bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐D‐AUD‐02: Comparison Between Collapsed Cone Convolution and Monte Carlo Dose Distributions for Small Lung Lesions
Authors: Liu H , Rassiah‐Szegedi P , Stathakis S , Shi C , Papanikolaou N
Published: July 2007

Purpose: To quantify the accuracy of a collapsed cone convolution superposition (CCCS) algorithm against Monte Carlo (MC) simulations for small lung lesions subject to electronic disequilibrium. Method and materials: IMRT plans for several lung patients were created using Pinnacle 7.6 planning system. The lung lesions measured less than 3 cm diameter and less than 27 cm3 Method and were treated in our institution with SBRT. The optimized intensity maps for each plan were then used to calculate the dose distributions using the CCCS algorithm. The linear accelerator was modeled using MC code EGSnrc\BEAMnrc and verified against commissioned measured data. Phase space file information was then scored at the plane above the collimating jaws. The intensity maps for each plan and the patient CT data from the treatment planning system were exported to our MC software. All patients were planned using 5 field IMRT on a 120 leaf MLC and Varian 2100C 6 MV beam. The dose distributions were calculated and normalized so that the isocenter receives 45Gy. The isodose distributions, DVH, and ROI statistics were used for comparison between the two methods. Results: MC results show that the PTV coverage is worse than the Pinnacle CCCS algorithm. The differences in the PTV coverage is about 10% (43Gy covers 90% of PTV on Pinnacle, but only 39Gy covers 90% of PTV on Monte Carlo) The DVH differences in the lungs are not as profound since these organs are a lot larger when compared to the GTV. Conclusion: There is about a 15% difference in the coverage of the PTV as shown by the DVHs between CCCS algorithm and MC for small lung lesions. The differences arise because of the limitations of the CCCS algorithm to accurately account for electronic disequilibrium.
TU‐D‐AUD‐04: Comparison of Three Different Source Models for Head Scatter Facto Calculation
Authors: Yan G , Liu C , Li J
Published: July 2007

Purpose: to evaluate three different source models for the calculation of head scatter factors. Method and Materials: The three different source models evaluated in this work are (1) The three‐source model (Yang et al) (2) The Gaussian analytic model (Jiang et al) (3) The numerical source model (Chui et al). These source models were developed based on different LINAC models. These source models were implemented and their results reproduced. Each of the source models was then applied to the other's measurement in order to cross‐validate accuracy. The effect of the monitor backscattering on the source model was also investigated. Finally, measurement data from a Varian Trilogy machine was used to evaluate each of the source models. The behavior of each model for different SSD data was also evaluated. Results: Measured output factors exhibit ∼1% difference at largest field sizes. The Gaussian analytic model gives 0.2% accuracy when fitting Yang's data, while the three‐source model has problem at large fields with error >15% when attempted on Jiang's data. So was the numerical model. Inclusion of the monitor backscattering effect into the source models significantly improved the agreement. When applying the models to the Trilogy measurement, the Gaussian analytic model gives the best agreement (<0.3%) while the three‐source model has trouble in asymmetric and large symmetric fields again. The numerical source model didn't fit those fields either. While the other two source models gave consistent results for data measured at different SSD, the numerical source model gave large errors (>0.5%). Conclusion: The Gaussian analytic model gave excellent fit to head scatter factor for a variety of LINAC models. Reasonable accuracy can be achieved if monitor backscatter effect were built into the other two source models.

Research sponsored by Sun Nuclear Corp.
TU‐D‐AUD‐09: Monte Carlo Investigation of the Effects of An IMRT Compensator On Linear Accelerator Beam Output
Authors: Niven D , Lewis J
Published: July 2007

Purpose: A comparison between Pinnacle calculated and Monte Carlo dose distributions was performed for patient treatments implementing physical compensators to deliver intensity modulated radiation therapy (IMRT). Method and Materials: Two 3D conformal radiation treatment (CRT) plans were created in Pinnacle using targets placed in the head and neck region of an anthropomorphic phantom. Compensators were generated in Pinnacle and were also modeled in DOSXYZnrc. Dose was calculated in both Pinnacle and Monte Carlo for cases with and without the compensator, and the dose distributions were compared using the chi‐comparison test with tolerances set to a 3% dose difference and a 3 mm distance‐to‐agreement. The dose distributions in the presence of a compensator were also compared for one beam of a five‐field IMRT treatment plan generated using actual patient CT data. Results: For the two 3D CRT plans, the number of voxels which failed the chi‐comparison criteria increased when the compensator was included in the simulations. In a (15 × 15 × 15) cm3 volume centered on the target, the percentage of voxels in disagreement rose from 4.99% to 9.46% for the first plan and from 4.60% to 5.19% for the second plan. For the IMRT plan with a compensator, the number of voxels failing the chi‐comparison test in a (10 × 10 × 10) cm3 volume centered on the target was 4.14%. Conclusion: The results demonstrate that dose calculations performed by Pinnacle in the presence of compensators are not necessarily representative of the dose delivered to the patient. This can be attributed to the fact in calculating the dose through the compensator during the compensator thickness optimization, Pinnacle accounts only for the attenuation of the primary fluence and does not consider scatter or beam hardening effects.
TU‐D‐BRA‐04: Laser‐Accelerated Protons for Radiation Therapy
Authors: Fourkal E
Published: July 2007

Recent developments in the field of laser engineering, specifically the invention of chirped pulse amplification technique made it possible to achieve laser light intensities reaching 1022 W/cm2 range. In this review, we will show that such laser intensities are sufficient to accelerate protons to therapeutic energy ranges, provided that proper laser‐target parameters are chosen. In the majority of recent laser‐matter interaction experiments, the proton energy spectra coming out of the interaction chamber are thermal making it impossible to use these protons in hadron therapy. This necessitates the development of a particle selection device that would deliver quasi‐monoenergetic particles suitable for medical applications. We will discuss earlier proposed particle selection system and show the dosimetric characteristics of protons coming out of this device. Using “real” patient data and physical characteristics (phase‐space distribution) of selected particles we will discuss the inter‐comparison studies between photon intensity‐modulated plans on one hand and intensity‐modulated plans based on laser‐accelerated protons on the other. In concluding remarks, we will describe the current challenges facing the project and ways to resolve them.
TU‐EE‐A4‐01: Dose Saving and Scatter Reduction in Volume‐Of‐Interest (VOI) Cone Beam CT — a Monte Carlo Simulation Study with Geant4
Authors: Chen L , Shaw C , Altunbas M , Lai C , Ding X , Liu X , Han T , Wang T
Published: July 2007

Purpose: To estimate and study the dose saving and scatter reduction properties of the VOI cone beam CT technique. Method and Materials: To implement the VOI scanning technique, a filter with a circular or rectangular opening is inserted between the x‐ray source and the patient to deliver a higher level x‐ray exposure inside the VOI and a lower exposure level outside the VOI in acquiring the projection images. This technique is expected to result in higher image quality inside the VOI with lower entire patient dose and significantly lowered scatter‐to‐primary ratios (SPRs) within the VOI. Modeling the patient as a cylinder of soft tissue, we have developed Monte Carlo simulation programs based on the Geant4 package to estimate the dose to the patient and the SPRs at the detector input. Simulation was performed at selected locations to estimate the variation of the dose level and SPRs from inside to the outside of the VOI. Simulation was also performed to estimate the reduction of the dose levels and SPRs with the VOI scanning technique as compared to full field cone beam CT. Results: Our simulation results show that with the exposure level reduced by the VOI filter, dose levels for the entire scan were significantly reduced both inside and outside the VOI. Scatter intensities at the detector input were also shown to decrease significantly both inside and outside the VOI in the projection images. Conclusion: Our simulation study successively demonstrated the ability of the VOI scanning technique to reduce patient dose and x‐ray scatter for improved image quality. Acknowledgement: This work was supported in part by a research grant EB000117 from the NIH‐NIBIB and a research grant CA104759 from the NIH‐NCI. The author also would like to thank Dr. Ioannis Sechopoulos and Yu Chen for consulting assistance in Geant4 programming.
TU‐EE‐A4‐04: A New Antiscatter Grid for High‐Resolution Region‐Of‐Interest (ROI) X‐Ray Imaging
Authors: Yadava G , Rudin S , Kuhls A , Bednarek D
Published: July 2007

Purpose: A new custom‐designed antiscatter grid for high‐resolution angiographic detectors is presented that would improve the image quality without introducing substantial grid‐line artifacts. Method and Materials: The new antiscatter grid is a custom‐made, parallel‐focus, crisscross cellular grid that employs gold septa material (CREATV MicroTech, Potomac, MD). The prototype 4.25 cm × 4.25 cm field‐of‐view grid has 20 μm thick septa with interspace distance of 380 μm, height 1.95 mm, and grid‐ratio of 5. This study was performed with the Microangiographic detector (43 μm pixel, 1024×1024 pixel matrix, 4.5 cm × 4.5 cm field‐of‐view, 250‐μm‐thick structured CsI(Tl) scintillator coupled to a CCD camera via minifying taper) in simulated neurovascular angiographic conditions, where a uniform head‐equivalent phantom was used as scattering media. The air‐gap between the phantom and the detector‐with‐grid was kept at 2.5 cm as used in clinical conditions for minimal blurring, but increased scatter. The standard lead‐beam‐stop technique was employed to determine the scatter‐fraction with and without the grid. In order to evaluate the low‐contrast imaging performance of the grid, phantoms with three different bone patterns of varying thickness and three different simulated iodinated vessel inserts in acrylic were imaged with and without‐grid at 70 kVp.

Results: The grid demonstrated approximately 59% scatter reduction at 70 kVp for the uniform head‐equivalent phantom without introducing substantial grid‐line artifacts following flat‐field correction. The average contrast‐improvement‐factor for the low‐contrast vessel‐phantom was found to be 1.75, whereas for the relatively higher contrast bone‐phantom it was 1.5. The primary transmission factor was measured to be 66%. Conclusion: The grid demonstrated significant scatter reduction when used in simulated neurovascular angiographic conditions even for the small FOV. Use of this grid with the Micro‐angiographic detector with reduced air‐gap can provide substantially improved image quality.

(Partial support: NIH R01‐NS43924, R01‐EB002873, Toshiba Medical System Corp.)
WE‐B‐BRB‐02: Patient Motion: Adaptive RT
Authors: Bortfeld T , Trofimov A , Unkelbach J , Chan TCY , Martin B
Published: July 2007

Organ motion blurs dose distributions. The blurring can be described in a statistical way by use of a motion probability (density) function (PDF). The motion‐blurred dose distribution is obtained by a convolution of the “sharp” (static case) dose distribution with the motion PDF. This holds true for both inter‐ and intra‐fraction motions. If intra‐fraction motion is present during an IMRT treatment, the dose distribution will also be affected by an “interplay” effect, in addition to the blurring. It has been shown that the interplay effect averages out during the course of a fractionated treatment, and that it is usually negligible after a typical number of fractions. The convolution model relies on the linear superimposition principle, which holds true for dose values but not for the biological effect. This issue has recently been addressed and will be discussed.

Several investigations have now looked at the feasibility of un‐doing the motion blur through the use if intensity‐modulation. In principle it should indeed be possible to de‐convolve the motion PDF from the intensity maps, to compensate for motion effects. This approach has been called 4D optimization or 4D inverse planning. Motion de‐convolution cannot, however, compensate motion effects exactly and it cannot be applied in a naïve straight‐forward way, because that would lead to undeliverable intensity maps with sharp spikes and negative values. The method of choice is rather to include the motion PDF in the IMRT optimization process. It has been shown that this can indeed yield a surprisingly high degree of motion compensation and it can even compete with other motion compensation methods such as gated delivery. However, this is only true if the motion characteristics (the PDF) are known with great precision. If the actually realized motion PDF deviates substantially from the planned PDF, the method becomes less useful and can, in principle, make things worse.

More recently, uncertainties in the knowledge of the motion characteristics have been taken into account by use of robust optimization techniques. With these one can now compensate for motion effects in an approximate way for a large class of motion characteristics. In terms of the sparing of normal structures, the results are in between the use of conventional margins and the idealistic case of perfect motion compensation. The resulting intensity maps exhibit “horns”, which can shave off a few mm from the margins.

Educational Objectives:

1. Understand the concepts of motion blur and PDF.

2. Understand the idea of de‐blurring a dose distribution through “4D” motion optimization.

3. Be able to discuss the relative potential and limitations of 4D motion optimization in comparison with margins and gating.
WE‐C‐L100J‐01: Quantitative Assessment of Low‐Contrast Detectability in Fluoroscopic Imaging
Authors: Schueler B , Fetterly K
Published: July 2007

Purpose: Fluoroscopic low‐contrast detectability is commonly assessed by imaging a test object with targets of decreasing contrast and identifying the lowest contrast target visible. This approach suffers from problems with observer variability that makes consistent image quality assessment difficult. New fluoroscopic systems are being equipped with a “Fluoro Loop” feature that allows for storage of a fluoroscopy image sequence that can be output as a DICOM series. Utilizing this feature for equipment testing allows for quantitative measurements from low‐contrast detectability test object images. Method and Materials: Low contrast target images were obtained using an ACR Radiography Fluoroscopy Accreditation Phantom. This phantom consists of an abdomen‐equivalent thickness of PMMA and aluminum imaged with a test plate object which has an aluminum disk with 8 holes drilled to graduated depths. Recorded DICOM fluoroscopy image frames were analyzed on an external PC, using ROIs to determine signal, background and standard deviation values. CNR was calculated for each hole and plotted against hole depth as a graphic representation of fluoroscopic image quality. For validation, the test object was imaged with a Siemens Artis dTA angiography system. Fluoro loops for different dose settings were acquired and stored on a CD‐ROM for analysis. Results: CNR versus hole depth plots correlate well with visual image quality as expected from variations in dose settings. Plots fit to a line have correlation coefficients > 0.99. A CNR value of 1.0 corresponds approximately to lowest target visible by an observer. Using the hole depth corresponding to this CNR value from the line fit provides the minimum detectable percent contrast for the acquisition kVp. For the high, medium and low dose settings, threshold contrast values of 2.8%, 4.3% and 17% were obtained. Conclusion: Quantitative measurement of low contrast detectability provides a consistent and reproducible metric of fluoroscopic image quality.
WE‐C‐L100J‐02: Determination of Pixel‐Value to X‐Ray Path‐Length Conversion Factor From Single Angiograms
Authors: Erdemir E , Hoffmann K , Gopal A
Published: July 2007

Purpose: Currently, 3D vessel lumen data are available via intravascular ultrasound or multiple angiographic views. However, when the relationship between pixel value and x‐ray path length through the vessel is known, the 3D lumen shape can be estimated from only a single view. Therefore, we have developed methods to determine this relationship from single angiograms. Method and Materials: Angiograms are acquired, and vessel centerlines are indicated. Profiles are extracted perpendicular to the vessel centerlines. The background in each profile is estimated and subtracted, and the subtracted profiles are individually fit using elliptical models. The constants (K) relating pixel value to x‐ray path length are determined from the elliptical fits. A histogram of these constants is generated, and the constant corresponding to the maximum in the histogram is taken as the final value for K. Blurring is taken into account and used to refine the value of K. The ensemble of vessel profiles is convolved with a Gaussian the width of which is varied iteratively. The Gaussian providing the best fit over the ensemble is taken as an estimate of the resolution function. We evaluated our technique using computed simulated x‐ray images of cylindrical rods with blurring included, x‐ray images of aluminum rods and of clinical coronary angiograms. Results: In simulation studies, errors in K were less than 10% for signal to noise ratios as small as 5 and blurring of 1.0 mm widths. In phantom studies, the errors in K were less than 5%. For coronary vessels, K varies by less than 10% in three consecutive images. Conclusion: These techniques provide values for K and should provide the basis for reconstruction of the vessel lumen from a single view. Conflict of Interest: This study was supported by NIH Grant ♯ HL052567 and Toshiba Medical Systems Corporation.
WE‐C‐L100J‐03: The New Solid State X‐Ray Image Intensifier (SSXII): A Demonstration of Operation Over a Range of Angiographic and Fluoroscopic Exposure Levels
Authors: Kuhls A , Yadava G , Bednarek D , Rudin S
Published: July 2007

Purpose: To demonstrate the SSXII's capability to image at high angiographic to low fluoroscopic exposure levels using the built‐in adjustable gain. Method and Materials: The prototype SSXII is composed of a 1k×1k, 8μm pixel EMCCD camera system coupled to a 350 μm thick CsI(Tl) structured phosphor via a 1:1 fiber‐optic taper (FOT) and is designed for easy interchange of these front‐end components for task‐based optimization. Variable signal amplification (in solid state) from 1x to 2000x effectively eliminates image degradation due to read‐out noise over all input x‐ray intensities. Images were acquired of a stent crimped on a 1 mm diameter balloon‐tip catheter, for various x‐ray spectra, using both radiographic and fluoroscopic exposures ranging from 6 mR to 145 μR and 80 to 2.7 μR, respectively. The EMCCD gain was adjusted in order to maintain a constant output signal of ∼90% of maximum over these exposures (∼3700 digital units). Results: A series of images, obtained by halving the exposure while doubling the gain, offers a near textbook demonstration of the effect of incident SNR on the resulting image quality. Fine structures of a crimped stent are visible for the entire range of radiographic exposures tested, demonstrating the very high‐resolution capabilities of the SSXII. In pulsed fluoroscopic mode, resolving the crimped stent structures becomes difficult below 40 μR. Using high gain, the object was visible down to 2.7 μR, which corresponds to ∼0.1 incident x‐ray photons per pixel, demonstrating both tremendous sensitivity and extremely low effective instrumentation noise. Conclusion: Images obtained with the prototype SSXII, over a vast range of exposure levels, indicate this new dynamic x‐ray imager has the potential to provide significant improvements over current state‐of‐the‐art detectors (both FPDs and XIIs) for high‐resolution angiographic and low‐noise, real‐time fluoroscopic imaging.

(Partial support from the UB Foundation and NIH grants R01‐EB002873, R01‐NS43924.)
WE‐C‐L100J‐04: The Solid State X‐Ray Image Intensifier (SSXII): A Next‐Generation High‐Resolution Fluoroscopic Detector System
Authors: Rudin S , Kuhls A , Keleshis C , Kim D , Yadava G , Patel V , Ionita C , Hamwi H , Cartwright A , Verevkin A , Hoffmann K , Bednarek D
Published: July 2007

Purpose: Present the design for the new SSXII high‐resolution fluoroscope capable of overcoming lag, noise, and resolution limitations of current flat‐panel devices (FPDs). Method and Materials: The SSXII consists of an array of modules each featuring an electron multiplying (EM) CCD which views a structured phosphor through a fiber‐optic taper (FOT). The EMCCD operates like a standard frame‐transfer CCD; however, an additional row of multiplication elements enables on‐chip signal gains up to 2000X to overcome subsequent instrumentation‐noise degradation. The SSXII therefore has quantum‐limited performance at both fluoroscopic exposures with moderate gain, and radiographic exposures with low gain. The SSXII array design, through pixel binning and module selection, will enable rapid sequence and fluoroscopic imaging for either the full field‐of‐view (FOV) or high‐resolution regions‐of‐interest (ROIs). Results: A SSXII module was assembled with direct fiber‐optic coupling of the 350 micron thick CsI(Tl) phosphor and the EMCCD (Texas Instruments TC285SPD chip with 1004×1002 pixels). Operation at fluoroscopic and angiographic exposure levels was verified experimentally for gains of ∼80X and 1X, respectively, demonstrating sequences of a moving stent with no lag and bar‐pattern resolution up to 20 1p/mm with a 1:1 FOT. An array of four modules each with 6:1 FOTs will have an effective pixel size of 48 microns covering a FOV of 10×10 cm, sufficient for region‐of‐interest and neurovascular imaging. Larger arrays may be constructed to satisfy both cardiac imaging and general fluoroscopic applications. Module alignment, digital stitching, and distortion correction issues are being addressed. Conclusion: When assembled in an array of sufficient size, the new SSXII can be used in the same applications as current FPD's with advantages of high frame rates with no lag, high resolution due to the smaller pixels possible, and low‐effective‐noise, quantum‐limited fluoroscopic performance due to the on‐chip gain.

(Support: UB Foundation, NIH grants R01‐EB002873, R01‐NS43924).
WE‐C‐L100J‐05: Exploring the Effects of Photon Density and Object Size On Resolution Using a Statistical Star Pattern
Authors: Bakalyar D
Published: July 2007

Purpose: Critical elements in the visual resolution of small objects are object size, contrast and statistical noise. The purpose of this study is to explore the relationship between the limit of resolution, object size and noise under conditions of high contrast using a statistical star phantom. Method and Materials: In order to demonstrate the effects of photon density and spacing on resolution, software was written which generates a statistical star pattern, similar in form to the star phantoms used to determine focal spot size on x‐ray machines. Initially, the viewer sees a black background on the monitor. After starting, randomly selected pixels are lit (representing photons) and a random pattern within a circular region appears. As the photon count increases, the spokes of the pattern begin growing out of the randomness from the edge of the region toward the center. The user may stop the process at any time, display a concentric ring, and alter its size to indicate the perceived limit of resolution. Results: As the pixels light up, the pattern appears random and the radius of perceived order extends all the way to the border. At the limit of high density, the radius of perceived order is at its lower limit, due to the resolution of the monitor. In between, however, the radius appears to be inversely proportional to the number of lit pixels in the region. More specifically, the product of the number of photons, the radius of perceived order and the angle between the spokes of the star phantom is a constant. This is consistent with the Rose model of visual perception. Conclusion: The statistical star pattern developed for this project demonstrates and quantifies, in a continuous fashion, the effect of photon density and object size on resolution.
WE‐C‐L100J‐09: System for Determination of 3D Cardiac Motion From Biplane Imaging
Authors: Hoffmann K , Bazaz R , Kasodekar S , Walczak A , Cervi S
Published: July 2007

Purpose: Biplane imaging offers the ability to determine 3D motion of objects of interest at high frame rates (> 30 fps) and does not suffer from out of plane motion issues. We have developed methods for rapid determination of 3D motion of tagged objects, e.g., points of interest in the heart. Materials and Methods: Fourteen metallic spherical markers (Φ1.5 to 4.5mm) were surgically implanted to tag major muscle bundles in both atria in pigs. The pigs were then imaged by biplane fluoroscopy at 30 frames per second. Images were corrected for distortion, and markers indicated in one of the frames. Markers were identified automatically in subsequent frames using cross‐correlation techniques. The imaging geometry was determined using the enhanced‐Metz‐Fencil technique, after which, the 3D positions of the markers were determined and displayed for each time point. The motion of the various markers was analyzed using the Procrustes technique. The vectors of movement of individual points as they relate to other points were determined to identify centres of contraction. Results: Automated bead tracking takes approximately 1 minute and is 100 percent accurate for slowly moving beads and beads that do not overlap with approximately 80% accuracy overall. The 3D positions were reproducible across cardiac cycles. The average RMS difference of marker positions for the same cardiac phase was approximately 0.5 mm. The average point excursion during a heart cycle was 3.6 mm. Data analyses revealed a dominant dynamic directionality towards a central point or plane suggesting a common limb involved in bi‐atrial mechanics. Conclusion: This system provides rapid generation of 3D motion of tagged regions of interest in the atria. These data will provide a useful basis for analysis of cardiac motion. The ability to link structure and function by these techniques can impact the fields of cardiac surgery, pacing, and electro‐physiology.
WE‐C‐L100F‐02: Advances in CT: Dedicated Extremity Scanners
Authors: Bailey E
Published: July 2007

The first commercial CT system, introduced in 1972 under the leadership of Nobel Laureate Sir Godfrey Hounsfield, was designed as a Head‐only scanner. Despite long scan times and low image quality, it revolutionized Medical diagnostics with it's ability to “see” the internal structures of the human brain. In just the few years that followed, there began the commercial release of full‐body scanners which provided this gift of “sight” for all organs. This dramatic increase in overall utility immediately replaced the concept of single‐organ devices. For almost 30 years, CT systems have remained general purpose machines that are used for a great variety of diagnostic applications. Advances such as high speed gantries, helical scanning and multi‐slice detectors, have brought CT to the point where it is now able to produce diagnostic Cardiac images. But full‐body scanners remain large, expensive, complex, and costly to maintain. To this fact, there has recently emerged several dedicated extremity scanners such as for Head/Neck, Maxiofacial, ENT, Dental, Spine, Hands/Feet, and Breast. This lecture will discuss the clinical advantages, limitations, and technology that these devices bring to the market. It will also address the challenges that these devices present to Medical Physics. Join in and learn of the “Renaissance to Hounsfield”!
WE‐C‐L100F‐03: CT Algorithm Development and Applications
Authors: Pan X
Published: July 2007

Computed tomography (CT) has been employed as a versatile visualization tool in a wide variety of applications to human and small animal imaging, industrial non‐destructive detection, material research, and security scan. The fast‐imaging capability and superior spatial/contrast resolution offered by modern CT result in tremendous opportunities for developing additional applications and imaging protocols. In the last few years or so, there have been unprecedented breakthroughs in the development of innovative cone‐beam imaging algorithms for obtaining volumetric images in cone‐beam CT. In this presentation, I will discuss the algorithm advances in cone‐beam CT in the last few years. Emphasis will be placed on targeted imaging of region of interest (ROI) and on image reconstruction from incomplete data in CT. Examples will be used to illustrate that the current and potential applications promised by the new development of CT algorithms. Finally, I will briefly use examples to illustrate that, although the algorithms to be discussed were developed for CT, they can readily be generalized to addressing image reconstruction problems in other imaging modalities, including MRI, nuclear medicine imaging, and phase‐contrast CT.
WE‐C‐L100F‐04: Clinical X‐Ray Computed Tomography in 2007: Status and Future
Authors: Vannier M
Published: July 2007

Clinical X‐ray computed tomography has grown in importance for all of its applications, but most importantly for evaluation of the head, chest, abdomen, pelvis, and cardiovascular system. CT delivers an increasing fraction of the overall population radiation dose. Many limitations are present due to sensitivity to motion, metal artifacts, patient size, and limited functional information with a relatively high radiation dose. There are technical developments which promise to reduce these constraints, but at a significant cost. Most important are large area detectors with 64 to 256 rows of detectors, multiple energy channels, algorithmic improvements, and multimodality systems (especially PET/CT). CT is now the essential (and often the only) radiologic imaging procedure needed to manage many patients with acute or chronic diseases. Its speed and versatility, as well as reliability and simplicity of operation ensure that its role will continue for the foreseeable future. CT is used extensively for emergencies, cardiovascular, pulmonary, gastrointestinal, endocrine, neurological, orthopedic and other applications. Further technology development is aimed at common applications where reimbursement for CT scanning services is available or will likely become available. Multicenter clinical trials are underway that compare cardiac CT with other modalities, especially SPECT and cardiac catheterization. The most demanding CT applications are cardiovascular, where complex motion and small morphologic features coexist. Clinical cardiac CT consists of bolus intravenous contrast material injection with EKG gating and simultaneous x‐ray scanning. Larger area detectors and higher frame acquisition rates partly address but don't solve all of the problems encountered due to respiratory, random body, and cardiac motion, in a spectrum of patients from infant to massively obese adult sizes (< 1 kg to 250 kg or more). The challenges and pitfalls in CT will be delineated and evaluated relative to current and future technology.
WE‐C‐M100J‐03: Cryoablation: Scientific Foundation, Treatment Planning and Clinical Practice
Authors: Rewcastle J
Published: July 2007

Cryoablation: Scientific Foundation, Treatment Planning and Clinical Practice.

Interest in and utilization of cryoablation as a primary therapy for many types of cancer has increased markedly in the past decade. The procedure has evolved significantly from a technology perspective with engineering advances yielding greater control of ice formation within the body as well as enhanced visualization. This, coupled with isotherm modeling and treatment planning, has resulted in the ability to accurately target tissue for cryoablation. The organ to which these advances are most often applied is the prostate. This is due to the prostate being a relatively difficult structure to treat. The passage of the urethra through the gland necessitates the use of multiple cryoprobes and the procedure is confounded by the sensitivity of adjacent structures including the neurovascular bundles, external sphincter and rectum. Even with these obstacles, modern prostate cryoablation has emerged both as a primary prostate cancer treatment option and as a salvage therapy following failed radiation therapy.

This lecture will review the fundamentals of cryobiology and the seminal work which established clinical endpoints. The technological basis of the procedure will be discussed including both fundamentals of cryoprobe design and compatibility imaging modalities. Lastly, clinical outcomes of the prostate cryoablation will be compared to radical prostatectomy (the gold standard), external beam radiation therapy, brachytherapy and IMRT.

Educational goals:

1. Understand the damage mechanisms of cryoablation and how they differ from radiation damage.

2. Understand the fundamentals of how prostate cryoablation is performed and the technologies used to do so, and

3. Understand how the outcomes of cryoablation compare to other treatment modalities.
WE‐C‐BRB‐01: Practice Performance Improvement Introduction for Medical Physicists
Authors: Nagy P , Pawlicki T , Paliwal B , Morin R , Frey G
Published: July 2007

Practice Performance Improvement is a key component for analyzing and improving the practice of medical physics. It is also an important component of the maintenance of Certification Process for physicists certified by the American Board of Radiology. In order to use Practice Performance Improvement effectively physicists should have training in the techniques available. This session will provide the necessary training. The session is structured as follows:

Introduction

Practice Performance Improvement — Techniques and Methods.

Application of Practice Performance Improvement in Radiotherapy.

Examples of Practice Performance Improvement Projects from Diagnostic Radiology, Nuclear Medicine and Radiation Therapy.
WE‐C‐AUD‐02: Calculating Electron‐Beam Central‐Axis Depth Doses Using the Final Aperture Superposition Technique (FAST)
Authors: Chen J , Irion J , Faddegon BA
Published: July 2007

Purpose: To quickly calculate central‐axis depth doses for arbitrarily‐shaped electron inserts using precalculated differential dose data. Method and Materials: Monte Carlo simulation (EGS4) is used to obtain phase space distributions in a plane upstream from the insert. From these distributions, central‐axis dose in a water phantom is calculated for a) an open configuration with no insert in the applicator and b) a fully shielded configuration with a completely solid insert. Differential dose datasets are created by tagging the location of particles as they pass through the insert and scoring contributions to the dose from different regions. For arbitrarily‐shaped inserts, the Final Aperture Superposition Technique (FAST) code adds open and shielded contributions given an outline of the insert opening. Differential dose datasets are calculated for a range of energies (6–21 MeV), applicator sizes (10–25 cm), and source‐to‐surface distances (100–110 cm). FAST calculations are compared with full Monte Carlo simulation through the insert using the same initial phase space distributions. Results: FAST depth doses are similar to the full simulation but tend to be slightly lower in dose, particularly for higher energy beams. This “collimator effect” is due to the inability of FAST to score dose from particles that escape the shield through the edges of the insert opening. An average collimator effect curve has been defined using a linear fit to the average difference between full simulation and FAST for a 2 cm diameter opening and a fully open applicator. Using this curve to correct the FAST doses results in mean residual errors and standard deviations in these errors of less than a percent. Conclusion: With a minor correction for the collimator effect, the FAST program can accurately calculate central‐axis doses for a large range of treatment parameters.
WE‐C‐AUD‐05: Simulation of Neutron Dose Exposure for Pediatric Proton Therapy Patients Using Whole‐Body Age‐Dependent Voxel Phantoms
Authors: Jarlskog C Zacharatou , Lee C , Bolch W , Xu X , Paganetti H
Published: July 2007

Purpose: With the average age of radiation therapy patients decreasing due to early cancer detection and a larger proportion of patients being cured and thus at risk for treatment complications, there has to be a growing concern for the risk of developing cancer due to radiation treatments, in particular for pediatric and young patients. Age and gender specific whole‐body phantoms have been implemented in Geant4 in order to determine the dose from secondary radiation in patients undergoing proton treatment. Method and Materials: In a systematic study, we have used three methods to calculate the neutron organ equivalent dose to 14 organs distal to the target volume for six circular fields of varying diameters and range/modulation width combinations and for two patient fields that were previously used to treat two pediatric patients at the F. H. Burr Proton Therapy Center of Massachusetts General Hospital for brain lesions. Results using an adult phantom as well as phantoms of a 9‐month old male, a 4‐year old female, an 8‐year old female, an 11‐year old male and a 14‐year old male were analyzed. Results: The relative contribution to organ dose from secondary radiation from the treatment head and secondary radiation generated within the patient was evaluated. We found that the organ equivalent dose has a marked dependence on the phantom age, the distance between the organ and the PTV as well as on field characteristics. Overall, the organ equivalent doses were below 3 mSv per treatment Gy. Conclusions: The organ equivalent neutron dose for proton treatments of brain lesions in organs distal to the target was calculated for six age‐dependent phantoms. We found that the dose decreases with patient age and also depends on field size, beam energy and modulation.

Work supported by NIH/NCI RO1 CA 116743.
WE‐C‐AUD‐06: Radiation Safety of Pregnant Patients During Radiation Treatment: A Detailed Modeling of the Accelerator, Patient Anatomy, and Non‐Target Doses
Authors: Bednarz B , Taranenko V , Shi C , Xu X
Published: July 2007

Purpose: The cancer incidence rate in pregnant women is increasing, due to both the new trend for delaying pregnancy into late reproductive ages and early detection of common cancers associated with pregnancy. When radiation treatment is chosen, the safety concern for the mother and fetus must be fully addressed. However, previous studies of fetal dose, such as those reported by AAPM TG‐36, had been limited to homogenous water phantoms and surface measurements that are not quantitative. This paper presents our effort to develop medical accelerators and ICRP standard reference pregnant patient models for Monte Carlo calculations of nontarget doses during radiation treatments. Method and Materials: The Monte Carlo program MCNPX was used to develop a complete model of a Varian Clinac 2100C. Peripheral dose profiles in a water phantom were investigated for the following square fields defined by the jaws: 5 cm × 5 cm, 10 cm × 10 cm, and 20 cm × 20 cm. Anatomically‐realistic pregnant patient and fetal models at different stages of gestation representing ICRP reference female patients were developed using latest anatomical modeling technologies. Results: The peripheral dose characteristics as a function of distance from the field edge for 5 cm × 5 cm, 10 cm × 10 cm, and 20 cm × 20 cm field sizes at several depths are consistent with previous studies. The change in peripheral dose as a function of depth is small for each field size. The peripheral dose increases as field size increases. Conclusion: Calculations of organ doses to a pregnant patient and fetus have been demonstrated. Such data will help better assess the risks to the mother and fetus from radiation treatment procedures. The tools we have developed can be adopted for routine use to optimize the treatment planning for pregnant patients.
WE‐C‐AUD‐08: Sensitivity Analysis of a Non‐Cylindrically Symmetric Monte Carlo Beam Model of a Siemens Primus Accelerator
Authors: Schreiber E , Chen J , Sawkey D , Faddegon B
Published: July 2007

Purpose: To facilitate the development and commissioning of radiotherapy accelerator beam models by studying the impact of the variation of geometric and electron beam parameters on photon dose and fluence output for a Siemens Primus accelerator. In particular, the impact of lateral offsets of linac components and lateral and angular offsets of the electron beam were examined. Method and Materials: We have performed a sensitivity study examining the effect of varying beam and geometric parameters of a Monte Carlo model of a Siemens Primus accelerator. The accelerator and dose output were modeled using BEAMnrc and DOSXYZnrc, respectively. The BEAMnrc package was modified to allow for linear offsets of individual accelerator components, and lateral and angular offsets of the incident electron beam. Dose distributions were studied for 40 × 40 cm2 fields. Flatness, symmetry, OAR, and profile slope were studied. Results: The electron beam parameters having the greatest effect on the resulting dose distributions were found to be electron energy and angle of incidence, as high as 5% for a 0.25° deflection, with lateral offset of the electron beam and spot size having a smaller impact. Variations in target thickness were found to have a lesser effect than found in previous studies for electron beams. Small (∼2 mm) lateral offsets of the flattening filter altered the OAR by 5% for 6 MV and as much as 25% for 18 MV. Conclusion: Using large fields allows treatment head details to be more easily extracted. Lateral and angular offsets of beam and accelerator components have strong effects on dose distributions, and need to be included in any high‐accuracy beam model. Having a table cataloging the impact of model parameters on dose output can greatly facilitate beam model commissioning.

Support from NIH R01 CA104777‐01A2.
WE‐C‐AUD‐09: Dose Accuracy Gains by Use of Monte Carlo in Routine IMRT Treatment Optimization
Authors: Sikora M , Dohm O , Tung Z , Alber M
Published: July 2007

Purpose: To establish Monte Carlo (MC) as the primary dose engine for IMRT treatment plan optimization and quantify the benefits in routine use. Methods: A virtual particle source model (VSM) was developed for and commissioned to standard and mini MLC geometries for photon beams of 6 and 15 MV. The model uses three particle sources with variable energy spectra and a simplified particle transport through the MLC. The VSM was used together with the patient model MC code XVMC inside the MLC segment shape optimization loop of an IMRT TPS. The performance of the VSM was gauged by extensive film and ionization chamber measurements of clinical treatment plans. Results: The parameters of the VSM can be determined reliably from a set of large‐field measurements in air and water, amended by small field cross‐profile measurements for stereotactic applications (fields < 2 cm). An acceptance criterion of 2%/2mm can be met in almost all points. For stereotactic IMRT with a mini‐MLC, an acceptance criterion of 3%/1mm could be met. The VSM, combined with XVMC, is efficient enough for routine use with computation times in the order of 15–60 min. As a consequence of the reliability of dose computation, complicated MLC segment shapes need not be suppressed. Non‐standard applications like IMRT for brain metastases can be implemented easily. Conclusion: The accuracy of clinically used MC depends crucially on a properly commissioned accelerator head model. A dedicated VSM can be tuned to meet the highest clinically relevant accuracy criteria. Approximately 400 patients per year are treated with MC dose computation/IMRT at our hospital on three linacs. Individual patient QA measurements are performed only in exceptional cases.
WE‐C‐M100F‐01: Risk of Secondary Fatal Malignancies From Hi‐Art Tomotherapy IMRT
Authors: Lazar S , Followill D , Gibbons J , Mahajan A , Salehpour M , Stovall M , White R
Published: July 2007

Purpose: This work compares out‐of‐field secondary doses and associated risk of a fatal secondary malignancy from a Hi‐Art Tomotherapy machine and a conventional gantry based accelerator for an adult IMRT prostate and a pediatric cranio‐spinal treatment. Method and Materials: A conventional 3D and tomotherapy IMRT cranio‐spinal treatment plan were developed to deliver the same prescription to a pediatric anthropomorphic Rando phantom using a Philips Pinnacle and Hi‐Art Tomotherapy planning system, respectively. Similarly, an adult IMRT prostate treatment plan, using the Pinnacle and tomotherapy planning systems was developed to deliver the same prescription with the same constraints to an adult Rando phantom. The target and organs at risk (OAR) were contoured. TLD were located within each of the OARs selected. Each phantom was irradiated three times per plan. The out‐of‐field organ TLD doses for the gantry based delivery and tomotherapy treatments were compared. For each organ site, an average dose was determined and organ weighted linear non‐threshold dose response model risk factors were used to estimate the risk of a secondary fatal malignancy for each treatment. Results: Doses calculated from the adult TLD data were lower for all organs when treated with the Tomotherapy plan and the overall risk was lower. The pediatric TLD dose findings were mixed between the 3D and tomotherapy treatment, however because of the higher integral dose with the Tomotherapy, the overall risk is higher for the Tomotherapy treatment. Conclusion: The risk of a secondary fatal cancer was lower for the Hi‐Art Tomotherapy adult prostate treatment than the gantry based IMRT treatment due to due to the lower integral out‐of‐field secondary radiation doses. The risk for the pediatric case appears higher for the Hi‐Art Tomotherapy treatment than the 3D conformal cranio‐spinal treatment. Work supported by PHS grant CA10953 awarded by NCI.