bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐40: Lung Lesion Tracking Using Fixed‐Spaced Non‐Migrating Fiducial Markers in Robotic Radiosurgery
Authors: Gersh J , Reynolds K , DeWeese M
Published: June 2012

Purpose: With lung lesion treatment being a major indication of the use of the CyberKnife (CK) robotic radiosurgery system (Accuray Inc, Sunnyvale, CA), the ability for the CK's stereoscopic kV imaging system to accurately track implanted fiducial markers becomes vital in the accurate delivery of therapeutic radiation. This study examines a novel fixed‐space fiducial marker delivery system which is capable of delivering two VISICOIL (IBA Dosimetry America, Memphis, TN) non‐migrating fiducial markers simultaneously at a fixed spacing through a single 20‐gauge needle. More specifically, presented herein is a preliminary study which tests the CK'streatment localization system's (TLS) ability to track markers of varying size and spacing, comparing subsequent stereoscopic kV imaging to DRR's generated during the planning stages. Methods: Three markers were placed in an XLT Lung Phantom (CIRS Inc, Norfolk, VA); two markers inserted along a diagonal line in a coronal plane, separated by biocompatible spacersof varying size, and a common third marker being placed in a non‐varyinglocation in a coronal plane anterior to the marker pair. This third marker allows the calculation of rotational and translation corrections. Differentcombinations were scanned, planned, and simulated; 3.5mm‐ and 5.0mm‐ long markers, each 5mm in diameter, were separated by 15mm, 17mm, and 20mm spacers. Results: The TLS system was able to track each of the aforementioned configurations with standard lung imaging parameters.Longer markers were not included in the study since earlier studies showed that without the natural deformation that would occur upon implantation, the length would induce false tracking. Conclusions: This is a necessary firststep in determining the minimum spacing with which the CK's TLS can track, a study which can now proceed with the use of phantom treatments elivered to orthogonally‐overlapping radiochromic film, bisecting a tumor volume which is implanted with this fiducial marker system. Research supported in‐part by IBA Dosimetry America.
SU‐E‐J‐41: Fluoroscopy Based Adaptive Setup Approach for Thoracic Cancer IGRT
Authors: Chen T , Qin S , Jabbour S , Park J , Haffty B , Yue N
Published: June 2012

Purpose: To develop a fluoroscopy imaging based approach that can determine the magnitude and phase variation in respiratory motion against the treatment planning images in order to quantify the online patient setup deviation in thoracic cancer IGRT for the real time adaptive patient positionadjustment. Methods: A numerical phantom was generated to test the strength of the approach. The 2D phantom consist a static outside wall and an inner target moving in temporal pattern similar to the respiratory motion. Four motion parameters: frequency (0.5Hz∼2Hz), amplitude (40∼60mm), position offset (5∼10mm), and phase shift (starting phase 0, 45, and 90 degrees) vary to generate phantom image sets with different motions. White noise of level SNR=5 was added to all phantom images to simulate the impact of clinical image quality. A manifold based machine learning technique was used to construct the respiratory motion model under thestandard condition (frequency 1 Hz, amplitude 50mm, and no position offset and/or phase shift). Then the phase and position shift in other phantom image series were quantified by finding the MAP solution to fit theembedded motion to the standard motion model. Results: The proposed approach can detect the variation in motion patterns between two image sets. The method is insensitive to frequency changes and image noise up to SNR=5, but is very effective at capturing and quantifying the change in motion amplitude, position shift, and also the phase shift. Conclusions: This work proposed an effective mathematical approach to quantify the difference in motion between the pre‐treatment images and the treatment planning images by extraction of the motion model in fluoroscopy images using the machine learning technique. By applying the approach during online patient setup, the positioning deviation can be separated from the respiratory motion and adjusted to minimize the normal tissue toxicity in gated IGRT.
SU‐E‐J‐43: Autotuning Imaging Parameters in X‐Ray Fluoroscopic Tracking for Dose Savings
Authors: Siddique S , Fiume E , Jaffray D
Published: June 2012

Purpose: In fluoroscopy‐guided clinical procedures that involve tracking objects over long treatment times, there is a need for reducing the amount of imaging dose delivered to the patient and the operating staff. In this study, we introduce a feedback metric to minimize tube current while maintaining a targeting precision threshold.Method and Materials: An acrylic sphere (1.6mm in diameter) was imaged at tube currents ranging from 0.5 mA to 0.9mA (1s) at a fixed energy of 50kVp. The images were acquired on a Varian Paxscan 4030A (2048×1536 pixels, 1100 mm source‐to‐axis distance, 1570 mm source‐to‐detector distance). A state feedback metric (tr(C)) based on the current object position was computed and plotted as afunction of the tube current. Next, the sphere was tracked using a particle filter with a bowtie filter (4.3–764mm thickness, Al) in the background. The tr(C) was used a by a PID controller to modulate the tube current in order to maintain a specified precision as the sphere traversed regions of varying thickness corresponding to the bowtie filter. Result: Comparison of thefeedback framework with a similar system employing fixed exposurereveals a dose savings of up to 43% when using an operating uncertainty of 194 mm2. Conclusion: This work presents a relation between tr(C) and thetube current which can be leveraged to reduce imaging dose to patients and staff.
SU‐E‐J‐44: Dual Energy Subtraction Imaging to Improve Tumor Visibility at Oblique Angles
Authors: Hoggarth M , Luce J , Bray T , Block A , Roeske J
Published: June 2012

Purpose: To characterize the contrast improvement of simulated tumors in an anthropomorphic phantom using Dual Energy (DE) subtraction with a clinical on‐board imager (OBI) at oblique angles. Methods: An Alderson lung/chest anthropomorphic phantom with simulated tumors in the thoracic cavity was imaged using a sequential DE imaging methodology. High (120kVp) and low (60kVp) planar images were obtained in pairs every 100 in a full (3600) rotation using the OBI (Varian Medical Systems, Palo Alto, CA). Optimal mAs settings for DE component images were determined byvarying the x‐ray exposure time, while maintaining a constant tube current. DE images were created to best suppress the bone overlaying the simulated tumors. Tumor visibility in DE images was quantified using the Contrast‐to‐Noise Ratio (CNR). The ratio of the CNR from the DE image relative to a single image (standard protocol) was evaluated as a function of gantry angle.Results: CNR was improved with DE imaging by an average ratio of 1.66 over all gantry angles. The greatest improvement occurred at gantry angles where the tumor was obstructed by the ribs alone. More modest improvements were observed where the tumor overlapped other soft tissue structures (such as the heart) or the dense spine, on a given projection. Conclusions: This study illustrates the feasibility of performing DE imaging at oblique gantry angles using a clinical on‐board imaging system. Incorporating DE imaging into clinical practice may allow for verification of tumor position at oblique gantry angles, and may facilitate the development of markerless motion tracking techniques. Supported by a grant from Varian Medical Systems.
SU‐E‐J‐47: Evaluation of the Mismatches Between DRR's and Port Films for IMRT Fields
Authors: Vossler M
Published: June 2012

Purpose: To quantify the frequency and magnitude of mismatches between the MLC shape on the DRR created by the Pinnacle planning system and the corresponding port film MLC shape generated by the Mosaiq record‐and‐verify system for IMRT fields. Methods: A retrospective review was made of the most recent 60 patients to receive IMRT at our clinic. The MLC shape on the DRR created by the Philips Pinnacle planning system for each treatment field was reviewed (573 fields total) and compared with the MLC shape of the port film image, which was generated by the Mosaiq treatment planning system. Results: Of the 60 patients studied, 20 had at least one leaf mismatched between the MLC shape on the DRR and port film (142 of the 573 fields). Of the affected cases, on average 59% of the fields had a mismatch. The affected fields had an average of 6.7 leaves mismatched with a mean discrepancy of 27mm. The average maximum discrepancy for each affected patient was 69mm. Discrepancies were most common for head and neck cancers. Conclusions: The MLC shape Mosaiq generates for the port film is the CIAO, or Complete Irradiated Area Outline, which is the area that is actually treated. The Pinnacle DRR displays the maximum leafmotion, which can be different for larger fields in which the MLC leaves abut within the collimator jaw opening. The discrepancy can create substantially different MLC shapes. The problem can be solved by not filming the MLC shape and only using the films for isocenter placement; however, displaying the area receiving treatment can be a useful safety check, possibly preventing a treatment error. The persons assessing the films must be aware of this issue and evaluate the films carefully.
SU‐E‐J‐50: Measurement of the HVL Value for the 120keV Photon Beam of the X‐Ray Volume Imager (XVI) Using Ionization Chamber, Gafchromic Film XRQA2 and Diode
Authors: Yegingil Z , Cui Y , Giaddui T , Chen W , Xie J , Xiao Y , Yu Y
Published: June 2012

Purpose: The value of Half Value Layer (HVL) is essential in quantifying the ability of an x‐ray beam to penetrate the material being studied. This paper examines the use of three different types of detectors for measuring HVL of the 120keV photon beam of the X‐ray Volume Imager (XVI) cone beam CT system mounted on the Elekta Synergy (Crawley, UK) Linac: ionization chamber, Gafchromic film and diode. The effects of collimator diameters are presented and the chamber tip and chamber horizontalmethods are compared to investigate the source of variations in the measurement of HVL. Methods: The measurements are done in free airboth using an ionization chamber calibrated for absolute dosimetry [University of Wisconsin Accredited Dosimetry Laboratory] and the Gafchromic film dosimeters [XR‐QA2 (International Specialty Products, Wayne, NJ)]. The beam is collimated to the size of the detector to measure the exposed dose. The different thicknesses of the aluminum attenuators are added to beam to measure individual doses every time and repeated until the dose fell to below 50% of the initial unattenuated value. Dose measurements with a semiconductor diode detector [Barracuda MPD (RTI Electronics AB, NJ)] is also carried out. We plotted all results on a semi‐log graph to find HVL value. Results: When the measurements are made using ionization chamber with different collimator diameters we obtained 1.6% difference in HVL values. Measurements with chamber tip and horizontal methods agree with each other to within approximately 1.6% percentage difference. The percentage difference of the HVL values measured using the diode and ionization chamber is about 6.4% and that of using Gafchromic film and ionization chamber is about 8% percent. Conclusions: Gafchromic films and diodes can be used to measure HVL value of 120 keV photon beams. Recommendations for consistency in HVL measurements are provided.
SU‐E‐J‐55: Development of a Novel Cableless Radiolucent RF Coil for MR‐Guided Radiation Therapy (MRgRT™)
Authors: Hebb M , Winter J , Champagne K , McCurdy B , Zhu H , Petropoulos L
Published: June 2012

Purpose: To demonstrate the feasibility of a novel radiotherapy‐compatible cableless radiofrequency (RF) coil for an MR‐guided radiation therapy(MRgRT™) system that employs a movable MRI system. This coil technology will expedite clinical workflow by eliminating need for coil connections and cables, allowing RF coils to remain in place for treatment.
Methods: We quantified radiation transmission factors and surface dose changes for aluminum (Al), copper (Cu) and FR4 substrate typical of RF coils using a Varian Trilogy linear accelerator. Ion chamber measurements were performed by applying 6 MV fields of various sizes through sheets of each material and metal‐substrate combination. These measurements were repeated with the materials on a standard treatment couch. Material optimization provided input to build a prototype cableless coil and representative coil segment for surface dose measurements. Results: We observed expected patterns for radiation field sizes between 1 cm × 1 cm and 25 cm × 25 cm and expected variation with off‐axis distances < 12 cm. All metal‐substrate combinations had transmission factors > 0.996, the lowest being Cu‐FR4. Relative surface dose increases were similar for Cu‐FR4 (3.9) and Al‐FR4 (3.3) combinations. Couchtop relative surface dose increases were much greater than coil materials alone and did not increase substantially with the addition of coil materials (couch‐only = 6.6, couch with Cu‐FR4 = 7.3). Relative surface dose increase was 6.23 for prototype coil segment with capacitor, but the capacitors are not in the primary beam path for the coil design. Conclusions: Results indicate surface dose effectsare the dominant consideration in RF coil design for MRgRT. Similar Cu and Al surface dose effects suggest Cu is a viable coil inductor material for this application. Given that coil material contribution to surface dose is small compared to the couchtop material it is feasible to keep this cablelesscoil in place during radiation treatment. This work has received research personnel support from IMRIS.
SU‐E‐J‐59: Dual Imaging Guided Localization System for Spine Radiosurgery
Authors: Wen N , Kim J , Kim S , Glide‐Hurst C , Jin J , Gordon J , Nurushev T , Chetty I , Levin K , Movsas B , Ryu S
Published: June 2012

Purpose: To compare localization accuracies between an ExacTrac and cone beam computed tomography (CBCT) systems for single fraction spine adiosurgery. The work also aimed to evaluate the inherent systematic deviation of both ExacTrac and CBCT systems to achieve highly accurate localization in the spine radiosurgery. Methods: ExacTrac and CBCT imaging systems were evaluated using the linac isocenter as the mutual reference point. First, a BB was placed in an anthropomorphic pelvic phantom. The phantom was localized with both imaging systems and the procedure was repeated 12 times. These results were used to devise a localization protocol using both imaging systems in spine radiosurgery, and employed for 51 patients (81 isocenters) prescribed for single fraction treatment. The displacement discrepancy between the isocenter and two systems were quantified in four dimensions (three translations, one rotation). A Student's two‐tailed t‐test was used to test for significant differences between the two imaging systems. Results: The phantom study showed 1.4±0.5, 0.6±0.5, and 0.1±0.5 mm differences between the two imaging systems in the anterior/posterior (A/P), superior/inferior (S/I) and left/right (L/R) directions, respectively. The angular difference was minimal along all three axes. The patient study revealed similar isocenter discrepancies between ExacTrac and CBCT of 1.1 ± 0.7 mm, 1.0±0.9 mm, and 0.2±0.9 mm in the A/P, S/I, and L/R directions, respectively, with the A/P and S/I directions showing statistical significance ((t(80) = 13.5 and 7.6 respectively, p = 0.000). The couch yaw discrepancy was 0 ± 0.3°. Overall, 1 mm systematic differences were observed in the A/P and S/I directions between ExacTrac and CBCT localization systems, both in phantom and patient. A procedure was developed to mitigate this systematic discrepancy. Conclusions: These findings have justified our patient localization tolerance levels of 2 mm translation and 1 degree rotation for spine SRS treatment.
SU‐E‐J‐64: Towards a Patient Specific Deformation Model in the Male Pelvis for IGRT via Limited Angle Imaging
Authors: Frederick C , Chou C , Pizer S , Lalush D , Chang S
Published: June 2012

Purpose: To evaluate the feasibility of patient specific deformation models (PSDM) in the male pelvis for IGRT by limited angular imaging. Methods: In IGRT via limited angular imaging, insufficient angular projections are acquired to uniquely determine a 3D attenuation distribution. For highly limited geometries, image quality may be too poor for successful non‐rigid registration. This can be overcome by restricting the transformation space to one containing only feasible transformations learned from prior 3D images. This has been successfully applied in the lung region where a majority of deformation is due to respiratory motion which can be adequately observed at planning time with RCCT. Typically, the phases of the RCCT are registered together to form an group‐wise mean image and transformations to each training image. PCA is then performed on the transformation displacement vector fields. The transformation is found at treatment time by registration of digitally reconstructed radiographs of the transformed image to the measured projections, optimizing over the parameters of the PCA subspace. In the male pelvis, deformation is much more complicated than respiratory deformation and is largely inter‐fractional due to changes in bladder and rectal contents, articulation, and motion of the bowels. A similar model is developed for the male pelvis which takes into account pelvic anatomical information and handles the more complicated deformation space. Results: Using the leave‐one‐out method, dice similarity coefficients in the prostate compared with manual segmentations are increased over the those obtained by rigid registration and are comparable with those obtained by 3D non‐rigid registration methods. Conclusions: This method produces better results than rigid registration and is comparable with results obtained by 3D/3D registration even though it uses limited angle projections. However, its relies on daily training CTs, so it is not yet a viable clinical method. Funding provided in part by Siemens Medical
SU‐E‐J‐72: Design and Study of In‐House Web‐Camera Based Automatic Continuous Patient Movement Monitoring and Controlling Device for EXRT
Authors: Senthil kumar S , Suresh Babu SS , Anand P , Dheva shantha Kumari G
Published: June 2012

Purpose: The purpose of our study was to fabricate in‐house web‐camera based automatic continuous patient movement monitoring device and control the movement of the patients during EXRT. Methods: Web‐camera based patient movement monitoring device consists of a computer, digital web‐camera, mounting system, breaker circuit, speaker, and visual indicator. The computer is used to control and analyze the patient movement using indigenously developed software. The speaker and the visual indicator are placed in the console room to indicate the positional displacement of the patient. Results: Studies were conducted on phantom and 150 patients with different types of cancers. Our preliminary clinical results indicate that our device is highly reliable and can accurately report smaller movements of the patients in all directions. The results demonstrated that the device was able to detect patient's movements with the sensitivity of about 1 mm. When a patient moves, the receiver activates the circuit; an audible warning sound will be produced in the console. Through real‐time measurements, an audible alarm can alert the radiation technologist to stop the treatment if the user defined positional threshold is violated. Simultaneously, the electrical circuit to the teletherapy machine will be activated and radiation will be halted. Conclusions: Patient's movement during the course for radiotherapy was studied. The beam is halted automatically when the threshold level of the system is exceeded. By using the threshold provided in the system, it is possible to monitor the patient continuously with certain fixed limits. An additional benefit is that it has reduced the tension and stress of a treatment team associated with treating patients who are not immobilized. It also enables the technologists to do their work more efficiently, because they don't have to continuously monitor patients with as much scrutiny as was required.
SU‐E‐J‐77: Clinical Evaluation of a Three‐Dimensional Optical Surface Based Imaging Device for Breast Treatment Setup
Authors: Magnelli A , Tendulkar R , Macklis R , Xia P
Published: June 2012

Purpose: The purpose of this work is to evaluate the accuracy of a three‐dimensional surface based optical imaging device for treatment setup of breast patients. A commercial system has been used to acquire live surface contour data, which are registered with a reference surface contour for setup corrections. This work is to investigate the accuracy of this system when compared with conventional portal images. Methods: The system was clinically applied to twenty breast cancer patients receiving radiotherapy treatment. For each patient, conventional portal imaging before the first fraction was acquired and approved by clinicians. After approval of portal images, a reference surface contour was acquired. This reference contour was subsequently used to guide daily patient setup followed by weekly portal images. A total of 89 sets of portal images were acquired for these patients. On days when portal images were taken, optical images were used to guide for initial patient setup, then portal images were taken and evaluated in order to make direct comparison between the optical imaging system and the conventional portal images. Results: Among 89 sets of portal images taken after optical imaging guidance, 11 (12%) sets of portal images required further adjustments in order to achieve clinically acceptable criteria. The average vector adjustments for these 11 fractions were 0.65 cm ± 0.30 cm. Average vector shifts made according to the optical imaging for all fractions of 20 patients was 0.66 ± 0.33 cm. Conclusions: Our data show that the commercial optical system can improve the accuracy of treatment setup for breast patients without additional radiation exposure. The observed discrepancy between the portal images and optimal images requires further investigation. The optical imaging guidance can be routinely used between normally scheduled portal imaging.
SU‐E‐J‐81: Beveled Needle Tip Detection Error in Ultrasound‐Guided Prostate Brachytherapy
Authors: Leu S , Ruiz B , Podder T
Published: June 2012

Purpose: To quantify the needle tip detection errors in ultrasound images due to bevel‐tip orientation in relation to the location on template grid. Methods: Transrectal ultrasound (TRUS) system (BK Medical) with physical template grid and 18‐gauge bevel‐tip (20‐deg beveled angle) brachytherapy needle (Bard Medical, Covington, GA) were used. The TRUS was set at 6.5MHz in water phantom at 40°C and measurements were taken with 50% and 100% TRUS gains. Needles were oriented with bevel‐tip facing up (0‐degree) and inserted through template grid‐holes. Reference needle depths were measured when needle tip image intensity was bright enough for potentially consistent readings. High‐resolution digital vernier caliper was used to measure needle depth. Needle bevel‐tip orientation was then changed to bevel down (by rotating 180‐degree) and needle depth was adjusted by retracting so that the needle‐tip image intensity appeared similar to when the needle bevel‐tip was at 0‐degree orientation. Clinically relevant locations were considered for needle placement on the template grids (1st row to 9th row, and ‘a‐f’ columns). Results: For 50% TRUS gain, bevel tip detection errors/differences were 0.69±0.30mm (1st row) to 3.23±0.22mm (9th row) and 0.78±0.71mm (1st row) to 4.14±0.56mm (9th row) in columns ‘a’ and ‘D’, respectively. The corresponding errors for 100% TRUS gain were 0.57±0.25mm to 5.24±0.36mm and 0.84±0.30mm to 4.2±0.20mm in columns ‘a’ and ‘D’, respectively. These errors/differences varied linearly for grid‐hole locations on the rows and columns in between, smaller to large depending on distance from the TRUS probe. Observed no effect of gains (50% vs. 100%) along ‘D’ column, which was directly above the TRUS probe. Conclusions: Experiment results revealed that the beveled needle tip orientation could significantly impact the detection accuracy of the needle tips, based on which the seeds might be delivered. These errors may lead to considerable dosimetric deviations in prostate brachytherapy seed implantation.
SU‐E‐J‐83: Improving Respiration‐Gated IMRT Delivery Efficiency by Dual‐Gating at Inhale and Exhale: Evaluation of Planning on Eclipse and the Need for Accurate Image Registration
Authors: Geneser S , Fahimian B , Xing L
Published: June 2012

Purpose: Dual‐gated intensity modulated radiation therapy (DG‐IMRT) is a novel delivery method for speeding respiratory‐gated IMRT delivery in which dose is delivered during both inhale and exhale windows. To determine the feasibility of designing DG‐IMRT plans using current clinical treatment planning systems, we design and evaluate a lung patient plan using Eclipse. Methods: Tumor target volumes were contoured on inhale and exhale CTs for a lung cancer patient with ∼1mm motion. Separate 5‐field IMRT plans were optimized in Eclipse for the inhale PTV on the inhale CT and for the exhale PTV on the exhale CT. The inhale plan dose was mapped to the exhale geometry using several deformable medical image registration methods, and the two doses were summed to produce the DG‐IMRT dose. The accumulated dual‐gated dose for the best performing registration is presented. Results: Though the dual‐gated inhale and exhale plans meet clinical requirements, the accumulated dual‐gated dose performs quite poorly. Examination of the deformations indicates that only about two‐thirds of the voxels within the inhale PTV map to voxels within the exhale PTV, indicating an unacceptably low level of physiological accuracy. Conclusion: It is possible to design dual‐gated plans in Eclipse, but there is currently no accurate means of evaluated the summed dose. Furthermore, our results underscore the need for image registration methods that accurately model underlying tissue deformations before they can be used for dose accumulation in the presence of organ motion. This work was supported by the National Cancer Institute (T32 CA09695 ‐ Glazer) and the National Institutes of Health (1RO1 CA 133474 ‐ Xing).
SU‐E‐J‐88: Deformable Registration Using Multi‐Resolution Demons Algorithm for 4DCT
Authors: Li Dengwang , Yin Yong
Published: June 2012

Purpose: In order to register 4DCT efficiently, we propose an improved deformable registration algorithm based on improved multi‐resolution demons strategy to improve the efficiency of the algorithm. Methods: 4DCT images of lung cancer patients are collected from a General Electric Discovery ST CT scanner from our cancer hospital. All of the images are sorted into groups and reconstructed according to their phases, and eachrespiratory cycle is divided into 10 phases with the time interval of 10%. Firstly, in our improved demons algorithm we use gradients of both reference and floating images as deformation forces and also redistribute the forces according to the proportion of the two forces. Furthermore, we introduce intermediate variable to cost function for decreasing the noise in registration process. At the same time, Gaussian multi‐resolution strategy and BFGS method for optimization are used to improve speed and accuracy of the registration. To validate the performance of the algorithm, we register the previous 10 phase‐images. We compared the difference of floating and reference images before and after registered where two landmarks are decided by experienced clinician. We registered 10 phase‐images of 4D‐CT which is lung cancer patient from cancer hospital and choose images in exhalationas the reference images, and all other images were registered into the reference images. Results: This method has a good accuracy demonstrated by a higher similarity measure for registration of 4D‐CT and it can register a large deformation precisely. Finally, we obtain the tumor target achieved by the deformation fields using proposed method, which is more accurately than the internal margin (IM) expanded by the Gross Tumor Volume (GTV). Furthermore, we achieve tumor and normal tissue tracking and dose accumulation using 4DCT data. Conclusions: An efficient deformable registration algorithm was proposed by using multi‐resolution demons algorithm for 4DCT.
SU‐E‐J‐90: 2D/3D Registration Using KV‐MV Image Pairs for Higher Accuracy Image Guided Radiotherapy
Authors: Furtado H , Figl M , Stock M , Georg D , Birkfellner W
Published: June 2012

Purpose: In this work, we investigate the impact of using paired portal mega‐voltage (MV) and kilo‐voltage (kV) images, on 2D/3D registration accuracy with the purpose of improving tumor motion tracking during radiotherapy. Tumor motion tracking is important as motion remains one of the biggest sources of uncertainty in dose application. 2D/3D registration is successfully used in online tumor motion tracking, nevertheless, one limitation of this technique is the inability to resolve movement along the imaging beam axis using only one projection image. Methods: Our evaluation consisted in comparing the accuracy of registration using different 2D image combinations: only one 2D image (1‐kV), one kV and one MV image (1kV‐1MV) and two kV images (2‐kV). For each of the image combinations we evaluated the registration results using 250 starting points as initial displacements from the gold standard. We measured the final mean target registration error (mTRE) and the success rate for each registration. Each of the combinations was evaluated using four different merit functions. Results: When using the MI merit function (a popular choice for this application) the RMS mTRE drops from 6.4 mm when using only one image to 2.1 mm when using image pairs. The success rate increases from 62% to 99.6%. A similar trend was observed for all four merit functions. Typically, the results are slightly better with 2‐kV images than with 1kV‐1MV. Conclusions: We evaluated the impact of using different image combinations on accuracy of 2D/3D registration for tumor motion monitoring. Our results show that using a kV‐MV image pair, leads to improved results as motion can be accurately resolved in six degrees of freedom. Given the possibility to acquire these two images simultaneously, this is not only very workflow efficient but is also shown to be a good approach to improve registration accuracy.
SU‐E‐J‐94: Investigating the Use of Deformable Algorithms to Register MR Images Acquired with and Without an Endo‐Rectal Coil
Authors: Ueda U , Chen J , Hsu I , Reed G , Pouliot J
Published: June 2012

Purpose: Magnetic resonance spectroscopic imaging (MRSI) can identify the dominant intraprostatic lesion, which can then be boosted using high‐dose rate (HDR) brachytherapy. MRSI requires the use of an endo‐rectal coil, which deforms the prostate. We investigate the performance of deformable registration algorithms to deform MR images acquired with an endo‐rectal coil to images acquired without a coil for HDR brachytherapy planning. Methods: This study utilized MR images of five HDR brachytherapy patients acquired with and without an endo‐rectal coil during the same MRSI imaging study. The prostate was contoured on each set of ‘Coil‐In’ and ‘Coil‐Out’ MR images by an experienced radiation oncologist. The ‘Coil‐In’ and ‘Coil‐Out’ images were rigidly aligned such that the posterior margins of the prostate were as close as possible without deformation. Variations on a commercially available deformation algorithm using the B‐spline method were applied to a volume of interest that surrounded the prostate and excluded as much of the coil and rectum as possible. The Dice similarity index (DSI) was calculated between rigidly registered contours (DSI1), and compared to the DSI calculated between the ‘Coil‐In’ contour and the contour deformed from the ‘Coil‐Out’ image to the ‘Coil‐In’ image (DSI2). The difference was calculated between DSI2 and DSI1, where a positive change in DSI would indicate an improvement in contour agreement over rigid registration of the prostate in the ‘Coil‐Out’ and ‘Coil‐In’ images. Results: The B‐spline deformation algorithm designed specifically for MR images was most effective in deforming the ‘Coil‐Out’ to the ‘Coil‐In’ prostate contour with a mean change in DSI of 0.0124 with contrast correction, and 0.0004 without. Conclusions: Out of six algorithms tested, only the MR‐specific algorithm produced positive changes in DSI. The accuracy of the deformation algorithm on mapping the internal structures of the prostate between ‘Coil‐Out’ and ‘Coil‐In’ images is under investigation. We acknowledge Velocity for providing the registration software.
SU‐E‐J‐96: Investigation into the Accuracy of Deformable Registration Algorithms for Use in Dose Summation: A Case Study in Combined Modalities
Authors: Chuang C , Morin O , Pouliot J
Published: June 2012

Purpose: To better understand the accuracy and limitation of deformable registration algorithms for dose summation by studying the results produced through two different deformable registration techniques for a clinical case of combining a Cyberknife radiosurgery plan and an electron boost to the scar tissues. Methods: A patient was treated with a Cyberknife plan with supine CT and an electron boost plan with prone CT concurrently. The CT, RT structures and dose grids were exported from the Cyberknife MultiPlan system and the Pinnacle system and imported into two commercial DICOM viewing systems equipped with deformable registration algorithms. One of the systems uses intensity‐based free‐form deformable registration while the other uses B‐spline free‐form deformable registration. The electron boost plan was first registered to the CK plan using rigid registration, then secondly using deformable registration in each system. The region of interest used for registration was chosen to encompass the whole CT volumes due to the supine vs. prone positions. Results: The summation doses for the Cyberknife CTV and critical structures do not differ between rigid registration and deformable registration for both systems. The electron boost volume does show higher mean dose received for the deformable registration compared with rigid registration for both systems (12.90 Gy vs. 11.71 Gy and 12.39 Gy vs. 11.53 Gy). There are slight variations between the doses produced by the two systems for all the structures, with an averaged difference of approximately 0.02% to 2.63%. Conclusions: These results show that for cases like this one, where the two treatment volumes do not overlap, there will not be significant differences between rigid and deformable registration, and that the only significant difference in summation dose between the different deformable registration algorithms is where the volume is deformed the most, in this case, the electron boost volume.
SU‐E‐J‐99: Automated Registration Method Based on Multi‐Scale Edge Preserving Scale Space for PET‐CT Scanner
Authors: Li Dengwang , Li H , Yin Y
Published: June 2012

Purpose: The aiming is to improve the mutual information based registration method for PET‐CT scanner, which faces the challenges of high computational complexity and high likelihood of being trapped into local optima due to an absence of spatial information. Methods: In this work, new multi‐scale registration framework called EPMR was proposed based upon an edge preserving total variation L1 norm (TV‐L1) scale space representation. TV‐L1 scale space is constructed by selecting edges and contours of images according to their size rather than the intensity values of the image features. This ensures more meaningful spatial information with EPMR framework for MI based registration. Furthermore, we design an optimal estimation of the TV‐L1 parameter in EPMR framework by training and minimizing the transformation offset between the registered pairs for automated registration in medical system. We validated our EPMR method on multi‐modal medical datasets from clinical studies with a combined PET/CT scanner. We compared our registration framework with other traditional registration approaches. Results: Our experimental results demonstrated that our method outperformed other methods in terms of the accuracy and robustness for medical images. EPMR can always achieve small offset value, which is more close to the ground truth, and the speed can be increased by 10%–14% comparing with other method for PET‐CT registration under the same condition. Furthermore, clinical application by adaptive GTV (gross tumor volume) re‐contouring for clinical PET/CT image guided radiation therapy throughout the course of radiotherapy is also studied, and the overlap between the automatically generated contours for CT image and the contours delineated by the oncologist using for theplanning system are on an average 90%. Conclusions: In this work, we presented a novel scale space decomposition methodology to improve the traditional scale space decomposition and performance of Mutual information based image registration for PET‐CT scanner.
SU‐E‐J‐101: Weighted Voting Method for Multi‐Atlas Segmentation in CT Scans
Authors: Arbisser A , Sharp G , Golland P , Shusharina N
Published: June 2012

Purpose: We investigate automating the task of segmenting structures in head and neck CT scans, to minimize time spent manually contouring. We focus on the brainstem and left and right parotids. Methods: To generate contours for an unlabeled image, we assume an atlas of labeled images. We register each of these images to the unlabeled target image, transform their structures, and then use a weighted voting method for label fusion. Our registration method starts with multi‐resolution translational alignment, then applies a relatively higher resolution affine alignment. We then employ a diffeomorphic demons registration to deform each atlas to the space of the targetimage. Our weighted voting method acts one structure at a time to determine for each voxel whether or not it exists in a structure. The weight for a voxel's vote from each atlas depends on the intensity difference of the target and the transformed atlas at that voxel, in addition to the distance of that voxel from the boundary of the structure. Results: We applied our method to sixteen labeled images, generating automatic segmentations foreach using the other fifteen images as the atlas. We compared the resulting Dice and Hausdorff metrics with a majority voting method using the same registrations and saw remarkable improvement. Mean Dice scores were around .7, with maximum Hausdorff of about 15mm, and mean Hausdorffs around 2 or 3mm. Conclusions: Our method produces contours with boundaries usually only a few millimeters away from the manual contour, which could save physicians considerable time, because they only have to make small modifications to each slice instead of contouring from scratch.
SU‐E‐J‐102: The Impact of the Number of Subjects for Atlas‐Based Automatic Segmentation
Authors: Ducote JL , Sehgal V , Wong J , Al‐Ghazi M
Published: June 2012

Purpose: To determine the impact of atlas size on the performance of atlas‐based automatic segmentation (ABAS) in delineation of organs at risk for adaptive radiation therapy. Methods: A total of 25 patients who had undergone intensity modulated radiation therapy for various head and neck cancers were retrospectively selected for inclusion in a library to be used for ABAS with the MIM VISTA software package (MIM Software, Cleveland OH). Treatment planning computed tomography (CT) scans and subsequent organ at risk (OAR) contours generated as part of the treatment planning process for these patients were added to the library. This library of 25 patients was then successively pruned to generate 5 atlases with 25, 20, 15, 10, and 5 patient subjects respectively. Atlas based segmentation was performed on 10 retrospectively selected treatment planning CT scans to automatically generate right and left parotid glands and brainstem contours. These planning CT scans belonged to a unique set of 10 patient subjects different from the ones used for generating the atlases. One physician (JW), who was blinded to the ABAS results, manually delineated gold‐standard contours for the right and left parotid glands and brainstem. Dice similarity coefficients were calculated and analyzed as a function of atlas subject size. Results: For the sites selected in this study, the performance of ABAS was relatively insensitive to atlas size. Furthermore, some patient subjects were repeatedly selected implying that the adoption of a single standard patient for ABAS may be of benefit. Conclusions: Our preliminary results indicate that the performance of the atlas based segmentation module in MIM VISTA Version 5.2 for the organs studied here may be relatively insensitive to the atlas size.
SU‐E‐J‐104: Evaluation of Atlas‐Based Auto‐Segmentation on Daily In‐Room CT for Prostate Cancer
Authors: Li W , Zhong Y , Vassil A , Xia P
Published: June 2012

Purpose: Anatomy delineation is a major time consuming task to correct for inter‐fractional changes in anatomy. Atlas‐based auto‐segmentation (ABAS) was developed to expedite this process. This study aims to evaluate the performance of ABAS applying to high quality verification CT‐imaging acquired using a CT‐on‐rail system for prostate cancer. Methods: The prostate, rectum and bladder were manually contoured for seven prostate cancer patients. For each patient, three patient specific atlases were generated consisting of one, four and seven prior image and contour sets. ABAS was applied using these atlases for the last seven daily CT images of each patient. The auto‐ and manual‐contours were compared both geometrically and dosimetrically. The reproducibility of the observation was validated by an experienced radiation oncologist performing the same procedure. The performance of ABAS with patient and non‐patient specific atlases were also evaluated on 21 image sets. P<0.05 was considered statistical significant for two‐tailed paired student t‐test. Results: Contours obtained from ABAS agreed well with the manual ones. With 1‐image set atlas, the OI and DSC for the bladder were greater than 96% and 91%, respectively. Both indices were above 81% for rectum and prostate. The consistencies significantly improved by including 4 image sets in the atlas, while a further increase of atlas size to 7 did not show obvious benefits. Dose coverage for the auto‐ and manual‐contours was similar for all organs. Similar results were obtained by the second observer. Compared with non‐patient specific atlas, patient specific atlas yielded more accurate contours. The time for ABAS and manual contouring was ∼2 min and ∼20 min per image set, respectively. Conclusions: With diagnostic quality verification images, ABAS can provide fast and accurate delineations for prostate cancer on a daily basis. The inclusion of more than one CT set in atlas improves the contouring results.
SU‐E‐J‐114: Web‐Browser Medical Physics Applications Using HTML5 and Javascript
Authors: Bakhtiari M
Published: June 2012

Purpose: Since 2010, there has been a great attention about HTML5. Application developers and browser makers fully embrace and support the web of the future. Consumers have started to embrace HTML5, especially as more users understand the benefits and potential that HTML5 can mean for the future.Modern browsers such as Firefox, Google Chrome, and Safari are offering better and more robust support for HTML5, CSS3, and JavaScript. The idea is to introduce the HTML5 to medical physics community for open source software developments. The benefit of using HTML5 is developing portable software systems. Methods: The HTML5, CSS, and JavaScript programming languages were used to develop several applications for Quality Assurance in radiation therapy. The canvas element of HTML5 was used for handling and displaying the images, and JavaScript was used to manipulate the data. Sample application were developed to: 1. analyze the flatness and symmetry of the radiotherapy fields in a web browser, 2.analyze the Dynalog files from Varian machines, 3. visualize the animated Dynamic MLC files, 4. Simulation via Monte Carlo, and 5. interactive image manipulation. Results: The programs showed great performance and speed in uploading the data and displaying the results. The flatness and symmetry program and Dynalog file analyzer ran in a fraction of second. The reason behind this performance is using JavaScript language which is a lower level programming language in comparison to the most of the scientific programming packages such as Matlab. The second reason is that JavaScript runs locally on client side computers not on the web‐servers. Conclusions: HTML5 and JavaScript can be used to develop useful applications that can be run online or offline on different modern web‐browsers. The programming platform can be also one of the modern web‐browsers which are mostly open source (such as Firefox).
SU‐E‐J‐117: Computer‐Assisted Verification of Accumulated Dose Distribution during the Treatment Time Based on Estimation of Four‐Dimensional Dose Distribution Using an Electronic Portal Imaging Device
Authors: Arimura H , Mizoguchi A , Shioyama Y , Nakamura K , Yoshidome S , Hirose T , Anai S , Umezu Y , Honda H , Ohki M , Toyofuku F , Hirata H
Published: June 2012

Purpose: The accumulated dose distributions during the course of radiation treatment are substantially important for verifying whether treatment dose distributions are produced according to planned dose distributions. The purpose of this study was to develop a computer‐assisted verification method of accumulated dose distribution during the irradiation of a tumor based on estimation of four‐dimensional (4D) dose distribution using an electronic portal imaging device (EPID). Methods: The 4D ‘treatment’ computed tomography (CT) images during the irradiation were estimated based on affine transformations including respiratory motions, which were derived by registration between a planning portal dose image and treatment portal dose dynamic image. Planning portal dose images were calculated from planning CT images and an algorithm for calculation of dose spatial distribution. Treatment portal dose images were estimated from EPID dynamic images obtained during a treatment time. The planning portal dose images were registered to the treatment portal dose images to obtain the affine transformation, which could include respiratory motion in a patient body. The CT images at a treatment time were determined by deforming the planning CT images using the affine transformation matrix. 4D dose distributions during a treatment delivery were obtained by applying a dose calculation algorithm to the 4D treatment CT images. Finally, accumulated dose distributions during the course of radiation treatment were verified with planned dose distributions. Results: We applied the proposed method to EPID dynamic images of 2 lung cancer patients, and evaluated the difference in accumulated dose distribution between the plan and treatment using a gamma evaluation (3mm/3%). The average pass rate for 2 cases was 78.2%. Conclusions: The proposed method can be used for adaptively modifying the plan based on the dose discrepancy between the plan and treatment. This work was partially supported by Grant‐in‐Aid for Scientific Research (C) (22611011) and Okawa Foundation for Information and Telecommunications.