bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐I‐57: Estimation of Uterus Dose From Abdominal CT Examinations Using a New Patient‐Specific Monte Carlo Software Package
Authors: Damilakis J , Perisinakis K , Tzedakis A
Published: April 2010

Purpose: To investigate uterus radiation dose from abdominal CT examinations using a new Monte Carlo tool for patient‐specific dose simulations. Method and Materials: Thirty six consecutive female patients who underwent abdominal CT examination were included in this study. CT examinations were performed using a Siemens Sensation 16 multi‐detector CT scanner (Siemens AG, Forchheim, Germany). Patient images were imported in the ImpactMC patient‐specific and scanner‐specific dose calculation Monte Carlo software package (ImpactMC, Vamp GmbH, Germany). Voxelized models were created on the basis of image data of patients included in this study. Patient body size was defined according to the cross‐sectional area (CSA) of the CT slice containing the central area of the uterus. The Monte‐Carlo N‐particle (MCNP, version 5) transportation code was also used to model the Siemens Sensation 16 CT scanner. To calculate uterus dose using MCNP, a mathematical anthropomorphic phantom was used. This phantom represented the average adult female human body. Results: The dose to the uterus from an abdominal CT examination estimated using MCNP was 8.7 mGy/100 mAs. Uterus doses calculated using ImpactMC ranged from 4.6 to 12.9 mGy/100 mAs. Thus, differences between radiation doses calculated using ImpactMC and the dose calculated using MCNP ranged from −47% to +50%. CSA values ranged from 383 to 1074 cm2. A statistically significant relationship was found between CSA and uterus dose calculated by ImpactMC (p<0.001). Conclusions: Radiation dose from CT depends on patient size as well as on the size and position of organs. ImpactMC can provide dose distributions specific for individual patients. Patient‐specific dosimetry is important when accurate estimation of uterus dose from a CT procedure is needed, for example in case of inadvertent irradiation of a pregnant patient during a CT examination. Research sponsored by the European Community
SU‐FF‐I‐65: Relative Contributions of Rayleigh Scattering for PMMA in the Mammography Energy Range
Authors: Yamaguchi Y , Kawaguchi S , Arimura H , Morishita J , Ohki M , Uno Y , Ideguchi T , Tokumori K , Higashida Y , Toyofuku F
Published: April 2010

Purpose: The method of obtaining the primary x‐ray spectrum by the Compton scattering correction has been established for relatively high x‐ray tube voltages. However, the influence of Rayleigh scattering can not be neglected in the mammography energy range. Besides, accurate data of Rayleigh and Compton cross sections for the scatterer material are required for obtaining the primary x‐ray spectrum by correcting the scattered x‐ray spectrum in mammography. The purpose of this study is to investigate theoretically and experimentally the relative contributions of Rayleigh scattering for PMMA (polymethyl methacrylate) in the mammography energy range. Method and Materials: Fluorescent x‐rays in the energy range of 10 to 25 keV were generated by exciting four metal targets including molybdenum by synchrotron radiation. The fluorescent x‐rays were incident on a sphere of PMMA, and the scattered x‐rays were measured with a CdTe detector at scattering angles of 90, 120, 150, 165 degrees. The scattered fluorescent x‐ray spectrum was separated into the Rayleigh and Compton scattering peaks by using a curve fitting technique with two Gaussian functions. We compared the measured cross section data to those obtained from theoretical values. We also calculated the scattered fluorescent x‐ray spectra using the Monte Carlo simulation and compared them to the measured spectra. Results: The measured ratio of Rayleigh to total scattering cross section was about 30% at 10 keV. The maximum discrepancy of the measured and theoretically calculated values of the ratio was about 30% for the scattering angles of 90 to 165 degrees. However, at the angle of 120 degrees where the overall error might be minimum, the theoretical and experimental values agreed within 2%. Conclusion: Rayleigh and Compton scattering cross sections should be measured more precisely in order to improve the calculation of the primary mammography x‐ray spectrum from the scattered x‐ray spectrum.
SU‐FF‐I‐76: Accuracy of Quality Control Measurements with Solid‐State Detectors in Diagnostic Radiology
Authors: Jones A
Published: April 2010

Purpose: Recently, solid‐state detectors have been increasingly adopted as diagnostic physics survey equipment due to their compact size and convenience. A single piece of equipment can be used to measure many quantities, including “exposure”, kVp, and half‐value layer (HVL), with only a single irradiation. While these detectors perform well in certain beam qualities, they can deliver inaccurate results in others. Materials and methods: Diagnostic physics measurements including exposure, HVL, and entrance exposure rate were made on several types of equipment, including mammographic, standard radiographic, fluoroscopic, and angiographic systems. Measurements on the angiographic system were made with various amounts of added filtration, ranging from 0.1 to 0.9 mm Cu. Exposure and exposure rate were measured using both a 6 cc ionization chamber and a solid state dosimeter, and HVL was measured using both a 6 cc ionization chamber with Al 1100 and a solid‐state dosimeter. Results: While measurements made on mammographic (0.35 mm Al HVL) and standard radiographic systems (3.1 mm Al HVL) were in good agreement between traditional survey equipment and the solid‐state dosimeter, measurements made in X‐ray beams of other qualities differed between the two types of survey equipment. The solid‐state dosimeter reported a lower HVL than measured with the ionization chamber for beam qualities ranging from 3.8 mm Al HVL to 6.8 mm Al HVL, including measurements performed on commonly‐used fluoroscopic systems. For X‐ray beams with HVL greater than 6.8 mm Al, results were again in agreement between the two types of survey equipment. Also, entrance exposure rate measurements can be inaccurate if the device is used improperly. Conclusions: Caution should be used when making diagnostic physics measurements using solid‐state dosimeters. Proper positioning of the device is critical for accurate entrance exposure rate measurements, and accurate measurements may not be possible in certain X‐ray beam qualities.
SU‐FF‐I‐86: Esophagus Segmentation in Thoracic CT Images for Radiotherapy Planning
Authors: Kurugol S , Sharp G , Dy J , Brooks D
Published: April 2010

Purpose: Contouring organs at risk in thoracic CT images for radiotherapy planning is labor intensive. We propose a technique to semiautomatically segment the esophagus in thoracic CT images. Method and Materials: We used training datasets to learn the distribution of relative spatial location of esophagus centers with respect to neighboring structures and to construct models of their anterior‐posterior (x) and left‐right (y) coordinate trajectories as a function of cranial‐caudal (z) position after local normalization by transverse scaling and translation. In the z direction, we selected 8 anatomical reference points and matched these points for each training set. We observed that the centers can be modeled by a single cubic polynomial in the sagittal plane and by a shape‐preserving spline in the coronal plane. To segment the esophagus in a 3D dataset, we estimated the center based on histograms for each reference slice and fit the polynomial center models for other slices. We then used level‐sets to locate the esophagus wall. We initialized the level‐set function and shape prior using the estimated centers and updated to minimize an energy functional combining several existing region, shape and smoothness terms to impose a smooth slice‐to‐slice change of ellipse parameters. Results: Testing on 8 subjects against expert segmentations, the center‐estimation algorithm achieved 2mm average error in the x‐direction but was less accurate in the y‐direction with a 4.3mm average error. The level‐set method improved the average error in y‐direction to 2.8mm. Conclusion: Segmentation of the esophagus using prior information from training including spatial dependence between neighboring structures and models of the esophagus centers can be performed with a level set approach. Using spatial information and slice‐to‐slice smoothing improves the performance for regions with no contrast.

Acknowledgement: The work of first and fourth author was supported by NIH/NCRR Center for Integrative Biomedical Computing (CIBC), P41‐RR12553‐09.
SU‐FF‐I‐104: Development of a Deformable Lung Phantom for the Evaluation of Deformable Registration
Authors: Chang J , Suh T , Lee D , Cho G
Published: April 2010

Purpose: The deformable lung phantom prototype was developed to account for the patient breathing motion, and to evaluate for a deformable image registration algorithm. Method and Materials: The phantom consisted of an acryl cylinder filled with water and a latex balloon located in the inner space of the cylinder. A silicon membrane was attached to the inferior end of the phantom. The silicon membrane was designed to simulate a real lung diaphragm and to reduce motor workload. This specific design was able to reduce the metal use which may prevent infrared sensing of the real position management (RPM) gating system on 4D CT image acquisition. Verification of intensity based 3D .demon deformable registration was based on peak exhale and peak inhale breathing phases. Results: The registration differences ranged from 0.85 mm to 1.47 mm, and accuracy was determined according to inner target deformation. Conclusions: This phantom was able to simulate the features and deformation of real human lung and has the potential for wide application in 4D radiation treatment planning. Conflict of Interest: This research sponsored by the Seoul R&BD Program (10550) and the Mid‐ and Long‐Term Nuclear R&D Program of the Ministry of Science and Technology (M20706000007‐07M0600‐00710)
SU‐FF‐I‐105: Positional Accuracy of a B‐Spline Based Method for Image Registration in the H&N Area: Effect of Noise, Contrast and Registration Parameters
Authors: Meertens H , Brouwer C , Veld A
Published: April 2010

Purpose: Evaluation of the B‐Spline based Registration Method (BSRM) and the effect of contrast, signal to noise ratio and registration parameter settings on the accuracy of the restored voxel displacements in deformed H&N images. Method and Materials: CT images of a 8×15×25 cm3 phantom were constructed. The phantom contained spherical and elliptical structures simulating a tumor and several H&N organs. From this set, additional CT sets were constructed by: 1) affine transformation, 2) imposing shaped deformations up to 20 mm and 3) addition of noise of 10 HU up to 300 HU (1SD). The BSRM of the Insight Toolkit combined with Elastix was used to register the various distorted phantoms to the original phantom. The effect of different parameter settings of the registration has been investigated (number of iterations, spacing of the B‐ spline grid, number of resolution levels). Displacement vectors calculated in the deformable registration were compared with the imposed deformations. Average residual voxel displacement and other similarity measures were calculated. Results: Satisfactory convergence of the average residual displacement is reached after 64, 64 and 128 iterations for 3 levels of resolution. A grid spacing of 8–12 mm gives good results, although for sharp deformations a 6 mm grid is better in most cases. The increase in noise has a minor influence on the accuracy. An average tracking accuracy of better than 2 mm for parotid gland edges seems feasible. In some areas, however residual displacement errors up to 6–8 mm are observed. Conclusions: The BSRM seems to be suitable for intensity based deformable image registration of structures like the parotid and submandibular glands in the H&N region. Careful tuning of parameter values is important to obtain reliable results. References: ITK: www.itk.org, Elastix: www.isi.uu.nl/Elastix.
SU‐FF‐I‐108: Effect of Point Spread Function, X‐Ray Quantum Noise, and Additive Instrumentation Noise On the Accuracy of the Angulated Slit Method for Determination of Pre‐Sampled Detector MTF
Authors: Jain A , Kuhls‐Gilcrist A , Patel V , Hoffmann K , Bednarek D , Rudin S
Published: April 2010

Purpose: To evaluate the accuracy of the angulated‐slit method for determining the detector Modulation Transfer Function (MTF) and thus, for the first time to determine the accuracy of the method for various physical circumstances. We quantify the difference between “true” MTF's and “measured” MTF's obtained using the angulated‐slit method. Method and Materials: A series of simulated slit images were initially generated without blur, with different slit‐widths, different slit‐angles relative to the detector matrix, and with and without Poisson distributed x‐ray quantum noise. We used the angled‐slit method to calculate the MTF and compared it with the “true” MTF (a sinc‐function given by the pixel aperture). We then introduced known Gaussian blur and additive instrumentation noise to simulate more realistic slit images. The MTF's “measured” with the slit method and the “true” MTF's were compared. Results: For the ideal slit without blur, there was an increased error in the measured MTF with increasing slit‐angle and slit‐width, with the greatest error at higher spatial frequencies. Larger slit widths and angles resulted in even greater deviations. Slit images simulated using Poisson distributed quanta, known Gaussian blur, and additive instrumentation noise, resulted in an overall increase in the MTF when compared with the “true” MTF, especially at higher spatial frequencies and increasing deviation with increasing width of the Gaussian blur (around 15% difference at 50% of the Nyquist for a PSF with 3 pixels FWHM and 1% additive noise). Conclusion: These results show the angulated‐slit method to be sensitive to slit‐angle and slit‐width. The presence of quantum noise, additive instrumentation noise and the width of the blur function are shown to severely affect the angled‐slit method accuracy, especially at higher spatial frequencies. Although the slit method provides accurate MTF values at low spatial frequencies, it overestimates the MTF at higher spatial frequencies. (Support: NIH‐R01EB002873)
SU‐FF‐I‐119: KV Beam Model for OBI and Extraction of Water Equivalent Depths for Primary and Scatter Contributions
Authors: Bhagwat M , Blessing M , Lyatskaya Y , Bellon J , Zygmanski P
Published: April 2010

Purpose: To develop a phenomenological kV beam model and address attenuation/scatter in radiographic images obtained with the Varian OBI system for the purpose of cone‐beam imaging: CB‐CT/radiography/tomosynthesis. To perform realistic calculation of attenuation/scatter distributions (x,y). To characterize kV beam in terms of minimum number of parameters. Method and Materials: Radiographs of homogeneous solid water phantom for various depths and field sizes are taken, with/without bowtie filter. These images are then analyzed to determine parameters of the model, and their dependence on depth and field size is described by analytical functions. The model is applied to predict the detector signal for arbitrary objects. The detector response is conveniently factorized into different contributions, with each contribution having an analytical representation. A weighted sum of three Gaussians in each direction models the deposition kernel. Detector response arising from the first Gaussian term can be interpreted as primary signal while the second and third Gaussians constitute short‐ and long‐range scatter. Thus, a prediction of the detector response for a variable‐thickness phantom has primary and scatter components. Various techniques of scatter removal from the measured radiographs are investigated. Results: This model accurately predicts detector response of varying‐depth phantoms such as multi‐step and cylindrical phantoms. Scatter contributes over 30% to the total signal for 20cm‐thick phantom. Calculated Scatter‐to‐Primary Ratio (x,y) is large as reported in literature on Monte Carlo studies. Water equivalent thickness related to primary and scatter contributions are calculated from the measured radiographs. These results indicate an improved model‐based calibration technique suitable for CB‐CT reconstruction. Conclusion: A phenomenological kV beam model is found to be accurate in characterizing kV beam, prediction of detector responses for known objects, and calculation of water equivalent thickness from radiographs of unknown objects. Primary vs scatter contributions in detector response and water equivalent thicknesses are derived.
SU‐FF‐I‐121: Development of An Organ Surface Statistical Model for Uncertainty‐Weighted Deformable Image Registrations
Authors: Wu J , Murphy M , Weiss E , Williamson J
Published: April 2010

Purpose: To develop an organ surface statistical model for uncertainty‐weighted probabilistic deformable registrations. Materials and Methods: The contours of the prostate, the bladder, and the rectum were manually delineated by five observers on fan beam CT images of four prostate patients. The reliability of the organ boundary delineation was estimated by calculating the intra‐observer, the inter‐observer, and the inter‐modality variability (e.g., standard deviation) of the organ boundary surfaces. For each set of contours, an average surface was computed by first superimposing individual organ contours and generating a composite bitmap image. Then after smoothing, a matching tetrahedron algorithm was used to extract the average surface mesh. The distance map between each individual segmentation and the average surface mesh can be calculated based on the normal defined on 1) each vertex or 2) each triangle of the average mesh. A simple 3D visualization program was developed using OpenGL to interactively viewing 3D organ surfaces and standard deviation surface maps. Results: Population‐based organ surface statistical models of the prostate, the bladder, and the rectum were created by mapping the patient specific standard deviation surface maps to the population‐averaged surface. 3D visualization indicates that the boundary uncertainties are anatomical location dependent. Conclusions: We proposed a general method for objectively constructing surface maps of uncertainties derived from topologically complex organ boundary segmentations from multiple observers. The computed boundary uncertainties can be used as weighting factors for a surface‐based probabilistic deformable registration.

Supported in part by NIH grant P01CA116602
SU‐FF‐J‐30: Experimental Investigation of Moving Average Algorithm for Tracking Organ Motion
Authors: Yoon J , Suh T , Sawant A , Suh Y , Cho B , Keall P
Published: April 2010

Purpose: To investigate the geometric and dosimetric properties of the moving average tracking algorithm compared with real time tracking and static beam. Method and Materials: Patient motion traces from the Cyberknife Synchrony™ were categorized into 3 types of motion: a regular motion with/without baseline drift and irregular motion. Each motion trace was reproduced with the help of a 4D motion platform. Time averaged mean position of the phantom was used to control dMLC position in the perpendicular direction to the leaf travel. Geometric accuracy, delivery efficiency and dose distribution were evaluated for static, IMRT step‐and‐shoot and sliding window plan using simulated and patient motion traces. The geometric accuracy was calculated from the displacement between the target center and the beam center using a real‐time beam's‐eye‐view videos with a circular aperture. For dosimetric measurements, PTW ion chamber array (model 729) was sandwiched between 2 cm thickness of solid water phantoms and irradiated for one field. Dosimetric impact was quantified via gamma index with a 3% dose‐3mm criterion. Results: The difference of RMS geometric error (mm) between the real‐time tracking and moving average tracking was about 3 mm which was similar to errors caused by random motion. The percentages of failing points in the gamma analysis for moving average tracking were reduced by above half of the percent difference between no compensation and real‐time tracking. Delivery efficiencies for moving average tracking were above 97% comparable to static delivery case. Conclusions: Mean position tracking was useful for compensating a baseline drift to improve a geometric and delivery accuracy with high delivery efficiency.
SU‐FF‐J‐38: Evaluation of Positioning for Head and Neck Patients Using 2D and 3D Image Guidance
Authors: Kang H , Lovelock D , Yorke E , Kriminski S , Lee N , Amols H
Published: April 2010

Purpose: To determine and compare reduction of setup error by two‐dimensional (2D) and three‐dimensional (3D) image guidance for radiation therapy of head and neck cancer (H&N) patients immobilized by customized masks. Methods and materials: Ten patients, immobilized with custom thermoplastic masks, received weekly imaging sessions throughout treatment. A patient was first set up by matching lasers to surface marks (conventional) and then translationally corrected using manual registration of orthogonal kilovoltage radiographs with DRRs (2D/2D). A cone‐beam CT (CBCT) was acquired and manually registered to the simulation CT to determine further translational corrections (3D/3D‐manual). The registration structures were in‐field bony anatomy. A post‐treatment CBCT was acquired to assess intrafraction motion. We retrospectively evaluated the conventional, 2D/2D and 3D/3D‐manual setup with an in‐house automatic 3D/3D rigid‐body registration algorithm using translations‐only (3 degrees of freedom, DOF) and translations plus rotations (6 DOF). 56 treatment sessions (2–7 per patient) were analyzed. Results: Averaged over all sessions, 2D/2D registration led to translational corrections from conventional setup of magnitude 4±2 mm, range (0–8 mm). The addition of 3D/3D‐manual registration resulted in only small incremental adjustment (1±2 mm). For nine patients, the automatic 3 DOF registration agreed well with the final pre‐treatment position (overall 2±1 mm, range 1–7 mm). One patient showed significant differences (8±3 mm, range 4–12 mm); a loose‐fitting mask and resulting anatomical deformation were noted. However, the impact on dose even for this patient was minimal. For all patients, rotations determined by the 6 DOF registration of in‐field bony anatomy were < 4° around any axis. Intra‐fraction motion was < 2 mm and < 2° for all sessions. Conclusions: Manual 2D/2D registration of in‐field bony anatomy reduces positioning errors for mask‐immobilized H&N patients in most cases, and is easily implemented. 3D registration adds little improvement.
SU‐FF‐J‐43: Significance of Patient Rotation for Dosimetry in IGRT
Authors: Alfaro A , Qian Y
Published: April 2010

Purpose: Significance of Patient Rotation for Dosimetry in IGRT Method and Materials: Advances in technology has made IGRT widely available, especial Cone Beam CT (CBCT) for patient positioning. In our institution a Varian Trilogy was installed for IGRT using CBCT with On‐Board Imaging Device. The patient positioning is done by comparing and fusing the CBCT images with original CT simulation images. Once the fusion is done the system provides operator with patient shifting information in 4‐Dimension: Vertical Shift, Lateral Shift, Longitudinal Shift and Couch Rotation (Yaw), no information regarding Pitching and Roll is provided. While for majority of patient treatment on a flat (Carbon Fiber) Couch‐Top the pitching is minimum, the patient roll is not uncommon showing soft tissue fused well but clear boney mark discrepancy. Assuming patient translational shift has been corrected; we have studied the effect of patient roll and yaw for three typical sites: Prostate, Lung and Head&Neck treatment by simulating the patient rotation in computer planning system. Results: Histogram of GTV, OAR for Prostate, Lung and Head&Neck with various degrees of Roll and Yaw rotation are studied and compared with perfect matching. Up to 8 degree we found there is no effect of both roll and yaw rotation for prostate, small to negligible effect for lung. For Head and Neck IMRT treatment up to 3 degree roll, and 4 degree yaw, there is small effect in PTV 63 Gy region, but negligible effect in lower or higher dose region for treatment, and negligible effect for OAR. Conclusion: As long as patient translational shift correction is done, small degree of patient rotational shift will not effect both the dose coverage of GTV, and dose effect of OAR, at least in the 3 sites we have studied: Prostate, Lung and Head&Neck.
SU‐FF‐J‐52: Towards On‐Line Treatment Verification Using Cine EPID Images for Hypofractionated Lung IMRT
Authors: Tang X , Lin T , Jiang S , Sandhu A , Chang S , Lian J , Chaney E
Published: April 2010

Purpose: To develop a computational algorithm based on an artificial neural network (ANN) that allows treatment verification using an EPID in cine mode for hypofractionated lung IMRT. Method and Materials: We developed a novel ANN based technique that can extract tumor information from cine EPID images of each segment in an IMRT field and verify that we are treating the planned treatment area. We simulated training images for ANN using DRRs, by shifting DRRs relative to the beam aperture of the segment. We also carefully related each segment to the entire IMRT field in terms of tumor location. With a pre‐defined threshold p%, we associated category 1 to the training image if more than p% of the tumor projection in the beam eye view was in the corresponding entire treatment field of the training image, and category −1 otherwise. The trained network could therefore analyze the cine EPID images of IMRT segments obtained during the treatment and classify them into the corresponding category 1 or −1. Results: Two patients were included in our feasibility study. A radiation oncologist read the cine EPID images and classified them into category 1 or −1; this served as our ground truth. The ANN was applied to the training images to build the neural network. We set p% = 95% for this study. For each IMRT segment, one neural network needed to be built. Averaging over both patients and all segments, the trained network successfully classified 97% of the cine EPID images. Conclusion: We are the first who can analyze cine EPID images of hypofractionated lung IMRT without implanted fiducial markers. The proposed technique provides an important clinical safeguard—whenever the planned treatment area moves out of the irradiation segment, the treatment beam can be interrupted, so that radiation won't be unnecessarily delivered to normal tissues.
SU‐FF‐J‐54: Evaluation of Ultrasound Image Guidance Accuracy for Prostate by Comparison to Calypso Body GPS Data
Authors: Salter B , Wang B , Zhao H , Rassiah‐Szegedi P
Published: April 2010

Purpose: Ultrasound image guidance accuracy for prostate is evaluated by comparison to Calypso body GPS data Method and Materials: The Calypso localization system is a real time monitoring system with a precision of better than 0.5mm. Twenty (20) patients with a total of 661 fractions are included in this comparative evaluation of the accuracy of US alignment of prostate using the Calypso Body GPS as the gold standard. The sequence of the localization is as following. 1) patient is aligned to a setup isocenter based on skin tattoos. 2) BAT alignment is performed and the treatment couch is shifted accordingly. 3) Calypso localization is then used to align the patient. Thus, the shifts reported by Calypso can be interpreted to represent the residual uncertainty of the BAT alignment. Results: For the 661 fractions evaluated here, BAT residual uncertainty had mean ± standard deviation (SD) of −1.1 ± 2.7 mm (L/R), 0.3 ± 3.6 mm (I/S), 1.5 ± 4.5 mm (A/P). Our results agree well with a recent study published from Heidelberg University. 3D scatter plot of mean BAT residual uncertainty for each of the 20 patients studied here shows the majority of patients clustering within a bounding box of roughly ∼3 mm or less as compared to Calypso alignment position. We note that data from alignments presented here was performed by relatively new US operators with (initially) limited and widely ranging US training experience, early in the clinical training and implementation process. Conclusion: The BAT residual uncertainty averaged over 661 fractions is less than 2 mm in all three directions when evaluated using Calypso as a gold standard and it has the largest standard deviation in the A/P direction.
SU‐FF‐J‐56: Integrating Real‐Time Tracking Into Image Guided Radiation Therapy for Prostate Cancer Treatment
Authors: Zhu X , Bourland J , Yuan Y , Zhuang T , O'Daniel J , Thongphiew D , Wu Q , Das S , Yoo S , Yin F
Published: April 2010

Purpose: To investigate how a real‐time tracking technique, based on implanted transponders, could be effectively integrated into the current process for image‐guided radiation treatment of prostate cancer. Method and Materials: Current prostate IGRT process includes MR‐imaging for prostate delineation, CT simulation for treatment planning, and daily on‐board kV‐ and CBCT‐imaging for target alignment. The real‐time tracking technique uses implanted radiofrequency transponders and an external detector array (Calypso4D) to monitor prostate motion. This study assess (1) magnetic field induced displacement of transponders during MR imaging, (2) image artifacts introduced by transponders in CT and MR images, (3) image artifacts caused by the transponder detector antenna array in in‐room kV and CBCT images. A tissue‐equivalent phantom mimicking prostate tissue stiffness was constructed and implanted with 3 operational transponders prior to phantom solidification. CT scans were performed before and immediately after 1.5T and 3.0T MR imaging of the phantom, which used prostate‐typical pulse sequences. Transponder positions were independently localized by the Calypso system and by CT/CT image registration and evaluated for MR induced displacement. Image artifacts by modality were assessed in phantom and patient cases. Results: MR‐induced position displacements are minimal (<1.0mm) for both 1.5T and 3T scanners. The temperature variation due to MRI RF heating is <0.1°C. MR image artifacts are most significant with the gradient echo sequence, and have radii ∼1.5cm and length∼4.0cm. The detector array caused significant deterioration in the CBCT image quality. The visibility of transponders and bony anatomy was not affected on the kV images. Major changes of the IGRT protocol: (a) MR and CT imaging back‐to‐back for treatment planning is changed to MR prior‐ and CT post‐implant; (b) Daily CBCT prior‐ is changed to post‐treatment and with detector array removed. Conclusion: There are tradeoffs in the clinical IGRT flow to accommodate and minimize the substantial imaging artifacts.
SU‐FF‐J‐59: Adaptive Gating of Radiotherapy Treatment Based On Marker‐Less Tracking of Lung Tumors with KV Fluoroscopy
Authors: Aristophanous M , Rottmann J , Park S , Berbeco R
Published: April 2010

Purpose: We investigated using kV fluoroscopy for adapting the respiratory gating window prior to each radiation treatment fraction. The gate adaptation was based on marker‐less tracking of the target and correlating the internal motion trace with the external breathing signal. Method and Materials: A phantom study was performed with the on‐board kV imager of the Novalis Tx machine. A dynamic chest phantom with a water‐filled sphere placed inside a movable lung density insert was utilized. Breathing traces from patients that underwent lung SBRT were used to drive the target and external surrogate motion. The Varian RPM gating system was employed to obtain an external breathing signal, while acquiring kV fluoroscopy images. The moving target was tracked and an internal signal was generated. One kV acquisition was used for adapting the gating window based on the correlation of the internal and external signal and another one for verifying the gated position of the target. Gating at end‐exhale is the most commonly used technique in the clinic, while gating at mid‐ventilation makes it more likely that the tolerance window for residual motion includes the tumor during the entire breathing cycle. The two gating windows were investigated and the results were compared. Results: No significant difference in the gated target position errors was observed between the two gating windows. The target was in the expected position about 90% of the time for each one. The maximum deviation outside the tolerance window for residual motion was 1.9mm for the end‐exhale and 2.2mm for the mid‐motion gating windows. Conclusion: The adapt and verify procedure examined in this study, if applied in real‐time, has the potential to improve the accuracy of lung cancer radiotherapy by facilitating the reduction of safety margins used for moving tumors.

Conflict of Interest: Varian Medical Systems, Inc.
SU‐FF‐J‐72: Markerless Fluoroscopic Tracking of Lung Tumors Based On 4D CT
Authors: Li R , Lewis J , Cerviño L , Lawson J , Jiang S
Published: April 2010

Purpose: To develop a markerless fluoroscopic lung tumor tracking algorithm based on 4D CT generated reference templates. Method and Materials: Fluoroscopic images were acquired at a sampling rate of 15Hz using an on‐board X‐ray imaging (OBI) system. Each fluoroscopic image has a resolution of 768 by 1024, where each pixel represents a physical size of 0.26 mm. 4D CT was obtained from phase sorting based on internal anatomic features. DRRs were generated from 10 phases of the 4D CT, of which inhale and exhale DRRs were shifted to cover a greater motion range. These DRRs served as the reference templates for tracking purposes. GTV contours from the 4D CT give the reference tumor positions in the templates. Motion enhancement was applied to both DRR templates and fluoroscopic images. Pearson's correlation was calculated between each fluoroscopic image and each template in a given ROI. The tracking output is the weighted average of the tumor positions in those templates with largest correlation scores, weighted by the corresponding correlation scores. Results: RMS tracking error ranges between 0.65mm and 0.77mm. Absolute error at 95th percentile ranges between 1.41mm and 1.58mm. These values are well within the error bounds obtained from earlier studies, which require human‐marked tumor positions in the fluoroscopic images for training. Conclusion: This work demonstrates the feasibility of tracking lung tumor fluoroscopically based on 4D CT templates. Future work involves more sophisticated image processing and computer vision techniques to obtain more robust tracking results.
SU‐FF‐J‐140: Multiple Aspects of Approximated‐Returning‐To‐The‐Origin Probability (ARTOP) Diffusion Tensor Imaging for Better Observation High‐Graded Gliomas Treatment Responses
Authors: Chu A , Knisely J , Fulbright R , Constable R , Nath R
Published: April 2010

Purpose: This study is to provide multiple aspects of physio‐pathological information for early detecting cancer treatment responses and better clinical prognosis by using diffusion MRI modalities. The conventional apparent diffusion coefficient (ADC) is known as a sensitive tool to detect early treatment responses. In this study, the diffusion weighting range is further extended and analyzed by novel approximated returning to the origin probability (ARTOP) for observing slow diffusion compartments for high graded gliomas. Reports had shown higher‐graded gliomas correlating to slower water diffusing among the denser cells, the pathologically‐recognized pseudopalisading necroses, caused by degenerating vessels in progressive gliomas in early stage. Furthermore, slower water diffusion also occurs as malignant gliomas infiltrate preferentially along myelinated fiber‐tracks. Method and Material: The data were collected by Siemens Trio 3T magnet, and processed by 2nd order diffusion tensor with ARTOP q‐space analysis developed by homemade MatLab‐codes. The 5‐minute echo‐planar sequence with 2 averages for (∼40 slices, 112×128 pixels per slice) is equipped by 9‐level diffusion weighting (1∼4k sec/mm2), and each level is with 6‐direction of diffusion tensor imaging (DTI) encoding. Data are gathered from three scans on non‐resection Glioblastoma patients before, during and after radiation‐ and chemo‐therapies. The imaging registrations were performed by rigid‐body affine transformation. Results: ARTOP does not only clearly underline the slower‐diffusing water signals (i.e. higher possibility at its origin), but it's also feasible for clinical routine unlike other q‐space algorithms. So far, the newly migrating palisading glioma cells (as higher ARTOP and lower ADC) have been observed in the data of 3 out of 4 Glioblastoma patients. The increased extracellular spaces due to treatment illustrated as lower ARTOP, higher ADC, impaired fibers in fractional‐anisotropy (FA) map with T2‐weighting highlights all in one data set. Conclusion: The multi‐face diffusion information, ARTOP‐, ADC‐, and FA‐maps could suggest adaptive treatment in the future.
SU‐FF‐J‐152: Dosimetry On Gold Nanoparticle: A Microscopic and Macroscopic Study Using Monte Carlo Simulations
Authors: Chow J , Leung M , Chithrani D , Lee M , Oms B , Jaffray D
Published: April 2010

Purpose: This study investigated dosimetric characteristics of gold nanoparticle under a photon beam. A single gold nanoparticle (microscopic) and a mixture of gold and water (macroscopic) were considered using Monte Carlo simulations based on the Geant4‐ and EGSnrc‐based code, respectively. Methods and Materials: A single gold nanoparticle (diameter of 100 nm) was irradiated by photon beams with energies of 35.5keV, 73.3keV, 660keV, 1.2MeV and 6MeV in water. 250 million histories were used in Monte Carlo simulation to record different numbers of interactions (e.g. photoelectric and Compton) with and without the gold nanoparticle in water. Moreover, a mixture of gold and water was irradiated with photon beams. The dose enhancement ratios (dose of gold and water mixture/dose of water) were determined with different photon beam energies and concentrations of gold. Results: With a single gold nanoparticle, the number of photoelectric interaction was about 47 times larger than that of Compton for the 35.5keV photon beams. This was opposite to the 6MeV photon beams, where the number of Compton interaction was about 46.5 times larger than that of the photoelectric. Although the values of ratio were similar, the total number of interactions for the 35.5keV photon beams was in fact 348 times larger than that of the 6MeV. A larger energy deposition was therefore found when the photon beam energy was decreased from the MeV to keV range. This result agreed with that from a gold and water mixture. Moreover, increasing the concentration of gold increased the dose enhancement in water. Conclusions: Both microscopic and macroscopic study on gold nanoparticle agree that more energy deposition is found when the photon beam energy is decreased from MeV to keV range, due to the increase of photoelectric interaction. A higher concentration of gold can increase the dose enhancement in water.
SU‐FF‐J‐153: Photothermal Cancer Therapy Using Gold Nanorods
Authors: Fourkal E , Veltchev I , Tafo A Guemnie , Ma C , Khazak V , Skobeleva N
Published: April 2010

Purpose: Gold nanorods were used to investigate the effects of heat on PA‐1 ovarian cancer cells and their response to thermal treatment through laser irradiation. In addition, the question of how the combination of X‐ray radiation and nanoparticles affects cancer cell survival was also addressed. Method and Materials: Different concentrations of Gold nanorods of diameter 10 nm and length 40 nm coated in a dense layer of hydrophilic polymers were used and two configurations of laser light were employed. A picosecond laser pulse with 1000 Hz repetition rate yielding 1 Watt of average power, and a continuous wave delivery technique yielding 0.5 Watt of laser power. PA‐1 ovarian cancer cells were put into 96 well microtiter plate. Each well contained about 5000 cells plated in 100 μl of BME media. In addition, three wells containing cells and nanorods and three wells containing only cells were subjected to 1 Gy of photon dose. Results: Three different nanoparticle concentrations were used for the case of pulsed laser beam irradiating the cells. The highest concentration of 6×1012 nr/ml led to complete cell killing even without any laser irradiation. For nanorods concentration of 1.2×1011 nr/ml and 6×1010 nr/ml, the number of survived cells decreased as the laser irradiation time increased from 1 min to 20 min, reaching 59% at 20 min mark. For the case of continuous laser operation and nanoparticle concentration of 1.2×1012 nr/ml, the number of cancer cells surviving laser irradiation dropped to 0 at all time intervals from 2 min to 10 min. When cells were subjected to 1 Gy of photon dose, no visible advantage of using nanorods in conjunction with radiation was observed. Conclusions: Results of experimental studies show that nanorods are extremely effective agents in converting laser light into heat with promising thermal therapy applications for cancer treatment.
SU‐FF‐J‐163: Monte Carlo Simulation for Nanoparticle‐Enhanced Irradiation in Small Animals
Authors: Hsieh H , Tu S
Published: April 2010

Purpose: Report our computer simulation investigation on the nanoparticle‐enhanced irradiation for small animals in the hardware settings of a commercial micro CT imaging system. Method and Materials: PENELOPE, a Monte Carlo radiation transport code, was used in our simulation study. Three identical cylinder‐shaped water phantoms were created with diameter of 1.0 cm and length of 3.0 cm. An analytical ball‐shaped tumor with diameter of 1.0 mm was embedded at the center of each phantom. The first tumor model was filled with water. The second and third tumor models were filled with homogeneous mixtures of gold and magnetic nanoparticle solution separately. The geometrical scanning settings of a commercial micro CT (Skyscan 1076) were simulated in the irradiation model. The distance was 12.1 cm from the irradiation source to rotation center and 5.1 cm from the rotation center to detector. A variety of photon energies were simulated as the irradiation source, including 30, 50, 100, 150, 300, 500 KeV, and 1 MeV. Results: For larger photon energies including 300, 500 KeV and 1 MeV, dose built‐ups and penumbras were observed in the percentage depth dose curves and lateral beam profiles. Maximum dose occurred in the tumor region in the second and third tumor models for all energies. The lateral beam profiles show that all the maximum dose levels in the second and third tumor model are greater than the first model. This key finding suggested that nanoparticle based solution can be used as the dose‐enhanced agent. Conclusion: Percentage depth dose curves and lateral beam profiles were computed for different phantoms, including tumor models filled with different nanoparticle solutions. Nanoparticles had been previously shown to be the excellent imaging contrast medium and our simulation study indicated that nanoparticles can also be applied as an effective dose enhanced agent in small animal irradiation.
SU‐FF‐J‐165: Development and Application of Internal and External Motion Tracking System for Small Animal
Authors: Park S , Jung H , Kim K , Ji Y
Published: April 2010

Introduction: In this study, we developed the system that could analysis and store the data acquired by real‐time tracking the movement of abdominal surface due to reparation motion which have a high correlation with organ movement occurred by a reparation with a CCD camera and an image board, and then we performed the experiment of correlation between internal organ movement and external abdominal surface movement for the medium size animal of Guinea‐pig using the developed system Materials and Methods: The experimental system was consisted with imaging acquisition part and image signal analyzing part. The image acquisition of internal organ was performed with a C‐arm fluoroscopy system, and abdominal surface images were acquired with a CCD camera and NI image board. The developed system was applied to a Guinea‐pig prior as application experiment for small animal. The information of the internal organ movement was acquired with C‐arm fluoroscopy system by tracking the fiducial gold maker pre‐implemented into liver, which was used in Cyberknife radiation therapy. The data acquisition of internal organ movement due to respiration and abdominal surface movement was performed under general anesthesia. Results: In spite of a steady state, the movement feature of abdominal surface of the Guinea‐pig due to a respiration was more and less fluctuated in period and amplitude. The period of the breathing cycle ranged from 1.2 to 1.4 sec, and the frequency patterns for both the internal marker and the external marker were similar. The peak‐to‐peak motion of the internal marker was varied from 1.3 to 2.0 mm, and that of the external marker was varied from 1.4 to 2.2 mm. Conclusion: The inference of correlations between internal organ motion and external organ motion in the experiment using guinea‐pigs having relatively short breathing cycle would be help to perform clinical trials for patients in future.
SU‐FF‐J‐172: Deformable Fusion and Atlas Based Autosegmentation: MimVista Vs. CMS Focal ABAS
Authors: Harrison A , Galvin J , Yu Y , Xiao Y
Published: April 2010

Purpose: To compare two commercial atlas based auto segmentation (ABAS) contouring algorithms designed to expedite delineation of target volumes and organs at risk (OAR). Metrics include time to generate contours, and accuracy with respect to physicians' manual delineation volumes. Method and Materials: CMS FocalAbas and MimVista Atlas Segmentation were compared. Ten IMRT head and neck CT scans with physician‐drawn volumes were randomly selected. The scans were sent to MimVista where the CT scan was matched using deformable atlas segmentation to one of 57 atlas patients. The identified atlas patient was then transferred to the FocalAbas Atlas database. This allowed each system to run its auto segmentation process on the same blank CT scan with the identical atlas patient making differences solely a function of the software or hardware. Results: Four OARs were compared to physician volumes using the Dice index. The range of the index for cord was FocalAbas 0.23–0.50 and MimVista 0.26–0.66; for brainstem, FocalAbas 0.11–0.68 and MimVista 0.13–0.73; for right parotid, FocalAbas 0.14–0.70 and MimVista 0.18–0.60 and for left parotid, FocalAbas 0.09–0.77 and MimVista 0.29–0.60. The mean index of all volumes was FocalAbas 0.44±0.17 and MimVista 0.48±0.15, the two‐tailed P‐value=0.0443, which is statistically significant. Inter‐physician volume indexes have been documented at 0.7. The mean time to execute the ABAS was 00:11:11 on FocalAbas (HPXW8400 Workstation+Intel Xeon5160, 3.0GHz, 6.0G Ram) and 00:05:49 on MimVista (HPXW6400 Workstation+Intel Xeon 5150, 2.66GHz, 2G Ram). Conclusion: This study revealed that neither ABAS of OARs out‐performed the other. Although there is the need for improvement of the algorithms to attain a higher coefficient of agreement to physicians' delineations, these tools have been proven to generate a good first draft of clinical volumes and thusly reduce physician contouring time by sixty percent.