bluuebunny/crossref_metadata_2025 huggingface dataset:
RANS Simulation of Ducted Marine Propulsor Flow Including Subvisual Cavitation and Acoustic Modeling
Authors: Kim Jin , Paterson Eric G. , Stern Frederick
Published: July 2006

High-fidelity Reynolds-averaged Navier Stokes (RANS) simulations are presented for the ducted marine propulsor P5206, including verification and validation (V&V) using available experimental fluid dynamics data, and subvisual cavitation, and acoustics analysis using the modified Rayleigh-Plesset equation along the bubble trajectories with a far-field form of the acoustic pressure for a collapsing spherical bubble. CFDSHIP-IOWA is used with the blended k−ω∕k−ε turbulence model and extensions for a relative rotating coordinate system and overset grids. The intervals of V&V analysis for thrust, torque, and profile averaged radial velocity just downstream of rotor tip are reasonable in comparison with previous results. The flow pattern displays the interaction and merging of the tip-leakage and trailing edge vortices. In the interaction region, multiple peaks and vorticity are smaller, whereas in the merging region, there is better agreement with the experiment. The tip-leakage vortex core position, size, circulation, and cavitation patterns for σi=5 also show good agreement with the experiment, although the vortex core size is larger and the circulation in the interaction region is smaller. The simulations indicate globally minimum Cp=−σi=−8.8 on the suction side of the rotor tip at 84% chord from the leading edge and locally minimum Cp=−6.4 in the tip-leakage vortex at 8% chord downstream of the trailing edge, whereas EFD indicates σi=11 and the location in the tip-leakage vortex core 50% chord downstream of the trailing edge. Subvisual cavitation and acoustics analysis show that bubble dynamics may partly explain these discrepancies.
The curvature of sensitometric curves for Kodak XV‐2 film irradiated with photon and electron beams
Authors: van Battum L. J. , Huizenga H.
Published: July 2006

Sensitometric curves of Kodak XV‐2 film, obtained in a time period of ten years with various types of equipment, have been analyzed both for photon and electron beams. The sensitometric slope in the dataset varies more than a factor of 2, which is attributed mainly to variations in developer conditions. In the literature, the single hit equation has been proposed as a model for the sensitometric curve, as with the parameters of the sensitivity and maximum optical density. In this work, the single hit equation has been translated into a polynomial like function as with the parameters of the sensitometric slope and curvature. The model has been applied to fit the sensitometric data. If the dataset is fitted for each single sensitometric curve separately, a large variation is observed for both fit parameters. When sensitometric curves are fitted simultaneously it appears that all curves can be fitted adequately with a sensitometric curvature that is related to the sensitometric slope. When fitting each curve separately, apparently measurement uncertainty hides this relation. This relation appears to be dependent only on the type of densitometer used. No significant differences between beam energies or beam modalities are observed. Using the intrinsic relation between slope and curvature in fitting sensitometric data, e.g., for pretreatment verification of intensity‐modulated radiotherapy, will increase the accuracy of the sensitometric curve. A calibration at a single dose point, together with a predetermined densitometer‐dependent parameter will be adequate to find the actual relation between optical density and dose.
Automated localization of implanted seeds in 3D TRUS images used for prostate brachytherapy
Authors: Wei Zhouping , Gardi Lori , Downey Donal B. , Fenster Aaron
Published: July 2006

An algorithm has been developed in this paper to localize implanted radioactive seeds in 3D ultrasound images for a dynamic intraoperative brachytherapy procedure. Segmentation of the seeds is difficult, due to their small size in relatively low quality of transrectal ultrasound (TRUS) images. In this paper, intraoperative seed segmentation in 3D TRUS images is achieved by performing a subtraction of the image before the needle has been inserted, and the image after the seeds have been implanted. The seeds are searched in a “local” space determined by the needle position and orientation information, which are obtained from a needle segmentation algorithm. To test this approach, 3D TRUS images of the agar and chicken tissue phantoms were obtained. Within these phantoms, dummy seeds were implanted. The seed locations determined by the seed segmentation algorithm were compared with those obtained from a volumetric cone‐beam flat‐panel micro‐CT scanner and human observers. Evaluation of the algorithm showed that the rms error in determining the seed locations using the seed segmentation algorithm was in agar phantoms and in chicken phantoms.
Marker‐controlled watershed for lymphoma segmentation in sequential CT images
Authors: Yan Jiayong , Zhao Binsheng , Wang Liang , Zelenetz Andrew , Schwartz Lawrence H.
Published: July 2006

Segmentation of lymphoma containing lymph nodes is a difficult task because of multiple variables associated with the tumor's location, intensity distribution, and contrast to its surrounding tissues. In this paper, we present a reliable and practical marker‐controlled watershed algorithm for semi‐automated segmentation of lymphoma in sequential CT images. Robust determination of internal and external markers is the key to successful use of the marker‐controlled watershed transform in the segmentation of lymphoma and is the focus of this work. The external marker in our algorithm is the circle enclosing the lymphoma in a single slice. The internal marker, however, is determined automatically by combining techniques including Canny edge detection, thresholding, morphological operation, and distance map estimation. To obtain tumor volume, the segmented lymphoma in the current slice needs to be propagated to the adjacent slice to help determine the external and internal markers for delineation of the lymphoma in that slice. The algorithm was applied to 29 lymphomas (size range, in diameter; mean, ) in nine patients. A blinded radiologist manually delineated all lymphomas on all slices. The manual result served as the “gold standard” for comparison. Several quantitative methods were applied to objectively evaluate the performance of the segmentation algorithm. The algorithm received a mean overlap, overestimation, and underestimation ratios of 83.2%, 13.5%, and 5.5%, respectively. The mean average boundary distance and Hausdorff boundary distance were 0.7 and . Preliminary results have shown the potential of this computer algorithm to allow reliable segmentation and quantification of lymphomas on sequential CT images.
Neutron scattered dose equivalent to a fetus from proton radiotherapy of the mother
Authors: Mesoloras Geraldine , Sandison George A. , Stewart Robert D. , Farr Jonathan B. , Hsi Wen C.
Published: July 2006

Scattered neutron dose equivalent to a representative point for a fetus is evaluated in an anthropomorphic phantom of the mother undergoing proton radiotherapy. The effect on scattered neutron dose equivalent to the fetus of changing the incident proton beam energy, aperture size, beam location, and air gap between the beam delivery snout and skin was studied for both a small field snout and a large field snout. Measurements of the fetus scattered neutron dose equivalent were made by placing a neutron bubble detector below the umbilicus of an anthropomorphic phantom enhanced by a wax bolus to simulate a second trimester pregnancy. The neutron dose equivalent in milliSieverts (mSv) per proton treatment Gray increased with incident proton energy and decreased with aperture size, distance of the fetus representative point from the field edge, and increasing air gap. Neutron dose equivalent to the fetus varied from 0.025 to per proton Gray for the small field snout and from 0.097 to per proton Gray for the large field snout. There is likely to be no excess risk to the fetus of severe mental retardation for a typical proton treatment of 80 Gray to the mother since the scattered neutron dose to the fetus of is well below the lower confidence limit for the threshold of observed for the occurrence of severe mental retardation in prenatally exposed Japanese atomic bomb survivors. However, based on the linear no threshold hypothesis, and this same typical treatment for the mother, the excess risk to the fetus of radiation induced cancer death in the first 10 years of life is 17.4 per children.
Multithreaded cardiac CT
Authors: Kachelrieß Marc , Knaup Michael , Kalender Willi A.
Published: July 2006

Phase‐correlated CT, as it is used for cardiac imaging, is the most popular and the most important but also the most demanding special CT application in the clinical routine, today. Basically, it fulfills the four‐dimensional imaging task of depicting a quasiperiodically moving object at any desired motion phase with significantly reduced motion artifacts. Although image quality with phase‐correlated reconstruction is far better than with standard reconstruction, there are motion artifacts remaining and improvements of temporal resolution are required. As a well‐known alternative to simply decreasing rotation time, we consider a spiral cone‐beam CT scanner that has x‐ray guns and detectors mounted. We call this a multisource or a multithreaded CT scanner. Aiming for improved temporal resolution the relative temporal resolution , which measures the fraction of a motion period that enters the image, is studied as a function of the motion rate (heart rate) and the degree of scan overlap (pitch value) for various configurations. The parameters to optimize are the number of threads and the interthread parameters and , which are the angular and the longitudinal separation between adjacent threads, respectively. To demonstrate the improvements approximate image reconstruction of multithreaded raw data is performed by using a generalization of the extended parallel back projection cone‐beam reconstruction algorithm [Med. Phys. 31(6), 1623–1641 (2004)] to the case of multithreaded CT. Reconstructions of a simulated cardiac motion phantom and of simulated semi‐antropomorphic phantoms are presented for two and three threads and compared to the single‐threaded case to demonstrate the potential of multithreaded cardiac CT. Patient data were acquired using a clinical double‐threaded CT scanner to validate the theoretical results. The optimum angle between the tubes is 90° for a double‐threaded system, and for triple‐threaded scanners it is 60° or 120°. In all cases, results as an optimum, which means that the threads should be mounted in the same transversal plane. However, the dependency of the temporal resolution on is very weak and a longitudinal separation would not deteriorate image quality. The mean temporal resolution achievable with an optimized multithreaded CT scanner is a factor of better than the mean temporal resolution obtained with a single‐threaded scanner. The standard reconstructions showed decreased cone‐beam artifacts with multithreaded CT compared to the single‐threaded case. Our phase‐correlated reconstructions demonstrate that temporal resolution is significantly improved with multithreaded CT. The clinical patient data confirm our results.
Patient position verification using small IMRT fields
Authors: Bol G. H. , van der Heide U. A. , Nederveen A. J. , Kotte A. N. T. J. , Lagendijk J. J. W.
Published: July 2006

A commonly used approach to quantify and minimize patient setup errors is by using electronic portal imaging devices (EPIDs). The position of the tumor can be verified indirectly by matching the bony anatomy to a reference image containing the same structures. In this paper we present two off‐line methods for detecting the position of the bony anatomy automatically, even if every single portal image of each segment of an IMRT treatment beam contains insufficient matching information. Extra position verification fields will no longer be necessary, which reduces the total dose to the patient. The first method, the stack matching method (SMM), stacks the portal image of each segment of a beam to a three dimensional (3D) volume, and this volume is subsequently used during the matching phase. The second method [the averaged projection matching method (APMM)], is a simplification of the first one, since the initially created volume is reduced again to a 2D artificial image, which speeds up the matching procedure considerably, without a significant loss of accuracy. Matching is based on normalized mutual information. We demonstrate our methods by comparing them to existing matching routines, such as matching based on the largest segment. Both phantom and patient experiments show that our methods are comparable with the results obtained from standard position verification methods. The matches are verified by means of visual inspection. Furthermore, we show that when a distinct area of 40– of the EPID is exposed during one treatment beam, both SMM and APMM are able to deliver a good matching result.
Peripheral doses from pediatric IMRT
Authors: Klein Eric E. , Maserang Beth , Wood Roy , Mansur David
Published: July 2006

Peripheral dose (PD) data exist for conventional fields and intensity‐modulated radiotherapy (IMRT) delivery to standard adult‐sized phantoms. Pediatric peripheral dose reports are limited to conventional therapy and are model based. Our goal was to ascertain whether data acquired from full phantom studies and/or pediatric models, with IMRT treatment times, could predict Organ at Risk (OAR) dose for pediatric IMRT. As monitor units (MUs) are greater for IMRT, it is expected IMRT PD will be higher; potentially compounded by decreased patient size (absorption). Baseline slab phantom peripheral dose measurements were conducted for very small field sizes (from ). Data were collected at distances ranging from away from the field edges. Collimation was either with the collimating jaws or the multileaf collimator (MLC) oriented either perpendicular or along the peripheral dose measurement plane. For the clinical tests, five patients with intracranial or base of skull lesions were chosen. IMRT and conventional three‐dimensional (3D) plans for the same patient/target/dose , were optimized without limitation to the number of fields or wedge use. Six MV, 120‐leaf MLC Varian axial beams were used. A phantom mimicking a ‐old was configured per Center for Disease Control data. Micro and cylindrical ionization chambers were appropriated for the thyroid, breast, ovaries, and testes. The PD was recorded by electrometers set to the scale. Each system set was uniquely calibrated. For the slab phantom studies, close peripheral points were found to have a higher dose for low energy and larger field size and when MLC was not deployed. For points more distant from the field edge, the PD was higher for high‐energy beams. MLC orientation was found to be inconsequential for the small fields tested. The thyroid dose was lower for IMRT delivery than that predicted for conventional (ratio of IMRT/cnventional ranged from 0.47–0.94) doses , respectively. Prior phantom reports are for fields or greater, while pediatric central nervous system fields range from , and effectively much smaller for IMRT . Peripheral dose in close proximity ( from the field edge) is dominated by internal scatter; therefore, field‐size differences overwhelm phantom size affects and increased MU. Distant peripheral dose, dominated by head leakage, was higher than predicted, even when accounting for MUs ( of 3) likely due to the pediatric phantom size. The ratio of the testes dose ranged from 3.3–5.3 for IMRT/conventional. PD to OAR for pediatric IMRT cannot be predicted from large‐field full phantom studies. For regional OAR, doses are likely lower than predicted by existing “large field” data, while the distant PD is higher.
Rotating and static sources for gamma knife radiosurgery systems: Monte Carlo studies
Authors: Cheung J. Y. C. , Yu K. N.
Published: July 2006

Rotating gamma systems (RGSs), GammaART‐6000™, and its Chinese equivalents, such as OUR and MASEP, etc., are new radiosurgery systems that use rotating sources instead of the 201 static sources (Leksell gamma knife, LGK). The rotating sources of RGSs simulate an infinite number of beams and promote extremely high target to surface dose ratios. However, the results of Monte Carlo in this study shows that RGS variants (modeled as having the same latitude angles, source to focus distance, and the distance from the source to the end of the collimator as the LGK) have smaller beam profile penumbra in the direction, while LGK has smaller penumbra in the and directions. The differences are more significant in using larger collimators.
A Monte Carlo based three‐dimensional dose reconstruction method derived from portal dose images
Authors: van Elmpt Wouter J. C. , Nijsten Sebastiaan M. J. J. G. , Schiffeleers Robert F. H. , Dekker André L. A. J. , Mijnheer Ben J. , Lambin Philippe , Minken André W. H.
Published: July 2006

The verification of intensity‐modulated radiation therapy (IMRT) is necessary for adequate quality control of the treatment. Pretreatment verification may trace the possible differences between the planned dose and the actual dose delivered to the patient. To estimate the impact of differences between planned and delivered photon beams, a three‐dimensional (3‐D) dose verification method has been developed that reconstructs the dose inside a phantom. The pretreatment procedure is based on portal dose images measured with an electronic portal imaging device (EPID) of the separate beams, without the phantom in the beam and a 3‐D dose calculation engine based on the Monte Carlo calculation. Measured gray scale portal images are converted into portal dose images. From these images the lateral scattered dose in the EPID is subtracted and the image is converted into energy fluence. Subsequently, a phase‐space distribution is sampled from the energy fluence and a 3‐D dose calculation in a phantom is started based on a Monte Carlo dose engine. The reconstruction model is compared to film and ionization chamber measurements for various field sizes. The reconstruction algorithm is also tested for an IMRT plan using photons delivered to a phantom and measured using films at several depths in the phantom. Depth dose curves for both 6 and photons are reconstructed with a maximum error generally smaller than 1% at depths larger than the buildup region, and smaller than 2% for the off‐axis profiles, excluding the penumbra region. The absolute dose values are reconstructed to within 1.5% for square field sizes ranging from 5 to width. For the IMRT plan, the dose was reconstructed and compared to the dose distribution with film using the gamma evaluation, with a 3% and criterion. 99% of the pixels inside the irradiated field had a gamma value smaller than one. The absolute dose at the isocenter agreed to within 1% with the dose measured with an ionization chamber. It can be concluded that our new dose reconstruction algorithm is able to reconstruct the 3‐D dose distribution in phantoms with a high accuracy. This result is obtained by combining portal dose images measured prior to treatment with an accurate dose calculation engine.
Evaluation of uncertainty predictions and dose output for model‐based dose calculations for megavoltage photon beams
Authors: Olofsson Jörgen , Nyholm Tufve , Georg Dietmar , Ahnesjö Anders , Karlsson Mikael
Published: July 2006

In many radiotherapy clinics an independent verification of the number of monitor units (MU) used to deliver the prescribed dose to the target volume is performed prior to the treatment start. Traditionally this has been done by using methods mainly based on empirical factors which, at least to some extent, try to separate the influence from input parameters such as field size, depth, distance, etc. The growing complexity of modern treatment techniques does however make this approach increasingly difficult, both in terms of practical application and in terms of the reliability of the results. In the present work the performance of a model‐based approach, describing the influence from different input parameters through actual modeling of the physical effects, has been investigated in detail. The investigated model is based on two components related to megavoltage photon beams; one describing the exiting energy fluence per delivered MU, and a second component describing the dose deposition through a pencil kernel algorithm solely based on a measured beam quality index. Together with the output calculations, the basis of a method aiming to predict the inherent calculation uncertainties in individual treatment setups has been developed. This has all emerged from the intention of creating a clinical dose/MU verification tool that requires an absolute minimum of commissioned input data. This evaluation was focused on irregular field shapes and performed through comparison with output factors measured at 5, 10, and depth in ten multileaf collimated fields on four different linear accelerators with varying multileaf collimator designs. The measurements were performed both in air and in water and the results of the two components of the model were evaluated separately and combined. When compared with the corresponding measurements the resulting deviations in the calculated output factors were in most cases smaller than 1% and in all cases smaller than 1.7%. The distribution describing the calculation errors in the total dose output has a mean value of and a standard deviation of 0.47%. In the dose calculations a previously developed correction of the pencil kernel was applied that managed to contract the error distribution considerably. A detailed analysis of the predicted uncertainties versus the observed deviations suggests that the predictions indeed can be used as a basis for creating action levels and tracking dose calculation errors in homogeneous media.
Comparison of ghosting effects for three commercial EPIDs
Authors: McDermott L. N. , Nijsten S. M. J. J. G. , Sonke J.‐J. , Partridge M. , van Herk M. , Mijnheer B. J.
Published: July 2006

Many studies have reported dosimetric characteristics of amorphous silicon electronic portal imaging devices (EPIDs). Some studies ascribed a non‐linear signal to gain ghosting and image lag. Other reports, however, state the effect is negligible. This study compares the signal‐to‐monitor unit (MU) ratio for three different brands of EPID systems. The signal was measured for a wide range of monitor units (5–1000), dose‐rates, and beam energies. All EPIDs exhibited a relative under‐response for beams of few MUs; giving 4 to 10% lower signal‐to‐MU ratios relative to that of . This under‐response is consistent with ghosting effects due to charge trapping.
Basic investigations on the performance of a normoxic polymer gel with tetrakis‐hydroxy‐methyl‐phosphonium chloride as an oxygen scavenger: Reproducibility, accuracy, stability, and dose rate dependence
Authors: Bayreder Christian , Georg Dietmar , Moser Ewald , Berg Andreas
Published: July 2006

Magnetic resonance (MR)‐based polymer gel dosimetry using normoxic polymer gels, represents a new dosimetric method specially suited for high‐resolution three‐dimensional dosimetric problems. The aim of this study was to investigate the dose response with regard to stability, accuracy, reproducibility, and the dose rate dependence. Tetrakis‐hydroxy‐methyl‐phosphonium chloride (THPC) is used as an oxygen scavenger, and methacrylic acid as a monomer. Accuracy, reproducibility, and dose resolution were determined for MR protocols at low spatial resolution (typical for clinical scanners), medium, and microimaging‐resolution protocols at three different dose levels. The dose‐response stability and preirradiation‐induced variations in , related to the time interval between preparation and irradiation of the polymer gel, were investigated. Also postirradiation stability of the polymer gel was considered. These experiments were performed using a beam in a water phantom. Moreover, we investigated the dose rate dependence in the low, medium, and saturation dose region of the normoxic polymer gel using a linear accelerator at photon energy of . MR scanning was performed on a whole body scanner (MEDSPEC , BRUKER BIOSPIN, Ettlingen, Germany) using several coils and different gradient systems adapted to the acquired spatial resolution investigated. For ‐parameter selective imaging and determination of the relaxation rate , a multiple spin echo sequence with 20 equidistant echoes was used. With regard to preirradiation induced variations increases significantly with the increasing time interval between the polymer gel preparation and irradiation. Only a slight increase in can be observed for varying the postirradiation‐time solely. The dose reproducibility at voxel volumes of about is better than 2%. The accuracy strongly depends on the calibration curve. THPC represents a very effective oxygen scavenger in methacrylic acid and gelatin. Polymer gels containing THPC offer high sensitivity to dose but their dose response also strongly depends on dose rate in the medium and high dose region.
Temperture distribution and blood perfusion response in rat brain during selective brain cooling
Authors: Diao Chenguang , Zhu Liang
Published: July 2006

A rat model was used in this study to examine the transient temperature distribution and blood flow response in the brain during selective brain cooling (SBC) and rewarming. SBC was induced by a head cooling helmet with circulating water of or . It has been shown that the brain temperature reductions were ( beneath the brain surface) and ( beneath the brain surface) when the temperature of the water was (moderate cooling). The cooling of the brain tissue was more evident when the circulating water was colder (, deep cooling). The characteristic time that it took for the tissue temperatures to reach a new steady state after the initiation of cooling varied from 5 to more than and it depended strongly on the blood flow response to the cooling. We used an ultrasound flow meter to measure continuously the blood flow rate in the common carotid artery during the cooling and rewarming. The blood flow rate dropped by up to 22% and 44% during the cooling from its baseline in the moderate cooling group and in the deep cooling group, respectively. Although all brain temperatures recovered to their baseline values after the helmet was removed, the blood flow rate only recovered to 92% and 77% of its baseline values after the moderate and deep cooling, respectively, implying a possible mismatch between the blood perfusion and metabolism in the brain. The current experimental results can be used to study the feasibility of inducing brain hypothermia by SBC if the blood flow responses in the rat are applicable to humans. The simultaneous recordings of temperature and blood flow rate in the rat brain can be used in the future to validate the theoretical model developed previously.
Joint two‐view information for computerized detection of microcalcifications on mammograms
Authors: Sahiner Berkman , Chan Heang‐Ping , Hadjiiski Lubomir M. , Helvie Mark A. , Paramagul Chinatana , Ge Jun , Wei Jun , Zhou Chuan
Published: July 2006

We are developing new techniques to improve the accuracy of computerized microcalcification detection by using the joint two‐view information on craniocaudal (CC) and mediolateral‐oblique (MLO) views. After cluster candidates were detected using a single‐view detection technique, candidates on CC and MLO views were paired using their radial distances from the nipple. Candidate pairs were classified with a similarity classifier that used the joint information from both views. Each cluster candidate was also characterized by its single‐view features. The outputs of the similarity classifier and the single‐view classifier were fused and the cluster candidate was classified as a true microcalcification cluster or a false‐positive (FP) using the fused two‐view information. A data set of 116 pairs of mammograms containing microcalcification clusters and 203 pairs of normal images from the University of South Florida (USF) public database was used for training the two‐view detection algorithm. The trained method was tested on an independent test set of 167 pairs of mammograms, which contained 71 normal pairs and 96 pairs with microcalcification clusters collected at the University of Michigan (UM). The similarity classifier had a very low FP rate for the test set at low and medium levels of sensitivity. However, the highest mammogram‐based sensitivity that could be reached by the similarity classifier was 69%. The single‐view classifier had a higher FP rate compared to the similarity classifier, but it could reach a maximum mammogram‐based sensitivity of 93%. The fusion method combined the scores of these two classifiers so that the number of FPs was substantially reduced at relatively low and medium sensitivities, and a relatively high maximum sensitivity was maintained. For the malignant microcalcification clusters, at a mammogram‐based sensitivity of 80%, the FP rates were 0.18 and 0.35 with the two‐view fusion and single‐view detection methods, respectively. When the training and test sets were switched, a similar improvement was obtained, except that both the fusion and single‐view detection methods had superior test performances on the USF data set than those on the UM data set. Our results indicate that correspondence of cluster candidates on two different views provides valuable additional information for distinguishing FPs from true microcalcification clusters.
Application of Gafchromic® film in the dosimetry of an intravascular brachytherapy source
Authors: Song Haijun , Roa D. Eduardo , Yue Ning , d'Errico Francesco , Chen Zhe , Nath Ravinder
Published: July 2006

The methodology of brachytherapy source dosimetry with Gafchromic® MD 55‐2 film (ISP Technologies, Inc.) is examined with an emphasis on the nonlinearity of the optical density‐dose relation within the dynamic dose range, the radial distance‐dependent measurement uncertainty, and the format of data presentation. The specific source chosen for this study was a Checkmate™ (Cordis Corporation) intravascular brachytherapy system. The two‐dimensional dose distribution around the source was characterized by a comprehensive analysis of measurement uncertainties. A comparative analysis of the dosimetric data from the vendor and from the scientific literature showed a substantial consistency of the information available for the Checkmate™ source. Our two‐dimensional dosimetric data for the Checkmate™ source trains is presented in the form of measured along and away dose tables.
Numerical simulations of phase contrast velocity mapping of complex flows in an anatomically realistic bypass graft geometry
Authors: Lee Kuan Loke , Doorly D. J. , Firmin D. N.
Published: July 2006

Combined in vitro experiments and numerical simulations were performed to study flow artifacts in phase contrast (PC) velocity mapping of steady flow through an anatomically realistic aortocoronary bypass graft model. The geometry was obtained through imaging and computational reconstruction of a left anterior descending (LAD) coronary artery of a porcine heart. Simulated images of through‐plane velocity were obtained at selected slices of the geometry. These were then compared and contrasted with velocity images of corresponding sites that were obtained from in vitro experiments. The shift and distortion of the measured velocity profile was well predicted by the simulation, while trajectories obtained from particle tracking were shown to be useful in understanding the origins of the flow artifacts that were observed.
Data required for testicular dose calculation during radiotherapy of seminoma
Authors: Mazonakis Michalis , Kokona Georgiana , Varveris Haralambos , Damilakis John , Gourtsoyiannis Nicholas
Published: July 2006

The purpose of this study was to provide the required data for the direct calculation of testicular dose resulting from radiotherapy in patients with seminoma. Paraortic (PA) treatment fields and dog‐leg (DL) portals including paraortic and ipsilateral pelvic nodes were simulated on a male anthropomorphic phantom equipped with an artificial testicle. Anterior and posterior irradiations were performed for five different PA and DL field dimensions. Dose measurements were carried out using a calibrated ionization chamber. The dependence of testicular dose upon the distance separating the testicle from the treatment volume and upon the tissue thickness at the entrance point of the beam was investigated. A clamshell lead shield was used to reduce testicular dose. The scattered dose to testicle was measured in nine patients using thermoluminescent dosimeters. Phantom and patient exposures were generated with a x‐ray beam. Linear and nonlinear regression analysis was employed to obtain formulas describing the relation between the radiation dose to an unshielded and/or shielded testicle with the field size and the distance from the inferior field edge. Correction factors showing the variation of testicular dose with the patient thickness along beam axis were found. Bland‐Altman statistical analysis showed that testicular dose obtained by the proposed calculation method may differ from the measured dose value by less than 25%. The current study presents a method providing reasonable estimations of testicular dose for individual patients undergoing PA or DL radiotherapy.
Comparison of radiation shielding requirements for HDR brachytherapy using and sources
Authors: Lymperopoulou G. , Papagiannis P. , Sakelliou L. , Georgiou E. , Hourdakis C. J. , Baltas D.
Published: July 2006

has received a renewed focus lately as an alternative to sources for high dose rate (HDR) brachytherapy. Following the results of a recent work by our group which proved to be a good candidate for HDR prostate brachytherapy, this work seeks to quantify the radiation shielding requirements for HDR brachytherapy applications in comparison to the corresponding requirements for the current HDR brachytherapy standard. Monte Carlo simulation (MC) is used to obtain and broad beam transmission data through lead and concrete. Results are fitted to an analytical equation which can be used to readily calculate the barrier thickness required to achieve a given dose rate reduction. Shielding requirements for a HDR brachytherapy treatment room facility are presented as a function of distance, occupancy, dose limit, and facility workload, using analytical calculations for both and HDR sources. The barrier thickness required for is lower than that for by a factor of 4–5 for lead and 1.5–2 for concrete. Regarding HDR brachytherapy applications, the lead shielding requirements do not exceed , even in highly conservative case scenarios. This allows for the construction of a lead door in most cases, thus avoiding the construction of a space consuming, specially designed maze. The effects of source structure, attenuation by the patient, and scatter conditions within an actual treatment room on the above‐noted findings are also discussed using corresponding MC simulation results.
SU‐CC‐ValA‐06: A Novel Approach to Assessing Breast Density Utilizing Sound Speed Measurements
Authors: Glide C , Duric N , Littrup P
Published: July 2006

Purpose: Women with high mammographic breast density are at a 4‐ to 7‐ fold increased risk of developing breast cancer compared to women with fatty breasts. The purpose of this work is to investigate the potential of assessing breast density via acoustic velocity measurements obtained with ultrasound computed tomography. Method and Materials: A sample of approximately 50 patients was imaged with our computed ultrasound tomography clinical prototype. Each data set was comprised of 45 tomograms ranging from near the chest wall through the nipple region. Whole breast acoustic velocity was determined by creating image stacks and evaluating the sound speed frequency distribution. The acoustic measures of breast density were evaluated by comparing these results to two mammographic density measures: (1) qualitative, as determined by a certified radiologist using the BIRADS Categorical Assessment based on a 1 (fatty) to 4 (dense) scale, and (2) quantitative, via digitization and computerized analysis of archival mammograms. The former involved a radiologist's visual assessment of each mammogram, while the latter required scanning cranio‐caudal films with a Vidar VXR‐16 DosimetryPro digitizer and implementing semi‐automatic segmentation routines. Results: Approximately 60 m/s difference in acoustic velocity was found between the fatty and dense BIRADS categories. This investigation indicated a positive correlation between BIRADS category and acoustic velocity of the breast. In addition, a strong correlation between the mean acoustic velocity and quantitative measures of percent breast density was demonstrated (Pearson correlation coefficient 0.651, p < 0.001). Conclusion: These results support the hypothesis that utilizing acoustical velocity as an analogue to mammographic breast density is feasible. Our approach to evaluating breast density has the potential to provide a safer, non‐ionizing, and more quantitative means of evaluating breast density, thus better elucidating the relationship that exists between breast density and breast cancer risk.
SU‐CC‐ValA‐10: Cone‐Beam CT for Radiation Therapy with Reverse Helical Trajectory
Authors: Cho S , Pelizzari C , Pan X
Published: July 2006

Purpose: To propose and study a novel scanning trajectory, named reverse helical trajectory, for a cone‐beam CT (CBCT) imager mounted on a linear accelerator (LINAC) treatment system by applying an exact 3D backprojection filtration (BPF) algorithm. Method and Materials: A numerical study using 3D Shepp‐Logan phantom was performed. We applied the PI‐line‐based BPF algorithm to reconstruct exact 3D image from data acquired numerically for a reverse helical trajectory. It was revealed that there is a middle gap in the reconstructed image which is due to lack of PI‐lines passing through the gap. Application of a chord‐based BPF algorithm showed a reduction in the middle gap. Two kinds of line plus reverse helical trajectories were proposed and tested to reduce the middle gap further. One of them is a reverse helical trajectory with a short line segment between two helices separated apart. The other one is a reverse helical trajectory with a long line segment connecting the end points of the revere helices. Results: The middle gap in the reconstructed image was reduced by employing a chord‐based BPF algorithm. The gap was reduced further when we modified the scanning trajectory by inserting a line segment between two helices. The gap was removed completely when we used a reverse helical trajectory with a long line segment connecting the end points of the revere helices. Conclusion: A novel scanning geometry for a LINAC‐mounted CBCT imager was proposed, and a preliminary numerical study was performed. The middle gap in the reconstructed image obtained by PI‐line‐based BPF algorithm was effectively eliminated by using a chord‐based BPF algorithm with a line plus reverse helical trajectory.
SU‐DD‐A1‐03: IMRT Quality Assurance: Dosimetric Assessment of Three Current Methods
Authors: Hauger J , Beach M , Diez D , Duggan D , Durant J , Ding G , Coffey C
Published: July 2006

Purpose: To compare traditional IMRT quality assurance using film dosimetry and small volume ionization chamber measurements with two new commercial products, the Wellhofer® MatriXX ionization chamber array and Varian® Portal Dosimetry. Available analysis software, hardware requirements and approximate operator times for data preparation, measurement and analysis will also be examined. Method and Materials: Fluence patterns from several 6X and 18X IMRT treatment plans for pelvis and head and neck radiotherapy patients were measured using radiographic film, the MatriXX array, and the Portal Dosimetry array. In each case the fluence pattern predicted by the treatment planning system was compared to the measured fluence pattern using ordinary γ‐analysis. Absolute dose at a point in a low‐gradient region of the fluence was also measured in the solid water phantom with an ionization chamber and compared to the dose prediction of the TPS. The absolute dose measured at the same point by the MatriXX array was also compared. Results: The absolute dose measurements made in a region of low‐gradient using an ionization chamber were, on the average, within 3% of the TPS predicted dose. The absolute dose measurements made using the MatriXX were, on the average, within 5% of the predicted dose. The ion chamber and MatriXX agreed to within 3%. An average of about 4% of pixels failed an ordinary γ‐analysis using 5% dose agreement and 3mm DTA criteria for both film and MatriXX measurements. A smaller percentage of pixels measured using Portal Dosimetry failed. The time spent preparing the data was comparable for all methods. Data measurement and analysis times were significantly reduced using the MatriXX and Portal Dosimeter procedures. Conclusions: This work indicates significant time savings for the new methods. In addition, the MatriXX system measures absolute dose at each chamber position.
SU‐DD‐A2‐02: Variability of Waveforms and Probability Distributions in External Respiratory‐Surrogate Marker Data
Authors: Trofimov A , Sharp G , Bortfeld T
Published: July 2006

Purpose: To investigate intra‐ and inter‐fractional, inter‐subject variability in the motion patterns of external respiratory‐surrogate markers. A strong correlation between the motion of external markers and internal targets has been previously reported. Method and Materials: Varian real‐time position management (RPM) system is used clinically to monitor external marker motion. We analyzed over 450 RPM datasets (traces) from 186 4D‐CT, and 6 gated radiotherapy subjects (mean length: 235 seconds). Aperiodic (long‐term) motion components were subtracted by applying high‐pass filtering to Fourier transform of the data. Probability distribution functions (PDF) of the marker position were constructed, and variability bounds were calculated for the realized distributions. Trace‐average waveforms (TAW) were constructed from cumulative PDF, calculated separately for leading and trailing edges of motion cycles within the trace. Results: Inter‐ and intra‐fractional variability of PDF were reduced where the aperiodic motion components were subtracted from the data. The distribution of aperiodic shifts was approximately Gaussian over multiple fractions. Comparison between the data from various subjects showed that the PDF (when normalized to the mean amplitude of individual traces) was remarkably stable, indicating rather limited inter‐fractional and inter‐subject variability. While intra‐fractional variability of PDF appeared to be typically larger than either inter‐fraction or inter‐subject, as a wide variety of waveforms were realized within each trace. Conclusion: The marker position PDF and its variability bounds, constructed based on a single trace (e.g., pre‐treatment 4D‐CT), may serve as a conservative estimate of the expected variability in the PDF realized during a fractionated treatment. This information can be used in robust optimization of treatment planning for moving targets. The TAW may potentially be useful in subject classification by “respiratory personality”, and prediction of the realized PDF for a given expected uncertainty in the trace extrema positions (full exhale and inhale). Supported in part by the NCI grant 5P01‐CA21239‐25.
SU‐DD‐A3‐04: Quantitative Evaluation of Cone Beam Digital Tomosynthesis (CBDT) for Image‐Guided Radiation Therapy
Authors: Pang G , Au P , O'Brien P , Bani‐Hashemi A , Rowlands J A
Published: July 2006

Purpose: Cone beam digital tomosynthesis (CBDT) is a new imaging technique proposed by us recently as a rapid approach for creating cross sectional images of a patient in the radiotherapy treatment room. Similar to the cone beam computed tomography (CBCT) approach, the CBDT uses an X‐ray source and an X‐ray detector on a Linac to acquire projection data by rotation around the patient. Unlike CBCT, CBDT utilizes partial scans, typically in the range of 20–60 degrees of gantry arc. The purposes of this work are (1) to evaluate quantitatively the image quality of CBDT in terms of signal‐to‐noise ratio and spatial resolution; (2) to demonstrate that we can use CBDT to image soft tissue targets, e.g., the prostate. Method and Materials: An experimental CBDT system has been built on a Linac with a recently developed flat‐panel detector. A number of phantoms including a spatial resolution phantom, two contrast‐detail phantoms and a custom‐made anthropomorphic pelvic phantom (CIRS Inc.) were used in the evaluation. CBDT phantom images have been generated and analyzed for different degrees of gantry arc and compared to those from CBCT. Results: Quantitative results on signal‐to‐noise ratio and spatial resolution have been obtained for different degrees of gantry arc. Compared to CBCT, CBDT has a worse spatial resolution in the direction perpendicular to the planes of reconstruction but a better resolution in the parallel direction. The image quality of CBDT is acceptable in the planes most relevant to the treatment. It has been shown that the prostate is visible on CBDT reconstructed images of the pelvic phantom. Conclusion: This work indicates that the CBDT approach can be a viable and rapid tomographical imaging technique for treatment verification in radiotherapy. Conflict of Interest: This work was partially supported by Siemens Medical Solutions, Inc.
SU‐DD‐A4‐01: Quantifying Skin Effects After Accelerated Partial Breast Irradiation Using Digital Infrared Imaging (DII): Preliminary Feasibility Data
Authors: Mbibi O , Craciunescu O , Fatunase T , Marks L , Yin F
Published: July 2006

Purpose: Accelerated partial‐breast irradiation (APBI) is an emerging radiation technique that challenges standard whole breast irradiation. The larger fraction sizes used in these hypofractionated schedules may increase the risk of late normal tissue effects. Identification of the causes of variability in radiation sensitivity and normal tissue reactions could have important implications for breast cancer therapy. For this, a quantitative method of estimating early and late skin effects is needed. DII is recording instantaneous skin temperatures that are directly correlated with the skin blood flow, a parameter known to be an indicator of skin reaction. Material and Methods: An infrared digital camera IRSnapShot® was used to image breast cancer patients treated with APBI to a total dose of 3850 cGy over 10 fractions. The plans consisted of multiple external non‐coplanar photons +/− electron beams. The patients were imaged in a controlled temperature room before and after each fraction. They were also be imaged at regular intervals during their follow‐up. Two sets of orthogonal DII images were taken. The images were then transferred into Matlab where a GUI is being developed for image registration, thresholding and data analysis. Results: Five patients were imaged as described, three treated with photons only, and two with a combination of photons and electrons. The increase in maximum skin temperature from the baseline (pre treatment) to treatment completion is on average 2 to 4 degrees and depends on the techniques used, higher for plans including electrons, as expected due to their way of depositing dose. Conclusions: DII generated skin temperature information is a promising quantitative tool to estimate early and late effects in irradiated breast cancer patients. Our goal is to generate an “Index of Radiosensitivity” based on the early pattern of change in skin temperature that will allow individualization of radiotherapeutic prescription.