (Pearson product moment) correlation coefficients of −0.899, −0.420 and −0.857. The scatter plot of pO2 vs. image intensity resembled a sigmoidal, rather than a linear relationship. Conclusion: PET‐guided pO2 measurement is feasible using this prototype image‐guided robot system. To our knowledge, this is the first system of its kind — allowing direct point‐by‐point correlation of physiological probe measurements and image voxel values or, more generally, a physical action at a set of anatomic points identified on a preoperative image.
WE‐D‐330A‐04: Serial Flat Panel Computed Tomography Quantification of Bleomycin‐Induced Murine Lung Damage In Vivo
Authors: Cavanaugh D , Travis E , White R , Gladish G , Cody D
Published: July 2006

Purpose: To compare methods of quantifying lung damage based on noninvasive flat‐panel CT images with the standard method based on histologic section analysis. Method and Materials: Lung damage was induced in mice with bleomycin and damage progression followed with fpCT on days 10, 14, and 21 and with postmortem histological examination on day 21. Ten mice, five control and five treated, were scanned under breath hold with flat‐panel CT (fpCT). Prior to scanning, a tail vein catheter was inserted for administration of IV contrast. The percent lung damage calculated from fpCT (PLDfpCT) image data sets was compared to that obtained from sequential histological sections (PLDH). Results: IV contrast was helpful in separating vessels from regions of lung damage. PLDfpCT calculations were on average 2 times greater than PLDH calculations. Linear trendlines were fit between PLDH and PLDfpCT to all data (n=10) and then to only the treated mice (n=5); the resultant R2 values were 0.87 and 0.89, respectively. The fpCT scans allowed for observation of the progression of damage over time versus the single snapshot sampled with histology. Less damage was observed at day 14 than at either day 10 or day 21, which could be due to a transition from an acute inflammatory reaction to inflammation with formation of collagen. Conclusion: The quantification of lung damage based on fpCT images was strongly correlated to the conventional histological section analysis. Although the overall change in damage is consistent between histology and fpCT the magnitude of measured damage differs which may be explained by an inflammatory response throughout the lung which is not detected with histology. A potential strength of these longitudinal studies is the ability to follow individual animals over time to investigate biological affects such as a transition from acute to chronic damage patterns.
WE‐D‐330A‐05: Voxel‐Based MicroCT‐MicroPET Image Registration for Molecular Imaging Study
Authors: Schreibmann E , Cai W , Chen X , Xing L
Published: July 2006

Purpose: Registration of micro‐PET and micro‐CT images is important for the interpretation of multi‐modality images. Here we develop a voxel‐based image registration method to facilitate the co‐registration of multi‐modality imaging of small animals. Method: Rigid image registration (six degrees of freedom: three translational and three rotational parameters) was developed using an open‐source ITK/VTK platform for coregistering micro‐PET and micro‐CT data. Modules importing/exporting DICOM data (binary mask files of contours and image sets) and the scanner specific proprietary microPET/CT/MRI data were also developed. Automated registration procedures based on the normal cross‐correlation (NCC) metric and mutual information were implemented. To better “see” the bony landmarks in microPET, a strategy for enhancing the bone matrix uptake of radiotracer by adding a tracer amount of 18F during the FDG‐microPET imaging was investigated. The convergence behavior of the voxel‐based registration algorithms was analyzed and the global convergence of the calculation was demonstrated. The accuracy of the developed registration algorithm was assessed by measurements using dual‐modality external fiducial line sources incorporated into the mouse cradle. Results: A voxel‐based registration technique has been established for in vivo molecular imaging study. Application of the technique to a number of mice micro‐PET and micro‐CT registrations indicated that an accuracy of better than 0.2 mm is achievable with the help of 18F injection. Without lighting‐up of the bony structures, however, we found that it is difficult to obtain a registration better than 1mm for regular FDG‐microPET. Computationally, the setup based on the NCC metric performs better in comparison with the mutual information approach. Conclusion: A NCC metric coupled with the use of 18F injection allowed us to obtain sub‐millimeter accuracy in microPET‐microCT registration of mice. The robust registration procedure should be valuable for routine molecular imaging application.
WE‐E‐ValB‐03: Challenges and Opportunities in Image‐Guided Era
Authors: Chao K
Published: July 2006

Intensity‐modulated radiotherapy (IMRT) is evolving rapidly; the radiation therapy community has begun to regard IMRT as the future standard of care, rather than as experimental or leading‐edge treatment. The effectiveness and benefit of IMRT have been confirmed in multiple cancers, specifically in head and neck and prostate cancers. However, IMRT adoption rates vary widely and are impacted primarily by the learning curve for clinic staff, capacity, and physician's practice patterns. Because physicians must participate to a much higher degree in planning and quality assurance, their learning curves to acquire necessary knowledge and skills in cross section anatomical images are also steep. Image‐guided radiotherapy (IGRT) or adaptive radiotherapy is an emerging radiation therapy treatment methodology that complements IMRT. IGRT takes tumor and organ motion into consideration and monitor this motion in a near real time mode to make sure radiation is being delivered to the tumor. Furthermore incorporating functional images into management decision‐making has highlighted the future perspective of IGRT. However, to radiation oncology community the explosion of overwhelming technology has created challenges which include the lack of enabling tools to facilitate bench to bedside research, bridge knowledge gap, and improve quality and operational efficiency.
WE‐E‐224C‐01: Dose Reconstruction Quality Assurance for Helical Tomotherapy
Authors: Chase D , Ramsey C , Seibert R
Published: July 2006

Purpose: To determine if the dose calculation accuracy is suitable for the daily dose verification of patient treatment; and develop quality assurance tests for dose reconstruction with a commercial dose reconstruction system. Methods and Materials: Dose reconstruction accuracy was evaluated using MVCT and kVCT images of three test phantoms: 1.) A Electron Density Phantom phantom (Gammex); 2.) A water‐equivalent cylindrical phantom (TomoPhantom), and 3.) an anthropomorphic RANDO phantom. A parotid‐sparing head & neck plan was created for the phantoms. Using the kVCT images, inverse treatment plans simulating clinical prostate and head & neck helical tomotherapy treatments were created. The phantom MVCT images were fused with the kVCT images using a co‐registration algorithm. Planned‐Adaptive software was then used to re‐calculate the doses on the MVCT images. The kVCT‐based and MVCT‐based doses were then exported to the RIT113 Dosimetry System. Accurate dose reconstruction is dependent on the quality of the MVCT images used. As such, a genetic algorithm was developed to ensure proper image fusion and a principle component analysis was used to determine the most influential factors for image quality. Results: Based on the phantom results, the calculation accuracy of MVCT and kVCT images are typically within ±3% of each other. The greatest discrepancy occurs in the high‐dose gradient regions, which is most likely due to slight alignment errors between the two dose files. PCA indicated a correlation with the person performing the machine warm‐up and image quality. This was confirmed as MVCT dose reconstruction suffered due to an individual's error. Conclusions: Based on comparisons of calculated doses in phantom plans, the accuracy of using MVCT image data in dose reconstruction is typically within ±3%, subject to image quality. A process was developed for assessing the image contrast and resolution on a daily basis.
WE‐E‐224C‐02: Investigation of Simple IMRT Delivery to Stage I Lung Cancer Patients with Significant Respiratory Motion Using Respiratory Gated CT Scans
Authors: Reitz B , Colonias A , Parda D , Miften M
Published: July 2006

Purpose: To investigate the use of IMRT for the treatment of stage I lung cancer associated with significant respiratory motion using 4DCT data. Method and Materials: A 4DCT scan ‐ covering a full respiratory cycle in 10 phases ‐ of a patient with a 1.8 cm diameter lung cancer was used to design several static step‐and‐shoot IMRT plans. Three plans were designed: two using snapshots of the tumor (mid‐inhale, full‐exhale), one using the superposition of all phases. Because of the significant tumor motion (maximum excursion of 2.5 cm) the effect of different margins around the CTV were studied. To reduce interplay between the MLC movement and respiratory motion in an ungated delivery, the number of intensity‐levels was minimized while maintaining coverage to the PTV and minimizing dose to OARs. Results: In this case‐study five‐field IMRT plans were generated using 18 MV photons delivering a total dose of 66 Gy in 33 fractions to the PTV. Plans based on snapshot scans of the lung only resulted in full coverage, if large margins (3 cm) were incorporated. All plans based on superimposed scans achieved full coverage, while allowing tight margins and minimizing the dosage to OARs. A small number of intensity‐levels (3–5 per beam) were sufficient for PTV coverage, thereby reducing the risk of unwanted interplay effects between MLC movement and respiratory motion. Conclusion: Using snapshot free‐breathing CT scans for treatment planning can lead to geometrical misses and underdosage of the target volume unless large PTV margins are applied at the expense of increased dose to OARs. Taking the superimposed CT scans of all respiratory phases for treatment planning ensures the full coverage of the tumor volume, without increasing dose to OARs. For this case‐study only a small number of segments were needed, allowing the application of IMRT despite significant tumor motion.
WE‐E‐224C‐03: Advanced Mixed Beam Radiotherapy for Breast and Head and Neck
Authors: Ma C , Li J , Stathakis S , Leal A , DuPlessis F , Fan J , Chen Y , Chen L , McNeeley S , Price R
Published: July 2006

Purpose: This work investigates advanced mixed beam radiation therapy (MBRT) treatment of breast and head and neck cancer using energy‐ and intensity‐modulated electron (MERT) and photon (IMRT) beams. Methods and Materials: The new MBRT system consists of MLCs for both photon and electron beam modulation and associated software for dose calculation, treatment optimization, and beam delivery to ensure superior target coverage and normal tissue sparing. Accurate and efficient dose calculation tools for Monte Carlo based treatment planning, and effective treatment optimization and leaf sequencing algorithms for efficient and accurate beam delivery for advanced MBRT have been developed with the use of existing MLCs. This technique is being implemented clinically for breast and head and neck treatment through pilot studies and clinical trials that are specially designed for dose escalation and hypofractionation. Partial breast treatment is also investigated using advanced MBRT as it is being developed. Results: MBRT uses IMRT to achieve lateral dose conformity and MERT for conformity in the depth direction, which provides excellent target coverage for treatments involving shallow target volumes such as breast and head and neck. Our preliminary results based on 76 patients showed that grade II skin complications were significantly reduced in a hypofractionated breast trial. The whole breast received 20 fractions of 2.25Gy and the tumor bed received an additional 0.55Gy/day concurrent electron boost. The elimination of 10% hot spots in the whole breast volume ensures the whole breast dose to be under 2.5Gy beyond which significant skin complications have been reported in the literature. Conclusions: A set of software and hardware tools have been developed for conformal radiation therapy of shallow targets with much improved target dose conformity and uniformity, adequate skin coverage/avoidance and significant reduction in the dose to the adjacent normal organs and critical structures.
WE‐E‐224C‐04: A New CT Reconstruction Technique for Removal of Streak Artifacts Due to Metallic Dental Fillings and Implants for the Treatment of Head and Neck Cancer with Intensity Modulated Radiation Therapy
Authors: Song Y , Chan M , Burman C , Wang S , Dhawan A
Published: July 2006

Purpose: To remove or reduce the streak artifacts induced by metallic dental fillings and implants in CT images for head and neck patients treated with intensity modulated radiation therapy (IMRT). Materials and Method: A cylindrical phantom was constructed using tissue‐equivalent plastic to simulate a human head. The phantom was filled with distilled water. A piece of 1 cm‐wide half elliptic tissue‐equivalent bolus was attached to a thin circular plastic plate inside the phantom to mimic the gingiva. Two human second molars with metallic fillings were implanted into the bolus on each side. The phantom was scanned on a GE LightSpeed CT scanner with a slice thickness of 2.5 mm. The acquired CT images were first decomposed into spatio‐frequency components using a wavelet transform. The decomposition tree allowed us to examine and characterize different localized frequency information related to undesired artifacts. Once the spatio‐frequency signatures of metal objects were modeled, the corresponding coefficients in the wavelet domain were thresholded using a dynamic thresholding scheme. The thresholded images gave metal objets, which were then superimposed on a neighbor slice. New data were generated by re‐projecting the original slice and superimposed slice. The final image was reconstructed with no or reduced image artifacts due to dental fillings and implants. Results: Comparison of original images to reconstructed images indicates that the streak artifacts were either completely removed or significantly reduced. The structural details near the metal objects were clearly identifiable. The image quality was sufficient for target delineation in IMRT treatment planning. Conclusions: The proposed technique can greatly reduce the streak artifacts induced by metallic dental fillings and implants without sacrifice of spatial resolution. The technique has the potential to significantly improve the accuracy of target and critical organ delineation and dose calculation in the head and neck IMRT treatment planning.
WE‐E‐224C‐06: Differential Smoothing IMRT Planning for Head and Neck Cancer Patients with Mediastinal Involvement
Authors: Schofield D , Tishler R , Court L
Published: July 2006

Purpose: Head and neck cancer patients with mediastinal involvement present a planning challenge. The superior fields are ideal for IMRT but possible interplay effects between leaf and mediastinal motion makes IMRT less desirable for the inferior fields. A new, differential smoothing IMRT technique is compared to matched and extended field IMRT plans. Materials and Methods: The differential smoothing IMRT technique treated the superior portion of the target with 7 fixed, low smoothing rate (LSR) beams while the inferior portion was treated by 3–4 highly smoothed, fixed beams with an overlap region. All beams existed in a single IMRT plan and were optimized simultaneously. This technique was used to plan treatments for three head and neck cancer patients with mediastinal involvement. These patients were also planned using two alternative techniques: (1) A matched field technique, with conformal radiation therapy used for the inferior portion, and an LSR IMRT plan used for the superior portion; (2) An extended field LSR IMRT plan treating the full extent of the disease. The plans were compared dosimetrically. Results: The differential smoothing technique provided homogenous, continuous coverage throughout the target volume while the matched field plan demonstrated discontinuous coverage in the match region. The extended field IMRT plan had coverage comparable to the differential smoothing plan. However, patient and leaf motion could compromise coverage in practice. The average MLC leaf opening in the inferior differentially smoothed beams was 1.5–2 times greater than the average opening in any of the LSR beams (1.55cm for LSR beams verses 3.04cm for highly smoothed beams) thereby potentially reducing the impact of patient motion. Lung DVH's were similar for all three techniques. Conclusion: The differential smoothing technique offers continuous, more homogenous coverage than the matched field method and is probably less susceptible to patient motion than the extended field technique.
WE‐E‐224C‐07: Image‐Guided Helical Tomotherapy for Localized Prostate Cancer: Technique and Initial Clinical Observations
Authors: Ramsey C , Scaperoth D , Seibert R , Chase D , Harris C
Published: July 2006

Purpose: The purpose of this study was to develop a technique for daily CT based IGRT, and to report clinical observations on treatment planning, imaging and delivery based on the first two years of experience. Method and Materials: Patients with previously untreated stage T1 through T3 biopsy‐proven adenocarcinoma of the prostate were considered eligible for treatment with daily CT guided helical tomotherapy. The prostate was targeted daily using megavoltage CT (MVCT) images that were fused with treatment planning CT images based on anatomical alignments. All patients were treated at 2 Gy per fraction to 76 to 78 Gy (mean 76.7 Gy). Results: Thirty‐three prostate patients were planned, imaged, and treated as part of this study for a total of 1266 CT guided fractions. The prostate, rectum, bladder, femoral heads, and pubis symphysis were visible in one or more slices for all 1266 MVCT image sets. The typical range of measured prostate displacement in this study was 2–10 mm (3.4 mm standard deviation) in the anterior‐posterior direction, 2–8 mm (3.7 mm standard deviation) in the lateral direction, and 1–6 mm (2.4 mm standard deviation) in the superior‐inferior direction. The obese patients in this study had a substantially larger lateral variation (8.2 mm standard deviation) due to mobility of the external skin marks. Conclusions: A technique has been developed, and clinical implemented for daily MVCT based image‐guided radiation therapy. The level of conformal avoidance increased with treatment planning experience, and the level of conformal avoidance can be greater than fix‐gantry based intensity modulation.
WE‐E‐224A‐04: Potential and Challenges of Integrated Brachytherapy‐IMRT Planning
Authors: Williamson J
Published: July 2006

Combinations of external‐beam radiation therapy (EB) and brachytherapy (BT) and have been used for many years. Conventionally, the EB and BT components are planned independently and limited to combinations of doses and dose‐time‐fractionation patterns that have been directly validated by clinical outcome studies. Ongoing research in radiobiological modeling, deformable image registration, and quantification of dose delivery uncertainties has the potential to provide the scientific foundation for truly integrated EB‐BT planning that could significantly improve clinical outcomes. First, the complementary strengths and weaknesses of BT and highly conformal EB methods, such as intensity‐modulated radiation therapy (IMRT), will be reviewed. Both IMRT and BT can support high dose conformality. IMRT can treat large surgically inaccessible target volumes with relatively homogeneous dose distributions. Where BT can be surgically realized, large dose fractions can be delivered with much higher geometric precision than with current IMRT delivery techniques. Next, clinical settings where integrated BT‐IMRT can have benefit will be reviewed. One example is definitive treatment of cervical cancer in which IMRT is used to compensate for primary tumor underdosing or normal tissue overdosing by the intracavitary BT insertions as well as for conformal treatment of the pelvic lymph nodes. Finally, the scientific and clinical challenges to integrated BT‐IMRT will be reviewed. For example, in high dose‐rate (HDR) interstitial BT of the prostate combined with IMRT whole pelvic irradiation for intermediate risk disease, a major source of dose‐delivery uncertainty is the conversion from physical‐to‐isoeffective dose needed to account for differences in fractionation.