bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐I‐85: Impact of Partial Volume Effect On PET Image: Quantification Aspect
Authors: Villeneuve R , Risso R , Garnier N , Paulmier B , Serrano B
Published: July 2013

Purpose: Partial Volume Effect (PVE) is not taken to account in clinical routine although it is one of the major sources of error in quantification in PET image especially in small size lesion. Depending on its size, the uptake lesion is underestimated. It mainly depends on the spatial resolution of the system and the chosen sampling. The purpose of this study is to highlight this difference witch characterizes the camera. Methods: This study was performed on a new generation PET/CT (Siemens mCT), fitted with four rings and time of flight (TOF). We used an anthropomorphic TORSO phantom representing a patient. Spheres of various diameters (6 to 33mm) were introduced into the lungs (air density) and the thorax (water density). Total whole body concentration were between 3 and 5 MBq/kg. SUV (Standardized Uptake Value) values were fixed successively 2, 4 and 8. We compare those values with the maximal uptake level using SUVmax and SUVmean on PET acquisition. Parameters reconstructions were: 2 iterations, 21 subsets, gaussian filter (FWHM=2mm), matrix size 200×200 pixels, True X algorithm (OSEM+PSF) and TOF with acquisition time of 150 s. Results were expressed as mean +−sd. Results: The reproducibility for each acquisition of SUV max and mean was high (respectively r=0.96, p=0.0003 and r=0.95, p=0.0004). The largest sphere (diameter 33mm) was considered as the reference for the normalization of results. The average results of SUVmax normalized in water and air compared to theorical value were respectively below 4% and 20% for diameter below 14mm. For diameter under 14 mm it decreases drastically. For SUVmean the decay is progressive under 26mm in each medium. Conclusion: Following the SUVmax, wich is the clinical quantification parameter in PET images, PVE occurs at 14mm corresponding to 3 times the spatial resolution. These characteristics show the limits of the performance of our TEP camera.
SU‐E‐I‐89: Real‐Time Information and Decision Support for Radiological Emergency Response
Authors: Lee E , Pietz F
Published: July 2013

Purpose: Emergency response and medical preparedness for radiological incidents is one of the critical cornerstones for Homeland Security, along with biological and chemical incidents. The recent Fukushima Daiichi nuclear plant incidents underscore the paramount importance of such preparedness and response capability. Such needs are wide‐spread as many nations employ nuclear plants for energy generation. In this work, we focus on development and deployment of a real‐time simulation and decision support system, RealOpt‐CRC, along with the knowledge data bank that can be used by regional/local radiation/public health administrators to prepare for and deal with radiological emergency situations. Methods: Large‐scale simulator for modeling systems operations and performance, computer graphics for mouse‐click facility design and optimization for resource allocation are designed and implemented into a web‐base secured system. The RealOpt system offers operations capability to i)rapidly setup shelters to house the displaced/at‐risk population, ii)determine optimal resource allocation and operations for rapid screening and decontamination; iii)recommend and facilitate practical steps to minimize exposure risk; iv)perform effective population registry for long‐term health monitoring; and v)service the displaced population on day‐to‐day needs. Results: Comparison of current planning versus plans from our system shows a 5‐fold efficiency improvement. This translates to more people being screened and decontaminated within limited time and resources and thus improve safety and health monitoring for the affected population. Further, workers are more confident and operations are smoother and more organized, thus ensuring public confidence and team‐morale. Conclusions: The system has real‐time computation capability and can be used by emergency management administrators for actual strategic and operational planning and execution; to educate and train current and future personnel on decision making under uncertainties; and to simulate responses to catastrophic events through systematic analysis of numerous scenarios, including worst‐case, to learn of erratic as well as efficient response strategies. Real‐time data‐feeds allow re‐configuration on‐the‐fly as the event unfolds. National Science Foundation
SU‐E‐I‐90: Magnetoencephalography (MEG): Quantitative Comparison of Oscillations and Synchronization Differences/similarities in Post‐Surgery/pre‐Irradiation Patients and Control Subjects
Authors: McGowin I , Bourland J , Peiffer A , Simpson S , Rawley J , Godwin D
Published: July 2013

Purpose: To evaluate brain synchronization and connectivity differences in post‐surgery/per‐irradiation patients and healthy controls with two different MEG approaches: ECD (equivalent current dipole) and SAM (synthetic aperture magnetometry). Methods: An 8 min resting state scan was collected from 5 post‐surgery/pre‐irradiation patients and 5 sex/age‐matched control subjects. Scans were collected on a CTF MEG 275‐sensors system. All subjects were scanned in upright, open‐eyes position in a magnetically shielded room. MRI whole brain volume was divided into 4mm voxels allowing sensor signal space to be mapped into brain space. Measured signals were filtered into Δ, o/, α and β bandwidths and localized by ECD and SAM. SAM is a type of beamforming, a signal processing technique for sensor array data; the method works like a digital filter by focusing on each voxel while attenuating the majority of signal from all other voxels. Resultant SAM waveforms were evaluated to reject muscle and/or non‐physiological artifacts. The ECD method was applied to the same data and bandwidths to localize sources, its orientations and strengths. Statistical analysis evaluated connectivity and synchronization using dPLI (direct phase lag index) and IC (imaginary coherence). Resultant SAM and ECD maps were compared for differences and similarities. Results: Currently the project is collecting data. The full per‐irradiation data is expected to be completed by June 2013. The study goal is to establish the best method/approach to evaluate resting state MEG data. Conclusion: We expect 3 possible outcomes of the study: no difference, subtle difference, statistically significant difference in resting state analysis between these two methods. The two first outcomes are easy to address by choosing the most time‐efficient method. The last case will require further investigation of both methods to establish the ground of the difference and the most appropriate method analysis for the resting state. Partial support by Radiation Oncology and Neurology Departments at Wake Forest Baptist Health System and by Dalton McMichael Fund in Cancer Research. No conflict of interest is reported.
SU‐E‐I‐92: Vacuum Design of An X‐Ray Camera Using Triboelectric X‐Ray
Authors: Moya‐Sanchez Spectra E Ulises , Romo‐Espejel JA
Published: July 2013

Purpose: Design a low‐energy X‐ray imaging system with the method of triboelectric X‐rays with same penetration levels as a conventional X‐ray tube, intended for low‐energy diagnostics such as mammography. Methods: The results from triboelectric X‐rays experiments obtained by Camara and Hird, were characterized in terms of the beam penetration, using the Mo target data measured by Hird and Camara and the parametrized spectra data of an X‐ray tube with Mo anode that was computed with an equation proposed by J. Boone. Later, a vacuum chamber was built to reproduce a triboelectric X‐ray source, with a PMMA (C5O2H8)6 (1.19 g/cm3) and black Naylamid (1.16 g/cm3), and the thickness of the wall needed to be computed in order to obtain same penetration efficiency levels. Results: The results of the computation of HVL for both spectra were similar in respect to Al thickness, the HVL of the triboelectric source resulting in 0.17 mm of Al and from the X‐ray tube in 0.22 mm of Al. The same HVL of both spectrum is given when 32 kV are applied to the X‐ray tube. The vacuum chamber that was built had 6 mm of PMMA wall thickness. An electronic circuit has been designed to build a radiation detector in order to provide a full imaging system with a triboelectric X‐ray source and imaging detector. Conclusion: According to our computations it is possible to obtain a HVL from a triboelectric X‐ray source, same to a HVL from an X‐ray tube with enough beam penetration to obtain a low‐energy medical diagnostic image.
SU‐E‐I‐93: Effect of Exposure Response Function On Flat‐Field Non‐Uniformity Metrics to Assess Digital Detector Performance
Authors: Dave J , Gingold E
Published: July 2013

Purpose: To investigate how digital radiography flat‐field image quality metrics are affected by the exposure response function. Methods: Sets of four flat‐field images were acquired from 3 Carestream digital radiography detectors at 2 institutions using manufacturer specific calibration geometry over a range of input air kerma levels (2.4‐160μGy). The images were exported from the acquisition system with both logarithmic and linear data space conversions (i.e., exposure response functions). The images were also retrieved from PACS. The percent non‐uniformities in three characteristic metrics i.e., signal (mean), noise (standard deviation) and SNR were calculated; local non‐uniformities were based on a 100mm2 region and its nearest neighbors and global non‐uniformities were based on regions with extreme values of signal, noise and SNR. Results: Images exported from the acquisition computer with logarithmic exposure response function were labeled For‐Processing with Photometric Interpretation=Monochrome1, Pixel Intensity Relationship=Log and Relationship Sign=+1. Interestingly, the images with linear exposure response function also indicated a Log Pixel Intensity Relationship. For images exported from PACS, the corresponding DICOM attributes were For‐Presentation, Monochrome2, log and −1. As expected, the characteristic signal, noise and SNR values showed exposure dependency consistent with the exposure response function. Using logarithmic data space conversion as reference, the absolute differences in non‐uniformities calculated using linear data space conversion ranged from 0.1% to 10.7% and using images from PACS ranged from 0% to 11% for detectors configured with an appropriate gain map. For one detector configured with an inappropriate gain map, the discrepancy in calculated non‐uniformities between linear and log data ranged from 0% to 34.6%. These differences in non‐uniformities at only the calibration air kerma level were within 4.5%. Conclusion: The calculated non‐uniformity metrics showed a dependence on the exposure response function. Thus, for detector performance evaluation, comparisons and quality assurance testing, knowledge of the exposure response function is required.
SU‐E‐I‐95: Verification of AAPM TG 116 X‐Ray Beam Quality by CdTe Spectroscopy
Authors: Chung J , Willis C
Published: July 2013

Purpose: X‐rays produced by an x‐ray tube comprise a polychromatic spectrum. The American Association of Physicists in Medicine Task Group 116 (AAPM TG116) defined a method for producing a beam of standard quality for the purpose of calibrating digital x‐ray image receptors. The standard beam calibration condition is based on simulations of the International Electrotechnical Commission (IEC) RQA5. Our project was to measure the spectrum produced under TG 116 conditions and compare to the RQA5 spectrum predicted by simulation. Methods: X‐ray spectra were acquired using a CdTe solid state detector with a spectrum analyzer for three different x‐ray beams conforming to TG116 conditions. Acquired spectra were corrected for Cd and Te escape events using XRF‐XP software and for CdTe energy dependent efficiency. Spectra were simulated using the Tung1 computer program. Inherent filtration and tube potential were varied to obtain the best simulation of the RQA5 half‐value layer (HVL). Results: HVLs calculated from the acquired spectra are lower than HVLs measured. Under same kVp and inherent filtration, Al spectra and Cu spectra are very similar. Comparison of direct measurements with simulations reveals the strong influence of kVp on the resulting spectra. Acquired spectra are more similar to each other than to any of the simulated RQA5 spectra. Conclusion: Direct measurements of x‐ray spectra confirm the similarity of beams produced under TG116 conditions with either Cu or Al filtration. However, contrary to TG 116, the selection of kVp makes a significant difference in the spectra. Further work is needed to acquire spectra at the highest kVp allowed by TG 116 to fully assess the effect of kVp and HVL tolerances on the x‐ray spectrum.
SU‐E‐I‐96: Development of Monte Carlo Based Voxel Head Phantom for Dose Calculation in Periapical Radiography
Authors: Oh Y , Kang C , An S , Kim J , Ji y , Lee R
Published: July 2013

Purpose: Computational anthropomorphic phantoms represent human body using mathematical or voxelized description. The voxel phantom, which was modeled in tomography images of a human, consists of shape, material and mass of the human body composition. It can be used in calculating organ dose of humans. In this study, we develop the voxel head phantom on the basis of computed tomography (CT) image, and calculate organ doses using MCNPX simulation code and the voxel head phantom to evaluate the radiation dose delivered using a conventional and a novel periapical radiography. Methods: The voxel head phantom is developed based on CT images of RANDO phantom (The Phantom Laboratory, Salem, NY) designed to have the same absorption as human tissue at the radiography exposure levels. The voxel head phantom is constructed with bone, air and soft tissue applied through brightness levels of CT images. The Organ doses are calculated in head structures, such as bone marrow, thyroid, salivary gland, oesophagus, brain, skin and eye. To verify calculated doses, the calculated dose values are compared with measured dose values using dosimeters and a fabricated QA phantom for dose measurement. Results: A novel periapical radiography has lower absorbed doses than a conventional periapical radiography at head organs excepting the sublingual gland. And, the differences between the calculated dose values and the measured dose values are within 20 % according to the exposure energy and the depth of penetration. Conclusion: The voxel phantom and the procedure for calculating radiation doses using MCNPX simulation code are useful tools for detecting the absorbed organ dose, which cannot be measured directly in patients.
SU‐E‐I‐101: Multi Taper Coherence Measurements for Characterizing Scatterer Number Density
Authors: Rubert N , Varghese T
Published: July 2013

Purpose: Scatterer number density (SND) per resolution cell has been investigated by many authors as a useful tool for tissue classification in diagnostic ultrasound. SND has been shown to be capable of distinguishing between benign and malignant tumors in the breast, and of determining the degree of lens hardening in cataract formation. Low SND results in coherent scattering, which may be measured using the generalized spectrum (GS). The GS has been measured in ultrasound by correlating windowed FFT's of ultrasound radiofrequency (RF) data, where the data windows have been chosen ad hoc. We seek to improve GS calculations for distinguishing between tissue containing different number densities using Thomson's multi‐taper method. Methods: Three tissue‐mimicking (TM) phantoms consisting of glass beads and graphite powder suspended in agar were constructed. Scattering was mainly due to the glass beads and attenuation was mainly due to the graphite powder. The phantoms had number densities of 2, 10, and 400 glass beads per mm3. RF data was recorded using a 9L4 and 18L6 transducer from a Siemens S2000 system. In this study we compare two different methods of calculating spectral coherence. In one method we use a single taper and convolutionally smooth the GS. In the second method we compute the GS using Thomson's multi‐taper (MT) method. We show that the MT method outperforms diagonally smoothed single‐taper spectral estimates for distinguishing between the different phantoms. Results: We find that the MT method results in a greater separation between the mean coherence values with a lower standard deviation than single‐taper calculation methods, as the SND is varied. Conclusion: When SND is used to distinguish between different tissues, differences will be better captured if coherence is calculated with Thomson's multi‐taper method rather than a single taper.This work was supported by NIH‐NCI grants R01CA112192‐06 and T32 CA09206‐32.
SU‐E‐J‐01: Real‐Time Paraspinal Tumor Monitoring From CBCT Projections
Authors: Brunet D , Moseley D
Published: July 2013

Purpose: To assess the feasibility of an automatic near real‐time monitoring and tracking system for paraspinal SBRT. In particular, to measure the robustness of the 2D‐3D rigid registration between segmented volumes and kV fluoroscopic images as a function of the gantry angle in a VMAT system. Methods: Segmentation of an orthopedic fixation device fastened to the vertebral column was obtained by thresholding a CBCT volume. A 3D‐2D rigid registration with each of the kV fluoroscopic images was performed for all the 655 projection images taken at various gantry angles distributed through 360 degrees of rotation at a rate of 5.5 frames per second. In order to tackle the low contrast and high noise, a localized correlation measure was proposed as the objective function. An exhaustive search was carried on for all translations between ‐ 5 and 5 mm with 0.2 mm steps and each rotation between ‐ 5 and 5 degrees with 0.2 degrees steps. Results: For the majority of gantry angles, the minimizer is the identity transform as expected. Not surprisingly, translation and rotation for certain gantry angles proved harder to register than others depending if the registration is in‐plane or out‐of‐plane. The mean localization error (+/− 1 SD) for translation in mm was (L/R,S/I,A/P) = (0.04+/−0.4, 0+/− 0mm,0.05+/−0.4) and for rotation in degrees was (pitch, roll, yaw) = (0.16+/− 0.78, ‐ 0.46+/−2.95, 0.17+/−0.78). Conclusion: A feasibility study of a 3D‐2D rigid registration for monitoring paraspinal tumor in the presence of hardware was successfully undertaken. The generalization to the more challenging case without hardware will be studied in the future. A model of the patient movement during treatment will then be combined with the developed model for registration uncertainty in function of gantry angle for a full monitoring and tracking system. OCAIRO grant (Ministry of Research and Innovation, Government of Ontario)
SU‐E‐J‐04: On‐Treatment Volumetric Imaging During Respiratory Gated VMAT
Authors: Choi K , Xing L , Li R
Published: July 2013

Purpose: To obtain on‐treatment volumetric patient anatomy during respiratory gated VMAT. Methods: On‐board imaging device integrated with Linacs offers a viable tool for obtaining patient anatomy during radiation treatment delivery.In this study, we acquired beam‐level kV images during gated VMAT treatments using a Varian TrueBeam\texttrademark STx Linac. These kV projection images are triggered by a respiratory gating signal and can be acquired immediately before treatment MV beam on at every breathing cycle during delivery. Because the kV images are acquired with an on‐board imaging device during a rotational arc therapy, they provide the patient anatomical information from many different angles or projection views (typically 20– 40). To reconstruct the volumetric image representing patient anatomy during the VMAT treatment, we used a compressed sensing method with a fast first‐order optimization algorithm. The conventional FDK reconstruction was also used for comparison purposes. The method was tested on a dynamic anthropomorphic physical phantom as well as a lung patient. Results: The reconstructed volumetric images for a dynamic anthropomorphic physical phantom and a lung patient showed clearly visible soft‐tissue target as well as other anatomical structures,with the proposed compressed sensing‐based image reconstruction method. Compared with FDK, the compressed sensing method leads to a ∼2‐and 3fold increase in contrast‐to‐noise ratio around the target area in the phantom and patient case,respectively. Conclusion: The proposed technique provides on‐treatment volumetric patient anatomy, with only a fraction (<10%) of the imaging dose used in conventional CBCT procedures. This anatomical information may be valuable for geometric verification and treatment guidance, and useful for verification of treatment dose delivery, accumulation, and adaptation in the future.
SU‐E‐J‐05: Intrinsic Geometry Reconstruction for the Study of Geometric Variations in Linac‐Based CBCT System
Authors: Zou G , Chetty I , Jin J
Published: July 2013

Purpose: To develop a software to derive the intrinsic geometric parameters of a cone‐beam‐CT (CBCT) system from its projection images, for studying geometric variations in linac‐based CBCT. Methods: The projection images were taken with an IsoCal phantom, which has 16 steel ball‐bearings (BBs) with known geometry, using a Varian on‐board imaging system. The computational pipeline includes 4 components: 1) extraction of each BB position in the projection image with sub‐pixel precision using a progressive thresholding method followed by ellipse contour fitting; 2) computation of a 3‐by‐4 matrix which transforms each 3D‐phantom coordinates of BB into its corresponding 2D‐image coordinates; 3) derivation of a complete set of CBCT geometric parameters from the matrix in a phantom coordinate system; 4) distinguishing the effect of phantom setup by defining a new coordinate system intrinsic to the tractories of the moving gantry and minimizing the discrepancy between the transformed and nominal coordinates. The software was used to study the repeatability of CBCT geometric variations in a 2‐month period. Results: The source and imager showed repeatable 0.3–0.5 mm sine‐like variation patterns with random noise in both U and V directions during a 360° gantry rotation, consistent with our knowledge that the gantry‐head sagging may induce gantry‐angle dependent variation. The noise levels for the source‐U, source‐V, imager‐U, imager‐V were about 0.3, 0.1, 0.2 and 0.15 mm, respectively, suggesting the detection limits of the method. The source‐to‐imager axial direction variation for the source and imager showed ∼2 mm periodic noise patterns, possibly due to the fact that projection positions of BBs in the imager are not sensitive to the axial variation. Conclusion: We have developed a software module to derive geometric parameters of the CBCT system. The method has accuracies of 0.1–0.3 mm in the U− and V− directions, but is not as accurate in the axial direction. The study is supported by NIH Grant Number 5 R01 CA166948‐02.
SU‐E‐J‐06: Necessity of 4D Cone‐Beam CT Imaging in Patient Setup for Gated Stereotactic Body Radiation Therapy of Lung Cancer
Authors: Wu J , Chen F , Ye J , Mehta V , Loiselle C , Spiegel J
Published: July 2013

Purpose: To investigate the necessity of 4D‐CBCT imaging in patient setup for gated lung SBRT, and provide alternative solutions if 4D‐CBCT imaging is not available. Methods: 4D‐CT images were acquired for five patients underwent lung SBRT. Average Intensity Projection (AIP) CTs were reconstructed. Gating plans were generated using the 50% end‐exhalation (EE) CT with 30% duty cycle. PTV was created by adding a 5mm margin to the union of GTVs contoured on the 40%‐60% CTs. Prior to each treatment, localization images (3D‐CBCT and 4D‐CBCT) were acquired and registered to their reference CTs for setup comparison. Six registration scenarios were investigated. For the first four scenarios, localization images were registered to the reference images by matching tumor centers: EE‐CBCT to EE‐CT, EE‐CBCT to AIP‐CT, 3D‐CBCT to EE‐CT, and 3D‐CBCT to AIP‐CT. For the intermediate two scenarios, two additional registrations were performed by matching tumor superior edges. The EE‐CBCT to EE‐CT registration was taken as the bench mark. Relative tumor offsets of the remaining registrations to the bench mark were analyzed. Results: For tumor center matching, the relative tumor offsets of the EE‐CBCT to AIP‐CT registration were 0.1±0.1(LR), 0.5±0.1(SI), 0.1±0.1(AP)cm. The offsets for the 3D‐CBCT to EE‐CT registration were 0.0±0.0, 0.5±0.1, 0.1±0.1cm. The offsets for the 3D‐CBCT to AIP‐CT registration were 0.1±0.0, 0.1±0.0, 0.0±0.0cm. For tumor superior edge matching, the offsets of the EE‐CBCT to AIP‐CT registration were 0.1±0.1, 0.1±0.0, 0.1±0.1cm. The offsets of the 3D‐CBCT to EE‐CT registration were 0.0±0.1, 0.0±0.1, 0.0±0.0cm. Conclusion: 4D‐CBCT imaging is crucial to precisely localize the tumor within the gating window. If 4D‐CBCT imaging is not available, registration of 3D‐CBCT to AIP‐CT is recommended by matching tumor centers. If EE‐CT is used as the reference, tumor superior edges should be matched. Otherwise, either a larger PTV margin should be used or the tumor might be mistargeted.
SU‐E‐J‐07: 3‐D Commissioning for An Image‐Guided Small Animal Micro‐Irradiation Platform
Authors: Qian X , Admovics J , Wuu C
Published: July 2013

Purpose: In a high resolution image‐guided small animal micro‐irradiation platform, the mouse stage rotation for cone beam CT imaging is perpendicular to the gantry rotation for sub‐millimeter radiation delivery. As such, a 3‐D dosimeter, PRESAGE, can provide an excellent tool for verifying both imaging and irradiation coordinates in one system. Methods: The study was done by using PRESAGE dosimeters and optical scanner. In the small animal platform, both of the mouse stage and the gantry can rotate 360°. Isocentricity and coincidence of the mouse stage and gantry rotations were evaluated with starshots. A dosimeter was placed at the isocenter approximately on the mouse stage. Firstly, the gantry moved to 90° in the irradiation coordinate. The mouse stage rotated 360° while the x‐ray was delivered to the dosimeter at certain angles, then both of the gantry and mouse stage moved back to home position. Secondly, the gantry rotated 360° to deliver micro beams to the dosimeter at certain angles. Thirdly, steps one and two were repeated 3 times using 3 dosimeters to determine short‐term reproducibility. Finally, dosimeters were canned using an optical scanner to get results. Dosimetric measurements were also performed. Results: The gantry isocentricity is 1.09 ± 0.15 mm and the mouse stage rotation isocentricity is about 1.1 ± 0.15 mm. Agreement between the measured isocenters of irradiation and imaging coordinates was determined using each starshots from dosimeters. The short‐term reproducibility test yielded 0.5 ± 0.1 mm between the imaging isocenter and the irradiation isocenter, with a maximum displacement of 0.8 mm. The rest results will be presented. Conclusion: The 3‐D PRESAGE dosimeter can be very useful in precise verification of targeting for a small animal irradiation research. In addition, a single PRESAGE dosimeter can provide 3‐D information in both geometric and dosimetric uncertainty, which is crucial for translational studies.
SU‐E‐J‐08: Assessing and Minimizing the Dose From KV Cone Beam CT to Pediatric Patients Undergoing Radiation Therapy
Authors: Alaei P , Spezi E , Ehler E , Dusenbery K
Published: July 2013

Purpose: To assess the dose from kilovoltage cone beam CT to pediatric patients undergoing image‐guided radiation therapy and to compare the dose between standard and low dose protocols. Methods: Imaging dose to several pediatric patients undergoing image‐guided radiation therapy, and methods to reduce it, have been assessed using a treatment planning system (TPS) and Monte Carlo (MC). The imaging dose from an Elekta XVI kV CBCT system has been added to the treatment plans to calculate total dose to patients. The maximum dose and its location, dose to isocenter and various organs, and its correlation with patient size and body mass index (BMI), have been analyzed. The calculations have been performed using standard imaging protocols and low dose and/or modified ones. The TPS calculations have been supplemented with MC to assess the dose to bone and skin which cannot be accurately calculated using the TPS. Results: Employing a lower dose imaging technique for pediatric patients by: 1) Choosing a pre‐set imaging protocol using a lower technique that may be designated for a different anatomic region, i.e. using the Head and Neck protocol on a pelvic scan, or 2) Modifying a standard imaging protocol by reducing the mAs or number of frames, could substantially reduce the imaging dose. The image quality of the lower dose techniques has been found to be acceptable for patient position verification. Using a low dose or modified protocol could Result in an 18 fold decrease in the imaging dose. Conclusion: In order to most accurately track exposure, dose from daily kilovoltage CBCT can be added to pediatric patient treatment plans using previously commissioned kV CBCT beams in a treatment planning system and supplemented with Monte Carlo calculations. A technique for delivering lower dose is suggested and differences between standard and low dose protocols have been quantified.
SU‐E‐J‐09: Validation of TrueBeam Imager Tests with An Independent Analyzer Software
Authors: Valencia F , Figueroa E
Published: July 2013

Purpose: To set guidelines, protocols to follow and a quality assurance program for the TrueBeam imager installed at INCMNSZ. Validate the manufacturer software and tests comparing obtained parameters based on semi‐automated TrueBeam preset tests vs. an independent raw images analysis. Methods: We describe the detection and software of the TrueBeam System Imager. Winston‐Lutz test was performed. Catphan CTP504 phantom was scanned in order to evaluate different quality control image tests (spatial resolution, low contrast, uniformity, linearity CT number) using imageOwl software and based on AAPM report No. 104 recommendations. Results: The CBCT modes of this system use different filters and physical parameter combinations (kVp, mA, ms, rotation, gantry speed, framerate) depending on the anatomical regions: Head, Pelvis, Thorax, Spot Light, Thorax slow and Thorax very slow. The relationship between CT numbers and electron density for a range of materials is linear as expected (air, PMP [polymethylpentene], LDPE [low density polyethylene], water, polyestyrene, acrylic, Delrin and Teflon). Most of tests showed a good agreement to expected behavior according to gantry‐mounted systems described at AAPM104. Details will be shown in complete article and at meeting. Conclusion: Based on our validation results, the TrueBeam Imager system is a reliable, useful and comfortable gantry‐mounted imager system. We establish our own quality assurance program and protocols to be used according to future plans and requirements of Radio‐Oncology service at INCMNSZ.
SU‐E‐J‐10: Inter‐Fractional Tumor Motion Analysis Using 4D‐CT and CBCT
Authors: Xue M , Tan S , Reese A , Yi B , D' Souza W , Feigenberg S , Lu W
Published: July 2013

Purpose: To quantitatively evaluate the inter‐fractional variation in tumor volumes with repeated 4D‐CTs and repeated CBCTs for lung patients. To evaluate the uncertainties in patient set‐up that uses internal target volume (ITV) of 4D‐CT to match the soft tissue on CBCTs. Methods: We retrospectively selected 5 lung cancer patients: each with three 4D‐CTs (4D1, 4D2, and 4D3) and three CBCTs (C1, C2, and C3), and each CBCT was scanned within one week of a corresponding 4D‐CT. All CT images are registered to 4D1, together with contours on each image: ITV for 4D‐CT and gross tumor volumes (GTV) for CBCT. Then, these volumes are compared to ITV in 4D1 in terms of tumor volume, centroid distance, and volume overlap coefficient. Results: In each CBCT/4D‐CT pair, GTV in CBCT underestimate the ITV in 4D‐CT by 41.22±1.39 %. When normalized to the ITV volume in the 4D1, other ITVs of 4D‐CTs have an average volume of 1.07±0.13, and GTV in CBCTs have an average volume of 0.58±0.01. The centroid distance between ITV of 4D1 and a GTV of CBCT (5.6±11.9 mm) is larger than that between ITVs of 4D1and 4D2/4D3 (4.6±8.1 mm), while the CBCT GTV volumes are more included in the ITV of 4D1 (BinA: 0.863±0.018) than those of 4D2/4D3 (BinA: 0.735±0.033). From visual observation, the tumors presented in CBCTs are more similar to those in average projections compared to the ITVs of 4D‐CTs. Conclusions: The soft tissue alignment using 4D ITV on CBCT image has room for improvement. Although CBCT tumor seems more included, the centroid distance between CBCT‐GTV and 4D1‐ITV is larger than that between 4D2/4D3‐ITV and 4D1‐ITV. This, together with the underestimation of tumor volume from CBCT, makes current soft tissue alignment not as reliable as it seems. This work is supported in part by Philips Healthcare, Inc.
SU‐E‐J‐12: Evaluation of Setup Uncertainties for Electron Boost Field Treated Using Compression Device for Breast Cancer Irradiation
Authors: Wang X , Salehpour M , Howell R , Melancon A , Sun T , Woodward W , Smith B
Published: July 2013

Purpose: To investigate uncertainties of patient setup for electron boost field using an in‐house breast compression device for breast cancer irradiation. Method: Ten early stage breast cancer patients with deep seated tumor beds treated with post‐lumpectomy radiation were randomly selected. The patients underwent resimulation and treatment with the compression device to decrease the depth of tumor bed. A cone beam computed tomography (CBCT) scan was performed for each patient before treatment and fused with the simulation CT. Four surgical clips located in superior, inferior, left and right of tumor bed were identified in both CT and CBCT data sets for each patient. Set‐up uncertainties were estimated based on differences in the positions of the clips between scans relative to the marked isocenter. Results: For each patient, all clips shifted consistently in the same direction superior‐inferior (SI) and left‐right (LR) direction, but not in the anterior‐posterior (AP) direction because of the perturbation of the compression device. 50% of clips (20 out of 40 clips) shifted anteriorly, 60% shifted inferiorly, and 70% shifted left. Clip shifts in AP direction were smaller than in SI and LR direction. The 55% of clips shifted >1 cm, 18% of clips shifted > 1.5 cm, and only one clip shifted > 2cm which was out of the intended isodose coverage. The average shift of 4 clips for each patient in LR direction was correlated with the breast volume (R2=0.406), but the average shifts of 4 clips in AP and SI direction were not correlated breast volume (R2>0.02). Conclusion: For most patients whose breast boosts were treated with a compression device, a 2cm margin was sufficient to ensure target coverage based on set‐up uncertainties observed in this study. A larger margin might be necessary for electron boost fields for patients with large (volume >2000cc) and/or pendulous breasts.
SU‐E‐J‐13: Generation of Dual‐Energy CT Image Dataset From Single‐Energy CT Image Dataset
Authors: Dong Y , Huo J , Wang X , Wang P , Zhu X , Feng Y
Published: July 2013

Purpose: The capability of obtaining tissue‐specific information from dual‐energy imaging has the potential to be used in radiotherapy for gross‐tumor‐volume (GTV) definition and localization with enhanced accuracy in radiotherapy treatment planning and image guided delivery. However, there are not dedicated dual energy CT (DECT) simulators in radiotherapy clinics yet. This study is to develop a method to create a set of DECT data with the data from a conventional single‐energy CT simulator, i.e., to generate a set of CT images at energy B from a set of CT images obtained at energy A, and to explore the feasibility of utilizing the two CT data sets to create anatomical images with higher soft‐tissue‐contrast. Methods: CT images from 5 lung cancer patients were used in this feasibility study. The images were acquired with a Brilliance Big Bore CT simulator at energy A (CT?A, 120kVp). For each patient, one set of CT images at energy B (CT_B, 30keV) was generated from CT_A with a bilinear scaling method, two pairs of digitally reconstructed radiographs (DRRs) were created from CT_B and CT_A respectively and then a soft‐tissue‐only DRR pair (DRR_dualE) was obtained using an in‐house software of dual‐energy subtraction with DRR_CTA and DRR_CTB. The image quality of DRRs was quantitatively analyzed using signal‐difference‐to‐noise‐ratio (SDNR). Results: The results indicate that the generated CT images showed improved contrast and the DRRdualE showed that bony structure was eliminated, soft tissue contrast was improved. SDNR for GTV was improved from 1.94 ± 0.09 (in DRRCTA) to 4.31 ± 0.12 (in DRR_dualE). Conclusion: The feasibility study has shown the potential of utilizing a conventional single‐energy CT dataset to get another set of CT images at a different energy to achieve improved soft tissue contrast for GTV delineation or target localization when a DECT machine is not available. Corresponding:y_m_feng @yahoo.com National Science Foundation of China (NSFC‐81171342,81041107)
SU‐E‐J‐14: Evaluation of MV and KV Isocenter Displacement for An IGRT Linac with and Without An Add‐On Micro‐Multileaf Collimator
Authors: Nakada R , Tatsumi D , Takemura A , Ienaga A , Yomoda A , Inoue M , Ichida T , Hosono M
Published: July 2013

Purpose: The impact of the add‐on micro MLC (mMLC) on the MV and kV isocenters was investigated. Methods: Winston‐Lutz tests was performed with an add‐on mMLC, and a ball bearing (BB) was placed at the isocenter given by localization lasers. A square MV field was shaped by the mMLC, and the MV field center position relative to the BB position were measured by a portal imager with different gantry angles. A desirable BB position that minimizes the maximum deviation was obtained as an MV isocenter, and the BB center was aligned onto the revised MV isocenter. Using an on‐board kV imaging system, two‐dimensional BB image was acquired during gantry rotation. The displacement of the kV projection image center from the BB for each gantry angle was recorded as ‘flexmap’. After unmounting the mMLC, Winston‐Lutz test and the flexmap measurement were performed again. A phantom was placed on a couch and cone‐beam CT (CBCT) images were acquired with the two different flexmap data. The set‐up errors were calculated and the differences of required couch translations with each of the flexmap data were obtained. Results: After unmounting the mMLC, the MV field center and the kV image center were shifted approximately 0.4 mm and 0.05 mm upward, respectively. Assuming a perfect MV and kV isocenter coincidence with mMLC using the flexmap for CBCT reconstruction, the MV/kV isocenter discrepancy without the mMLC could be calculated by the difference of the above two values, 0.35 mm which satisfies AAPM TG179 guideline of 1 mm. The largest difference of required couch translations between the two flexmap data was 0.07 mm toward the vertical direction, which agreed well with the kV image center shift of 0.05 mm. Conclusion: The MV and kV isocenters defined with the add‐on mMLC are also applicable to image‐guided VMAT without the mMLC.
SU‐E‐J‐16: Evaluation of Image Quality From KV Cone‐Beam CT with Couch Offset for Two Image Protocols
Authors: Kim C , Ambrose R , Furhang E
Published: July 2013

Purpose: To evaluate kV cone‐beam CT image quality for two clinical reconstruction algorithms when the volume of interest deviates from isocenter Methods: The CatPhan phantom (The Phantom Lab.) was scanned using CBCT on a TrueBeam LINAC (Varian Medical Systems). The phantom contains various sections designed to assess certain image quality parameters. Images were acquired with the phantom centered about the imaging isocenter (as typically done for routine CBCT QA), and then also acquired with phantom offset 5 cm laterally and longitudinally. At each position, scans were taken using two techniques typically used in the clinic: Head & Pelvis. The centered‐phantom CBCT was used as a baseline, and image quality for this scan was compared against that for each offset scan. The end points of the image quality comparison were four parameters: MTF, low contrast detectability, uniformity and noise. Analysis of all CT sets were performed by the PIPSpro QA software (Standard Imaging, Inc.). Results: For the pelvis protocol, the critical frequency (f50, lp/cm) in lateral and longitudinal offset scans was worse than that of the reference position, meaning lowered small object detectability with high contrast in offset scans. There is no significant difference found in low contrast detectability and noise level for offset scans in both Pelvis and Head protocols. The uniformity index for the lateral shift cases better than the reference image sets. Conclusions: The results show that even though off‐centered CBCT is a useful tool to handle when the volume deviates from isocenter, a precaution is needed because of a decrease in high contrast detectability. A further study of image quality comparison for cou ch offset will co nsider different acquisition parameter settings.
SU‐E‐J‐18: A Rapid Joint Therapist‐Physicist QA Procedure for Sub‐Mm Verification of KV Imaging System‐Radiation Isocenter Alignment for Frameless SRS
Authors: Huang E , Wang P , Mechalakos J , Li G , Popovic A Ballangrud , kuo l , Lovelock D
Published: July 2013

Purpose: To assess the feasibility of a rapid and accurate joint therapist‐physicist QA procedure to verify the accuracy of the alignment kV imaging system with the MV radiation Isocenter prior to frameless SRS treatment. Methods: A Winston‐Lutz phantom was CT scanned with a slice spacing of .75 mm. The isocenter was placed to within 0.1 mm of the center of the sphere. A plan was created containing 4 static 2 × 2 cm MLC fields with corresponding MV portal images, and 4 kv setup fields both spaced at 90d gantry angles and CBCT setup field. Prior to the frameless SRS treatment, therapists place the WL phantom approximately at isocenter, then acquire all images planned. A physicist extracts the images from the R&V system and performs an automated image analysis to compute the systematic error between the radiation isocenter and the origin of the radiographic and CBCT systems. Spatial accuracy was assessed by placing a steel sphere on a micrometer stage and making known dispalcements.The therapists will do 3D‐3D match between acquired CBCT and planned CBCT and record the couch shifts. The planar MV and KV images are analyzed automatically offline to determine the systematic error between the kV imaging origin and the radiation isocenter before SRS treatment. Results: The localization uncertainty of the sphere, for both the KV and MV systems was ± 0.1mm. Uncertainty on the systematic error between the radiation isocenter and the imaging origin was found to be ±0.2 mm. The time required to verify the spatial imaging accuracy required about 15 minutes of therapist time and about 10 minutes of physicist time. Conclusion: The designed QA procedure can be performed easily by the therapists and physicists to speed up SRS room QA before patient treatments.
SU‐E‐J‐20: A Study On Rectal Complication Probability From Composite Volumes Derived From Daily CBCT in Prostate Cancer Radiotherapy
Authors: Ramachandran P , Oates R , Chang J , Jones D , Gill S , Cramb J
Published: July 2013

Purpose: Dose escalation improves local control in prostate cancer radiotherapy. However, dose escalation is limited due to late rectal toxicity. Bladder and rectal filling / rectal gas during the course of treatment tend to alter the dose to the target volume and critical structures. In this study, an effort has been made to assess the late rectal complication probability from a serial of cone beam computed tomography (CBCT) scans for prostate cancer with IMRT and 3D conformal radiotherapy. Methods: Twelve patients were selected for this study. All patients were treated with IMRT to a dose of 78 Gy with pre‐treatment kV/kV orthogonal imaging matched to gold seed fiducials. CBCT scans were acquired at the end of treatment on fractions 1–5 and then every alternate fraction. Alternatively, five field 3D‐CRT plans were generated for the above patients. Three different rectum volumes: (i) Plan rectum (ii) Boolean sum of rectum volume based on the CBCT for first 5 fractions (Rectum‐5) and (iii) Boolean sum of rectum volume from all the CBCTs (Rectum‐all) were used for computing the rectal complications. The Lyman‐Kutcher‐Burman normal tissue complication probability (NTCP) model has been used in this study to assess grade‐2 rectal toxicity. Results: The NTCP for rectum with IMRT as assessed from Plan‐Rectum, Rectum‐5, Rectum‐all and average rectum were 11.03 ± 4.91%, 17.45 ± 9.07%, 21.89 ± 7.66% and 13.83 ± 6.82% respectively whereas for 3D‐CRT it is 20.22 ± 9.45%, 21.61 ± 9.56%, 23.81 ± 8.62% and 19.78 ± 8.97% respectively. Statistically significant differences were observed between Plan‐Rectum, Rectum‐5 and Rectum‐All with IMRT. Conclusion: Our results show that large variation in NTCP for IMRT between Plan‐rectum, Rectum‐5 and rectum‐all indicates a potential role for adaptive radiotherapy for prostate cancer. This could in turn lead to dose escalation with IMRT for prostate cancer.
SU‐E‐J‐21: Entrance Dose Evaluation During KV‐CBCT Scans for Different KVp and FOV Settings
Authors: Nieto B Sanchez‐ , Caprile P , Lagos F , Lucic F , Gabriel Z
Published: July 2013

Purpose: The aim of this study is to evaluate the entrance dose of an imaged cylindrical phantom with a KV‐CBCT, using thermoluminescence dosimetry, for different settings. Methods: A KV‐CBCT unit, integrated in the Elekta Synergy linear accelerator, was used to image the commercial phantom Catphan 504. Dose measurements were performed with TLD‐100 chips distributed around the phantom surface for 100 and 120 KVp values, for different collimator cassettes and nominal values of mA (from 25 to 100) and ms (from 40 to 10), keeping the product constant. Results: The dose was not uniform over the surface for the same parameters, with differences up to 20%, being the largest dose at the posterior position. As expected, the dose increased with KVp, being the dose values for the 120 KVp around 60% larger than for the 100 KVp. Different superficial doses were obtained for collimators with the same projected field size at the isocenter. An average 25% increase in dose was observed for the S20 collimator cassette with respect to the M20, for the complete rotation of the unit. The largest relative dose was obtained for the posterior position, with 120KVp, using the S20 collimator. Eventhough mA*ms kept constant, for each KVp, entrance dose increased with mA. Conclusion: The variation over the surface could be attributed to the different relative proximity to surrounding scatter material (e.g., floor, walls, etc.). There is a clear impact of collimator cassette selection on the dose to the surface, being larger for smaller FOVs. This effect is minimized clinically; as when using smaller FOVs, a complete rotation is not required for image reconstruction (the S20 collimator is centered). Effectively, the collimator displacement to obtain larger FOVs, produces lesser dose. This Result could be explained by the heel effect, as it generates a reduced intensity towards the anode.