bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐I‐82: Image Signal‐To‐Noise Equalization in Whole Body PET Using Variable Acquisition Times
Authors: Dahlbom M , Kriszan A , Czernin J
Published: June 2012

Purpose: Whole Body PET scans are acquired at multiple axial positions, where the acquisition time at each position is constant. Although the acquisition time is adjusted for patient weight, the varying amount of attenuation and activity distribution for different sections, the image S/N can vary significantly. The aim of this work is to investigate the use of variable bed position scan times in WB‐PET to equalize the Signal‐to‐Noise ratio in the axial direction. Methods: Simulations of activity and attenuation distributions based on whole body CT scans were performed. Phantoms of different cross sections were also simulated and imaged. Image noise was estimated by generating multiple noise replicates by adding Poisson noise to the emission sinograms for the simulated images, and using a bootstrap method for the phantom patient measurements. By comparing the square of image noise (SD/Mean) for all the image slices, the acquisition time for each section could be adjusted to yield uniform image noise for all slices. The image noise was also compared to the average AC factors through the center of each body slice. Results: A polynomial function was found for both simulations and the measurements to accurately describe image noise as a function of AC factors. Using this relationship, the acquisition time at each axial position can be adjusted to produce images of relatively uniform S/N, independent of cross sectional thickness. This was confirmed in phantom and patient data. Conclusions: The noise properties of WB‐PET images can be equalized axially by adjusting the acquisition time according to the amount of attenuation. The acquisition time can be reduced in areas of lower attenuation and increased in more absorbing sections Since there is a correlation of the image noise and the CT‐derived AC factors, the acquisition times can quickly calculated using a simple functional relationship.
SU‐E‐I‐83: Detectability Limits of a New Positron Emission Mammography in Relation to Tumour‐Size, Tumour‐To‐Background Ratio and Activity Concentration
Authors: Gonzalez A Vicedo , Hernández T García , Granero D , Gonzalez L Brualla , Ferrando J Rosello , Sanchez R , Ferrer J
Published: June 2012

Purpose: Positron emission mammography (PEM) improves spatial resolution and sensitivity, making it suitable for early breast tumours detection. The aim of this study is to evaluate the limits of a dedicated breast PET in terms of tumour‐size, tumour‐to‐background activity concentration ratio (TBR) and activity concentration. Methods: A dedicated PEM is evaluated. To characterize the device, we use a phantom of 15 cm of diameter containing 6 inserts of inner diameters 18, 15, 11, 8, 5 and 3 mm. To evaluate the detectability limits images are acquired by varying the TBR from 10 to 2 and without background activity concentration. In all the studies the activity concentration for the 6 inserts is the same (3.7 kBq/ml). To asses the activity concentration limit, the SBR is maintained fixed and acquisitions at different times are performed. Results: When there is not background, all the inserts are visible in the PEM. Increasing the background decreases the detectability. With a SBR of 10, the smaller insert is still visible. For TBR between 10, inserts >= 5 mm can be seen With a TBR of 2, only inserts with a diameter higher than 5 mm are visible. When the TBR is fixed, decreasing the activity concentration, decreases the capability of detectability. Conclusions: The results suggest that PEM can be used for diagnosis of small lesions when TBR is higher than 2. Further clinical studies need to be carried out in order to validate these results
SU‐E‐I‐87: Tumor Positioning for PET‐CT Scanner by Jointly Registration and Segmentation
Authors: Li D , Yang J , Yin Y
Published: June 2012

Purpose: In order to achieve tumor positioning for radiotherapy planning automatically and accurately, an efficient tumor positioning method is proposed by jointly registration and segmentation for 18F‐FDG PET‐CT scans. Methods: At the first stage, the tumor is segmented from PET scans by region growing using the manual seeds which employs the SUV monotonous features, and then the tumor contours are transferred to corresponding CT images automatically for following radiation therapy planning by a new deformable registration method which is implemented by combining edge preserving scale space with the free form deformation. The edge preserving scale space which is able to select edges and contours of an image according to their geometric size is derived from the total variation model with the L1 norm (TV‐L1). At each scale, the selected edges and contours are sufficiently strong to drive the deformation using the FFD grid, then the deformation fields are gained by a coarse to fine manner.Datasets were collected from 5 patients treated under the PET‐CT scanner (GE medical systems, Discovery LS). Before treatment planning, the GTV (gross tumor volume) is delineated on every section of the PET scans by the radiation oncologist and the Result will be compared with proposed automatic segmentation method. Of the 5 patients investigated here, all are non‐small cell lung carcinoma (NSCLC) patients. Results: After evaluation of the experiment results by three clinical oncologists, they concluded that the segmentation results are very close to the manual results and the GTV contours on CT scan which is produced by the deformation field automatically can be used for radiation therapy planning. The volumetric overlap is on an average 90%–97% comparing with manually segmented tumors by oncologists. Conclusions: We can conclude that an efficient tumor positioning method is proposed by jointly registration and segmentation for FDG PET‐CT datasets.
SU‐E‐I‐89: Applying Image Gently and Image Wisely in Nuclear Medicine
Authors: Jafari M , Daus A
Published: June 2012

Purpose: To demonstrate how principles and recommendations of the Image Gently® and Image Wisely™ campaigns can be clinically implemented. Methods: Implementation of Image Gently® and Image Wisely™ guidelines was a quality and safety improvement project for our Nuclear Medicine department in 2011. Pediatric administered radiopharmaceutical doses were compared to recommended doses in the North American Consensus Guidelines for AdministeredRadiopharmaceutical Activities in Children and Adolescents and the European Association of Nuclear Medicine Paediatric Dose Card. Adult administered radiopharmaceutical doses were compared to administered doses in NCRP Report No. 160 and IAEA Report No. 40. Results: Evaluation of site administered radiopharmaceutical doses showed that nearly all doses were comparable to those recommended by national and international advisory bodies. Administered doses for the pediatric renogram and the adult gastric emptying were adjusted to match the recommendations and resultant image quality evaluated. Conclusions: Radiation dose from nuclear medicine procedures should not be overlooked in the focus on CT dose reduction. An estimated 19.7 million nuclear medicine procedures are done annually in the U.S., with doses comparable to that from CT scans. Nuclear medicine departments should evaluate their pediatric administeredradiopharmaceutical doses against the North American Consensus Guidelines for Administered Radiopharmaceutical Activities in Children and Adolescents and evaluate their adult doses against national and international standards. Administered doses that are not comparable to the recommended values should be adjusted accordingly. Additional steps to reduce patient radiation dose include decision support to reduce inappropriate ordering, technique optimization for the CT scan portion of SPECT/CT and PET/CT, use of vendor's dose reduction camera and software technology, use of shorter lived radiopharmaceuticals, and ‘right sizing’ patient doses by weight.
SU‐E‐I‐90: Fast and Robust Algorithm Towards Vessel Lumen and Stent Strut Detection in Optical Coherence Tomography
Authors: Mandelias K , Tsantis S , Karnabatidis D , Katsakiori P , Mihailidis D , Nikiforidis G , Kagadis GC
Published: June 2012

Purpose: Optical Coherence Tomography (OCT) is a catheter‐based imaging method that employs near‐infrared light to produce high‐resolution cross‐sectional intravascular images. We propose a new segmentation technique for automatic lumen area extraction and stent strut detection in intravascular OCT images for the purpose of quantitative analysis of neointimal hyperplasia (NIH). Methods: Two clinical dataset of frequency‐domainOCT scans of the human femoral artery were analyzed. First, a segmentation method based on Fuzzy C‐Means (FCM) clustering and Wavelet Transform (WT) was applied towards inner luminal contour extraction. Subsequently, stent strut positions were detected by utilizing metrics derived from the local maxima of the wavelet transform into the FCM membership function. Results: The inner lumen contour and the position of stent strut were extracted with very high accuracy. Compared with manual segmentation by an expert physician, the automatic segmentation had an average overlap value of 0.917 ± 0.065 for all OCT images included in the study. The strut detection procedure successfully identified 6.7 ± 0.5 struts for each OCT image. Conclusions: A new fast and robust automatic segmentation technique combining FCM and WT for lumen border extraction and strut detection in intravascular OCT images was designed and implemented. The proposed algorithm may be employed for automated quantitative morphological analysis of in‐stent neointimal hyperplasia.
SU‐E‐I‐91: Development of a Compact Radiographic Simulator Using Microsoft Kinect
Authors: Ono M , Kozono K , Aoki M , Mizoguchi A , Kamikawa Y , Umezu Y , Arimura H , Toyofuku F
Published: June 2012

Purpose: Radiographic simulator system is useful for learning radiographic techniques and confirmation of positioning before x‐ray irradiation. Conventional x‐ray simulators have drawbacks in cost and size, and are only applicable to situations in which position of the object does not change. Therefore, we have developed a new radiographic simulator system using an infrared‐ray based three‐dimensional shape measurement device (Microsoft Kinect). Methods: We made a computer program using OpenCV and OpenNI for processing of depth image data obtained from Kinect, and calculated the exact distance from Kinect to the object by calibration. Theobject was measured from various directions, and positional relationship between the x‐ray tube and the object was obtained. X‐ray projection images were calculated by projecting x‐rays onto the mathematical three‐dimensional CT data of a head phantom with almost the same size. The object was rotated from 0 degree (standard position) through 90 degrees in increments of 10 degrees, and the accuracy of the measured rotation angle values was evaluated. In order to improve the computational time, the projection image size was changed (512*512, 256*256, and 128*128). Results: The x‐ray simulation images corresponding to the radiographic images produced by using the x‐ray tube were obtained. The three‐dimensional position of the object was measured with good precision from 0 to 50 degrees, but above 50 degrees, measured position error increased with the increase of the rotation angle. The computational time and image size were 30, 12, and 7 seconds for 512*512, 256*256, and 128*128, respectively. Conclusions: We could measure the three‐dimensional position of the object using properly calibrated Kinect sensor, and obtained projection images at relatively high‐speed using the three‐dimensional CTdata. It was suggested that this system can be used for obtaining simulated projection x‐ray images before x‐ray exposure by attaching this device onto an x‐ray tube.
SU‐E‐I‐105: Optimizing Bomb Squad X‐Ray Systems for Incidental Human Exposures
Authors: Hill C , Rutel I , Cain F
Published: June 2012

Purpose: A current terrorist tactic involves strapping an explosive device to a live victim. Technicians wishing to x‐ray the device need to use appropriate exposures to create clear images while mitigating incidental health problems for the live victim. This project involves characterizing and optimizing a popular radiographic system in the explosive investigation community, both for general use and, more specifically, for generating x‐rays with a human subject in the beam path. This project seeks to minimize the dose to a victim incidentally located in the beam path, while maximizing image quality, thereby allowing appropriate image evaluation to neutralize the explosive threat. Methods: Image quality and dose optimization begins with characterization of the x‐ray source. The source in this study is an XRS‐3, a portable device developed by Golden Engineering, which nominally produces a 270 kVp beam. Characterization of the beam involves verifying the actual kVp, as well as determining the average energy of the beam with various amounts of filtration added to the beam path. The kVp was verified using a noninvasive technique, utilizing the measurement of the dose attenuation through lead and then modeling the energy dependent attenuation curve of the lead using specific mass attenuation coefficients and parameters suggested by Joseph (Joseph, P.M., Med. Phys. Vol. 2, July/Aug1975; 201–207) in order to calculate the kVp through linear regression. Results: The average energy of an unfiltered beam was 52 keV, and increases through adding various combinations of Cu and brass filters to a maximum value of 121 keV with 3 mm copper + 3 mm brass filtration. The calculated kVp was 290 kV. Conclusions: The average energies using filtration fall within the diagnostic range. The kVp fits well within the manufacturer's specifications of 15% deviation. Optimization can be accomplished with these parameters. University of Oklahoma Health Sciences Center‐ Department of Radiological Sciences
SU‐E‐I‐110: Minimized Pediatric Dose in Direct Radiography (DR)
Authors: So J , Nickoloff E , Dutta A , Jambawalikar S
Published: June 2012

Purpose: Pediatric x‐rays techniques are not standardized. They depend upon: patient size, anatomical localized and equipment manufacturers. Most pediatric techniques use the default factory settings. This project's goal is to find the best compromise between dose to pediatric patients and optimal image quality. Methods: Low contrast discrimination is the key to image quality. The manufacturers (Philips and GE) specific techniques were used to establish baseline values. The following factors were evaluated: kVp, mA, time, use of grid, collimation, focal spot size, AEC/manual, and added filters. The entrance skin exposure, entrance exposure to detector, equipment exposure index (EI) and contrast to noise ratio (CNR) for different thickness from neonatal to average child were assessed. Results: Overall, some manufacturer's specific pediatric exposures techniques have higher entrance skin exposure than typical specified techniques. Equipment reported exposure index are not accurate enough to be used as ‘dosimeter’. Lower kVp, mA with longer exposure time will increase the low contrast detectability with better CNR but these also change the entrance skin exposure. Removal of grid, filters do reduce the entrance skin exposure, but these also reduce low contrast detectability. Focal spot size does not make a big impact in image quality due to the average detector pixel size. Collimation does make a difference in AEC sensitivity and exposure index (EI). Conclusions: There is no single technique that is the best technique. It is all depend upon many factors like exam type and the size of the patients. Moreover, it is difficult to program the generator to use low kVp techniques, add or remove of filters, collimation, and use of AEC or manual mode, grid on or off in order to optimize the image quality while minimizing the dose to the patients. Some pediatric techniques with their associate CNR and radiation dose will be presented.
SU‐E‐I‐112: Pre‐Clinical Imaging with an Ultra‐High Resolution X‐Ray Detector
Authors: Singh V , Loughran B , Pope L , Bednarek D , Rudin S
Published: June 2012

Purpose: To explore the possible applications for a newly developed ultra‐high resolution, small field‐of‐view (FOV) micro‐solid state x‐ray image intensifier (micro‐SSXII) detector. Methods: The micro‐SSXII is based on an 8 micron, 1004 by 1002 electron‐multiplying CCD (EMCCD) optically coupled to a 100‐micron thick CsI(Tl) phosphor through a fiber optic window resulting in a FOV of 8 mm with a resolution limit of more than 20 lp/mm. The system has the capability of providing real‐time images at low exposures because of the high variable gain of the EMCCD. Several phantoms were prepared by filling catheter tubes of 470 micron internal diameter with separate mixtures of a casting resin with different ratios of three different contrast agents (Omnipaque 350, barium sulphate, tantalum powder). These were imaged with the micro‐SSXII at 50 kVp to help select the best mixture for use in making a cast of a rat kidney whose vasculature would then be made radiopaque and visualized. Results: The images of all phantoms showed clumping of these contrast agents within the resin resulting in a non‐uniform mix. The image of the phantom filled with Omnipaque and resin in a 1:4 ratio showed the best mixture although large bubble formation of the iodine was observed. This combination was used to make a cast of a rat kidney vasculature and imaged with the micro‐SSXII. Small iodine bubbles with diameters as small as 25 microns were clearly delineated in the rat kidney vessels confirming the sharp detail capability of the micro‐SSXII. Conclusions: The micro‐SSXII in combination with a soft x‐ray spectrum can provide excellent images of small animal casts prepared with an appropriate radiopaque resin to study finer details of the vasculature. This new imager has the potential to be used for region‐of‐interest x‐ray image guidance for interventional studies in small animals. Supported in part by: NIH Grants R01‐EB008425, R01‐EB002873 and an equipment grant from Toshiba Medical Systems Corp.
SU‐E‐I‐115: Wavelet Analysis of Ultrasound Image for the Diagnosis of Sjögren's Syndrome
Authors: Murakami Y , Shiraishi A , Sumi T , Nakamura T , Ohki M
Published: June 2012

Purpose: Sjögren's syndrome (SS) is an auto‐immune disease presenting with dry eyes and mouth (keratoconjunctivitis sicca and xerostomia). Ultrasonography is used for the initial and non‐invasive investigation of the parotid gland in the disease. The purpose of this study is to develop an image processing for diagnosis of SS by applying wavelet analysis to ultrasound image. Methods: Ultrasound B‐mode images of the parotid gland were captured and analyzed by a personal computer. A square region of interest (ROI) was set on the image and two‐dimensional discrete wavelet transform was performed within the ROI. As a Result, the image was decomposed into an approximate image and three detailed images in vertical, horizontal and diagonal directions in different scales. A feature quantity for image classification was defined by calculating from the wavelet coefficients of detailed images within selected scales. The ultrasound images of 80 patients who had been referred to Nagasaki University Hospital because of suspicion of SS were analyzed. A total of 37 patients fulfilled the criteria for SS, whereas the remaining 43 patients did not. The severity of SS was graded into four degrees by sialography. The images with each feature quantity were classified by statistical cluster analysis. Results: In this method, the images can be divided into two groups which mainly contained SS and non‐SS. The sensitivity and specificity in the detection of SS was 78% and 95%, respectively. It was also found that the defined feature quantity tended to change with the severity of SS. Conclusions: In ultrasonography, the image analysis based on wavelet transform was useful for the diagnosis of Sjögren's syndrome.
SU‐E‐J‐13: A Study to Establish the Effect of CBCT Image Rotational Displacement on IGRT and ART Lung SBRT Treatments
Authors: Yeager C , Lin H , Ayan A , McDonough J , Both S
Published: June 2012

Purpose: To determine whether the accuracy of CBCT based IGRT and ART lung SBRT treatments may require extra quality assurance (QA) steps. Methods: During CBCT Rando phantom acquisition we detected an unexpected ∼2° image rotation when comparing the CW and CCW acquired scans. Misregistered angular coordinates may Result in a rotated reconstructed image and the target localization may lead to an under‐ or over‐dosage of the target volume (TV) and organs at risk (OARs). The effect of image rotation on CBCT‐guided lung SBRT was retrospectively examined in a group of six patients treated at our institution. Patient CT sets were rotated by 1,2, and 3°. Treatment plans were recalculated using these rotated images to examine changes of dose‐volume histogram indicators for IGRT and ART guided treatments. C++ simulations were run to evaluate the effect of CBCT image rotation. Results: We determined through mathematical analysis that the dose coverage of the TV is dependent on its shape, location and orientation relative to isocenter. Dosimetric evaluation of lung SBRT patients showed that even for 1< Ñ2<3°, changes in D95 to the PTV were from 2.3 ± 2.1 to 11.5 ± 3.9% for IGRT and from 8.5 ± 8.4 to 16.6 ± 8.0% for ART. Significant changes were also detected at critical structure level. Conclusions: When IGRT and ART are employed for lung SBRT treatments, significant dosimetric changes may Result from the rotation of CBCT image data sets. The extent of alterations in dose indicators depends on both the shape of the TV and its relative location to isocenter. Based on our results, angular alignment of CBCT to <1° is essential in maintaining accurate dose delivery of IGRT and ART based lung SBRT treatments.
SU‐E‐J‐15: Calculating the Dose from KV Cone Beam CT Within and Outside the Treatment Volume Using a Treatment Planning System
Authors: Alaei P , Spezi E , Reynolds M
Published: June 2012

Purpose: To assess the dose from kilovoltage cone beam CT from two image acquisition protocols, pelvis and head and neck, by addition of the dose to the patient treatment plans. Methods: A total of 20 patients (10 pelvis and 10 head and neck) undergoing radiation therapy were selected and the dose from kV CBCT was calculated using a treatment planning system previously commissioned for this purpose. The imaging dose was added to the CT images used for treatment planning. Daily shifts as a Result of imaging were recorded and applied to imaging beam whenever the sum of the shifts exceeded 0.5 cm. The kV CBCT dose can also be computed prior to planning, in case of IMRT treatments, and used during optimization. Results: The additional dose as a Result of daily CBCT is in the order of few cGy for head and neck and up to 90 cGy for the pelvis cases using the standard head and neck and pelvis protocols. The pelvic dose is especially dependent on patient size, being higher for smaller patients. Due to the low energy of the kV CBCT beam, the maximum energy deposition is at or near the surface with the highest dose being on the patient's left side for the head and neck and on the posterior for the pelvic cases. Conclusions: Dose from daily kilovoltage CBCT can be added to patient treatment plans using previously commissioned kV CBCT beams in a treatment planning system. In the case of IMRT planning, optimization can be done accounting for kV CBCT dose.
SU‐E‐J‐21: An Intercomparison of Imaging Performance of Two Linac‐Mounted Imaging Systems Used in Radiation Therapy: TrueBeam and Trilogy
Authors: Kim C , Furhang E , Lazos D , Harrison L
Published: June 2012

Purpose: To evaluate and compare the performance of the imaging systems of two linear accelerators, used in radiation therapy. The study includes the following imaging components: electronic portal imaging device (EPID), kilovoltage projection imaging and kilovoltage cone‐beam CT.Method and Materials: The imaging systems mounted on the Varian Trilogy (Varian Medical Systems) and Varian TrueBeam, were evaluated. Image quality of two EPID systems (ASI‐1000) and the two kV flat panel imagers (PaxScan 4030CB) was evaluated in terms of spatial resolution and contrast‐to‐noise ratio (CNR) using the QC‐3 and QCkV‐1 phantoms (Standard Imaging, Inc.). Cone‐beam CT image sets of the CatPhan phantom (The Phantom Lab.) were obtained for standard dose head (100kVp, 0.4mAs per projection) and body (125kVp, 1.04mAs) protocols. Imaging parameters of the default clinical settings were used. The end points of the comparison were spatial resolution, CT number linearity, low contrast detectability and image uniformity. Analysis of all types of images was performed by the PIPSpro software (Standard Imaging). Results: The critical frequency (f50 in units of lp/mm) of 0.446 and 0.403 were obtained for TrueBeam and Trilogy MV detectors, respectively. The CNR was found double for Trilogy. For kilo‐voltage detectors the f50 was 1.337 and 1.363, while the CNR was better by 6% in Trilogy machine. The CBCT comparison showed a 30% higher uniformity index for the TrueBeam system for pelvis protocol and 50% higher head. No significant difference was found in low contrast detectability and CT number linearity and resolution, 5 lp/mm. The Trilogy image was noisier by 35% and 30% for pelvis and standard head protocol, respectively. Conclusions: The critical frequencies of both kV and MV detectors were found better in TrueBeam, while CNRs were found better in Trilogy. TrueBeam preformed superiorly in CBCT in terms of image uniformity and noise level.
SU‐E‐J‐22: Effect of MLC Leaf Width on MLC Leaf Shifting Algorithm for Concurrent Treatment of Prostate and Pelvic Lymph Nodes
Authors: Shang Q , Qi P , Vassil A , Huang G , Xia P
Published: June 2012

Purpose: Our previous study showed that adjusting selected MLC leaf pairsto follow prostate movement is an effective strategy to account for daily prostate displacement during concurrent treatment with pelvic lymph nodes. MLC leaf width affects the quality of MLC shifting plans for longitudinal prostate motion compensation. This study is to investigate the effect of the MLC leaf width in compensation of the prostate movement. Methods: Fifty‐one daily CT on‐rail scans from three patients were available for this study. On these CTs, the prostate, bladder and rectum were manually contoured, and the lymph nodes contours were transferred from the planning CT after rigid bony registration. For each patient, three different IMRT plans were created based on a planning CT using leaf width of 2.5, 5, and 10 mm, respectively. For each CT, the prostate displacement was determined by dual imaging registration and compensated by shifting MLC resulting in a total of 153 MLC shifted plans. Results: Among 51 daily CTs, the average prostate movement along the superior/inferior direction was 1.1±3.7 mm (range: −6 to 6.5 mm). The differences in D99 of the prostate between the dose of the day and dose of the plan were 2.3±3.3%, 1.3±2.0%, and 4.4±5.1% for 2.5, 5, and 10 mm leaf width plans, respectively (p<<0.05). The corresponding differences in D99 of the lymph nodes were 0.7±0.9%, 0.6±0.9%, and 1.4±0.8%. The mean differences in D50 were 0.8%, 1.6%, and 2.7% for the bladder, and 10.0%, 3.9%, and 5.7% for the rectum, respectively. Conclusions: Using the MLC Shifting method to compensate for prostate movement in the longitudinal direction depends on the MLC leaf width and the magnitude of the prostate motion. The use of leaf width of 5 mm can provide sufficient tumor coverage without significantly affecting doses to the critical structures.
SU‐E‐J‐26: Automated Estimation Method of Patient Setup Errors Using Simulated Portal Images for Prostate Cancer Radiotherapy
Authors: Matsushita N , Arimura H , Shioyama Y , Magome T , Nakamura K , Umezu Y , Yoshitake T , Anai S , Yoshidome S , Honda H , Ohki M , Toyofuku F , Hirata H
Published: June 2012

Purpose: We developed a novel automated estimation method for patient setup errors based on simulated and real portal images for prostate cancer radiotherapy. Methods: The estimation of patient setup errors in this study was based on a template matching technique with a cross‐correlation coefficient and Sobel filter between the real portal image and localized pelvic template of reference image, which were DRR (digitally reconstructed radiography) images and simulated portal images. The simulated portal image was derived by projecting a CT image according to an inverse exponential power law of x‐ray attenuation for a water‐equivalent path length of each voxel of the CT image on each ray from a source to each pixel on the EPID (electric portal imaging device). A localized pelvic template of each patient in AP (anterior‐posterior) or lateral view was automatically extracted from the DRR or simulated portal images by cropping a rectangular region, which was determined by using the mean pelvic template and four anatomical feature points. We applied the proposed method to three prostate cancer cases, and evaluated it using the residual error between the patient setup error obtained by proposed method and the gold standard setup error determined by two radiation oncologists. Results: The average residual errors of the patient setup error for the DRR and simulated portal images were 0.79 and 1.26 mm in the left‐right (LR) direction, 3.17 and 2.05 mm in the superior‐inferior (SI) direction, 1.69 and 5.82 mm in the anterior‐posterior (AP) direction, 3.84 and 6.94 mm in Euclidean distance (ED), respectively. If we used the simulated portal image for LR and SI directions and the DRR image for AP direction, the Euclidean distance was 3.22 mm. Conclusions: The proposed method has a potential to correctly estimate patient setup errors for prostate cancer radiotherapy.
SU‐E‐J‐27: Effects of Metal Artifacts of KV and MV CT Images on Structure Delineation and Tissue Electron/Mass Density Calculation
Authors: He T , Tanyi J , Crilly R , Laub W
Published: June 2012

Purpose: To quantitatively evaluate effects of image artifacts of hip prostheses on the accuracy of structure delineation and tissue density calculation on kV and MV CT images. Methods: Five hip prostheses made of stainless steel, titanium and cobalt chrome alloys were positioned inside a water tank and scanned respectively on a Philips CT and a Tomotherapy Hi‐Art unit. Prostheses were positioned to mimic single and bilateral implantations. Rods of tissue materials of lung, water and bone were placed at locations next and distal to metal implants near femoral head, neck and stem of prostheses. kV and MV CT scans were repeated for each placement. On CT images, cross‐sectional outlines of metal implants and tissue rods were delineated. Densities of rod materials were determined and compared to the true values. Results: Metal artifacts were severe on kV CTs and minimal on MV CTs. Cross‐sectional outlines of metal implants and tissue rods on kV CTs were severely distorted by artifacts while those on MV CTs remained clearly identifiable. For kV CTs, deviations of measured tissue density from true value were up to 51.3%, 30.6% and 40.9% respectively for lung, bone and solid water. The magnitude of deviation was generally larger at locations closer to metal implants and greater with bilateral implants than single implant. For MV CTs, deviations of measured density from true value were less than 6% for all three tissue materials either with single or bilateral implants. Magnitude of deviation appeared to be uniform and independent of locations relative to metal implants. Conclusions: High Z metal artifacts on kV CTs can have severe impact on the accuracy of structure delineation and tissue density calculation, while on MV CTs, the impact is substantially less and insignificant. MV CTs should be considered for treatment planning on patients with high Z metal implants.
SU‐E‐J‐29: Evaluation of Effectiveness of Immobilization Devices for Radiation Therapy with Repeated CBCT Studies
Authors: Li H , Zhang L , Balter P , Dong L , Gillin M , Zhu X
Published: June 2012

Purpose: To evaluate the effectiveness of three different immobilization devices for lung radiation therapy with daily and/or weekly cone‐beam CTs (CBCT). Methods: Three different immobilization devices, short (IM1) and long (Im2) Vac‐lok cushion with wing boards (Civco), BodyFix (Im3, Elekta), were investigated. Repeated CBCT images for 3 SBRT patients immobilized with Im3, and 6 IMRT patients immobilized with IM1 and Im2 (3 each) were acquired. Each SBRT patient received 70 Gy in 10 fractions and setup daily with CBCT, while IM1 and Im2 patients were setup daily with orthogonal kV, and weekly CBCT (week 0–6). The day 1, 6 and 10 CBCT for Im3 were considered week 0–2 CBCT. Patient setup was first based on skins markers then shifts were made based on bony landmarks in kV and GTV with CBCT. Skin contours, which are further away from the isocenter and thus more sensitive to rotation and skin folding, were extracted in each CBCT data set and the difference on skin contours were investigated for both before and after shifts. Results: Over 2 weeks of treatment, Im3 has the smallest standard deviation for setup shifts (0.09, 0.16, 0.20 cm on LR, UD and IO directions) compared to IM1 (0.29, 0.35, 0.34 cm) and Im2 (0.11, 0.19, 0.40 cm), which indicates setup based on skin markers were the most reproducible for Im3. Over 6 weeks of treatment, Im2 (0.16, 0.18, 0.42 cm) is more reproducible than IM1 (0.44, 0.45, 0.35 cm). All 3 patients with IM1 and 2 patients with Im2 were found to have >1 cm difference in skin contour even after shifts were made. 1 patient with IM1 was found to have non‐reproducing skin folding of >3 cm difference. Conclusions: Information derived from repeated CT images could be used to evaluate the effectiveness of the immobilization devices.
SU‐E‐J‐36: A Flexible Integration of Key Technologies in Image‐Guided Radiotherapy for Accurate Radiotherapy System (ARTS‐IGRT)
Authors: Jia J , Liu F , Ren Q , Pei X , Cao R , Wu Y
Published: June 2012

Purpose: Image‐guided radiotherapy (IGRT) is becoming increasingly important in the planning and delivery of radiotherapy. With the aim of implementing the key technologies in a flexible and integrated way in IGRT for accurate radiotherapy system (ARTS), a prototype system named as ARTS‐IGRT was designed and completed to apply main principles in image‐guided radiotherapy. Methods: The basic workflow of the ARTS‐IGRT software was completed with five functional modules including management of patient information, X‐ray image acquisition, 2D/2D anatomy match, 2D/3D match as well as marker‐based match. For 2D/2D match, an image registration method was proposed based on maximization of mutual information with multi‐resolution and regions of interest. For the 2D/3D registration, optimizations have been employed to improve the existing digitally reconstructed radiography generation algorithm based on ray‐casting, and also an image registration method based on implanted markers with different numbers was adopted for 3D/3D match. In additional, the kV X‐Ray imaging on rail device was finished for a better internal anatomy image checking at any angle. Together with an infrared device, a positioning and tracking system was developed as well for accurate patient setup and motion monitoring during each treatment. Results: A lot of tests were carried out based on the head phantom to testify the availability of the improved algorithms. Compared with a set of controlled experiments adopted on the released commercial IGRT platform in the hospital, the functions of both software and hardware were testified comprehensively. The results showed a validity verification of ARTS‐IGRT. Conclusions: The accuracy and efficiency of ARTS‐IGRT on both software and hardware proved to be valid. And also with a flexible and user‐friendly interface it can meet the principles of clinical radiotherapy practice. Supported by the Natural Science Foundation of Anhui Province (11040606Q55) and the National Natural Science Foundation of China (30900386).
SU‐E‐J‐39: Minimizing IGRT Imaging Exposures: KV Radiograph Vs. KV‐CBCT Vs. MV Portal Images
Authors: Ding G , Munro P
Published: June 2012

Purpose: To compare the IGRT doses from MV, kV and CBCT images. Methods: kV imaging systems integrated into Varian Trilogy and TrueBeam accelerators were modeled using BEAMnrc/DOSXYZnrc Monte Carlo codes and the dose to calibration phantoms for a variety of kV beams(kVp, bow‐tie filters, etc.) were calculated. The doses to the same phantoms and kV beams were then measured experimentally using calibrated ion‐chambers.The “calibrated” Monte Carlo kV beams were used to calculate dose to CT images of patients. Organ doses were analyzed using DVHs. Results: The doses to the prostate are 0.015 and 2.2cGy using AP kV and MV images; are 0.06 and 2.3cGy using lateral kV and MV images; and, are 1.7 cGy using CBCT images. For head and neck images, the doses to the eye are 0.08 and 0.001 cGy using AP and PA kV images; are 2.3 and 1.8cGy using AP and PA MV images; are 0.001 and 2.4cGy for lateral kV and MV images; and, are 0.2 cGy for CBCT images. For kV radiographs, organ doses can be further reduced, by over 30%, by using bow‐tie filters. CBCT doses to the prostate are 1.6 and 0.9cGy for OBI and TrueBeam pelvis scans; a >40% dose reduction for the same image quality. For OBI CBCT head scans the doses to the eye and brain stem are 0.2 and 2.8cGy, respectively. Conclusions: Due to the low penetration of kV beams,selecting beam angles so that the sensitive organs are near the beam exit, and/or using bow‐tie filters, can substantially reduce organ doses when using kV radiographs. For daily positioning of pediatric brain patient with a set of orthogonal kV images, a CBCT scan, or a set of orthogonal MV images, the doses to the eyes are 0.1, 0.2, and 4.7 cGy, respectively.
SU‐E‐J‐49: Reliability Study of ExacTrac‐ System Image Isocenter Using an On‐Demand QA Procedure
Authors: Wang X , Zhao Z , Du W , Li X , Yang J
Published: June 2012

Purpose: To develop a pointer based quality assurance (QA) procedure that quickly verifies the congruence of ExacTrac® image isocenter with the radiation isocenter of a linear accelerator (linac), and use it to study the accuracy and reliability of the ExacTrac® image isocenter. Method and Materials: A 6 mm diameter tungsten ball was aligned with the room laserusing a pointer alignment system. By measuring the positions of ExacTrac®image isocenter and linac radiation isocenter relative to the ball, thedeviations between the two isocenters was easily calculated. The ExacTrac®image isocenter relative to the ball was measured using the built‐in Winston‐Lutz Pointer test, in which kV images of the ball are projected to flat panels and the center of the ball to the image isocenter are calculated by ExacTrac® software. The linac radiation isocenter relative to the ball was measured by taking the portal images of the ball at four gantry angles, 0,90, 180 and 270 with a 6 × 6 cm2 field. An in‐house developed software was used to identify the center of the ball and the center of the radiation. This procedure was used in weekly QA for a year in this work. Results: A simple QA procedure was developed to ensure the accuracy of ExacTrac® imageisocenter against the linac radiation isocenter. The procedure can be executed in less than 20 minutes. The data show the position error were ‐ 0.27±0.30, 0.52±0.24, 0.18±0.22 mm in the lateral, vertical and longitudinal directions, and the max deviation were 0.86, 0.89 and 0.54 mm respectively. Conclusion: The weekly verification data showed the ExacTrac® image isocenter can be very reliable with sub‐millimeter accuracy. This level of imaging alignment accuracy is necessary for imaging guided SBRT procedures. The quick QA procedure can be applied on‐demand to ensure the accuracy of ExacTrac® isocenter.
SU‐E‐J‐54: Bone Detection in MR Images and Absorbed Dose in a Material Behind Bones in Radiotherapy
Authors: Korhonen J , Kapanen M , Keyriläinen J , Seppälä T , Tuomikoski L , Tenhunen M
Published: June 2012

Purpose: To determine whether bones could be localized accurately by using MR images only in radiotherapy treatment planning. Furthermore, to measure absorbed dose in a material behind different parts of the bone, and to evaluate dose calculation error in a pseudo‐CT image by assuming a single electron density for the bones. Methods: A dedicated phantom was constructed using fresh deer bones and gelatine. The accuracy of the bone edge location and the bone diameter in MR images were evaluated by comparing those in the images with the actual measures. The absorbed dose behind the bones was measured by a matrix detector at 6 and 15 MV. Thedose calculation error in the bulk density pseudo‐CT image was quantified by comparing the calculation results with those obtained in a standard CT image by superposition and Monte Carlo algorithms (TPSs: Xio 4.60 and Monaco 3.00, Elekta CMS Software). Results: The examination of bone position revealed that the bones can be localized within a 1‐mm‐pixel‐size in the MR images. The measured dose behind less than 2.5‐cm‐thick femur indicated that the absorbed dose behind the middle part of the bone is approximately one percentage unit (6 MV: 1.3%, 15 MV: 0.9%) smallerthan that of the physically narrower bone edge. The calculations illustrated that the bulk density pseudo‐CT image used causes errors up to nearly 2% to the dose behind the middle part, but also, the edge of the femur. Conclusions: This research ascertains that the bone localization is not a restrictive issue for radiotherapy treatment planning by using MR imageonly. The work indicates also that the decrease in absorbed dose is not necessarily dependent on the diameter of the bone. Future research shouldinvestigate the generation of more complex pseudo‐CT images and the dosecalculations by using these. Supported by Elekta.
SU‐E‐J‐61: Multi‐Criteria Optimization for IGRT Decision Processes
Authors: Winey B , Balter J
Published: June 2012

Purpose: To develop a multi‐criteria optimization framework for image guided radiotherapy decision processes. Methods: An algorithm is proposed for a multi‐criteria framework for the purpose of patient setup verification decision processes. Optimal patient setup shifts and rotations are not always straightforward, particularly for deformable or moving targets of the spine, abdomen, thorax, breast, head and neck and limbs that change as a Result of treatment. The algorithm relies upon dosimetric constraints and objectives to aid in the patient setup and plan delivery such that the patient is positioned or the plan is optimized to maximize tumor dose coverage and minimize dose to organs at risk while allowing for daily clinical changes. A simple 1D model, a lung lesion are presented and a spine lesion. Results: The algorithm delivers a multi‐criteria optimization framework allowing for clinical decisions to accommodate patient target variation which make setup decisions less straightforward. With dosimetric considerations, optimal patient positions and plan parameters can be derived. Conclusions: A multi‐criteria framework is demonstrated to aid in the patient setup and determine the most appropriate daily position considering dosimetric goals. Future implementations include optimizations relying upon multiple plans, field parameters, and other dose metrics (TCP, NTCP, EUD, etc).
SU‐E‐J‐65: Feasibility Study of Backscatter Imaging for Image‐Guided Radiotherapy
Authors: Sensakovic WF , Wang S , Yao R , Turian J , Chu J
Published: June 2012

Purpose: Tracking tumor motion during external beam radiation therapy is a major factor limiting the treatment of lung tumors. Several tracking techniques have been previously reported; however, these are limited to 2D motion, fail to capture image data during treatment delivery (e.g., patient setup imaging), fail to capture motion along the beam axis (MV CineMode), or increase patient dose (kV fluoroscopy). Creating images from radiation that is naturally scattered from the patient during treatment could overcome the limitations of other techniques. This study investigated the feasibility of using photon scatter to create images during external beam radiation delivery. Methods: A prototype imager was created using a Trilogy Linac, pinhole collimator, and computed radiography (CR) plate. Two small cylinders (solid water and cerrobend) were placed in the path of a 6MV beam. The collimator/CR plate was placed at 45° and 90° from the gantry head and 2000MU was delivered. Optically‐stimulated luminescent (OSLD) detectors were placed on the surface of the CR plate to measure photon dose. Contrast‐to‐noise ratios (CNR) were calculated for each peg to assess image quality. Results: At 45°, OSLD dose was 1.3±0.2cGy and the CNRs were 1.5 and 5.3 for water and cerrobend, respectively. OSLD dose increased to 2.6±0.3cGy and CNR increased to 14.8 and 18.3 at 90°. Scatter from the gantry head and the pinhole collimator are the major sources of noise which limit image quality. The measured CNR satisfied the Rose criteria for detectability (CNR > 3–5) for the 90° gantry orientation. Further, scatter imaging should satisfy the Rose criteria if output is reduced from 2000MU to 200MU. Conclusions: Preliminary results confirm the feasibility of using scatter imaging for in situ treatment monitoring. Future work will investigate creation of tomosynthesis images and improving image quality using increased shielding and a multi‐pinhole collimator.
SU‐E‐J‐78: Enhance Patient Positioning Accuracy with Optically Guided Frameless Target Localization Technique for Intracranial Radiation Therapy
Authors: Zhu J , Crossan P
Published: June 2012

Purpose: To make use of the optical guided frameless stereotactic target localization technique to detect the interfraction and intrafraction patient positioning errors and correct the patient position for fractional intracranial therapy, therefore, to enhance the patient positioning accuracy. Methods: Four patients who underwent fractionated intracranial intensity modulated radiation therapy (IMRT) were studied. For each patient, in addition to the thermoplastic head mask, frameless array and bite‐block were used for patient positioning. Optical guided frameless planning was utilized to define the coordinates of the isocenter during the treatment planning procedure. In each treatment fraction, the patient was first set up by matching the room lasers to the BB markers attached on the mask. The optical guided frameless system then captured the patient position and reported displacements of the current patient position to the planned patient position. These displacements were called interfraction errors. The treatment plan was designed to have up to 8 non‐coplanar fields. Dose delivery of the non‐coplanar fields required couch rotation which introduced isocenter displacements called intrafraction errors. Population statistics of interfraction and intrafraction errors (4 patient, 110 fractions) were calculated. The optical guided frameless system monitored the patient positioning errors and provided guidance for correction prior to the dose delivery. Results: Among all patients and radiation treatment fractions, the overall detected interfraction error was 3.6±1.3 mm (mean ±SD) and the intrafraction error was 1.4±0.8 mm. Both types of errors were online corrected with the guidance of optical guided frameless system. Conclusions:: Conventional laser guided thermoplastic mask patient position for intracranial therapy has interfraction and intrafraction errors. The optical guided frameless target localization technique allows clinicians to dectect and correct these errors online, therefore, to enhance the patient positioning accuracy for intracranial radiation therapy.