bluuebunny/crossref_metadata_2025 huggingface dataset:
Monte Carlo techniques for scattering foil design and dosimetry in total skin electron irradiations
Authors: Ye Sung‐Joon , Pareek Prem N. , Spencer Sharon , Duan Jun , Brezovich Ivan A.
Published: June 2005

Total skin electron irradiation (TSEI) with single fields requires large electron beams having good dose uniformity,at the skin surface, and low bremsstrahlung contamination. To satisfy these requirements, energy degraders and scattering foils have to be specially designed for the given accelerator and treatment room. We used Monte Carlo (MC) techniques based onEGS4user codes (BEAM,DOSXYZ, andDOSRZ) as a guide in the beam modifier design of our TSEI system. The dosimetric characteristics at the treatment distance ofsource‐to‐surface distance (SSD) were verified experimentally using a linear array of 47 ion chambers, a parallel plate chamber, and radiochromic film. By matching MC simulations to standard beam measurements atSSD, the parameters of the electron beam incident on the vacuum window were determined. Best match was achieved assuming that electrons were monoenergetic at, parallel, and distributed in a circular pattern having a Gaussian radial distribution with full width at half. These parameters were then used to simulate our TSEI unit with various scattering foils. Two of the foils were fabricated and experimentally evaluated by measuring off‐axis dose uniformity and depth doses. A scattering foil, consisting of aaluminum plate ofthickness and placed at isocenter perpendicular to the beam direction, was considered optimal. It produced a beam that was flat withinup tooff‐axis distance, dropped by not more than 8% at a distance of, and had an x‐ray contamination of. For stationary beams, MC‐computed,, andagreed with measurements within. The MC‐predicted surface dose of the rotating phantom was 41% of the dose rate atof the stationary phantom, whereas our calculations based on a semiempirical formula in the literature yielded a drop to 42%. The MC simulations provided the guideline of beam modifier design for TSEI and estimated the dosimetric performance for stationary and rotational irradiations.
SU‐CC‐J‐6C‐06: A Generalized Field Splitting Algorithm for Optimal IMRT Delivery Efficiency
Authors: Kamath S , Sahni S , Li J , Palta J , Ranka S
Published: June 2005

Purpose: The purpose of this work is to develop an algorithm for optimally splitting a large intensity‐modulated field for delivery with a MLC into two or more adjacent subfields that maximizes MU efficiency, and to provide mathematical proofs that the algorithm is optimal in the most general cases. Method and Materials: The field split can be stated as the following mathematical problem: given a fluence matrix which exceeds the largest field size limitation of the delivery system, find two or three subfields, each of which satisfies the field size limitation constraint, that combine to give the original fluence map, and with the additional constraint that the sum of the delivered MUs of the subfields be minimized. In this general formalism, the subfields can overlap and the field split does not have to be in a straight line. We first construct an optimal MU leaf sequence for the large field ignoring the width constraint. The optimal field split is then generated by appropriate partitioning of the optimal leaf sequence into leaf sequences for the subfields. The overlapping region of the subfields creates a natural feathering area which is clinically desirable. Results: Compared to a simple field splitting that cuts through the center of a fluence map, our algorithm showed an average decrease in total MU of about 19% on 32 clinical fluence maps with the largest decrease in total MU of 45%. In many cases, the total MU of the split fields does not increase from the MU of the original sequence when the width constraint is ignored. Conclusion: We have developed an algorithm that solves the most general version of the field splitting problem for large intensity modulated fields. We provide rigorous mathematical proofs that the proposed algorithm for field splitting is optimal in MU efficiency.
SU‐CC‐J‐6C‐08: Automated Beam Direction Selection for IMRT Based On Geometrical Concepts of Viewability and Orthogonality
Authors: Clark V , Alaly J , Zakarian K , Deasy J
Published: June 2005

Purpose: To develop a fast and reliable algorithm to automatically select beam angles for intensity‐modulated radiation therapy (IMRT) treatment planning. We hypothesized that such an algorithm could be developed based on purely geometrical concepts as a pre‐planning step. Method and Materials: We define any point in the target as viewable by a given beam if a ray from that beam, which passes through the point, does not intersect any critical structures (i.e., the point can be ‘viewed’ by that beam). The beam angle selection problem can then be generalized to the multi‐set cover problem, a difficult (NP‐hard) computer science problem. We also consider orthogonality, which captures beam non‐overlap outside the target. We hypothesize that increasing 3‐viewability (fraction of points viewable by at least 3 beams) and increasing orthogonality typically results in higher quality IMRT dose distributions. This was tested by comparing, for 30 random sets of 5 beam angles, the objective function based on 3‐viewability and orthogonality vs. the final objective function value output of a weighted quadratic IMRT optimization. Our beam angle selection algorithm extends a greedy set cover algorithm and aims to find a set of coplanar angles that will make a maximum fraction of target points at least k‐viewable while also maximizing orthogonality. Results: For an IMRT case where beam angle selection impacted IMRT objective function values, there was a strong correlation between the viewability‐orthogonality objective function value and the final objective function value of a weighted quadratic IMRT optimization (Spearman correlation coefficient 0.63 (p<0.0004)). Our proposed algorithm determines beam angles for a typical plan in 2–4 minutes on a 2 GHz PC. Conclusion: We conclude that the purely geometrical concepts of viewability and orthogonality can be used as a basis for automatically and efficiently selecting IMRT beam angles using the class of algorithms proposed.
SU‐DD‐A2‐03: Influence of Equipment Variables Upon Cardiac Radiation Levels
Authors: Nickoloff E , Lu Z , Dutta A , So J , Moses J
Published: June 2005

Purpose: The main goal is to demonstrate the effects of varying imaging equipment parameters have upon patient radiation dose in modern cardiac catheterization x‐ray systems. The parameters examined include: pulse rate, Field‐of‐View (FoV), patient thickness, fluoroscopy versus record mode, SID settings and ABC programs. Method and Materials: A Siemens flat panel Axion Artis FC cardiac unit was used. The patient was simulated by sheets of acrylic varying in thickness from 10 cm to 30 cm. The exposure rate was measured at the entrance surface of the acrylic with an ionization chamber. Results: The entrance exposure rate varied with the (FoV)N where −2 <N< −3. The exposure rate varied directly with pulse rate in both fluoroscopy and record mode; in comparison to continuous or 30 pps, 15 pps reduced the radiation levels by 50%. The plus mode increased radiation levels by 40–50% and the minus mode reduced the levels by 40–50%. One minute of record imaging is equivalent to about 10 minutes of fluoroscopy. For both modes, the radiation levels increase approximately as an exponential function of thickness with an HVL in acrylic of about 2.8 cm. Maximum exposure rates for large patients can be 10 – 20 R/min in fluoroscopy and over 100 R/min in record mode. Conclusions: Although typical cardiac catheterization radiation levels are available for image intensifier and cine film systems, these data provide information related to a modern flat panel and digital recording system. Data about the relative effects permit significant dose savings to be realized by judicious selection of settings. In comparison to older equipment without these modern features, utilization of all the dose reduction steps can result in a dose savings of over 90%. Conflict of Interest: Some free software upgrades to equipment were provided during evaluations; no other financial conflicts exist.
SU‐EE‐A2‐03: Visualization and Identification of Breast Glandular Tissue in Breast CT Volume Data
Authors: Nelson T , Boone J , Seibert J , Kuhn B , Kwan A , Yang K
Published: June 2005

Purpose: Breast glandular tissue architecture complicates mammography image interpretation due to superposition. We have built a dedicated breast CT (BCT) scanner to produce volumetric images of the breast and begun a preliminary clinical trial in volunteers and selected patients. The purpose of this study was to evaluate visualization and identification of breast landular tissue patterns in BCT volume data and its potential to improve lesion detection compared to mammography. Method and Materials: A dedicated BCT scanner was constructed and previously described. Volunteer and patient imaging was performed using 80 kVp at doses comparable to a standard 2‐view mammogram and reconstructed using a modified Feldkamp algorithm. BCT data of 512^3 voxels have an approximately isotropic resolution of 300 μm. Volume data were analyzed and viewed on a specially designed volume workstation and were displayed using blending, maximum‐intensity‐projection (MIP) and summation projection algorithms. Interactive review was possible for the entire volume. Breast glandular structures were identified based on CT number, voxel histograms and structural features. Results: BCT images showed impressive breast parenchyma and glandular structure detail with excellent contrast resolution. Volume rendering, especially summation projection, and thick slices provided optimization of viewing of ductal structures. Multi‐planar slices permitted rapid scrolling through slices. Voxel CT numbers, histograms and architectural features were effective in differentiating glandular from fat, skin and connective tissues. MIP images clearly demonstrated calcifications. Conclusion: BCT provides high‐quality volume data that enhanced visualization of breast glandular tissue and architecture compared to other breast imaging methods. Voxel CT numbers plus direct interactive viewing provided the mammographer clear views of breast architecture and glandular tissues. Workstation display flexibility presented data appearing similar to mammograms plus additional tomographic slices further enhancing conspicuity of breast architecture. A small number of mammographically demonstrated cancers were readily identified in BCT data.
SU‐EE‐A3‐04: Comparison of Breath‐Hold and Free Breathing Approaches for 4DCT Data Acquisition
Authors: Saba O , Bayouth J , Hoffman E
Published: June 2005

Purpose: The objective of this study was to compare two separate respiratory techniques available for four‐dimensional computed tomography (4DCT). Regional lung density and spatial displacement of airway tree bifurcations (BPs) were studied and compared between regulated (breath hold) and free breathing techniques. Method and Materials: Fifteen normal adult participants were subjected to CT scanning triggered by the lung volume controller system using breath hold and free breathing respiratory techniques. Lung volumes were compared using pneumotachometers (PNT) and respiratory inductance plethysmography. A LabVIEW‐based lung volume controller system that allows monitoring/control of lung volumes and provides gating capabilities for CT image acquisition was built. Each subject's slow vital capacity was measured and lung CT images were obtained at two volumes: ∼65% vital capacity and the end expiratory phase of tidal breathing (∼20% vital capacity). For the free breathing, these represent end inspiration and end expiration. Results: The mean difference in location of BPs between inspiration and expiration using breath hold technique [15.3 ± 5.0mm] and free breathing techniques [18.5 ± 7.3mm] were large but similar. Regional mean lung density differences between breath hold and free breathing was insignificant using paired t‐test (p > 0.05). The BPs spatial uncertainty between breath hold and free breathing, both at end inspiration and end expiration were small: the mean difference in the distance between the carina and any other branch point pair matched was 2.0 mm (±2.0 mm) at end inspiration and 2.8 mm (±2.0 mm) at end expiration. Conclusion: Both breath hold and free breathing respiratory techniques significantly (∼50%) reduce the uncertainty in branch point localization. In addition, both techniques produce similar regional lung densities. The uncertainty in branch point location with respect to the carina is reduced by 2–3 mm for breath hold compared to free breathing techniques.
SU‐EE‐A1‐04: Integrated Complementary IMRT Combined with Image‐Guided HDR Brachytherapy for Cancers of the Uterine Cervix
Authors: Duan J , Shen S , Brezovich I , Kim R , Popple R , Ye S , Wu X , Pareek P
Published: June 2005

Purpose: Conventional HDR (CHDR) brachytherapy for cervical cancers often fails to cover the entire gross tumor volume (GTV). CT/MRI‐based 3‐D planning allows optimization of dwell times for improved target coverage, but often at the cost of substantially higher doses to organs at risk (OARs). In the present study, we integrate image‐guided HDR brachytherapy with concomitant complementary IMRT to boost target coverage and maintain low doses to OARs. Method and Materials: Treatment planning CT and MRI images of 6 patients were acquired with CT/MRI‐compatible carbon‐fiber applicator. HDR plans were obtained by modifying CHDR plans to keep bladder and rectum dose below 80%. Based on these HDR plans, IMRT plans were subsequently optimized to complement the dose coverage of GTV with 3‐mm margin (GTV+) and the uterus. To prevent anatomical deformation, IMRT plans were to be delivered immediately following image‐guided HDR treatment with applicator in place. V95% (Target volume receiving 95% prescription dose) and D2 (minimum dose in 2.0‐cm3 OAR volume receiving the highest dose) were used to compare IMRT‐HDR technique with CHDR and HDR optimized for target coverage (OHDR). Results: The MRT‐HDR technique substantially improved target coverage while maintaining bladder and rectum doses at acceptable low level. For the six patients, V95% for GTV+ and the uterus improved from the average of 56.8% and 51.4% in CHDR to 92.5% and 95.3% in IMRT‐HDR, respectively. Average D2 doses to bladder and rectum were 88.7% and 65.2% for CHDR and 72.4% and 71.4% for IMRT‐HDR. In contrast, OHDR improved target coverage, but D2 doses to bladder (>119%) and rectum (87.3% to > 200%) were unacceptably high. Conclusion: Integrated complementary IMRT combined with image‐guide HDR significantly improves dose coverage to the targets while maintaining low doses to OARs. It is dosimetrically and logistically feasible to clinically implement this technique for potentially improved outcome.
SU‐FF‐E‐04: Using the Internet for Real‐Time Education and Knowledge Exchange in Medical Physics
Authors: Woo M , Ng KH
Published: June 2005

Purpose: This work provides an update to the ongoing project of Remote Real‐Time Learning. (http://www.neteinfach.com/rrtl/index.htm). The goal of the project is to promote the use of Internet to provide classroom style real‐time interactive education in Medical Physics. Method and Materials: This project was started 3 years ago as a collaboration between the Department of Medical Physics at the Toronto‐Sunnybrook Regional Cancer Centre in Canada and the Department of Radiology at the University of Malaya in Malaysia. A class of Medical Physics graduate students at the University of Malaya attended lectures provided by lecturers in Toronto, using the Internet as the main tool of communication. As part of the study, the different methods that can be used to provide real‐time interactive remote education were explored, and various topics including traditional classroom lectures as well as hands‐on workshops were also delivered. Results: Based on our experience, a reasonably stable methodology has been established. This methodology allows a fairly smooth set‐up and conduction of the lectures, at an insignificant cost, while offering flexible convenience to the lecturers as well as the students, despite the widely different time zones. Conclusion: The current plan is to expand the process to allow students at multiple sites of the world to attend the online lectures at the same time. Our project welcomes the participation of both lecturers and students who are interested in taking advantage of the advance of the Internet to promote greater accessibility of quality education in the field.
SU‐FF‐I‐13: Accurate Measurement of Lead Shielding In‐Situ
Authors: Rutel I , Yester M
Published: June 2005

Purpose: To design a protocol for measuring or verifying the amount of lead in a wall of unknown thickness for purposes of radiation shielding in a diagnostic x‐ray room. The aim is to develop a method of accurate measure for thicknesses up to 1/8 inch of lead that can be used with a simple scintillation counter attached to a standard survey meter. Method and Materials: We employed a simple scintillation detector connected to a digital rate/meter scaler combination and a scintillation detector attached to a multi‐channel analyzer (MCA). Measurements were made for a Tc‐99m source in a vial placed in a lead cylinder in alignment with a 1 inch by 1 inch scintillation detector. Lead sheets (2′ × 2′) were placed half‐way between the source and detector. The energy spectra were obtained as well as integrated counts with the survey meter. Background was determined and subtracted from the measurements. Different regions of the spectrum were investigated by integrating over varying energy ranges (variable low energy to 195 keV). A plot of the counts as a function of lead thickness were obtained and compared to the expected attenuation curve for a good geometry. In addition we have investigated the effect of collimation and source geometry. Results: As expected the results for a window about only the photopeak produced the expected logarithmic variation as a function of thickness given sufficient count statistics. At lower energy thresholds, the scatter caused significant deviation from the expected behavior beyond 1/16 inch. An effective half‐value layer was derived as a function of lower energy threshold and thickness. Conclusion: We have developed a method to determine with reasonable accuracy the value of an unknown thickness of lead in the wall of an x‐ray room using a scintillation detector with a digital survey meter.
SU‐FF‐I‐18: A Comparison of NCRP 147 CT Shielding Methods
Authors: Blechinger J
Published: June 2005

Purpose: The NCRP report 147 describes two methods to calculate the shielding, one using a scattered fraction of the CTDI, and another using the scatter plot supplied by the manufacturer. The two methods are used to calculate shielding for a model CT suite, and the results compared. The calculation complexity and gantry attenuation are major differences. Method and Materials: The scatter fraction method only requires the CTDI, which is supplied by the manufacturer or available at IMPACTscan. The scatter plot needs to be adjusted to the room scale and overlayed. Results: The scatter fraction was simple but no consideration for attenuation of the gantry is made. The scatter plot gives the best information for the radiation near the ganrty.
SU‐FF‐I‐26: Performance Characterization of a New 41cm by 41cm A‐Si Flat Panel X‐Ray Detector
Authors: Axmann L , Bachmann R , Burchert R , Maolinbay M , Zhao J , Giambattista B
Published: June 2005

Purpose: To quantify and report the performance of an a‐Si flat panel X‐ray detector with a new generation electronics design in terms of electronic noise, dynamic range and linearity, as well as to quantify the imaging performance such as MTF and DQE. Method and Materials: The new detector was designed to provide low noise, wide dynamic range and programmable gain for a wide signal range. The signal readout chip has 128 channels, and each consists of a charge integration amplifier, followed by a correlated double sampling stage and a 128:1 multiplexer. The output voltage from the multiplexer is digitized by a 16‐bit analog‐to‐digital converter. The programmable gain can provide settings ranging from the most sensitive of ∼250 electrons per counts (e‐/c) to the least sensitive ∼4,000 (e‐/c). The detector uses a 41cm by 41cm a‐Si flat panel with 200μm pixel pitch and was coated with CsI(Tl). The MTF and DQE measurements were carried out in accordance with the IEC standard. Results: The total detector electronic noise is ∼3200 electrons (500 e‐/c), dynamic range was 78.3dB and the non‐linearity is +/−1.5% over 10–90% of full signal scale range. The MTF and DQE were measured both with and without the protective front cover. Conclusion: The detector with the new readout electronics has met all the major design goals and has raised detector performance to a higher level.
SU‐FF‐I‐27: The Effects of Fog On the Detectability of Radiographic Signals
Authors: Bunch P
Published: June 2005

Purpose: To evaluate the effects of fog on the detectability of radiographic signals. Method and Materials: The effects of added fog on a general‐purpose medical radiographic film were quantitatively evaluated in terms of threshold signal detectability using the CDRAD phantom under general radiographic conditions. Six observers evaluated threshold detectability within this phantom's uniformly exposed background at 36 combinations of x‐ray exposure and added fog. Additionally, the visibility of faint radiographic signals was visually assessed by experienced observers for 20 different film brands, using an aluminum step wedge as a background for faint signals. These 20 films span a wide range of contrast and speed. Results: In all instances, adding background fog to radiographic film samples had minimal effect or improved the subjectively perceived and CDRAD phantom‐assessed detectability of faint signals. Conclusion: The threshold detectability of radiographic films is not very sensitive to added fog level under the broad experimental conditions used. However, many current regulations and guidances prescribe very small tolerances within which fog should be maintained, sometimes as small as 0.03 in optical density. These data indicate that fog should be considered as a simple issue of meeting a radiologist's preference, and fog is not appropriate as a strictly proscribed performance specification. However, one may use short‐term fog changes, assessed using a properly stored single box of film, as an indictor of potential film processing quality control problems. Conflict of Interest: The author is an employee of the Eastman Kodak Company.
SU‐FF‐I‐30: Evaluation of Glass Capillary Material for Suitability of Use in a DTI Quality Assurance Phantom
Authors: Yanasak N , Allison J
Published: June 2005

Purpose: To evaluate whether glass fiber capillaries, having inside diameters (∼50 microns) somewhat similar to cellular dimensions, are a suitable candidate for use in a quality assurance (QA) phantom to characterize MR diffusion tensor imaging techniques. Method and Materials: Two phantoms containing glass capillary arrays were constructed. The first was designed to examine the success of injecting water into capillaries, and to show scanning characteristics in a high SNR/high‐resolution scan series. This phantom was imaged in a 7T Bruker PharmaScan MRI scanner, and signal intensities in the capillary arrays were examined for uniformity of water injection. Diffusion anisotropy and eigenvectors were also calculated. The second phantom was designed to test the performance of capillary arrays in a clinical magnet, as per a QA phantom. Images from a 1.5T GE scanner were acquired, and processed to determine fractional anisotropy and principle diffusion eigenvectors. Results: Based on the methods above, water can be successfully injected into the capillaries based on the uniformity of signal after injection. Eigenvectors show diffusion primarily along the axis of the capillary array. Images from the clinical series also show diffusion along the axis of the array, even at the SNR and resolution typical of a clinical protocol. Conclusion: The work performed in this study suggests that glass capillary arrays could be used successfully in a QA phantom, in principle. Future investigations will determine the allowable range of capillary fiber inner‐ and outer‐diameters, based on SNR constraints. Flexible arrays will also be investigated.
SU‐FF‐I‐43: Problems and Techniques in Gamma Camera Imaging of Yttrium‐90 Labeled Radiopharmaceuticals
Authors: Luo J , Zimmer M , Miller D , Rao P , Mistretta M , Spies S
Published: June 2005

Purpose: This study was to identify problems and investigate camera parameters that would create effective biodistribution images for treatment planning and dosimetry in patients receiving Y‐90 radionuclide therapy. Method and Materials: Y‐90 energy spectra under different interacting conditions were recorded from MCA, uptake probe and gamma camera. Y‐90 (17.6 MBq) was added to an Anthropomorphic Torso Phantom, with or without water in its tank, with following distribution: liver, 70% with water; right lung, 15% with water; left lung, 15% without water. Imaging was performed on a Siemens eCam, dual head camera with HEGP/MEGP collimators at various energy settings. Y‐90 patient imaging was performed with retained activities of 1.52 GBq and 6.7 kBq Y‐90 labeled microspheres and with 3.7 GBq Y‐90 labeled Zevalin. At 30 minutes post Zevalin injection, a whole body scan was performed using a 194 cm bed length (5 cm/min, total 48 min), 256 × 1024 × 16 matrix without zooming. Results: Y‐90 spectra indicated a characteristic X‐ray peak (Pb. K‐alpha) at 75 keV along with characteristic Bremsstrahlung distribution. Phantom tests found an energy window of 75 keV/50% to produce practical images. Significant uptake in the right lung of the phantom versus other structures was identified. Patient's lungs could not be easily visualized. Conclusion: An energy window (75keV/50%) is adequate for characteristic X‐ray and Bremsstrahlung imaging. Y‐90 imaging depends on scatter characteristic of tissue and does not provide direct biodistribution of Yttrium‐90. Further investigations of imaging technique are needed to assess effective Y‐90 patient imaging.
SU‐FF‐I‐50: Detectability Study on OCT in the Presence of Speckle with Hotelling Observer
Authors: Cheong K , Clarkson E
Published: June 2005

Purpose: To study the detectability performance of an Optical Coherence Tomography imaging system in the presence of speckles within the framework of the Hotelling observer. Method and Materials: Optical Coherence Tomography (OCT) is a non‐invasive imaging modality widely used in in‐vivo study of tissues. Optical propagation in biological samples is dominated by scattering due to fluctuations in refractive index. This random fluctuation in the index makes it necessary to model the samples as random fields and statistical analysis the tool of choice. The Hotelling observer, a numerical observer that forms its test statistic based on the covariance of the input data, will be used in the classification task of distinguishing one class of sample from the other. The input of the Hotelling observer (i.e., the OCT signal) is considered to be generated by mixing the reference beam with the backscattering of the mean field in the sample. The scattering is handled by using the 1st Born approximation. Poissonian imaging noise will be considered. Results: An expression of the detectability index is derived for a classification task within the framework of the Hotelling observer. With this expression, we study how the sample properties and the layout of the optical system affect the performance of an OCT system. Conclusion: This work sets the foundation for the assessment of the OCT system and system optimization with respect to a classification task. The stochastic model used to describe the sample is more general in the sense that it goes beyond Gaussian statistic, and the functional form is easy to adjust to include different types of sample.
SU‐FF‐I‐53: The Impact of Portal Imager Shifts and the Assumption of Rigid Isocentricity On Megavoltage Cone Beam CT Images
Authors: Morin O , Bose S , Chen J , Aubin M , Pouliot J
Published: June 2005

Purpose: Linear accelerators and the current flat panel positioners do not represent a rigid isocentric imaging system. To correct for this effect in the reconstruction process of Megavoltage Cone Beam CT, the group uses projection matrices that are obtained from geometric calibration. This project studies the effect of deviations in detector position from the calibrated geometry which may occur over time. Method and Materials: To simulate the effect of portal imager shifts, we translated projection images before performing the reconstruction. Synthetic projection matrices that assume perfect isocentricity were also produced to study the utility of our geometric calibration. To accentuate the observed effects, we first used noise‐free simulated projections of a CT phantom as well as reconstructions of small, high‐contrast ball bearings. We also acquired anatomical images of a Rando head with an acceptable clinical dose (8 MU) to verify our capacity to identify the previously observed artifacts. Results: A pure flat panel shift of 2 mm along the longitudinal direction causes the same shift in the reconstruction volume. A 2 mm shift in the lateral direction however, greatly degrades the image quality with streaking and half‐moon shadow artifacts. The orientation of those artifacts depends on the start and end angle of the acquisition. Since most of the flat panel flex was previously measured to be in the longitudinal direction, the use of synthetic projection matrices caused a blurring of the image in the longitudinal direction. Conclusion: The calibrated projection matrices play an important role at conserving the image quality around high contrast objects. A 2 mm lateral shift away from the calibration will likely be detectable in high contrast regions of anatomical images. Longitudinal shifts will not degrade the image but will cause a positioning error. Conflict of Interest: This research is supported by Siemens OCS.
SU‐FF‐J‐51: Auto‐Regressive‐Moving‐Average Modeling of Respiratory Motion in Radiation Therapy
Authors: Luo M , Zheng W , Jeraj R , Fain S
Published: June 2005

Purpose: To construct a linear regression model of respiratory motion for prediction of future behavior from past records. Combined use of accurate respiration prediction and adaptive beams would ensure more accurate delivery of planned radiation, which is normally degraded due to patient breathing during treatment, especially for tumors in abdominal and thoracic regions. Method and Materials: Respiratory data were obtained by tracking a fiducial marker placed on the lateral chestwall of a female volunteer in supine position, using 2D dynamic MRI with a temporal resolution of 0.8 sec/frame. The data were analyzed using Auto‐Regressive‐Moving‐Average modeling with the mathematical form , where { yt } is the fiducial position with mean adjusted to zero, { et } is the fiducial localization error assumed to be Gaussian white noise, p and q respectively represent orders of auto‐regression and moving‐average, and the a′is and b′js are autoregressive and moving‐average coefficients. The model was identified as Auto‐Regressive (AR), Moving‐Average (MA), or Auto‐Regressive‐Moving‐Average (ARMA) by visual inspection of the autocorrelation and partial‐autocorrelation functions of { yt }. The order(s) of the model, i.e. p and/or q, were determined by minimizing the Akaike's Information Criterion (AIC) value, a widely used goodness‐of‐fit measure compromising least‐square fitting and number of parameters to be estimated. Results: A 5th‐order autoregressive model was determined for the respiratory data. Qualitative observation of the actual and predicted breathing traces illustrated their similarity to each other. Quantitative analysis, which included autocorrelation function and histogram inspection of the prediction error, showed its randomness (uncorrelated in time) and small magnitude, indicating validity and reliability of the model. Conclusion: A prospective modeling and prediction method has been demonstrated for respiratory motion compensation in radiation therapy without prolonged treatment time. We will further test the approach on different volunteers and patients, with regular and irregular breathing traces.
SU‐FF‐J‐54: CCTV‐Based Patient Setup Aids and Monitoring System in RT
Authors: Cho W , Huh S , Ha S , Park Y
Published: June 2005

Purpose: To analyze patient motions as well as patient positioning during conventional radiation therapy, a radio frequency (RF)‐based CCTV system with semi‐beam's eye views (BEV's) is to verify patient setup. Method and Materials: In order to capture patient images in semi‐beam's eye views, 4 small cameras are installed in the blocking tray, which is mounted in the treatment head of linear accelerators: right, left, superior, and inferior oblique angles towards the isocenter of the linear accelerator. Each camera has its own 2.7GHz RF module (minimize the cross‐talk interference between RF source of linear accelerator and the CCTV system), and transmits the signal to the receivers, which are placed in the wall of the treatment room. The semi‐BEV images are monitored before and during irradiations and saved in the computer. The CCTV images and port films taken and analyzed in the first day, then are used as reference images. Also, a special laser with a point and a circle is attached in the tray to make a reference point for 4 cameras and a magnification factor (can be used as SSD meter) Results: The CCTV images are captured in semi‐BEV's, thus very useful to compare the room lasers, cross hairs, and anatomical landmarks in patient contours. Because of wide dynamic range of the video amplifier, it can provide the patient images as well as room laser, and light field with room lights off. The radiation effects appear as a pepper and salt noise, which can be eliminated by employing averaging kernel in the computer. Conclusion: This CCTV system will be expanded to correlate with CT images in future and under progress. Also, the CCTV‐based images will be connected to the internet, so that the doctors can be able to monitor patient setup in remote site.
SU‐FF‐J‐60: Effectiveness of MVCBCT for Patients with Implanted High‐Z Material
Authors: Aubin M , Morin O , Bucci K , Chen J , Roach M , Pouliot J
Published: June 2005

Purpose: To exploit the penetrability of high‐energy photons of Megavoltage ConeBeam CT system (MVCBCT) to obtain 3D images of the anatomy in presence of “Non‐compatible CT” objects made of high‐Z material. Methods and Material: A new MVCBCT system integrated onto a clinical Linac was used to acquire 3D images of different phantoms and patients. The grey levels of different electron density inserts (lung to dense bone) in a CT phantom were measured with and without the presence of a small Cerrobend rod (10×15mm) on a regular CT and with the MVCBCT. MVCBCT of a Rando phantom with implanted gold markers and tooth fillings as well as patients with dental implants or with gold markers implanted in prostate were also obtained. Results: The presence of the Cerrobend object in the CT phantom scanned with a regular CT creates strong artifacts around the object and disturbs the quality of the entire image, modifying the Hounsfield numbers by an average of 10%, even 15 cm away from the rod. The grey levels of the density inserts in the CT phantom remain unchanged within 3% in presence of the Cerrobend rod for MVCBCT. Similarly, gold markers appear with the typical star pattern artifact on CT images where a well‐defined dot is seen on MVCBCT. The tooth fillings in the MVCBCT Rando phantom do not disturb the soft tissue information around the teeth. Conclusion: Compared to the kV energy range, the presence of high‐Z material has relatively little impact on image quality of MVCBCT. Therefore, MVCBCT can complement missing information for planning or patient position verification purposes when high‐Z materials such as gold markers, tooth fillings, dental implants or hip prostheses are present. Clinical examples of each of these items will be presented. Conflict of Interest: Siemens supports this Research.
SU‐FF‐J‐61: Evaluation of Two Fluoroscopic Imaging Setups for Online Dose Delivery Adaptation
Authors: Nill S , Unkelbach J , Dietrich L , Oelfke U
Published: June 2005

Purpose: One aim of ART is the observation of organ motion followed by a subsequent adaptation of the treatment plan. Two imaging configurations were evaluated for their potential of online tracking and correction of organ motion by using fluoroscopic images: x‐ray tube in line with a flat panel detector mounted at (A) 90 or (B) 180 degree offset to the MV‐beam. Method and Materials: For one lung case two IMRT plans with 5 beams were optimized for two MLCs with 10mm and 2.75mm leaf width. The motion of the target was modeled by a rigid transformation. Respiratory motion in the lung was investigated for different amplitudes. The dose distributions for different cases (no‐movement, uncorrected movement, correction for the movement perpendicular to the monitoring kV‐beam) were evaluated. Results: For the simulated movement with a small amplitude (3mm) in the AP direction the dose distributions resulting from the correction of the displacement vector using system (A) or (B) showed similar results independent of the collimator. They were in good agreement with the dose distribution of the static (not moving) patient. Increasing the amplitude in the AP direction to 6mm or even 9mm leads for both amplitudes and both MLCs to almost the DVHs of the static dose distribution if system (B) is used for the online correction. For the dose distribution resulting from the correction based on system (A) the difference between the static and the corrected doses is continuously increasing especially for the more conformal static dose distribution of the 2.75mm MLC. Conclusion: For motion amplitudes up to 6mm both systems can create dose distributions similar to the static dose distribution. For increasing amplitudes in the AP or LR direction the imaging system (B) will create dose distributions equal or superior to system (A). Conflict of Interest: Research supported by Siemens‐OCS.
SU‐FF‐J‐64: Influence of Respiratory Motion On Cone‐Beam CT (CBCT) Imaging of Thorax and Abdomen
Authors: Kim G , Li T , Yang Y , Schreibmann E , Thorndyke B , Boyer A , Xing L
Published: June 2005

Purpose: To quantify the interplay between respiratory motion and CBCT imaging in thoracic and abdominal region. Method and Materials: A Varian Acuity CBCT simulator was used to scan a motion‐simulation phantom and three patients (a pancreatic and two lung cases). Motion phase of the phantom or the patients was stamped with a Varian RPM system. For phantom study, three CBCT gantry rotation speeds (5°, 10°, and 15° per second) were used. Several different motion patterns and speeds of the phantom, simulating a variety of clinical situations, were also investigated with CBCT gantry speed of 10°/s. The patient scans were done with 10°/s rotation speed. The resultant images were compared against the 4D‐CT images acquired on a GE LightSpeed scanner. The HU profiles of the two types of images were analyzed. Results: Given the fact that a regular breathing cycle takes ∼4s, a CBCT scan is usually a time‐average over ∼10 breathing cycles. Large artifacts and anatomical distortions were observed in both phantom and patient scans. In the phantom study, the onset of motion artifacts started at very low “breathing” motion rate, suggesting that CBCT is less proof against motion. The CBCT image quality was worsen as the “breathing” rate increased but this became saturated when the phantom motion rate reached to a certain level. For the patient study, the discrepancies between the CBCT and 4D CT images were also found to be large. The tumor contours, for example, delineated based on the two types of images can differ up to 1cm Conclusion: Respirator motion greatly degrades the quality of CBCT and presents a problem in thorax and abdomen imaging. It is urgently needed to develop a clinically practical means to minimize the adverse effect of breathing motion.
SU‐FF‐J‐67: Monte Carlo Dose Calculation in Prostate Patients Aided by 3D Ultrasound Imaging
Authors: Mark C , Chang A , DeBlois F , Cury F , Vuong T , Falco T , Verhaegen F
Published: June 2005

Purpose: To investigate the use of Monte Carlo (MC) dose calculations for improved assessment of the daily treatment dose for prostate patients using novel 3D ultrasound imaging. Method and Materials: Prostate displacements were measured in 39 prostate cancer patients undergoing external‐beam radiotherapy with a 3D ultrasound image guided radiotherapy system (RESTITU, Resonant Medical Inc). The system resides in both the CT‐Sim and treatment rooms. It acquires 3D ultrasound (US) data of the pelvic region just prior to the CT‐sim, with the 3D US image registered in absolute space. Subsequent 3D US images are also acquired before treatment delivery, resulting in a set of 3D US images of the time‐evolving geometry. The system also calculates prostate displacement between the CT‐Sim and treatment data sets. An algorithm was developed to combine CT images in a MC dose calculation system with 3D US information such as organ shifts and contours. Dose distributions for both shifted and unshifted CT data were calculated using both a conventional planning system (CADPLAN) and a MC dose calculation system. Results: MC calculated dose distributions in prostate patients were found to differ significantly from conventional dose calculations using the CADPLAN system, mainly due to the influence of the femoral heads. Incorporation of the 3D US measured prostate shifts in the MC dose calculations clearly show severe tumour underdosage would result if no correction was applied to the patient setup. When correcting the patient setup, calculations taking the time‐evolving 3D US contours into account show that significant differences in the dose distributions in the target and surrounding tissue occur compared to a single planning dose calculation. Conclusion: Ultrasound information from a 3D US system opens up the possibility to obtain improved dose assessments for daily treatment fractions using MC dose calculation techniques, leading eventually to image‐guided adaptive radiotherapy.
SU‐FF‐J‐68: Motion‐Compensation in IMRT Employing Probability Distribution of Target Location: Phantom Tests and Computer Simulation
Authors: Trofimov A , Fernald M , Martin B , Sharp G , Jiang S , Bortfeld T
Published: June 2005

Purpose: To investigate potential utility of the probability density function (PDF) of target location in managing the detrimental effect of target motion on the delivered dose distribution. Method and Materials: Recent advances in 4‐D imaging allowed for a more detailed and precise observation and description of internal organ motion due to respiration. Realistic average target trajectories and corresponding PDF were obtained from the analysis of 4D‐CT data. It was assumed that these motion patterns were stable and reproducible during treatment delivery. Dose calculation and treatment plan optimization were performed with a modified “motion kernel”, obtained by superimposing pencil beam doses delivered to different instances of anatomy (phases of motion), or, in the first approximation, through convolution of the generic pencil beam kernel with the PDF of target location. With this approach, sample motion‐compensated plans were optimized and delivered in fractions to a movable phantom, which reproduced preset motion patterns in two dimensions. Dose measurements were performed with diagnostic film for the linac rates of 100, 300 and 500 MU/minute. Robustness of treatment plans with respect to delivery errors and variations in target motion, as well as interplay with the MLC leaf movement, was further investigated in a computer simulation. Results: While optimized fluence patterns showed deviation of as much as 50% between standard and motion‐compensated plans (for 2‐cm peak‐to‐peak amplitude of target motion), the doses delivered in a single fraction deviated by less than 15% point‐by‐point, and were within 3% of prescription after 30 fractions (reduced approximately as the inverse square root of the number of fractions). Conclusion: Phantom tests showed that the use of motion kernel for treatment planning allowed maintaining the conformality of dose distribution delivered over multiple fractions, without expanding planning margins beyond the CTV. Supported in part by the NCI grant 5P01‐CA21239‐25, AAPM Summer Undergraduate Fellowship.
SU‐FF‐J‐73: Treatment Simulation for 4D Image Guided Radiation Therapy
Authors: Yan Y , Weng X , Ratanatharathorn V , Penagaricano J , Berkley L , Shi C , Youssef E , Papanikolaou N
Published: June 2005

Purpose: To investigate the feasibility of a dynamic treatment simulation system, PortSim± for four‐dimensional image guided radiation therapy (4DIGRT) and respiratory gated Intensity Modulated Radiation Therapy (RGIMRT). Method and Materials: PortSim± is an in‐house developed software package that allows for simulation of 4DIGRT and RGIMRT. The software is integrated with our conventional simulator. Prior to simulation, a set of DRRs at different respiration phases along with the corresponding anatomic contours were imported from the treatment planning station. The respiratory rhythm and cycle of the patient is captured using a radio‐opaque marker which reflects the circumference change of a binding belt around patient's chest. The marker correlates with the respiratory cycle and can be easily detected. In 4DIGRT simulation, the displayed reference DRR and corresponding MLC is triggered by the respiratory cycle. Similarly for RGIMRT, the MLC overlay is linked to the respiration phase and duty cycle threshold. Once the dynamic MLC characteristics are accounted for, both 4DIGRT and RGIMRT can be simulated prior to delivery in order to ensure that patient is positioned accurately and the treatment is delivered as planned. Results: PortSim± incorporates live acquisition of high quality fluoroscopic images (1024 × 1024), image intensifier distortion correction, breathing phase detection, reference DRRs and MLC display. The software runs on a Pentium IV 2.2 GHz, with 1G RAM computer. Initial results show that the system can successfully detect the breathing cycle and sequence the display and superposition of DRRs and dMLC. The complete simulation can be recorded at a rate of 30 frames per second for later review and analysis. Conclusion: The initial experience with this system indicates that uncertainties in set‐up and delivery of 4DIGRT and RGIMRT treatment can be greatly reduced. The recorded simulation provides information that could influence field design and plan development.