bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐I‐148: Self‐Sorted Four‐Dimensional Magnetic Resonance Imaging: A Feasibility Study
Authors: Cai J , Chang Z , Yin F
Published: August 2010

Purpose: Considerable imaging dose to health tissue of patient from 4D‐CT is often a concern. This study is to develop a four‐dimensional magnetic resonance imaging (4D‐MRI) technique based on retrospective sorting strategy that uses body volume as respiratory surrogate. Method and Materials: Respiratory signals are determined by body volume changes at each slice location. Respiratory phases were subsequently calculated for each image and used in 4D‐MRI retrospective sorting. The technique was tested on motion phantom (in a sinusoidal motion pattern: amplitude 2.0cm, period 5 seconds) and on three healthy volunteers. Phantom images were acquired on 1.5T GE MR scanner using fast imaging employed steady state acquisition (FIESTA) sequence and human images were acquired on 1.5T Siemens MR scanner using similar sequence (True‐FISP) with the following imaging parameters (TR/TE, 3.7ms/1.21ms; Matrix, 256×166; FOV, (300–350)×(227–300)mm; flip angle, 52°; slice thickness, 5mm). Frame rate was around 2.5frames/second. All image sets were acquired in axial planes with multiple slices to cover entire interested volume. Each slice was imaged for slightly more than one breathing cycle. A single sagittal cine‐MRI was also acquired on phantom to serve as a reference for motion evolution. Results: Sinusoidal motion of phantom was clearly seen in all three planes with minimal artifacts. Sagittal images from 4D‐MRI matched with those from sagittal cine‐MRI (mean difference in amplitude: −0.3±0.5mm). In volunteers' study, internal organ motion of the lungs, liver, and/or kidneys were clearly revealed in 4D‐MRI. Image artifacts were more noticeable than in phantom study, presumably due to subjects' breathing irregularity. Conclusions: These preliminary results on phantom and healthy volunteers demonstrated the feasibility 4D‐MRI using body volume as the respiratory surrogate. This technique has the potential to evaluate tumor motion in most body sites without any radiation dose.
SU‐GG‐I‐150: Voxel Location Dependence of Brain Metabolites as Determined by Magnetic Resonance Spectroscopy
Authors: Ewell L , Bhullar A , Stea B
Published: August 2010

Purpose: To quantify the spatial variation of absolute metabolite concentration in the human brain as determined by magnetic resonance spectroscopy (MRS). Method and Materials: Multivoxel (PRESS) magnetic resonance spectroscopy data has been analyzed in an attempt to map out brain anatomy. Phantom data, along with spectra from a healthy volunteer and protocol patients were compared in order to detect trends that can be correlated with anatomy and/or disease. A 7×7 voxel grid was utilized, with a 2×2cm voxel size along with a 1cm slice thickness for all MRS scans. Phantom metabolites concentrations were similar to a healthy human brain: 3.0, 10.0 and 12.5mM for Cho, Cr and NAA respectively. Gaussian fits were used to estimate peak area. Results: The phantom absolute voxel metabolite concentration variation is fit by a second degree polynomial, ax2 + bx +c. Average R2 (Pearson product) for the six different fits (three metabolites × two directions) varied from 0.93±0.08 (st. dev.) for the left‐right fit for NAA to 0.98±0.02 for the anterior — posterior fit for Cr . Absolute metabolite concentration from the healthy volunteer show a consistent trend when plotted in the left right direction with the most medial voxel having a low value of metabolite concentration, followed by a relative maximum in the mid — lateral cerebrum, with a relative minima on the most lateral voxels. This minimum is likely the result of low metabolite concentrations near the mid‐hemisphere/ventricle region of the cerebrum. NAA concentrations from a protocol patient show roughly consistent functional spatial dependence for three anterior rows, with a posterior row distinct. Lactate/lipid contamination is likely the cause of this differentiation. Conclusion: Determining the functional spatial dependence of metabolite concentrations can aid in the deciding the value of diagnostic clinical MRS scans. Acknowledgment: This work was funded by the Arizona Biomedical Research Commission.
SU‐GG‐I‐151: Reduced Number of Signal Averages for Diffusion Imaging Using Compressed Sensing
Authors: Miao J , rayan S , Li W , Yu X , Wilson D
Published: August 2010

Purpose: Diffusion‐weighted imaging is an important clinical tool in neurological and body MRI. However, low contrast to noise ratios (CNR) of parameter maps (e.g., fractional anisotropy (FA)), force numerous signal averages to achieve useful CNR. Diffusion Tensor Imaging (DTI) requires at least six diffusion directions, which can lead to extremely lengthy protocols. Here, we present a method for using Compressed Sensing (CS) processing to decrease the number of signal acquisitions needed to achieve a given CNR. Method and Materials: The CNR was calculated for the FA (Fractional Anisotropy) map of celery DTI data acquired on a 9.4T vertical Bruker BioSpec. The 2‐D Fourier coefficients of FA map were first decomposed into multiple sets of incoherent subsamples by the application of complementary random masks with equal sampling ratios, such that all of the coefficients were used at least once. Data subsampling was performed in both directions. CS reconstruction was applied to each subset of Fourier coefficients to recover multiple fully sampled FA maps. Finally, the CS reconstructed FA maps were averaged (in Fourier space) to produce a less noisy FA map. Results: The CS processed FA maps mostly contained significantly less noise than unprocessed FA maps by both calculated CNR and visual inspection. Conclusion: We found that the CS processed FA maps mostly contained significantly less noise than unprocessed FA maps. However, our celery phantom datasets started out with high CNR, which does not reproduce in vivo noise conditions. Therefore, application of this method to a phantom dataset might not fully demonstrate the its capabilities, meaning that the method should be tested on more realistic MR data before any practical significance can be attached to these results.
SU‐GG‐I‐153: A Novel Relevance Feedback Approach for Efficient Mammogram Image Retrieval
Authors: Oh J , Yang Y , El Naqa I
Published: August 2010

Purpose: With the rapid increase of medical databases and PACS (picture archiving and communication systems) image volumes, it became critical to develop new tools to retrieve images from these archives more effectively and efficiently for routine clinical practice. A key factor for successful image retrieval systems lies in the development of efficient methods that can derive high‐level semantic concepts from low‐level image content features. Despite many efforts, an efficient retrieval system for medical images still remains a challenging problem due to their complex contents in relation to disease conditions. Towards this goal we have developed a machine learning framework that utilizes expert's knowledge for online retrieval of relevant mammogram images based on clustered microcalcifications. Method and Materials: We tested a database of 200 clinical mammograms that were taken from 104 patients with known pathology. To automatically retrieve mammograms from the database that are perceptually similar to a given query image, we proposed an efficient relevance feedback algorithm based on support vector machine (SVM) regression and incremental learning that dramatically reduces the processing time, avoiding the retraining of the retrieval system. Results: We conducted various experiments to evaluate the developed algorithm under varying user's interactions. It was observed that our proposed method showed significant superiority over off‐line learning. In particular, in a matching fraction test where the top‐k retrieved images were compared with the disease condition of the query image (benign or malignant) after the user's relevance feedback, the proposed method achieved a matching fraction as high as 82.4%. Conclusions: We have developed a novel relevance feedback method for effective retrieval of relevant mammogram images. Our experimental results demonstrated that the proposed method is not only better in performance, but more computationally efficient than offline SVM based on re‐training, while maintaining its effectiveness for online clinical application.
SU‐GG‐I‐156: Determining Focal Spot Performance in Mammography Using Self Developing Film
Authors: Coleman K , Shepard J
Published: August 2010

Purpose: The lack of mammography cassettes, film and wet chemistry processing in the ever more common fully digital imaging facilities makes it necessary to facilitate the determination of High Contrast Limit of Resolution focal spot performance with a new system. Methods and Materials: Due to the relative insensitivity of commercially available self developing film, it was necessary to have constructed a 5– 20 lp/mm phantom in a support essentially radiolucent at beam energies available in mammography. It was then necessary to assure that the commercially available self developing film did nor limit the measured resolution. Results: It was determined that this system is easily capable of resolutions through 20 lp/mm and the evaluation of High Contrast Limit of Resolution in a clinical environment without wet chemistry processing is thereby simplified. Conclusions: This is a viable process for High Contrast Limit of Resolution which is currently required for ACR accreditation stereotactic and useful in other aspects of mammography system performance. The results are immediately available and easily assessed in a clinical environment. Statement of Conflict: At o charge to the authors, the final version of the High Contrast Limit of Resolution was provided for evaluation by the manufacturer and the manufacturer of the self developing film provided for testing film rejected by their QC.
SU‐GG‐I‐161: Multi‐Resolution Cumulative Summation (CUSUM) Images for Monitoring Gamma Camera Detector Uniformity
Authors: Lofton B , Wendt R
Published: August 2010

Purpose: Detect trends in gamma camera uniformity in order to predict service events. Materials and Methods: Cumulative summation statistical control (CUSUM) effectively detects subtle shifts in the expected mean of normally distributed data. This technique was applied to each pixel in a time series of gamma camera quality control floods to detect nonuniformities that might otherwise have gone undetected in any single flood image using NEMA uniformity calculations. One hundred statistically independent 10 M count uniformity floods were sequentially acquired in a 1024×1024 matrix. A progressively worsening nonuniformity was simulated beginning in the thirtieth flood image, where an attenuation disk 8 cm in diameter (∼1% count loss) was positioned in the central field‐of‐view (FOV). Additional disks were added to the stack every ten subsequent acquisitions in order to mimic progressive count loss, up to the point that normal NEMA analysis was expected to yield differential uniformity values that exceeded our institution's action limit of 3%. Mean and error images were calculated with respect to time using the first thirty floods in the series, and the time series was normalized to these values. The CUSUM images were calculated by summing the deviations between a reference value of one‐half of the standard deviation and each normalized pixel, adding to that the previous value of the CUSUM at each pixel location. Thus, the CUSUM images represent the accumulation of deviations between each normalized and expected pixel value. The process was repeated for larger pixel sizes and composite images were formed. Results and Conclusion: The results show a distinct signal at the location of the non‐uniformity by time point 60, well in advance of reaching the level of degradation expected to cause a single flood to fail clinical criteria, given the rate of degradation. Thus, this technique sensitively detects non‐uniformity trends.
SU‐GG‐I‐165: Determination of Tissue Optical Properties in ALA‐Mediated Head & Neck PDT
Authors: Dimofte A , Zhu T , Finlay J , Sandell J
Published: August 2010

Purpose: The main objective of this study was to determine the optical properties (scattering and absorption coefficients) in vivo by interstitial measurements during H&N PDT.Methods and Matierals: We developed a model for quick and accurate determination of tissue optical properties (absorption coefficient ⌈a and transport scattering coefficient ⌈s') in semi‐infinite medium, which is theoretically suitable for determination of optical properties head and neck with ALA‐mediated PDT. We measured and determined the optical properties at the treatment wavelength. Measurements were performed before and after the delivery of the light treatment. The light detection device consists of two parallel light transmitting catheters placed 5mm apart. Diffuse light, from a 2mm cylindrical diffusing tip, is collected by an isotropic detector with a 0.5mm scattering bulb whose position is determined by a computer controlled step motor. The system automatically records and plots the light fluence rate per unit source power as a function of position. Results: The result is fitted with a diffusion equation to extrapolate ⌈a and ⌈s'. A theory based on light source on semi‐infinite medium has been developed to interpret the measured data. Another measurement was done using a fiber‐optic based probe. This probe was placed on the tissue surface, and white light was delivered to the tumor surface by one of its source fibers. The diffusely reflected white light was collected by a spectrograph and analyzed to determine the absorption and scattering spectra of the tissue. Results from both methods were compared for accuracy. To test the ability of this algorithm to accurately recover the optical properties of the tissue, we made measurements in tissue simulating phantoms. Conclusion: We developed a model for quick and accurate determination of tissue optical properties in semi‐infinite medium, which is theoretically suitable for determination of optical properties head and neck PDT.
SU‐GG‐I‐166: Design and Evaluation of an Optical Tactile Imaging Device for Tumor Detection
Authors: Lee J , Won C , Yan K , Yu Y
Published: August 2010

Purpose: To present a novel tactile imaging device for cancer detection. Method and Materials: Unlike traditional tactile devices, which are formed of pressure sensor array, this new device uses an optical waveguide and total internal reflection principle to maximize the tactile resolution. In order to emulate the detection range of the human tactile sensation, a multi‐layer polydimethylsiloxane waveguide has been fabricated as a sensing probe. The elastic modulus of each layer has been matched to the dermis, epidermis, and subcutaneous of the human finger. The light is illuminated under the critical angle for full reflection within the waveguide. When a waveguide is compressed by an object, the contact area of the waveguide deforms, which causes the light to scatter. The scattered light is then captured by a high resolution camera. The applied forces can be detected by measuring changes in the amount of diffused light. To test the performance of the proposed device, a realistic tissue phantom with hard inclusions is developed. Total of nine inclusions with different diameters and depth were placed in the phantom. We estimated the diameter and the depth of the inclusions with the tactile imaging device. We also performed experiments using the mice with globus tumors. We grew three different sizes of tumors and imaged them using the proposed device. Results: The result showed that the proposed sensor can estimate the inclusion diameter within 4.09% and the inclusion depth within 7.55%. The mice test results show that the proposed device successfully detects the tumors. In the animal study, the sensor detected a subsurface tumor as small as 2.74 mm. Conclusion: A novel tactile imaging device for tumor identification has been designed and experimentally evaluated to be effective.
SU‐GG‐I‐167: Light Fluence Rate Calculation for Intracavity Photodynamic Therapy
Authors: Sandell J , Chang C , Zhu T
Published: August 2010

Purpose: To develop an algorithm used to calculate the fluence rate in real time for intracavitory photodynamic therapy using an infrared (IR) camera tracking system. Method and Materials: Diffusion approximation is used to derive an analytical form of light fluence rate in a spherical cavity inside the cavity and the tissue. The results of our resulting analytical solution are compared with a Finite Element Model (FEM) for the sphere. The FEM method can be used to calculate the fluence rate in tissue in any arbitrary geometries. An light fluence rate calculation algorithm is developed in the chest cavity while taking into account the effect of multiple scattering. We then use a chest phantom and an IR camera system to obtain a 3D map of a chest cavity. This map is then read into our algorithm and the fluence rate is then calculated on the chest surface. We compare our calculations to measured phantom data to determine how accurately our algorithim determines the light fluence in treatment‐like setting. Measurements are made using an in‐situ dosimetry system. Results: Detailed derivation of the light fluence rate in The fluence measurements taken of our chest phantom are currently being analyzed and compared with the fluence rate calculated under the same optical properties from our algorithm. This comparison will help us constrain our algorithm to better fit the observed results and create a more precise treatment planning tool. Conclusion: The work presented here presents the foundation for a valuable new tool in PDT of the pleural cavity in humans. By calculating the fluence rate for patient specific geometries treatment can become more effective and robust. The possibility of developing the work of this paper into a real‐time fluence rate monitoring system provides a new level of exactness in treatment planning for the pleural region.
SU‐GG‐I‐168: Image Reconstruction in an Attenuating Medium with Two Different Attenuation Coefficients Using Photoacoustic Tomography
Authors: Modgil D , La Riviere P
Published: August 2010

Purpose: The goal of this research is to incorporate the effect of attenuation of the surrounding medium and accurately reconstruct the optical absorption distribution of the photoacoustic source. Method and Materials: Photoacoustic tomography (PAT) reconstructs an image of the optical absorption of an object using the pressure signals that are generated when the object is illuminated via pulsed electromagnetic radiation. The effect of ultrasonic attenuation can be significant since photoacoustic tomography uses broadband detection and the ultrasonic attenuation varies with frequency. Previous studies have related the detected pressure to the optical absorption coefficient when there is uniform attenuation. In this work, we specifically consider the practically important problem of an photoacoustic source embedded in a medium (such as tissue) with an attenuation coefficient, surrounded by a matching medium (such as water) with a different attenuation coefficient. The photoacoustic pressure that is measured by the detector in this case is not directly related to the optical absorption coefficient of the source. We have derived an analytical expression relating the photoacoustic pressure in the contact plane to the pressure in the detector plane. We can then reconstruct an image using the calculated pressure on the contact plane and the standard image reconstruction techniques for PAT. Results: Preliminary results in 2D suggest that the analytic expression that we derived to relate the photoacoustic pressure on the detection plane with that in the contact plane provides a suitable method for obtaining the photoacoustic source lying in an attenuating medium. Conclusion: The attenuation effect of the surrounding medium have been incorporated into image reconstruction in photoacoustic tomography. This work will be useful to accurately reconstruct the image in PAT when the attenuation coefficient of the object (such as tumor) differs from that of the surrounding medium (healthy tissue).
SU‐GG‐I‐170: Differentiation of Seborrheic Keratosis and Verruca Plana with Reflectance Confocal Microscopy: A Preliminary Study
Authors: Gao M , Liu M
Published: August 2010

Background: Seborrheic keratoses (SK) are the most common benign tumor in older individuals, Sometimes the differentiation of SK and Verrucca Plana (VP) is a challenge. Reflectance Confocal Microscopy (RCM) has been proved to be useful in the diagnosis of skin diseases; however, to date, there is no report on the differential study of the two diseases with RCM. Objectives: To investigate whether RCM could be used in the differentiation of SK and VP. Methods: We recruited 10 patients with typical lesions, of SK and 10 patients with typical VP lesions, imaged with RCM and biopsied to obtain the features under RCM images based on histology analysis. Then, we attempt to summarize and refine those imaging characteristics collected to obtain the most significant ones. All the cases with lesions suggestive of SK or VP were advised to undergo imaging with RCM, and if RCM imaging reflected discordantly with the clinical diagnosis, a biopsy was suggested for the exact lesion imaged. Those cases with RCM and histology results were collected. Finally, two clinical dermatologists, who had no previous experience with RCM, were tested with the simplified features of RCM images to differentiate the suspected lesions of SK and VP among the cases collected. Results: In total, there were 58 cases with RCM images and histology results collected, in which, 40 cases were diagnosed as SK and 18 cases as VP by histology. The two blinded dermatologists' judgments were identical to histology analysis. Conclusion: RCM proved to be valuable in the differential diagnosis of SK and VP. The simplified characteristics are easily understood and acceptable to those with no previous experience of RCM. Key words: reflectance confocal microscopy, RCM, seborrheic keratosis, verruca plana
SU‐GG‐I‐171: Diffuse Optical Measurements of Blood Oxygenation and Flow for Monitoring CMRO2 in Neonates with Congenital Heart Defects
Authors: Minkoff DL , Busch DR , Buckley EM , Durduran T , Licht DJ , Yodh AG
Published: August 2010

Purpose: Improve quantification of Cerebral Metabolic Rate of Oxygen (CMR02) by developing a diffuse optical instrument for use in continuous bedside monitoring of neonatal patients with congenital heart defects. Method and Materials: A compact (17″×l7&″×l4&″) Time‐Domain Diffuse Optical Spectroscopy (TD‐DOS) system has been developed and combined with a Diffuse Correlation Spectroscopy (DCS) system. The TD‐DOS system is composed of 3 lasers (685, 785, and 830 nm), 2 PMTs, 2 time correlated single photon counting (TCSPC) cards, and control electronics; the DCS system consists of 2 long‐coherence length 785nm lasers, 8 photon‐counting APDs, and a customized correlator. TD‐DOS allows absolute measurement of optical scattering and absorption, which permits calculation of absolute values for local hemoglobin concentration and tissue oxygen saturation (StO2); DCS measures relative changes in microvascular blood flow. We approximate CMRO2 changes using a compartmentalized model of the cerebral vasculature and Fick's law. However, this calculation relies upon knowledge of baseline physiological properties, namely, blood oxygen saturation and volume, both obtainable from TD‐DOS. Simultaneously, relative changes in cerebral blood flow will be measured by DCS. Together, these diffuse optical modalities will allow us to calculate CMRO2 based on the individual physiological parameters of each subject. Results: Previous works on neonates with congenital heart defects have utilized instrumentation incapable of measuring absolute optical properties. Calculations of CMRO2 were therefore based upon sparse literature reports of baseline quantities obtained from healthy subjects, who are not representative of our patient population. We will demonstrate an improved quantification of CMRO2 by eliminating the questionable assumptions of blood oxygenation and volume in neonatal brains in favor of direct measurements. Conclusion: By combining TD‐DOS measurements of absolute tissue optical properties with DCS measurements of relative microvascular blood flow, these TD‐DOS data will permit an improved calculation of CMRO2 by providing individualized baseline values.
SU‐GG‐I‐173: GPU‐Accelerated Digitally Reconstructed Radiograph Generation for Radiation Therapy
Authors: Yuan J , Chang S , Tsang C , Chen W , Jette D
Published: August 2010

Purpose: To evaluate the speed up and image quality for digitally reconstructed radiograph (DRR) calculations using a graphic processing unit (GPU) comparing with a central processing unit (CPU). Method and Materials: We developed an application for DRR image calculations using a faster incremental Siddon ray tracing algorithm. The implementation of the core integration loop was the same for the CPU and the GPU except that single‐precision operations were used on the GPU with CUDA 1.2. The GPU runs on NVIDIA GeForce GTX 280M with 1 GB video memory. To validate the correctness of the algorithm, we employed a clinical three‐field plan as an example. The CT volume image and the RT plan were exported from a commercial treatment planning system and read by our application to generate the DRR images. Results: By comparing visually with the bony structures from our DRR images and the commercial software generated DRR images, we have confidence in the correctness of our fast ray tracing implementation on both CPU and GPU. The accuracy of the GPU calculations comparing with the CPU calculation is well acceptable as only about 3% of the total pixels have less than 0.1% pixel values difference from the CPU calculations for the test fields. Conclusions: The DRR calculations using GPU is more than an order of magnitude faster than using a general purpose CPU. The image quality by the two methods is very similar where the difference comes from the float point operation type. This accelerated DRR computation has potential to reduce the patient‐positioning time during the 2D/3D registration where inline DRR calculations are required in the iteration.
SU‐GG‐I‐174: Use of Line‐Focus Principle to Increase the Beam Intensity While Maintaining a High Generalized MTF for the Microangiographic Fluoroscope (MAF) System
Authors: Gupta S , Jain A , Bednarek D , Rudin S
Published: August 2010

Purpose: Achieving superior GMTF for the micro‐angiographic fluoroscope (MAF) system requires a small focal spot which could limit the range of possible beam intensities. We take advantage of the Line‐Focus Principle by using the medium focal spot viewed from the anode side rather than the small focal spot at the central axis to enable increased tube loading with no compromise in resolution. Method and Materials: We have calculated the GMTF at five different positions along the anode‐cathode direction parallel to the tube axis for the newly developed high resolution MAF (35 micron pixel). Focal spot measurements were done with a pin‐hole assembly using the same technique parameters at all positions. Small and medium focal spots and different object magnifications were used for GMTF comparisons. X‐ray intensity was determined at different positions parallel to the tube axis. Results: The comparison between the small focal spot at the center and the medium focal spot toward the anode direction demonstrated that there was only as small difference in resolution between these locations with only a 20% decrease in x‐ray intensity toward the anode side. Despite this decrease in x‐ray intensity due to the Heel effect, since the maximum tube loads were 500 and 160 mA for the two focal spots, respectively, the total increase in intensity for the medium focal spot can be a factor of 2.5 times that of the small focal spot. Focal spot blooming with the higher tube current for the medium focal spot was found to be negligible. Conclusions: This work demonstrates that by using the Line‐Focus Principle and a medium focal spot instead of a small focal spot at the center, a substantial increase in x‐ray output can be realized with minimal loss of total system spatial resolution or GMTF. (Support from: NIH Grants R01EB002873 and R01EB008425)
SU‐GG‐I‐177: The Dosimetric Comparision of RapidArc with Fixed Gantry Static IMRT for Liver Metastatic Carcinoma
Authors: Ma C , Yin Y
Published: August 2010

Objective To compare the dosimetric difference of RapidArc and fixed gantry static IMRT for liver carcinoma.Methods Ten CT datas of liver cancer patients were studied retrospectively. The IMRT and RapidArc plans were generated using either one or two arcs.The PTV Dosimetric distrubition, the OAR dose, the normal tissue dose, mornitor units and treatment time were compared. Results The maximum dose of PTV of RapidArc was lower than IMRT and there was statistically significant. RapidArc had an improved 90% prescription dose conformity index than IMRT(CI90=1.35±0.20 for RA1, 1.33±0.18 for RA2 and 1.62±0.41for IMRT) and there was statistically significant. For organs at risk all techniques respected planning objectives. RapidArc plan had a lower dose in V40 of stomach and Small bowel than IMRT plan, but higher in mean dose of left kidney. Concerning the V5 V10 and V15 of healthy tissue RapidArc plan was lower than IMRT plan. The V20 V25 and V30 of healthy tissue of RapidArc plan was lower than IMRT plan. The number of computed MU/fraction of Rapid Arc plan was 40% or 46%of IMRT Plan and the treatment time reduced at least60%. Conclusion All techniques respected planning objectives. RapidArc showed improvements in conformity index and healthy tissue sparing with uncompromised target coverage. This, In combination with the less MU and short delivery time, can lead to clinically significant advances in the liver cancer. Key words: RapidArc IMRT Liver metastatic carcinoma Dosimetric
SU‐GG‐I‐179: Ultrasound‐Image Guided Radiation Treatment with Amplitude‐Based Gating System
Authors: Lin T , Hossain M , Price R , Ma C
Published: August 2010

Purpose To employ the first step for implementing UltraSound (US) imaging during radiation treatment, perform real‐time, zero‐dose 4D target tracking and implement amplitude‐based gating. Treatment volume can be reduced by gating or synchronizing the treatment machine with US‐based 4D target tracking. Methods and Materials Varian IX2300 is to be used with NOMOS BAT system. Organ motion study is tested with an in‐house moving station, which is coupled with a geometric phantom. The B‐mode BAT system consisting of a PC, Ultrasound unit, and an articulated arm is employed. The system uses contour data from a patient's CT simulation in combination with positional information derived from the BAT's articulated arm for target localization. An additional computer system called the BAT Workstation is also used to create the BAT studies. US probe is set at 22 cm maximum detection depth and 8 cm focus point. Videos of target movements are recoded during delivery in slices of TIF format. Results For 19 patients, a total of 185 treatment isocenter alignments were performed. Averaged positional adjustments in each axis are between 2.6 mm to 4.2 mm. US image quality was studied to verify radiation effects on the US transducer. A small noise ratio can be induced when the radiation is on the US probe and fields. Signal to noise ratio is estimated as 25 dB. An in‐house program can easily eliminate the noise and track the target volume. This suggests target tracking is possible with US during radiation treatment. Conclusion UltraSound image can be used as target localization with similar accuracy as CBCT or other invasive technique as below 1 mm resolution. A small noise ratio can be induced when the radiation is on the US probe and fields, but can also be easily eliminated by software. Therefore, US image guided radiation therapy is achievable.
SU‐GG‐J‐07: Respiratory Phase Effect on Tumor Shrinkage Analysis
Authors: Vaidya M , Al‐Lozi R , Yang D , Low D , El Naqa I
Published: August 2010

Purpose: Despite recent advances in image‐guided techniques, radiation treatment outcomes of lung cancer patients remains relatively poor. One of the main challenges is the change in tumor position due to breathing motion, which may lead to inaccurate tumor volume estimates. We are investigating the possibility of differences in measured tumor volumes at different breathing phases. Accurate quantification of these volume differences and identification of an “ideal” respiratory phase for volume measurement would likely improve prediction of tumor response. Methods and Materials: We evaluated the shrinking tumor volume at four specific respiratory phases for 7 NSCLC patients. The corresponding 3D‐CT image for a specific respiratory phase was reconstructed from 4D‐CT acquisition data. For each phase, the mid‐treatment and end of treatment scans were fused to the treatment planning CT using rigid registration. Pre‐treatment GTV and PTV contours were copied to the mid‐treatment and end of treatment scans, and further used for tumor segmentation using a registration‐assisted approach based on the level‐set deformable algorithm. After segmentation, the tumor volume was calculated for the two time‐points during the course of RT. The differences in measured tumor volumes for four respiratory phases (mid‐inhalation (MI), end‐of‐inhalation (EI), mid‐exhalation (ME), end‐of‐exhalation (EE)) at two time‐points in treatment were investigated. Results: Our preliminary analysis show that tumor volume measurements can differ at different respiratory phases, however, effects on tumor shrinkage analysis is small. Relatively, it is noted that volumes reconstructed at EI and ME phases tend to underestimate the shrinkage effect while MI and EE tend to overestimate the shrinkage effect. Conclusions: Our preliminary results show differences in volume measurements at different respiratory phases. A larger patient population would be required to select the ideal respiratory phase to provide accurate tumor volume changes. This will be a step further towards better understanding of radiation treatment efficacy.
SU‐GG‐J‐08: Physics‐Based Respiration‐Simulating Model Incorporating Pressure‐Volume Parameters for Lung: What Can We Learn from the Biomechanical Modeling Community?
Authors: Na Y , Eom J , Han B , Shi C , De S , Xu X
Published: August 2010

Purpose: A lung tumor moves during radiation therapy as a result of respiratory motion, discrepancies between planned and actually delivered radiation doses can be significant. It is desirable to accurately model the lung motion and the tumor location so that the radiation dosimetry involving such a moving target can be evaluated. This paper describes, in collaboration with mechanical engineers, the development of a patient‐specific, physiologically relevant respiratory motion model which is capable of predicting lung tumor motion over a complete breathing cycle. Method and Materials: Each patient specific non‐linear finite element (FE) lung model was developed under physiologically relevant conditions. The modeling was based on 4D CT data set of four lung cancer patients. Each 4D CT data was categorized according to multiple breathing phases. Non‐Uniform Rational B‐Spline (NURBS)‐based surfaces were reconstructed and converted into suitable FE meshes. A hybrid anatomical modeling method was employed to integrate the deformable lung model with other organs adopted from a whole‐body anatomical model consisting of 140 internal organs. Results: The FE simulations took more than 3 hours on an Intel Core2 Quadcore 2.83‐GHz CPU machine with 8‐GB RAM. Expert‐based validation using 48 landmarks of anatomical points in the lungs from the 4D CT data sets was summarized. The mean position errors between the FE model and 4D CT data are within 3 mm over the complete respiratory cycle. Conclusion: Working with a team of mechanical engineers, we have developed true physics‐based respiration model of the lung using a non‐linear finite element method. The FE model has been validated shows good agreements between simulated motion and measured motion in 4D CT. A 4D respiratory motion simulating phantom has been demonstrated for the future study of complex radiation interactions in tissues and dose distribution patterns for various radiation delivery strategies using advanced Monte Carlo simulations.
SU‐GG‐J‐16: Impacting Parameter Analysis for IMRT Quality
Authors: Wu H , Cao M , Zhao Q , Das I
Published: August 2010

Introduction: Intensity‐modulated radiation therapy (IMRT) accurately delivers radiation doses with high degree of conformity by modulating the intensity of the radiation beam in multiple small segments. Usually small fields have large variation in dose. For some TPS, there are no restrictions on plan parameters. Guideline for plan optimization is needed that allows the IMRT QA to pass satisfactorily. IMRT plan parameters are analyzed to correlate the success and failure of an IMRT QA plan. Materials and Methods: Based on IMRT QA results, 15 IMRT treatment plans, divided into 3 groups, are studies. Plans in group 1 passed IMRT QA with high gamma index passing rates and plan in group 2 passed with marginal passing rates. Plans in group 3 failed the IMRT QA. Statistical analysis has been performed on plan parameters, including beam number, segment number for each beam, MU in total or for each segment, the width variations of the leaf/jaw positions for each segment, the segment area sizes, and dose delivery for different segments of each beam, to discover the relationships between IMRT quality and these parameters. Results: The statistical results showed there is no correlation between plan quality and MU or beam/segment numbers. However, there are noticeable correlations between the IMRT quality and the segment sizes and widths. For each plan group, the IMRT quality decreased with the decreasing field sizes and segment widths. The histograms of these factors showed that failed IMRT plans have peak distributions with small field sizes (< 30cm2) and narrow widths (<20mm). Conclusion: Initial results showed that the passing rates of IMRT treatment plans have strong correlation with the segment field sizes and the opening widths of the leaf/jaw positions. Large number of segments with small fields produces unacceptable IMRT QA and should be avoided during IMRT planning.
SU‐GG‐J‐19: Electromagnetic Detection and Real‐Time DMLC Correction of Rotation during Radiotherapy
Authors: Wu J , Ruan D , Cho B , Sawant A , Petersen J , Newell L , Cattell H , Keall P
Published: August 2010

Purpose: A novel system has been developed to detect and correct tumor rotation in real‐time during radiotherapy delivery. The aim of this study was to quantify the geometric accuracy of the system. Method and Materials: A research Calypso system was integrated with a real‐time DMLC tracking system, employed on a Varian IX linac. Three 3mm diameter tungsten balls (markers) were embedded in the phantom, along with implanted electromagnetic transponders. EPID images were acquired for an elliptical beam, from which the beam aperture and tungsten balls were synchronously observed. For static rotation, the couch was used; for dynamic rotation, the couch was manually rotated continuously from 90 deg to 180 deg through the console. The dynamic rotation experiment was also performed by overlying the EM embedded phantom on a motion platform, rotating with a period of approximately 8 seconds. For all measurements, the beam‐target rotational alignment was determined as the difference between the major axis of the ellipse best fitting the rotated beam aperture and the marker orientation of the rotated target. The beam‐target translation alignment was determined by the different between the beam aperture center and the geometric center of the markers. Results: For static rotation, the beam‐target rotational alignment error was 0.9±1.7°. For dynamic rotation the alignment error was 0.3±1.4°. Both tests demonstrate sub‐degree accuracy for the tracking system. The beam‐target translational alignment error was 0.2±0.2mm. Conclusion: For the first time, real‐time target rotation has been accurately detected and corrected during treatment via MLC adaptation. The beam‐target rotational alignment accuracy is <1 degree; translational alignment is <1mm. The results show promise for improving radiotherapy targeting accuracy for a variety of tumor sites and motion types. Conflict of Interest: Supported by Calypso, NIH R0193626 and Varian.
SU‐GG‐J‐21: Direct Investigation of Geometric Coincidence among Calypso System, Onboard KV Imaging, and MV Treatment Beam Imaging
Authors: Mao W , Wang J , Foster R , Song K , Solberg T
Published: August 2010

Purpose: The Calypso 4D localization system and onboard kV imaging systems have been developed and applied clinically to improve accuracy of tumor localization for radiation therapy, particularly for Stereotactic Body Radiation Therapy (SBRT). However, the accuracy of the treatment and the dose delivery depends on the coincidence of both the treatment beam and localization systems. These are calibrated separately, and nominally to the room lasers which have additional sources of uncertainty. The purpose of this study is to investigate a direct method for determining the geometric accuracy and coincidence of treatment beam and localization systems. Method and Materials: A CIRS prostate phantom with three Calypso Beacons was imaged by both MV and kV beams at a series of gantry angles on a Synergy accelerator while the Beacon positions were simultaneously tracked using the Calypso system. A kV cone‐beam CT (CBCT) scan was also performed to locate the Beacons. Beacons were automatically detected on kV and MV projection images using in‐house software and their 3D positions were calculated from MV orthogonal pairs (MV‐pair), kV orthogonal pairs (kV‐pair), and CBCT scans, and then compared with Calypso. A special geometric QA procedure was developed to assess geometric accuracy of MV and kV imaging systems at every gantry angle. Geometric parameter deviations, particularly detector center offsets, were applied to correct the 3D position calculations. Results: Systematic differences among Calypso, kV‐pair, kV CBCT, and MV‐pair results were observed. Using geometric QA corrected MV‐pair results as treatment positions, averaged deviation of Calypso results is 1.1 mm. Deviations from MV‐pair, kV‐pair, and CBCT results drop from 1.7 mm, 1.1 mm, 1.0 mm to 0, 0.1 mm, and 0.2 mm, respectively, after geometric QA correction. Conclusion: Systematic deviations among Calypso, kV pairs, kV CBCT, and MV results were directly and quantitatively evaluated with a geometric QA.
SU‐GG‐J‐22: Comparison of Gold, Carbon, and Polymer Fiducial Markers Using different Imaging Modalities to Determine Optimal Marker Material for Image Guided Radiotherapy
Authors: Levinson L , Yue N , Zhou J , Goyal S
Published: August 2010

Purpose: To evaluate the visibility and artifact created by gold, carbon, and polymer fiducial markers across standard imaging modalities, including computed tomography (CT), kilovoltage (kV) and megavoltage (MV) linear accelerator imaging, Tomotherapy imaging, and ultrasound. Method and Materials: A 30×31×15 cm phantom was constructed using Superflab bolus. Three of each type, gold (0.9×3 mm), carbon (1×3 mm), and polymer (1×5 mm) markers, were inserted into the center layer of bolus. The phantom was imaged with CT, linac based kilovoltage and megavoltage x‐ray imaging systems, normal and fine Tomotherapy imaging, and ultrasound using various imaging parameters. The visibility and artifacts produced by each marker were assessed qualitatively and quantitatively; quantitative evaluations included analysis of contrast produced by each marker to assess visibility, and histograms and the standard deviation of the pixel values of a ring of increasing radius around each marker to evaluate artifacts. Results: All tested markers could be seen clearly under CT, kV, and ultrasound imaging, with the gold markers demonstrating the highest contrast. Under CT imaging, gold produced significant artifacts, while no artifacts were observed around polymer markers. Only the gold markers were visible when using linac based MV and Tomotherapy imaging. For linac based kV images, the contrast increased with kV and mA values for all the markers with the gold being the most pronounced. On CT images, the contrast increased with kV for the gold markers while decreasing for the polymer and carbon marker. We observed that the contrast significantly increased with slice thickness for the gold markers while the impact on the carbon and polymer markers was minimal. Conclusion: For kV based treatment verification, polymer and carbon markers are the preferred choice in CT simulation. For MV based treatment verification, gold markers should be used despite the artifacts they create on the simulation CT images.
SU‐GG‐J‐23: Optical Guidance System vs. CBCT for Phantom and Patient Setup
Authors: Jefferson Thomas
Published: August 2010

Purpose: To quantify the discrepancy between Varian optical guidance (OG) frameless localization system and Varian Trilogy on board imaging (OBI) system for setting up phantom and SRS patient. Materials and Methods: Two different phantoms were used in this study. One is a custom‐made phantom; the other is Penta‐Guide phantom. The bite‐tray used for frameless SRS localization is fixed on both phantoms. After CT scan, images were exported to Pinnacle and FastPlan treatment planning systems, where the same isocenter was identified and then the images were exported to Mosaiq and OG system respectively. On the Varian Trilogy, OG was used to position phantom. Then kV‐kV, conebeam CT (CBCT) and portal imager were used to image the phantom and calculate the isocenter shift. The same method has been used for four SRS frameless patients to check the OG setup, two patients' shifts were recorded and one patient's planning CT and CBCT images were fused and analyzed. Results & Discussion: For both phantom studies, the shift performed by CBCT, kV‐kV and MV were all within 1 mm. However, for actual patient setup, the shifts were greater than 2mm between OG and CBCT for two patients. The impact of bite‐tray fixation was studied by changing the angle of bite‐tray slightly; significant shift up to several mm was observed by OBI system. The isocenter change with the angle has been calculated based on a real patient's geometry. Conclusions: The discrepancy between CBCT and OG for setting up phantoms is less than 1mm, but can be greater for setting up SRS patients. The bite‐tray repositioning in patient's mouth is the major factor to cause this discrepancy.