bluuebunny/crossref_metadata_2025 huggingface dataset:
Proof of principle study of the use of a CMOS active pixel sensor for proton radiography
Authors: Seco Joao , Depauw Nicolas
Published: February 2011

Purpose:

Proof of principle study of the use of a CMOS active pixel sensor (APS) in producing proton radiographic images using the proton beam at the Massachusetts General Hospital (MGH).

Methods:

A CMOS APS, previously tested for use in s‐ray radiation therapy applications, was used for proton beam radiographic imaging at the MGH. Two different setups were used as a proof of principle that CMOS can be used as proton imaging device: (i) a pen with two metal screws to assess spatial resolution of the CMOS and (ii) a phantom with lung tissue, bone tissue, and water to assess tissue contrast of the CMOS. The sensor was then traversed by a double scattered monoenergetic proton beam at 117 MeV, and the energy deposition inside the detector was recorded to assess its energy response. Conventional x‐ray images with similar setup at voltages of 70 kVp and proton images using commercial Gafchromic EBT 2 and Kodak X‐Omat V films were also taken for comparison purposes.

Results:

Images were successfully acquired and compared to x‐ray kVp and proton EBT2/X‐Omat film images. The spatial resolution of the CMOS detector image is subjectively comparable to the EBT2 and Kodak X‐Omat V film images obtained at the same object‐detector distance. X‐rays have apparent higher spatial resolution than the CMOS. However, further studies with different commercial films using proton beam irradiation demonstrate that the distance of the detector to the object is important to the amount of proton scatter contributing to the proton image. Proton images obtained with films at different distances from the source indicate that proton scatter significantly affects the CMOS image quality.

Conclusion:

Proton radiographic images were successfully acquired at MGH using a CMOS active pixel sensor detector. The CMOS demonstrated spatial resolution subjectively comparable to films at the same object‐detector distance. Further work will be done in order to establish the spatial and energy resolution of the CMOS detector for protons. The development and use of CMOS in proton radiography could allowin vivo proton range checks, patient setup QA, and real‐time tumor tracking.
On the use of computed radiography plates for quality assurance of intensity modulated radiation therapy dose distributions
Authors: Day R. A. , Sankar A. P. , Nailon W. H. , MacLeod A. S.
Published: February 2011

Purpose:

As traditional film is phased out in most radiotherapy centers, computed radiography (CR) systems are increasingly being purchased as a replacement. CR plates can be used for patient imaging, but may also be used for a variety of quality assurance (QA) purposes and can be calibrated in terms of dose. This study looks at their suitability for verification of intensity modulated radiation therapy (IMRT) dose distributions.

Methods:

A CR plate was calibrated in terms of the relative dose and the stability of response over 1 year was studied. The effect of exposing the CR plate to ambient light and of using different time delays before scanning was quantified. The CR plate was used to verify the relative dose distributions for ten IMRT patients and the results were compared to those obtained using a two dimensional (2D) diode array.

Results:

Exposing the CR plate to 10 s of ambient light between irradiation (174 cGy) and scanning erased approximately 80% of the signal. Changes in delay time between irradiation and scanning also affected the measurement results. The signal on the plate was found to decay at a rate of approximately 3.6 cGy/min in the first 10 min after irradiation. The use of a CR plate for IMRT patient‐specific QA resulted in a significantly lower distance to agreement (DTA) and gamma pass rate than when using a 2D diode array for the measurement. This was primarily due to the over‐response of the CR phosphor to low energy scattered radiation. For the IMRT QA using the CR plate, the average gamma pass rate was 97.3%. For the same IMRT QA using a diode array, the average gamma pass rate was 99.7%. The gamma criteria used were 4% dose difference and 4 mm DTA for head and neck treatments and 3% dose difference and 3 mm DTA for prostate treatments. The gamma index tolerance was 1. The lowest 10% of the dose distribution was excluded from all gamma and DTA analyses.

Conclusions:

Although the authors showed that CR plates can be used for patient specific IMRT QA, the practical problems such as the over‐response to low energy scatter and signal fading with light exposure and time mean that alternative detectors such as radiochromic film or diode arrays will be a more sensible choice for most radiotherapy departments.
A compact mechatronic system for 3D ultrasound guided prostate interventions
Authors: Bax Jeffrey , Smith David , Bartha Laura , Montreuil Jacques , Sherebrin Shi , Gardi Lori , Edirisinghe Chandima , Fenster Aaron
Published: February 2011

Purpose:

Ultrasound imaging has improved the treatment of prostate cancer by producing increasingly higher quality images and influencing sophisticated targeting procedures for the insertion of radioactive seeds during brachytherapy. However, it is critical that the needles be placed accurately within the prostate to deliver the therapy to the planned location and avoid complications of damaging surrounding tissues.

Methods:

The authors have developed a compact mechatronic system, as well as an effective method for guiding and controlling the insertion of transperineal needles into the prostate. This system has been designed to allow guidance of a needle obliquely in 3D space into the prostate, thereby reducing pubic arch interference. The choice of needle trajectory and location in the prostate can be adjusted manually or with computer control.

Results:

To validate the system, a series of experiments were performed on phantoms. The 3D scan of the string phantom produced minimal geometric error, which was less than 0.4 mm. Needle guidance accuracy tests in agar prostate phantoms showed that the mean error of bead placement was less then 1.6 mm along parallel needle paths that were within 1.2 mm of the intended target and 1° from the preplanned trajectory. At oblique angles of up to 15° relative to the probe axis, beads were placed to within 3.0 mm along a trajectory that were within 2.0 mm of the target with an angular error less than 2°.

Conclusions:

By combining 3D TRUS imaging system to a needle tracking linkage, this system should improve the physician's ability to target and accurately guide a needle to selected targets without the need for the computer to directly manipulate and insert the needle. This would be beneficial as the physician has complete control of the system and can safely maneuver the needle guide around obstacles such as previously placed needles.
CT image construction of a totally deflated lung using deformable model extrapolation
Authors: Sadeghi Naini Ali , Pierce Greg , Lee Ting‐Yim , Patel Rajni V. , Samani Abbas
Published: February 2011

Purpose:

A novel technique is proposed to construct CT image of a totally deflated lung from a free‐breathing 4D‐CT image sequence acquired preoperatively. Such a constructed CT image is very useful in performing tumor ablative procedures such as lung brachytherapy. Tumor ablative procedures are frequently performed while the lung is totally deflated. Deflating the lung during such procedures renders preoperative images ineffective for targeting the tumor. Furthermore, the problem cannot be solved using intraoperative ultrasound (U.S.) images because U.S. images are very sensitive to small residual amount of air remaining in the deflated lung. One possible solution to address these issues is to register high quality preoperative CT images of the deflated lung with their corresponding low quality intraoperative U.S. images. However, given that such preoperative images correspond to an inflated lung, such CT images need to be processed to construct CT images pertaining to the lung's deflated state.

Methods:

To obtain the CT images of deflated lung, we present a novel image construction technique using extrapolated deformable registration to predict the deformation the lung undergoes during full deflation. The proposed construction technique involves estimating the lung's air volume in each preoperative image automatically in order to track the respiration phase of each 4D‐CT image throughout a respiratory cycle; i.e., the technique does not need any external marker to form a respiratory signal in the process of curve fitting and extrapolation. The extrapolated deformation field is then applied on a preoperative reference image in order to construct the totally deflated lung's CT image. The technique was evaluated experimentally usingex vivo porcine lung.

Results:

Theex vivo lung experiments led to very encouraging results. In comparison with the CT image of the deflated lung we acquired for the purpose of validation, the constructed CT image was very similar. The intensity mean absolute difference between these two images was calculated to be at 1%. Tumor center as well as a number of anatomical fiducial markers were traced in different corresponding slices of the two images. The average misalignment obtained for the constructed CT image was (0.64, 0.39, 0.11) mm, which indicates a very desirable accuracy for lung brachytherapy applications.

Conclusions:

The image construction accuracy obtained in this research is suitable for intraoperative tasks; e.g., tumor localization and fusing with real time navigation data in lung brachytherapy. These applications involve image registration with intraoperative U.S. images in order to enhance their poor quality. The proposed technique is also useful for preoperative tasks such as planning of lung brachytherapy treatment.
Co‐60 tomotherapy: A treatment planning investigation
Authors: Cadman Patrick , Bzdusek Karl
Published: February 2011

Purpose:

The authors investigate the plan quality and treatment times that may be achieved with Co‐60 tomotherapy delivery for clinical IMRT cases.

Methods:

A research version ofPINNACLE treatment planning system software (V9.1) enabled the authors to specify custom source profiles for modeling of cylindrical Co‐60 sources. The calculated profiles were validated against measurements for simulated MLC leaf openings. The reduction in dose due to a partially obscured source was analyzed. The thread effect was investigated for a source of typical linac spot dimensions and 2.0 and 2.8 cm diameter cylindrical Co‐60 sources. Co‐60 tomotherapy plans for three clinical treatment sites—prostate, brain, and head‐and‐neck—were generated for the Co‐60 sources and compared to linac‐based segmental IMRT plans in terms of the DVHs produced. Treatment times were also determined.

Results:

The custom source profile utility allowed the authors to obtain good agreement between calculated and measured profiles for simulated MLC leaf openings with the commercial Co‐60 source. It was found that the thread effect is significantly reduced for Co‐60 sources and is not a clinical concern even for the large slice width (4.8 cm) and pitch value (0.5) studied. Co‐60 tomotherapy plans for three clinical treatment sites compared favorably to the original segmental IMRT plans in terms of the DVHs produced. Treatment times, comparable to the actual segmental IMRT treatment times, may be achieved for a high activity Co‐60 source and dual‐slice delivery may reduce these times further.

Conclusions:

It may be possible to achieve clinically viable treatment times with Co‐60 tomotherapy delivery without unacceptable loss of plan quality in terms of the DVHs produced.
Organ and effective dose estimates for patients undergoing hepatic arterial embolization for treatment of liver malignancy
Authors: Dauer Lawrence T. , Thornton Raymond , Boylan Daniel C. , Holahan Brian , Prins Robert , Quinn Brian , St. Germain Jean
Published: February 2011

Purpose:Effective doseis useful as a dose index for patient exposures in interventional radiology; therefore, the authors estimatedfrom the kerma‐area productutilized during hepatic embolization interventional radiology cases performed at a cancer center and determined the variation of such doses over a representative patient population.

Methods:A single‐center, IRB‐approved retrospective study was performed to estimate doses from consecutive hepatic embolization procedures performed during 2006. Organ dosesandwere determined from patient height, weight,, procedure geometry factors, beam quality, thePCXMCMonte Carlo model, and the International Commission on Radiological Protection organ weighting factors.

Results:One hundred thirteen patients were included in the study population, 72 males and 41 females, with a median age of 63 yr (29–89 yr), weight of 79 kg (42–111 kg), height of 170 cm (147–188 cm), andof.was directly correlated with, with a medianof. Theratio was inversely and exponentially correlated with weight. The median(mSv) for the study patient population was 44 mSv (2.0–255 mSv).

Conclusions:Values ofcan be estimated utilizing patient‐specific and procedure‐specific parameters. The strong inverse correlation ofwith patient weight allows simple estimation offromand patient weight. There is a wide variation in effective dose in oncologic hepatic embolizations with doses up to an order of magnitude higher than diagnostic imaging of the abdomen by CT radiology. Variation is likely due to patient geometry, clinical technique factors, and procedure complexity.
The feasibility of patient size‐corrected, scanner‐independent organ dose estimates for abdominal CT exams
Authors: Turner Adam C. , Zhang Di , Khatonabadi Maryam , Zankl Maria , DeMarco John J. , Cagnon Chris H. , Cody Dianna D. , Stevens Donna M. , McCollough Cynthia H. , McNitt‐Gray Michael F.
Published: February 2011

Purpose:

A recent work has demonstrated the feasibility of estimating the dose to individual organs from multidetector CT exams using patient‐specific, scanner‐independent‐to‐organ‐dose conversion coefficients. However, the previous study only investigated organ dose to a single patient model from a full‐body helical CT scan. The purpose of this work was to extend the validity of this dose estimation technique to patients of any size undergoing a common clinical exam. This was done by determining the influence of patient size on organ dose conversion coefficients generated for typical abdominal CT exams.

Methods:

Monte Carlo simulations of abdominal exams were performed using models of 64‐slice MDCT scanners from each of the four major manufacturers to obtain dose to radiosensitive organs for eight patient models of varying size, age, and gender. The scanner‐specific organ doses were normalized by corresponding values and averaged across scanners to obtain scanner‐independent ‐to‐organ‐dose conversion coefficients for each patient model. In order to obtain a metric for patient size, the outer perimeter of each patient was measured at the central slice of the abdominal scan region. Then, the relationship between ‐to‐organ‐dose conversion coefficients and patient perimeter was investigated for organs that were directly irradiated by the abdominal scan. These included organs that were either completely (“fully irradiated”) or partly (“partially irradiated”) contained within the abdominal exam region. Finally, dose to organs that were not at all contained within the scan region (“nonirradiated”) were compared to the doses delivered to fully irradiated organs.

Results:

‐to‐organ‐dose conversion coefficients for fully irradiated abdominal organs had a strong exponential correlation with patient perimeter. Conversely, partially irradiated organs did not have a strong dependence on patient perimeter. In almost all cases, the doses delivered to nonirradiated organs were less than 5%, on average across patient models, of the mean dose of the fully irradiated organs.

Conclusions:

This work demonstrates the feasibility of calculating patient‐specific, scanner‐independent‐to‐organ‐dose conversion coefficients for fully irradiated organs in patients undergoing typical abdominal CT exams. A method to calculate patient‐specific, scanner‐specific, and exam‐specific organ dose estimates that requires only knowledge of the for the scan protocol and the patient's perimeter is thus possible. This method will have to be extended in future studies to include organs that are partially irradiated. Finally, it was shown that, in most cases, the doses to nonirradiated organs were small compared to the dose to fully irradiated organs.
Position‐probability‐sampled Monte Carlo calculation of VMAT, 3DCRT, step‐shoot IMRT, and helical tomotherapy dose distributions using BEAMnrc/DOSXYZnrc
Authors: Belec Jason , Ploquin Nicolas , La Russa Daniel J. , Clark Brenda G.
Published: February 2011

Purpose:

The commercial release of volumetric modulated arc therapy techniques using a conventional linear accelerator and the growing number of helical tomotherapy users have triggered renewed interest in dose verification methods, and also in tools for exploring the impact of machine tolerance and patient motion on dose distributions without the need to approximate time‐varying parameters such as gantry position, MLC leaf motion, or patient motion. To this end we have developed a Monte Carlo‐based calculation method capable of simulating a wide variety of treatment techniques without the need to resort to discretization approximations.

Methods:

The ability to perform complete position‐probability‐sampled Monte Carlo dose calculations was implemented in the BEAMnrc/DOSXZYnrc user codes of EGSnrc. The method includes full accelerator head simulations of our tomotherapy and Elekta linacs, and a realistic representation of continous motion via the sampling of a time variable. The functionality of this algorithm was tested via comparisons with both measurements and treatment planning dose distributions for four types of treatment techniques: 3D conformal, step‐shoot intensity modulated radiation therapy, helical tomotherapy, and volumetric modulated arc therapy.

Results:

For static fields, the absolute dose agreement between the EGSnrc Monte Carlo calculations and measurements is within 2%/1 mm. Absolute dose agreement between Monte Carlo calculations and treatment planning system for the four different treatment techniques is within 3%/3 mm. Discrepancies with the tomotherapy TPS on the order of 10%/5 mm were observed for the extreme example of a small target located 15 cm off‐axis and planned with a low modulation factor. The increase in simulation time associated with using position‐probability sampling, as opposed to the discretization approach, was less than 2% in most cases.

Conclusions:

A single Monte Carlo simulation method can be used to calculate patient dose distribution for various types of treatment techniques delivered with either tomotherapy or a conventional linac. The method simplifies the simulation process, improves dose calculation accuracy, and involves an acceptably small change in computation time.
Technical Note: A fast laser‐based optical‐CT scanner for three‐dimensional radiation dosimetry
Authors: Papadakis A. E. , Maris T. G. , Zacharakis G. , Papoutsaki V. , Varveris C. , Ripoll J. , Damilakis J.
Published: February 2011

Purpose:

To introduce a novel laser‐based optical‐CT scanner for the readout of three‐dimensional (3D) radiation dosimeters.

Methods:

The scanner employs a diode laser, a cylindrical lens, a motorized linear rail, a rotation stage, and a charge‐coupled device camera. The scanner operates in a translate‐rotate fashion and may be set up in two configurations depending on the orientation of the cylindrical lens. The attenuation coefficient versus dose response was determined for a normoxic N‐vinylpyrrolidone based polymer gel dosimeter. Cylindrical dosimeters, 2 cm diameter, were homogenously irradiated to known doses up to 60 Gy using a 6 MV linear accelerator. For a test irradiation, a 5 cm diameter dosimeter was irradiated along its cylindrical axis using a rectangular irradiation beam. The dose readout of this scanner was compared to the corresponding readout of a common wide illumination and area detector optical‐CT scanner.

Results:

The attenuation coefficient versus dose response of the laser‐based system was found to be linear up to 60 Gy compared to the wide field illumination based optical‐CT scanner, which exhibits linearity up to 32 Gy . The noise in the reconstructed attenuation coefficient maps was versus for the laser‐based system and the wide field illumination system, respectively.

Conclusions:

We have developed a novel laser‐based optical‐CT scanner, which is capable of generating fast 3D dosimetric data using a scattering polymer gel dosimeter. Our data demonstrate that the dose readout of this scanner preserves the advantage of existing laser‐based optical‐CT scanners in providing measurements, which are minimally affected by scattered light. For accurate reconstruction of the attenuation coefficients, noise reduction techniques need to be applied.
Modification of Kirchhoff migration with variable sound speed and attenuation for acoustic imaging of media and application to tomographic imaging of the breast
Authors: Schmidt Steven , Duric Nebojsa , Li Cuiping , Roy Olivier , Huang Zhi‐Feng
Published: February 2011

Purpose:

To explore the feasibility of improving cross‐sectional reflection imaging of the breast using refractive and attenuation corrections derived from ultrasound tomography data.

Methods:

The authors have adapted the planar Kirchhoff migration method, commonly used in geophysics to reconstruct reflection images, for use in ultrasound tomography imaging of the breast. Furthermore, the authors extended this method to allow for refractive and attenuative corrections. Using clinical data obtained with a breast imaging prototype, the authors applied this method to generate cross‐sectional reflection images of the breast that were corrected using known distributions of sound speed and attenuation obtained from the same data.

Results:

A comparison of images reconstructed with and without the corrections showed varying degrees of improvement. The sound speed correction resulted in sharpening of detail, while the attenuation correction reduced the central darkening caused by path length dependent losses. The improvements appeared to be greatest when dense tissue was involved and the least for fatty tissue. These results are consistent with the expectation that denser tissues lead to both greater refractive effects and greater attenuation.

Conclusions:

Although conventional ultrasound techniques use time‐gain control to correct for attenuation gradients, these corrections lead to artifacts because the true attenuation distribution is not known. The use of constant sound speed leads to additional artifacts that arise from not knowing the sound speed distribution. The authors show that in the context of ultrasound tomography, it is possible to construct reflection images of the breast that correct for inhomogeneous distributions of both sound speed and attenuation.
The effects of compensator and imaging geometry on the distribution of x‐ray scatter in CBCT
Authors: Bootsma G. J. , Verhaegen F. , Jaffray D. A.
Published: February 2011

Purpose:

X‐ray scatter contributes significantly to image degradation in cone‐beam CT (CBCT) reconstructed images in the form of CT number inaccuracy image artifacts and loss of contrast. The need for an understanding of the relationship between the scatter distribution and common imaging parameters (cone angle, air gap, filtration, object size) is an essential element to developing methods for efficiently correcting for the effects of scatter in CBCT. The first objective of this study is to validate the scatter distributions calculated using a CBCT Monte Carlo (MC) model against measured scatter estimates. The second objective is to use the CBCT MC model to investigate the effects of common imaging parameters and bowtie compensators on the resulting scatter distribution.

Methods:

This investigation employs the use of a CBCT MC model, developed using the EGSnrc code, to simulate the primary and scatter fluence arriving at the detector. The simulation is validated against projection images, scatter‐to‐open field ratio (SOR), and scatter‐to‐primary ratio (SPR) measurements taken using a bench‐top CBCT system. The CBCT MC model is used to simulate the scatter distribution arriving at the detector for different cone angles {1.4°, 2.8°, 5.7°, and 11.3°}, source‐to‐axis distances (SADs) {50, 75 and 100 cm}, and axis‐to‐detector distances (ADDs) {9, 18, 30, 44, 56 cm} for both a 16.4 and 30.6 cm diameter water cylinder. The effects of different bowtie filters are also simulated using the CBCT MC model for the aforementioned cylinder sizes.

Results:

Profiles of the simulated and measured projection images agree within 6%. The measurements of the SOR and SPR, taken using beam stop techniques, show good agreement with the simulated results. Limitations of current beam stop techniques in estimating scatter profiles of objects with varying thickness are also demonstrated. A functional relationship between scatter (SOR, SPR) and air gap, cone angle is reported. The bowtie filter was found to have the beneficial effect of decreasing the magnitude of scatter in the projection images (SPR decreased by 56%) as well as altering the spatial distribution of the scatter.

Conclusions:

The CBCT MC model accurately simulates scatter and primary fluences in the CBCT imaging components and geometry. The CBCT MC model provides a useful tool in investigating the effects of varying CBCT imaging parameters on the scatter distribution. Increasing the air gap, decreasing the cone angle, and the use of bowtie filtration were all found to be effective ways to minimize scatter in CBCT. The bowtie filter was particularly effective in both minimizing the magnitude and modifying the spatial distribution of the scattered photons. This observation directs further research in optimizing bowtie filter design in an effort to minimize scatter induced artifacts.
Irradiation of gold nanoparticles by x‐rays: Monte Carlo simulation of dose enhancements and the spatial properties of the secondary electrons production
Authors: Leung Michael K. K. , Chow James C. L. , Chithrani B. Devika , Lee Martin J. G. , Oms Barbara , Jaffray David A.
Published: February 2011

Purpose:

The aim of this study is to understand the characteristics of secondary electrons generated from the interaction of gold nanoparticles (GNPs) with x‐rays as a function of nanoparticle size and beam energy and thereby further the understanding of GNP‐enhanced radiotherapy.

Methods:

The effective range, deflection angle, dose deposition, energy, and interaction processes of electrons produced from the interaction of x‐rays with a GNP were calculated by Monte Carlo simulations. TheGEANT4 code was used to simulate and track electrons generated from a 2, 50, and 100 nm diameter GNP when it is irradiated with a 50 kVp, 250 kVp, cobalt‐60, and 6 MV photon beam in water.

Results:

When a GNP was present, depending on the beam energies used, secondary electron production was increased by 10‐ to 2000‐fold compared to an absence of a GNP. Low‐energy photon beams were much more efficient at interacting with the GNP by two to three orders of magnitude compared to MV energies and increased the deflection angle. GNPs with larger diameters also contributed more dose. The majority of the energy deposition was outside the GNP, rather than self‐absorbed by the nanoparticle. The mean effective range of electron tracks for the beams tested ranged from approximately to 1 mm.

Conclusions:

These simulated results yield important insights concerning the spatial distributions and elevated dose in GNP‐enhanced radiotherapy. The authors conclude that the irradiation of GNP at lower photon energies will be more efficient for cell killing. This conclusion is consistent with published studies.
GPUMCD: A new GPU‐oriented Monte Carlo dose calculation platform
Authors: Hissoiny Sami , Ozell Benoît , Bouchard Hugo , Després Philippe
Published: February 2011

Purpose:

Monte Carlo methods are considered as the gold standard for dosimetric computations in radiotherapy. Their execution time is, however, still an obstacle to the routine use of Monte Carlo packages in a clinical setting. To address this problem, a completely new, and designed from the ground up for the GPU, Monte Carlo dose calculation package for voxelized geometries is proposed:GPUMCD.

Method:

GPUMCDimplements a coupled photon‐electron Monte Carlo simulation for energies in the range of 0.01–20 MeV. An analog simulation of photon interactions is used and a class II condensed history method has been implemented for the simulation of electrons. A new GPU random number generator, some divergence reduction methods, as well as other optimization strategies are also described.GPUMCDwas run on a NVIDIA GTX480, while single threaded implementations of EGSnrc andDPMwere run on an Intel Core i7 860.

Results:

Dosimetric results obtained withGPUMCDwere compared to EGSnrc. In all but one test case, 98% or more of all significant voxels passed the gamma criteria of 2%‐2 mm. In terms of execution speed and efficiency,GPUMCDis more than 900 times faster than EGSnrc and more than 200 times faster thanDPM, a Monte Carlo package aiming fast executions. Absolute execution times of less than 0.3 s are found for the simulation of 1M electrons and 4M photons in water for monoenergetic beams of 15 MeV, including GPU‐CPU memory transfers.

Conclusion:

GPUMCD, a new GPU‐oriented Monte Carlo dose calculation platform, has been compared to EGSnrc andDPMin terms of dosimetric results and execution speed. Its accuracy and speed make it an interesting solution for full Monte Carlo dose calculation in radiation oncology.
Characterization of a gated fiber‐optic‐coupled detector for application in clinical electron beam dosimetry
Authors: Tanyi James A. , Nitzling Kevin D. , Lodwick Camille J. , Huston Alan L. , Justus Brian L.
Published: February 2011

Purpose:

Assessment of the fundamental dosimetric characteristics of a novel gated fiber‐optic‐coupled dosimetry system for clinical electron beam irradiation.

Methods:

The response of fiber‐optic‐coupled dosimetry system to clinical electron beam, with nominal energy range of 6–20 MeV, was evaluated for reproducibility, linearity, and output dependence on dose rate, dose per pulse, energy, and field size. The validity of the detector system's response was assessed in correspondence with a reference ionization chamber.

Results:

The fiber‐optic‐coupled dosimetry system showed little dependence to dose rate variations (coefficient of variation ±0.37%) and dose per pulse changes (with 0.54% of reference chamber measurements). The reproducibility of the system was ±0.55% for dose fractions of. Energy dependence was within ±1.67% relative to the reference ionization chamber for the 6–20 MeV nominal electron beam energy range. The system exhibited excellent linear response compared to reference ionization chamber in the dose range of 1–1000 cGy. The output factors were within ±0.54% of the corresponding reference ionization chamber measurements.

Conclusions:

The dosimetric properties of the gated fiber‐optic‐coupled dosimetry system compare favorably to the corresponding reference ionization chamber measurements and show considerable potential for applications in clinical electron beam radiotherapy.
Multimodal image registration using IECC as the similarity measure
Authors: Itou Takeshi , Shinohara Hiroyuki , Sakaguchi Kazuya , Hashimoto Takeyuki , Yokoi Takashi , Souma Tsutomu
Published: February 2011

Purpose:

The registration of images from positron emission tomography (PET) to those from magnetic resonance imaging (MRI) using mutual information is usually effective, but fails occasionally because of small region of overlap, low‐activity defects in the PET image, difference in spatial resolution, etc. In this article, the authors propose the pixel‐based individual entropy correlation coefficient (IECC) as a new, more accurate and more robust registration criterion.

Methods:

The authors compare it to the current criteria: Mutual information (MI), normalized mutual information (NMI), and the entropy correlation coefficient (ECC). The anatomical region to be registered was the head. A rigid‐body registration was used; no deformation was employed. The authors established the effectiveness of IECC by both simulated data and clinical studies using brain fluorodeoxyglucose (FDG) PET and MRI. Both a normal‐activity FDG model and a FDG model with a perfusion defect were used for the PET image. Reconstruction by both filtered backprojection and by ordered subset‐expectation maximization was investigated.

Results:

The mean errors and SDs of IECC were for translation and for rotation in clinical PET. Those of MI, NMI, and ECC were , , and for translations and , , and for rotations. The mean errors and SDs of IECC were for translation and for rotation in clinical PET model with a 30% perfusion defect. Those of MI, NMI, and ECC were , , and for translations and , , and for rotations. The mean errors and SDs of IECC were for translation and for rotation in clinical PET model with a 50% perfusion defect. Those of MI, NMI, and ECC were , , and for translations and , , and for rotations. The significant differences between IECC and each of the other three criteria were found for displacement misregistration in almost all parameters .

Conclusions:

Accuracy of the IECC criterion was higher than that of the other criteria, usually in a statistically significant way.
Localizing intracavitary brachytherapy applicators from cone‐beam CT x‐ray projections via a novel iterative forward projection matching algorithm
Authors: Pokhrel Damodar , Murphy Martin J. , Todor Dorin A. , Weiss Elisabeth , Williamson Jeffrey F.
Published: February 2011

Purpose:

To present a novel method for reconstructing the 3D pose (position and orientation) of radio‐opaque applicators of known but arbitrary shape from a small set of 2D x‐ray projections in support of intraoperative brachytherapy planning.

Methods:

The generalized iterative forward projection matching (gIFPM) algorithm finds the six degree‐of‐freedom pose of an arbitrary rigid object by minimizing the sum‐of‐squared‐intensity differences (SSQD) between the computed and experimentally acquired autosegmented projection of the objects. Starting with an initial estimate of the object's pose, gIFPM iteratively refines the pose parameters (3D position and three Euler angles) until the SSQD converges. The object, here specialized to a Fletcher–Weeks intracavitary brachytherapy (ICB) applicator, is represented by a fine mesh of discrete points derived from complex combinatorial geometric models of the actual applicators. Three pairs of computed and measured projection images with known imaging geometry are used. Projection images of an intrauterine tandem and colpostats were acquired from an ACUITY cone‐beam CT digital simulator. An image postprocessing step was performed to create blurred binary applicators only images. To quantify gIFPM accuracy, the reconstructed 3D pose of the applicator model was forward projected and overlaid with the measured images and empirically calculated the nearest‐neighbor applicator positional difference for each image pair.

Results:

In the numerical simulations, the tandem and colpostats positions and orientations were estimated with accuracies of 0.6 mm and 2°, respectively. For experimentally acquired images of actual applicators, the residual 2D registration error was less than 1.8 mm for each image pair, corresponding to about 1 mm positioning accuracy at isocenter, with a total computation time of less than 1.5 min on a 1 GHz processor.

Conclusions:

This work describes a novel, accurate, fast, and completely automatic method to localize radio‐opaque applicators of arbitrary shape from measured 2D x‐ray projections. The results demonstrate accuracy while compared against the measured applicator projections. No lateral film is needed. By localizing the applicator internal structure as well as radioactive sources, the effect of intra‐applicator and interapplicator attenuation can be included in the resultant dose calculations. Further validation tests using clinically acquired tandem and colpostats images will be performed for the accurate and robust applicator/sources localization in ICB patients.
CT scanner x‐ray spectrum estimation from transmission measurements
Authors: Duan Xinhui , Wang Jia , Yu Lifeng , Leng Shuai , McCollough Cynthia H.
Published: February 2011

Purpose:

In diagnostic CT imaging, multiple important applications depend on the knowledge of the x‐ray spectrum, including Monte Carlo dose calculations and dual‐energy material decomposition analysis. Due to the high photon flux involved, it is difficult to directly measure spectra from the x‐ray tube of a CT scanner. One potential method for indirect measurement involves estimating the spectrum from transmission measurements. The expectation maximization (EM) method is an accurate and robust method to solve this problem. In this article, this method was evaluated in a commercial CT scanner.

Methods:

Two step‐wedges (polycarbonate and aluminum) were used to produce different attenuation levels. Transmission measurements were performed on the scanner and the measured data from the scanner were exported to an external computer to calculate the spectra. The EM method was applied to solve the equations that represent the attenuation processes of polychromatic x‐ray photons. Estimated spectra were compared to the spectra simulated using a software provided by the manufacturer of the scanner. To test the accuracy of the spectra, a verification experiment was performed using a phantom containing different depths of water. The measured transmission data were compared to the transmission values calculated using the estimated spectra.

Results:

Spectra of 80, 100, 120, and 140 kVp from a dual‐source CT scanner were estimated. The estimated and simulated spectra were well matched. The differences of mean energies were less than 1 keV. In the verification experiment, the measured and calculated transmission values were in excellent agreement.

Conclusions:

Spectrum estimation using transmission data and the EM method is a quantitatively accurate and robust technique to estimate the spectrum of a CT system. This method could benefit studies relying on accurate knowledge of the x‐ray spectra from CT scanner.
Liquid compressibility effects during the collapse of a single cavitating bubble
Authors: Fuster D. , Dopazo C. , Hauke G.
Published: February 2011

The effect of liquid compressibility on the dynamics of a single, spherical cavitating bubble is studied. While it is known that compressibility damps the amplitude of bubble rebounds, the extent to which this effect is accurately captured by weakly compressible versions of the Rayleigh–Plesset equation is unclear. To clarify this issue, partial differential equations governing conservation of mass, momentum, and energy are numerically solved both inside the bubble and in the surrounding compressible liquid. Radiated pressure waves originating at the unsteady bubble interface are directly captured. Results obtained with Rayleigh–Plesset type equations accounting for compressibility effects, proposed by Keller and Miksis [J. Acoust. Soc. Am. 68, 628–633 (1980)], Gilmore, and Tomita and Shima [Bull. JSME 20, 1453–1460 (1977)], are compared with those resulting from the full model. For strong collapses, the solution of the latter reveals that an important part of the energy concentrated during the collapse is used to generate an outgoing pressure wave. For the examples considered in this research, peak pressures are larger than those predicted by Rayleigh–Plesset type equations, whereas the amplitudes of the rebounds are smaller.
Vocal tract changes caused by phonation into a tube: A case study using computer tomography and finite-element modeling
Authors: Vampola Tomáš , Laukkanen Anne-Maria , Horáček Jaromír , Švec Jan G.
Published: February 2011

Phonation into a glass tube is a voice training and therapy method that leads to beneficial effects in voice production. It has not been known, however, what changes occur in the vocal tract during and after the phonation into a tube. This pilot study examined the vocal tract shape in a female subject before, during, and after phonation into a tube using computer tomography (CT). Three-dimensional finite-element models (FEMs) of the vocal tract were derived from the CT images and used to study changes in vocal tract input impedance. When phonating on vowel [a:] the data showed tightened velopharyngeal closure and enlarged cross-sectional areas of the oropharyngeal and oral cavities during and after the tube-phonation. FEM calculations revealed an increased input inertance of the vocal tract and an increased acoustic energy radiated out of the vocal tract after the tube-phonation. The results indicate that the phonation into a tube causes changes in the vocal tract which remain also when the tube is removed. These effects may help improving voice production in patients and voice professionals.
On the stability of adaptation process in active noise control systems
Authors: Ardekani Iman Tabatabaei , Abdulla Waleed H.
Published: February 2011

The stability analysis of the adaptation process, performed by the filtered-x least mean square algorithm on weights of active noise controllers, has not been fully investigated. The main contribution of this paper is conducting a theoretical stability analysis for this process without utilizing commonly used simplifying assumptions regarding the secondary electro-acoustic channel. The core of this analysis is based on the root locus theory. The general rules for constructing the root locus plot of the adaptation process are derived by obtaining root locus parameters, including start points, end points, asymptote lines, and breakaway points. The conducted analysis leads to the derivation of a general upper-bound for the adaptation step-size beyond which the mean weight vector of the active noise controller becomes unstable. Also, this analysis yields the optimum step-size for which the adaptive active noise controller has its fastest dynamic performance. The proposed upper-bound and optimum values apply to general secondary electro-acoustic channels, unlike the commonly used ones which apply to only pure delay channels. The results are found to agree very well with those obtained from numerical analyses and computer simulation experiments.
Quantitative acoustic measurements for characterization of speech and voice disorders in early untreated Parkinson’s disease
Authors: Rusz J. , Cmejla R. , Ruzickova H. , Ruzicka E.
Published: February 2011

An assessment of vocal impairment is presented for separating healthy people from persons with early untreated Parkinson’s disease (PD). This study’s main purpose was to (a) determine whether voice and speech disorder are present from early stages of PD before starting dopaminergic pharmacotherapy, (b) ascertain the specific characteristics of the PD-related vocal impairment, (c) identify PD-related acoustic signatures for the major part of traditional clinically used measurement methods with respect to their automatic assessment, and (d) design new automatic measurement methods of articulation. The varied speech data were collected from 46 Czech native speakers, 23 with PD. Subsequently, 19 representative measurements were pre-selected, and Wald sequential analysis was then applied to assess the efficiency of each measure and the extent of vocal impairment of each subject. It was found that measurement of the fundamental frequency variations applied to two selected tasks was the best method for separating healthy from PD subjects. On the basis of objective acoustic measures, statistical decision-making theory, and validation from practicing speech therapists, it has been demonstrated that 78% of early untreated PD subjects indicate some form of vocal impairment. The speech defects thus uncovered differ individually in various characteristics including phonation, articulation, and prosody.
Temporal weighting functions for interaural time and level differences. II. The effect of binaurally synchronous temporal jitter
Authors: Brown Andrew D. , Stecker G. Christopher
Published: February 2011

Recent work has demonstrated that sensitivity to interaural time differences (ITD) carried by high-rate cochlear implant pulse trains or analogous acoustic signals can be enhanced by imposing random temporal variation on the stimulus rate [see Goupell et al. (2009). J. Acoust. Soc. Am. 126, 2511–2521]. The present study characterized the effect of such “temporal jitter” on normal-hearing listeners’ weighting of ITD and interaural level differences (ILD) applied to brief trains of Gabor clicks (4 kHz center frequency) presented at nominal interclick intervals (ICI) of 1.25 and 2.5 ms. Lateral discrimination judgments were evaluated on the basis of the ITD or ILD carried by individual clicks in each train. Random perturbation of the ICI significantly reduced listeners’ weighting of onset cues for both ITD and ILD discrimination compared to corresponding isochronous conditions, consistent with enhanced sensitivity to post-onset binaural cues in jittered stimuli, although the reduction of onset weighting was not statistically significant at 1.25 ms ICI. An additional analysis suggested greater weighting of ITD or ILD presented following lengthened versus shortened ICI, although weights for such “gaps” and “squeezes” were comparable to other post-onset weights. Results are discussed in terms of binaural information available in jittered versus isochronous stimuli.
Saxophonists tune vocal tract resonances in advanced performance techniques
Authors: Chen Jer-Ming , Smith John , Wolfe Joe
Published: February 2011

The acoustical impedance spectrum was measured in the mouths of saxophonists while they played. During bugling and while playing in the very high or altissimo range, experienced players tune a strong, but relatively broad, peak in the tract impedance to select which peak in the bore impedance will determine the note. Less experienced players are unable to produce resonances with impedance peaks comparable in magnitude to those of the bore and consequently are unable to play these notes. Experienced players can also tune their tracts to select which combinations of notes are played simultaneously in multiphonics or chords, and to produce pitch bending, a technique in which notes are produced at frequencies far from those of the peak of impedance of the instrument bore. However, in normal playing in the standard range, there is no consistent tuning of the tract resonances. The playing frequency, in all cases, lies close to the peak in the impedance of the reed in parallel with the series combination of the impedances measured in the mouth and the instrument bore on either side of the reed (ZMouth + ZBore) ∥ ZReed.
Ensemble statistics of active and reactive sound intensity in reverberation rooms
Authors: Jacobsen Finn , Molares Alfonso Rodríguez
Published: February 2011

This paper examines fundamental statistical properties of the active and reactive sound intensity in reverberant enclosures driven with pure tones. The existing theory for sound intensity in a diffuse sound field, which is based on Waterhouse’s random wave model and therefore limited to the region of high modal overlap, is extended to the region of low modal overlap by taking account of the random fluctuations of the sound power emitted by the source that generates the sound field. The validity of the extended model is confirmed by experimental and numerical results.