bluuebunny/crossref_metadata_2025 huggingface dataset:
A new 2D segmentation method based on dynamic programming applied to computer aided detection in mammography
Authors: Timp Sheila , Karssemeijer Nico
Published: May 2004

Mass segmentation plays a crucial role in computer‐aided diagnosis (CAD) systems for classification of suspicious regions as normal, benign, or malignant. In this article we present a robust and automated segmentation technique—based on dynamic programming—to segment mass lesions from surrounding tissue. In addition, we propose an efficient algorithm to guarantee resulting contours to be closed. The segmentation method based on dynamic programming was quantitatively compared with two other automated segmentation methods (region growing and the discrete contour model) on a dataset of 1210 masses. For each mass an overlap criterion was calculated to determine the similarity with manual segmentation. The mean overlap percentage for dynamic programming was 0.69, for the other two methods 0.60 and 0.59, respectively. The difference in overlap percentage was statistically significant. To study the influence of the segmentation method on the performance of a CAD system two additional experiments were carried out. The first experiment studied the detection performance of the CAD system for the different segmentation methods. Free‐response receiver operating characteristics analysis showed that the detection performance was nearly identical for the three segmentation methods. In the second experiment the ability of the classifier to discriminate between malignant and benign lesions was studied. For region based evaluation the areaunder the receiver operating characteristics curve was 0.74 for dynamic programming, 0.72 for the discrete contour model, and 0.67 for region growing. The difference invalues obtained by the dynamic programming method and region growing was statistically significant. The differences between other methods were not significant.
An automated procedure for the quality assurance of electron beam output and energy
Authors: Woo M. K. , Videla N. G.
Published: May 2004

In this article, we report on the development of a simple and accurate method for quality assurance of electron beam output and energy. Aluminum disks of thicknesses or of the particular electron energy are positioned sequentially over a parallel‐plate ion chamber and the ratio of the two signals is compared to the standard. The positioning of the aluminum disks is carried out remotely and automatically to eliminate the necessity of multiple setups. One method utilizes the remote control feature of the treatment couch and another employs a motor‐driven carousel. The superior sensitivity over a commercially available energy monitor is illustrated.
Phantom validation of coregistration of PET and CT for image‐guided radiotherapy
Authors: Lavely William C. , Scarfone Christopher , Cevikalp Hakan , Li Rui , Byrne Daniel W. , Cmelak Anthony J. , Dawant Benoit , Price Ronald R. , Hallahan Dennis E. , Fitzpatrick J. Michael
Published: May 2004

Radiotherapy treatment planning integrating positron emission tomography (PET) and computerized tomography (CT) is rapidly gaining acceptance in the clinical setting. Although hybrid systems are available, often the planning CT is acquired on a dedicated system separate from the PET scanner. A limiting factor to using PET data becomes the accuracy of the CT/PET registration. In this work, we use phantom and patient validation to demonstrate a general method for assessing the accuracy of CT/PET image registration and apply it to two multi‐modality image registration programs. An IAEA (International Atomic Energy Association) brain phantom and an anthropomorphic head phantom were used. Internal volumes and externally mounted fiducial markers were filled with CT contrast and ‐fluorodeoxyglucose (FDG). CT, PET emission, and PET transmission images were acquired and registered using two different image registration algorithms. CT/PET Fusion (GE Medical Systems, Milwaukee, WI) is commercially available and uses a semi‐automated initial step followed by manual adjustment. Automatic Mutual Information‐based Registration (AMIR), developed at our institution, is fully automated and exhibits no variation between repeated registrations. Registration was performed using distinct phantom structures; assessment of accuracy was determined from registration of the calculated centroids of a set of fiducial markers. By comparing structure‐based registration with fiducial‐based registration, target registration error (TRE) was computed at each point in a three‐dimensional (3D) grid that spans the image volume. Identical methods were also applied to patient data to assess CT/PET registration accuracy. Accuracy was calculated as the mean with standard deviation of the TRE for every point in the 3D grid. Overall TRE values for the IAEA brain phantom are: CT/PET overall TRE values for the anthropomorphic head phantom are: CT/PET Precision (repeatability by a single user) measured for CT/PET Fusion: IAEA and anthropomorphic head (AMIR has exact precision and so no measurements are necessary.) One sample patient demonstrated the following accuracy results: CT/PET Semi‐automatic and automatic image registration methods may be used to facilitate incorporation of PET data into radiotherapy treatment planning in relatively rigid anatomic sites, such as head and neck. The overall accuracies in phantom and patient images are and respectively, using either registration algorithm. Registration accuracy may decrease, however, as distance from the initial registration points (CT/PET fusion) or center of the image (AMIR) increases. Additional information provided by PET may improve dose coverage to active tumor subregions and hence tumor control. This study shows that the accuracy obtained by image registration with these two methods is well suited for image‐guided radiotherapy.
Heterogeneity phantoms for visualization of 3D dose distributions by MRI‐based polymer gel dosimetry
Authors: Watanabe Yoichi , Mooij Rob , Mark Perera G. , Maryanski Marek J.
Published: May 2004

Heterogeneity corrections in dose calculations are necessary for radiation therapy treatment plans. Dosimetric measurements of the heterogeneity effects are hampered if the detectors are large and their radiological characteristics are not equivalent to water. Gel dosimetry can solve these problems. Furthermore, it provides three‐dimensional (3D) dose distributions. We used a cylindrical phantom filled with BANG‐3® polymer gel to measure 3D dose distributions in heterogeneous media. The phantom has a cavity, in which water‐equivalent or bone‐like solid blocks can be inserted. The irradiated phantom was scanned with an magnetic resonance imaging (MRI) scanner. Dose distributions were obtained by calibrating the polymer gel for a relationship between the absorbed dose and the spin–spin relaxation rate of the magnetic resistance (MR) signal. To study dose distributions we had to analyze MR imaging artifacts. This was done in three ways: comparison of a measured dose distribution in a simulated homogeneous phantom with a reference dose distribution, comparison of a sagittally scanned image with a sagittal image reconstructed from axially scanned data, and coregistration of MR and computed‐tomography images. We found that the MRI artifacts cause a geometrical distortion of less than 2 mm and less than 10% change in the dose around solid inserts. With these limitations in mind we could make some qualitative measurements. Particularly we observed clear differences between the measured dose distributions around an air‐gap and around bone‐like material for a 6 MV photon beam. In conclusion, the gel dosimetry has the potential to qualitatively characterize the dose distributions near heterogeneities in 3D.
Measurement of mesothelioma on thoracic CT scans: A comparison of manual and computer‐assisted techniques
Authors: Armato Samuel G. , Oxnard Geoffrey R. , MacMahon Heber , Vogelzang Nicholas J. , Kindler Hedy L. , Kocherginsky Masha , Starkey Adam
Published: May 2004

Our purpose in this study was to evaluate the variability of manual mesothelioma tumor thickness measurements in computed tomography (CT) scans and to assess the relative performance of six computerized measurement algorithms. The CT scans of 22 patients with malignant pleural mesothelioma were collected. In each scan, an initial observer identified up to three sites in each of three CT sections at which tumor thickness measurements were to be made. At each site, five observers manually measured tumor thickness through a computer interface. Three observers repeated these measurements during three separate sessions. Inter‐ and intra‐observer variability in the manual measurement of tumor thickness was assessed. Six automated measurement algorithms were developed based on the geometric relationship between a specified measurement site and the automatically extracted lung regions. Computer‐generated measurements were compared with manual measurements. The tumor thickness measurements of different observers were highly correlated however, the 95% limits of agreement for relative inter‐observer difference spanned a range of 30%. Tumor thickness measurements generated by the computer algorithms also correlated highly with the average of observer measurements We have developed computerized techniques for the measurement of mesothelioma tumor thickness in CT scans. These techniques achieved varying levels of agreement with measurements made by human observers.
Performance of electronic portal imaging devices (EPIDs) used in radiotherapy: Image quality and dose measurements
Authors: Cremers F. , Frenzel Th. , Kausch C. , Albers D. , Schönborn T. , Schmidt R.
Published: May 2004

The aim of our study was to compare the image and dosimetric quality of two different imaging systems. The first one is a fluoroscopic electronic portal imaging device (first generation), while the second is based on an amorphous silicon flat‐panel array (second generation). The parameters describing image quality include spatial resolution [modulation transfer function (MTF)], noise [noise power spectrum (NPS)], and signal‐to‐noise transfer [detective quantum efficiency (DQE)]. The dosimetric measurements were compared with ionization chamber as well as with film measurements. The response of the flat‐panel imager and the fluoroscopic‐optical device was determined performing a two‐step Monte Carlo simulation. All measurements were performed in a 6 MV linear accelerator photon beam. The resolution (MTF) of the fluoroscopic deviceis larger than of the amorphous silicon based systemwhich is due to the missing backscattered photons and the smaller pixel size. The noise measurements (NPS) show the correlation of neighboring pixels of the amorphous silicon electronic portal imaging device, whereas the NPS of the fluoroscopic system is frequency independent. At zero spatial frequency the DQE of the flat‐panel imager has a value of 0.008 (0.8%). Due to the minor frequency dependency this device may be almost x‐ray quantum limited. Monte Carlo simulations verified these characteristics. For the fluoroscopic imaging system the DQE at low frequencies is about 0.0008 (0.08%) and degrades with higher frequencies. Dose measurements with the flat‐panel imager revealed that images can only be directly converted to portal dose images, if scatter can be neglected. Thus objects distant to the detector (e.g., inhomogeneous dose distribution generated by a modificator) can be verified dosimetrically, while objects close to a detector (e.g., a patient) cannot be verified directly and must be scatter corrected prior to verification. This is justified by the response of the flat‐panel imaging device revealing a strong dependency at low energies.
An experimental method of determining relative phase‐contrast factor for x‐ray imaging systems
Authors: Wu Xizeng , Liu Hong
Published: May 2004

The relative phase‐contrast factor (RPF) represents a quantitative measure of the phase‐contrast transfer in x‐ray in‐line phase‐contrast imaging. The larger the modulus of is, the more the phase‐contrast manifests. In this work we show how the RPF can be determined by measurements of the focal spot size and x‐ray spectra for a x‐ray imaging system with a micro‐focus x‐ray tube. The results show the significant effects of x‐ray beam hardening on the visibility of phase‐contrast, and reveal a new dimension in seeking optimal techniques for x‐ray phase‐contrast imaging.
Monte Carlo modeling of a High‐Sensitivity MOSFET dosimeter for low‐ and medium‐energy photon sources
Authors: Wang Brian , Kim Chan‐Hyeong , Xu X. George
Published: May 2004

Metal–oxide–semiconductor field effect transistor (MOSFET) dosimeters are increasingly utilized in radiation therapy and diagnostic radiology. While it is difficult to characterize the dosimeter responses for monoenergetic sources by experiments, this paper reports a detailed Monte Carlo simulation model of the High‐Sensitivity MOSFET dosimeter using Monte Carlo N‐Particle (MCNP) 4C. A dose estimator method was used to calculate the dose in the extremely thin sensitive volume. Efforts were made to validate the MCNP model using three experiments: (1) comparison of the simulated dose with the measurement of a Cs‐137 source, (2) comparison of the simulated dose with analytical values, and (3) comparison of the simulated energy dependence with theoretical values. Our simulation results show that the MOSFET dosimeter has a maximum response at about 40 keV of photon energy. The energy dependence curve is also found to agree with the predicted value from theory within statistical uncertainties. The angular dependence study shows that the MOSFET dosimeter has a higher response (about 8%) when photons come from the epoxy side, compared with the kapton side for the Cs‐137 source.
A calibration procedure for beam monitors in a scanned beam of heavy charged particles
Authors: Jäkel O. , Hartmann G. H. , Karger C. P. , Heeg P. , Vatnitsky S.
Published: May 2004

An international code of practice (CoP) for dosimetry based on standards of absorbed dose to water has recently been published by the IAEA [Technical Report Series No. 398, 2000] (TRS‐398). This new CoP includes procedures for proton and heavy ion beams as well as all other beam qualities. In particular it defines reference conditions to which dose measurements should refer to. For proton and ion beams these conditions include dose measurements in the center of all possible modulated Bragg peaks. The recommended reference conditions in general are used also for the calibration of beam monitors. For a dynamic beam delivery system using beam scanning in combination with energy variation, like, e.g., at the German carbon ion radiotherapy facility, this calibration procedure is not appropriate. We have independently developed a different calibration procedure. Similar to the IAEA CoP this procedure is based on the measurement of absorbed dose to water. This is translated in terms of fluence which finally results in an energy‐dependent calibration of the beam monitor in units of particle number per monitor unit, which is unique for all treatment fields. In contrast to the IAEA CoP, the reference depth is chosen to be very small. The procedure enables an accurate and reliable determination of calibration factors. In a second step, the calibration is verified by measurements of absorbed dose in various modulated Bragg peaks by comparing measured against calculated doses. The agreement between measured and calculated doses is usually better than 1% for homogeneous fields and the mean deviation for more inhomogeneous treatment fields, as they are used for patient treatments, is within 3%. It is proposed that the CoP in general, and in particular the IAEA TRS‐398 should include explicit recommendations for the beam monitor calibration. These recommendations should then distinguish between systems using static and dynamic beams.
Improving radiochromic film's sensitivity by wrapping it with UV phosphor
Authors: Geso Moshi , Ackerly Trevor , Patterson William
Published: May 2004

The main advantage of radiochromic‐film dosimeters is the coupling of rapid full planar‐acquisition, high‐spatial resolution and dose linearity. Their main limitation, however, is their low radiation sensitivity. This precludes their application to measuring doses below a few Gy. Radiochromic films are sensitive to ultraviolet radiation. In this note the results of exposing radiochromic films to x rays through an UV imaging cassette, which converts and amplifies x rays to UV radiation, are presented. These results indicate a clear increase (around 50%) in radiochromic film's sensitivity to MV x rays (6, 10, and 18 MV) when exposed through the UV phosphor.
Korean adult male voxel model KORMAN segmented from magnetic resonance images
Authors: Lee Choonsik , Lee Jaiki , Lee Choonik
Published: May 2004

A voxel model of Korean adult male, KORMAN, was developed by processing whole‐body magnetic resonance (MR) images of a healthy volunteer who represents an approximately average Korean in height and weight. Layer by layer the MR images were semi‐automatically segmented and indexed using a graphic software and digitizer to construct data arrays consisting ofof a size ofTo assess the utility of the model, some illustrative dosimetric calculations were made to obtain organ absorbed doses and effective doses to the KORMAN placed in broad parallel photon fields with energies ranging from 0.05 to 10 MeV. The results were compared with those based on the medical internal radiation dose (MIRD)‐type models given in ICRP74. The effective doses of ICRP74 were higher than those of KORMAN with percent differences ranging from 6% (LLAT, 10 MeV) to 30% (PA, 0.05 MeV). Significant differences of more than 40% were observed in organ absorbed doses for some organs including bone surface (AP), stomach (PA), and testes (LAT) for low photon energy. These are mainly caused by difference in trunk thickness between MIRD‐type model and KORMAN, and differences in organ positions in the body.
Solid‐state fluoroscopic imager for high‐resolution angiography: Parallel‐cascaded linear systems analysis
Authors: Vedantham Srinivasan , Karellas Andrew , Suryanarayanan Sankararaman
Published: May 2004

Cascaded linear systems based modeling techniques have been used in the past to predict important system parameters that have a direct impact on image quality. Such models are also useful in optimizing system parameters to improve image quality. In this work, detailed analysis of a solid‐state fluoroscopic imaging system intended for high‐resolution angiography is presented with the use of such a model. The imaging system analyzed through this model uses four 8×8 cm three‐side buttable interlined charge‐coupled devices (CCDs) specifically designed for high‐resolution angiography and tiled in a seamless fashion to achieve a field of view (FOV) of 16×16 cm. Larger FOVs can be achieved by tiling more CCDs in a similar manner. The system employs a CsI:Tl scintillator coupled to the CCDs by straight (nontapering) fiberoptics and can potentially be operated in 78, 156, or 234 μm pixel pitch modes. The system parameters analyzed through this model include presampling modulation transfer function, noise power spectrum, and detective quantum efficiency (DQE). The results of the simulations performed indicate that DQE(0) in excess of 0.6 is achievable, with the imager operating at 156 μm pixel pitch, 30 frames/s, and employing a 450‐μm‐thick CsI:Tl scintillator, even at a low fluoroscopic exposure rate of 1 μR/frame. Further, at a nominal fluoroscopic exposure rate of 2.5 μR/frame there was no noticeable degradation of the DQE even at the 78 μm pixel pitch mode suggesting that it is feasible to perform high‐resolution angiography hitherto unattainable in clinical practice.
Clinical implementation of intensity‐modulated tangential beam irradiation for breast cancer
Authors: Li J. S. , Freedman G. M. , Price R. , Wang L. , Anderson P. , Chen L. , Xiong W. , Yang J. , Pollack A. , Ma C.‐M.
Published: May 2004

A Monte Carlo based intensity‐modulated radiation therapy (IMRT) treatment planning system has been developed and used for breast treatment. An iterative method was used for optimization to generate IMRT plans and a step‐and‐shoot technique was used for beam delivery. The patient setup and incident beam directions were the same as those for conventional tangential photon treatment. The weights for the opposed beamlets in the two tangential beams were determined first by the doses at the depths of the maximum dose at both sides to minimize hot spots. The intensity of an individual beamlet pair was then optimized based on the dose at the midplane. Fine tuning was made to achieve optimal target dose uniformity and to reduce the dose to the heart when necessary. The final dose calculations were performed using the Monte Carlo method and the plans were verified by phantom measurements. The dose distributions and dose‐volume‐histograms of IMRT plans were compared with those of conventional plans that were generated using a commercial treatment planning system and recalculated using an in‐house Monte Carlo system for the first 25 patients. The dose comparisons showed that the percentage volume receiving more than 95% of the prescription dose (V95) and the percentage volume receiving more than 100% of the prescription dose (V100) for the clinical target volume (CTV) of IMRT plans were about the same as those of conventional plans. The percentage volume receiving more than 105% of the prescription dose (V105) for the CTV was reduced from 23.1% to 7.9% on average. The percentage volume of the lung receiving more than 20 Gy dose (V20 Gy) during the entire treatment was reduced by about 10%. The percentage volume of the heart receiving more than 30 Gy dose (V30 Gy) is reduced from 3.3% to 0.3%. Further studies revealed that a less than change in couch angle and collimator angle at patient setup had no significant effect on the dose coverage of CTV but had significant effect on the dose to the lung and heart. The study on the effect of beam spoiler showed that it increased the dose at the buildup region by 0–13% that varies with location. The machine output linearity and stability for small monitor unit delivery of Siemens accelerators used for this study was checked and found to be suitable for breast IMRT. The total effect of variations was calculated to be less than 1% for typical breast treatments. The beam delivery time was increased by about 2 min compared with conventional tangential treatments. The whole treatment including patient setup and beam delivery can be completed in a 15 min slot. The IMRT technique has been proven practical for breast treatment clinically. The results showed that tangential IMRT improved the dose homogeneity in the breast and reduced the dose to the lung and heart.
Ultrasonic tissue characterization using 2‐D spectrum analysis and its application in ocular tumor diagnosis
Authors: Liu Tian , Lizzi Frederic L. , Silverman Ronald H. , Kutcher Gerald J.
Published: May 2004

We are investigating the utility of a new ultrasonic tissue characterization technique, specifically two‐dimensional (2‐D) spectrum analysis of radio‐frequency backscatter signals, which promises to provide quantitative measures of the physical properties of tissue microstructures. Previously successful 1‐D spectrum analysis is expanded to 2‐D to more fully characterize diagnostically significant features of biological tissue. Two new spectral functions, radially integrated spectral power (RISP) and angularly integrated spectral power (AISP), are defined to quantitatively characterize tissue properties. This new approach is applied to the diagnosis of in vivo ocular melanomas. Our initial results indicate that 2‐D spectrum analysis can provide significant new information on tissue anisotropy that are not apparent in 1‐D spectra. Acoustic scattering models are applied to relate the 2‐D spectral parameters to the physical properties (e.g., size and shape) of biological tissues.
On the development of consensus values of reference dosimetry parameters for interstitial brachytherapy sources
Authors: Chan Gordon H. , Nath Ravinder , Williamson Jeffrey F.
Published: May 2004

The American Association of Physicists in Medicine recommends that the reference dose‐rate distribution, used for treatment planning for low‐energy photon brachytherapy sources in routine clinical use, must be based on at least two independent determinations: one using experimentally measured dose rates and one using Monte Carlo simulation dosimetry techniques. In this work, we present an approach for developing consensus dosimetry parameters from various independent reference dosimetry studies for interstitial brachytherapy sources. This approach is applied to four recently published papers on the dosimetric properties of the BrachySeed™ Model LS‐1seed. Consensus values for the dose‐rate constant, radial dose function, and anisotropy parameters are presented for the LS‐1 Modelseed.
First proton radiography of an animal patient
Authors: Schneider Uwe , Besserer Jürgen , Pemler Peter , Dellert Matthias , Moosburger Martin , Pedroni Eros , Kaser‐Hotz Barbara
Published: May 2004

The purpose of this work is to show the feasibility of proton radiography in terms of radiation dose, imaging speed, image quality (density and spatial resolution), and image content under clinical conditions. Protons with 214 MeV energy can penetrate through most patients and were used for imaging. The measured residual range (or energy) of the protons behind the patient was subtracted from the range without an object in the beam path and used to create a projected image. The image content is therefore proportional to the range that protons have lost in the patient. We took proton images of the head of a dog after it received proton radiotherapy treatment of a nasal tumor. The spatial resolution by measuring for each proton separately its coordinate in front of and behind the patient was approximately 1 mm. The acquisition time was on the order of several seconds and was limited by the patient table movement. The range sensitivity of the images was approximately 0.6 mm, which is good enough to use the images for therapy range verification. The dose that the dog received during exposure was 0.03 mGy, which is approximately a factor 50–100 smaller than for a comparable x‐ray image. The potential to obtain quantitative images of proton ranges with satisfying spatial and range resolution and low dose to the patient suggests that proton radiography should be applied to patients who are under proton radiotherapy treatment.
IMRT optimization: Variability of solutions and its radiobiological impact
Authors: Mattia Maurizio , Del Giudice Paolo , Caccia Barbara
Published: May 2004

We aim at (1) defining and measuring a “complexity” index for the optimization process of an intensity modulated radiation therapy treatment plan (IMRT TP), (2) devising an efficient approximate optimization strategy, and (3) evaluating the impact of the complexity of the optimization process on the radiobiological quality of the treatment. In this work, for a prostate therapy case, the IMRT TP optimization problem has been formulated in terms of dose‐volume constraints. The cost function has been minimized in order to achieve the optimal solution, by means of an iterative procedure, which is repeated for many initial modulation profiles, and for each of them the final optimal solution is recorded. To explore the complexity of the space of such solutions we have chosen to minimize the cost function with an algorithm that is unable to avoid local minima. The size of the (sub)optimal solutions distribution is taken as an indicator of the complexity of the optimization problem. The impact of the estimated complexity on the probability of success of the therapy is evaluated using radiobiological indicators (Poissonian TCP model [S. Webb and A. E. Nahum, Phys. Med. Biol. 38(6), 653–666 (1993)] and NTCP relative seriality model [Kallman et al., Int. J. Radiat. Biol. 62(2), 249–262 (1992)]). We find in the examined prostate case a nontrivial distribution of local minima, which has symmetry properties allowing a good estimate of near‐optimal solutions with a moderate computational load. We finally demonstrate that reducing the a priori uncertainty in the optimal solution results in a significant improvement of the probability of success of the TP, based on TCP and NTCP estimates.
Scanning‐slit photon counting x‐ray imaging system using a microchannel plate detector
Authors: Shikhaliev Polad M. , Xu Tong , Le Huy , Molloi Sabee
Published: May 2004

An experimental prototype of a novel photon counting x‐ray imaging system was evaluated. This system is based on an “edge‐on” microchannel plate (MCP) detector and utilizes scanning slit imaging configuration. The detector is capable of photon counting, direct conversion, high spatial resolution, controllable physical charge amplification, quantum limited and scatter free operation. The detector provides a 60 mm wide field of view (FOV) and its count rate is 200 kHz for the entire FOV. The count rate of the current system is limited by the position encoding electronics, which has a single input for all events from the entire detector, and incorporates a single channel ADC with 1 μs conversion time. It is shown that the count rate can potentially be improved to clinically acceptable levels using multichannel application specific integrated circuit (ASIC) electronics and multi‐slit image acquisition geometry. For a typical acquisition time used in this study, the image noise was measured to be less than the typically acceptable noise level for medical x‐ray imaging. It is anticipated that the noise level will be also low after the implementation of the ASIC electronics. The quantum efficiency of the detector was measured to be 40%–56% for an energy range of 50–90 kVp for MCPs used in this study and can be improved tousing MCPs with the optimized parameters. Images of resolution and anthropomorphic phantoms were acquired at an x‐ray tube voltage of 50 kVp. The value of contrast transfer function for the detector was measured to be 0.5 at a spatial frequency of 5 lp/mm. The intrinsic spatial resolution of the system is 28 μm FWHM and was limited by the accuracy of the time‐to‐digital conversion of the position encoding electronics. Given the advantages of the edge‐on MCP detector such as direct conversion and physical charge amplification, it can potentially be applied to mammography and chest radiography.
Computerized interpretation of breast MRI: Investigation of enhancement‐variance dynamics
Authors: Chen Weijie , Giger Maryellen L. , Lan Li , Bick Ulrich
Published: May 2004

The advantages of breast MRI using contrast agent Gd‐DTPA in the diagnosis of breast cancer have been well established. The variation of interpretation criteria and absence of interpretation guidelines, however, is a major obstacle for applications of MRI in the routine clinical practice of breast imaging. Our study aims to increase the objectivity and reproducibility of breast MRI interpretation by developing an automated interpretation approach for ultimate use in computer‐aided diagnosis. The database in this study contains 121 cases: 77 malignant and 44 benign masses as revealed by biopsy. Images were obtained using a T1‐weighted 3D spoiled gradient echo sequence. After the acquisition of the precontrast series, Gd‐DTPA contrast agent was injected intravenously by power injection with a dose of 0.2 mmol/kg. Five postcontrast series were then taken with a time interval of 60 s. Each series contained 64 coronal slices with a matrix of and an in‐plane resolution of Slice thickness ranged from 2 to 3 mm depending on breast size. The lesions were delineated by an experienced radiologist as well as independently by computer using an automatic volume‐growing algorithm. Fourteen features that were extracted automatically from the lesions could be grouped into three categories based on (I) morphology, (II) enhancement kinetics, and (III) time course of enhancement‐variation over the lesion. A stepwise feature selection procedure was employed to select an effective subset of features, which were then combined by linear discriminant analysis (LDA) into a discriminant score, related to the likelihood of malignancy. The classification performances of individual features and the combined discriminant score were evaluated with receiver operating characteristic (ROC) analysis. With the radiologist‐delineated lesion contours, stepwise feature selection yielded four features and an value of 0.80 for the LDA in leave‐one‐out cross‐validation testing. With the computer‐segmented lesion volumes, it yielded six features and an value of 0.86 for the LDA in the leave‐one‐out testing.
Distance and angular dependence of intensity ratios in laser‐induced autofluorescence techniques
Authors: Kwek L. C. , Fu Sheng , Chia T. C. , Tang C. L.
Published: May 2004

Laser‐induced autofluorescence techniques have the potential to be used for the detection of preinvasive human cancer cells. For colorectal and gastrointestinal cancer cells, the light is introducedin vivothrough endoscopic means and the probe tip is brought gently into contact with the tissue under investigation. However, it is often assumed that there is no distance or angular dependence in the intensity of the light collected from the probes. We performed anin vitroexperiment in which we showed that there was indeed no angular dependence provided the angle of inclination of the probe to normal incidence is small. However, we find substantial fluctuation in the intensities of peaks for changing distances. These fluctuations can be eliminated by considering the ratio of the intensities from two spectral lines.
Advantage and limitations of weighting factors and weighted dose quantities and their units in boron neutron capture therapy
Authors: Rassow J. , Sauerwein W. , Wittig A. , Bourhis‐Martin E. , Hideghéty K. , Moss R.
Published: May 2004

Defining the parameters influencing the biological reaction due to absorbed dose is a continuous topic of research. The main goal of radiobiological research is to translate the measurable dose of ionizing radiation to a quantitative expression of biological effect. Mathematical models based on different biological approaches (e.g., skin reaction, cell culture) provide some estimations that are often misleading and, to some extent, dangerous. Conventional radiotherapy is the simplest case because the primary radiation and secondary radiation are both low linear energy transfer (LET) radiation and have about the same relative biological effectiveness (RBE). Nevertheless, for this one‐dose‐component case, the dose–effect curves are not linear. In fact, the total absorbed dose and the absorbed dose per fraction as well as the time schedule of the fractionation scheme influence the biological effects. Mathematical models such as the linear‐quadratic model can only approximate biological effects. With regard to biological effects, fast neutron therapy is more complex than conventional radiotherapy. Fast neutron beams are always contaminated by γ rays. As a consequence, biological effects are due to two components, a high‐LET component (neutrons) and a low‐LET component (photons). A straight transfer of knowledge from conventional radiotherapy to fast neutron therapy is, therefore, not possible: RBE depends on the delivered dose and several other parameters. For dose reporting, the European protocol for fast neutron dosimetry recommends that the total absorbed dose with γ‐ray absorbed dose in brackets is stated. However, boron neutron capture therapy (BNCT) is an even more complex case, because the total absorbed dose is due to four dose components with different LET and RBE. In addition, the terminology and units used by the different BNCT groups is confusing: absorbed dose and weighted dose are both to be stated in grays and are never “photon equivalent.” The ICRU/IAEA made proposals, which should be followed by all BNCT groups, to report always the four absorbed dose components, boron dose proton dose γ‐ray dose and neutron dose as well as the sum of all components, as total absorbed dose, together with the total weighted dose (to be used only for internal purposes, indicating the used weighting factors) at all points of interest and the treatment conditions.
A new algorithm for determining collimator angles that favor efficiency in MLC based IMRT delivery
Authors: Wang David , Hill R. W. , Lam S.
Published: May 2004

A new algorithm to determine collimator angles that favor delivery efficiency of intensity modulated radiotherapy plans was developed. It was found that the number of segments and monitor units (MUs) were largely reduced with the set of collimator angles determined with the new algorithm without compromising plan quality. The improvement of delivery efficiency using the new algorithm depends on the size and shape of the target(s), the number of modulation levels, and the type of leaf‐sequencing algorithm. In a typical prostate case, when a sweeping leaf‐sequencer is used for Varian 120 leaf (0.5×0.5 cm2 beamlet), 80 leaf (1×1 cm2 beamlet) and Elekta 40 leaf (1×1 cm2 beamlet), the number of segments was reduced by 42%, 29%, and 5%, respectively. The number of MUs was reduced by 41%, 35%, and 10%. For the Siemens MLC (IMFAST™ leaf sequencer, 1×1 cm2 beamlet) the segment reduction was 32% and the MU reduction was 14%. Comparison of the plans using the new and Brahme algorithms, in terms of target conformity index and dose volume histogram of the organs at risk, showed that the quality of the plans using the new algorithm was uncompromised. Similar results were obtained for a set of head and neck treatment plans.
Dosimetric characteristics of the Novoste Beta‐Cath source trains at submillimeter distances
Authors: Roa Dante E. , Song Haijun , Yue Ning , d'Errico Francesco , Nath Ravinder
Published: May 2004

Measurements were performed on the 30, 40, and 60 mm β‐emitter source trains used in the Novoste Beta‐Cath system to determine their dosimetric characteristics at submillimeter distances and provide the necessary TG‐60 parameters for mapping their dose distributions. These measurements were carried out in a Solid Water™ phantom where MD55‐2 Gafchromic™ films were placed in direct contact with a 5 French (F) catheter used for the 30 and 60 mm source trains and a 3.5F catheter used for thinner 30 and 40 mm source trains. A data set consisted of three pieces of Gafchromic film irradiated for periods of 1.5, 5, and 10 minutes, respectively. This 3‐film irradiation technique provided reliable dose data at short, intermediate and long distances from a source train. Three data sets per source train were collected in this study. For the 30 mm source train with a 5F catheter, data were collected with the source axis at proximal (0.41 mm) and distal (1.19 mm) positions to the film surface in order to investigate dosimetric effects due to the off centering of the source train lumen within the catheter. Absolute doses were determined by calibrating the Gafchromic film in a high‐energy electron beam from a radiotherapy accelerator. The absolute dose rates at a distance of 2 mm along the source trains transverse axis were found to be within 13.7% of the values provided by Novoste. Radial dose functions were within 13% compared to source train data constructed from Soares' single seed data and within 17% and 25% compared to Monte Carlo data by Ye et al., and Wang et al., respectively. Discrepancies of 33% and 19% were observed at short radial distances between the Novoste Monte Carlo and the 3.5F and 5F catheter measured data, respectively. The source off centering data showed higher dose contribution from the source train at its distal rather than proximal position. Radial dose function comparisons between the Novoste Monte Carlo and the measured data, calculated as a function of radial distance from the catheter's center showed good agreement
Image‐based high dose rate brachytherapy for prostate cancer
Authors: Kim Yongbok
Published: May 2004

The passage from conventional radiographic film‐based to image‐based high dose rate (HDR) brachytherapy for prostate cancer has significantly improved our ability to define the targets and organs at risk (OAR). Three‐dimensional (3D) anatomical information are obtained from Computed Tomography (CT) or Magnetic Resonance Imaging (MRI), and cancer areas are validated using functional imaging with magnetic resonance spectroscopy imaging (MRSI). Together with inverse planning optimization, image‐based HDR brachytherapy can deliver a highly conformal dose distribution to the target while sparing OAR. However, uncertainties inherent to the use of the new imaging modalities may impact on the dose distribution. In this work, we have selected the major uncertainties and studied their impact within the context of the clinical procedures of ultrasound guided HDR prostate brachytherapy delivered in two fractions. The feasibility of using functional imaging to guide the delivery of higher dose to dominant intraprostatic lesions (DIL) within the prostate was also investigated. The average cranio‐caudal displacement of catheters between fractions was 2.7 mm and 5.4 mm for bony anatomy and gold seed marker measurement, respectively. Either increase or reduction of prostate volume was observed with an average of 7.8% and a maximum of 17% between fractions, resulting in minimal dose changes. The dose uncertainty due to the planning CT slice thickness showed a relative error of 1% on average for current 3 mm planning CT, independent of the transversal region of the prostate. A retrospective study taking advantage of MRI/MRSI for the dose escalation of the DIL demonstrated that high dose areas could be redistributed to boost the DIL by 120% without any additional dose delivered to OAR compared to a reference plan. On average, the rigid endorectal probe was shown to rotate the prostate anteriorly by to expand it in the antero–posterior direction by 1.2 mm, and compress it in lateral direction with 1.5 mm. Finally, MRI scans with and without the probe could be registered with a 2 mm precision using translation only. The use of 3D anatomical and functional information combined with inverse planned HDR brachytherapy is a precise procedure for the treatment of localized prostate cancer with potential for dose escalation.
A conceptual design of a beam‐shaping assembly for boron neutron capture therapy based on deuterium–tritium neutron generators
Authors: Martı́n Guido , Abrahantes Arian
Published: May 2004

A conceptual design of a beam‐shaping assembly for boron neutron capture therapy using deuterium–tritium accelerator based neutrons source is developed. Calculations based on a simple geometry model for the radiation transport are initially performed to estimate the assembly materials and their linear dimensions. Afterward, the assembly geometry is produced, optimized and verified. In order to perform these calculations the general‐purpose MCNP code is used. Irradiation time and therapeutic gain are utilized as beam assessment parameters. Metallic uranium and manganese are successfully tested for fast‐to‐epithermal neutron moderation. In the present beam‐shaping assembly proposal, the therapeutic gain is improved by 23% and the accelerator current required for a fixed irradiation period is reduced by six times compared to previous proposals based on the same D–T reaction.
Constructal theory of flow architecture of the lungs
Authors: Reis A. H. , Miguel A. F. , Aydin M.
Published: May 2004

Here we explain the reasons why we have a bronchial tree with 23 levels of bifurcation. Based on Bejan's Constructal Principle we found that the best oxygen access to the alveolar tissues as well as carbon dioxide removal is provided by a flow structure composed of ducts with 23 levels of bifurcation (bronchial tree) that ends with spaces (alveolar sacs) from where oxygen diffuses into the tissues. The model delivers the dimensions of the alveolar sac, the total length of the airways, the total alveolar surface area, and the total resistance to oxygen transport in the respiratory tree. A constructal law also emerges: the length defined by the ratio of the square of the airway diameter to its length is constant for all individuals of the same species and is related to the characteristics of the space allocated to the respiratory process and determines univocally the branching level of the respiratory tree.
Dose perturbation induced by radiographic contrast inside brachytherapy balloon applicators
Authors: Kirk Michael C. , Hsi Wen C. , Chu James C. H. , Niu Honquan , Hu Zenan , Bernard Damian , Dickler Adam , Nguyen Cam
Published: May 2004

Phantom measurements and Monte Carlo calculations have been performed for the purpose of characterizing the dose perturbation caused by radiographic contrast inside the MammoSite breast brachytherapy applicator. Specifically, the dose perturbation is quantified as a heterogeneity correction factor (HCF) for various balloon radii and contrast concentration levels. The dose perturbation is larger for larger balloon radii and higher contrast concentrations. Based on a validated Monte Carlo simulation, the calculated HCF values are 0.99 for a 2 cm radius balloon and 0.98 for a 3 cm radius balloon at 6% contrast concentration levels, and 0.89 and 0.87 for 2 and 3 cm radius balloons, respectively, at 100% contrast concentrations. For a typical implanted balloon radius of 2.4 cm, the HCF values decrease from 0.99 at 6% contrast concentration to 0.90 at 100% contrast concentration. For balloons implanted in patients at our institution, the mean HCF is 0.99, corresponding to a dose reduction of approximately 1%. The contrast effect results in a systematic reduction in the delivered dose, therefore the minimal amount of radiographic contrast necessary should be used.
Experimental evaluation of analytical penumbra calculation model for wobbled beams
Authors: Kohno Ryosuke , Kanematsu Nobuyuki , Yusa Ken , Kanai Tatsuaki
Published: May 2004

The goal of radiotherapy is not only to apply a high radiation dose to a tumor, but also to avoid side effects in the surrounding healthy tissue. Therefore, it is important for carbon‐ion treatment planning to calculate accurately the effects of the lateral penumbra. In this article, for wobbled beams under various irradiation conditions, we focus on the lateral penumbras at several aperture positions of one side leaf of the multileaf collimator. The penumbras predicted by an analytical penumbra calculation model were compared with the measured results. The results calculated by the model for various conditions agreed well with the experimental ones. In conclusion, we found that the analytical penumbra calculation model could predict accurately the measured results for wobbled beams and it was useful for carbon‐ion treatment planning to apply the model.