Ziad Abou Saleh - Profile on Academia.edu (original) (raw)
Papers by Ziad Abou Saleh
Journal of Contemporary Brachytherapy, 2020
Purpose AccuBoost is a complex non-invasive brachytherapy procedure for breast treatment. This te... more Purpose AccuBoost is a complex non-invasive brachytherapy procedure for breast treatment. This technique requires a radiation oncologist to manually select applicator grid position and size by overlaying transparencies over a mammographic image to encompass surgical clips and resected tumor bed. An algorithm was developed in MATLAB™ to automate the selection of round applicators based on surgical clip position. Material and methods A total of 42 mammograms belonging to 10 patients were retrospectively analyzed. Images were pre-processed by masking imprinted localization grid and regions around the grid. A threshold was applied to isolate high-intensity pixels and generate a binary image. A set of morphological operations including region dilation, filling, clearing border structures, and erosion were performed to segment the different regions. A support vector machine classification model was trained to categorize segmented regions as either surgical clips or miscellaneous objects b...
Journal of applied clinical medical physics, Jan 13, 2018
The deep inspiration breath hold (DIBH) and prone (P) position are two common heart-sparing techn... more The deep inspiration breath hold (DIBH) and prone (P) position are two common heart-sparing techniques for external-beam radiation treatment of left-sided breast cancer patients. Clinicians select the position that is deemed to be better for tissue sparing based on their experience. This approach, however, is not always optimum and consistent. In response to this, we develop a quantitative tool that predicts the optimal positioning for the sake of organs at risk (OAR) sparing. Sixteen left-sided breast cancer patients were considered in the study, each received CT scans in the supine free breathing, supine DIBH, and prone positions. Treatment plans were generated for all positions. A patient was classified as DIBH or P using two different criteria: if that position yielded (1) lower heart dose, or (2) lower weighted OAR dose. Ten anatomical features were extracted from each patient's data, followed by the principal component analysis. Sequential forward feature selection was imp...
SU‐E‐J‐62: Estimating Plausible Treatment Course Dose Distributions by Accounting for Registration Uncertainty and Organ Motion
Medical Physics, 2014
Purpose:Dose accumulation following deformable image registration (DIR) is challenging. In this s... more Purpose:Dose accumulation following deformable image registration (DIR) is challenging. In this study, we used a statistical sampling approach, which takes into account both DIR uncertainties and patient‐specific organ motion, to study the distribution of possible true dose distributions.Methods:The study included ten patients (six CT scans/patient) treated with radiotherapy for prostate cancer. For each patient, the planned dose was re‐calculated on the repeated geometries, following rigid registration based on fiducial markers. The dose re‐calculated on the first CT served as our snapshot dose distribution (D1) and the average of the first five repeat scans as our treatment course reference dose distribution (Dref). Patient‐specific motion and DIR‐uncertainties, at each voxel in CT1, were assessed using a previously developed DIR performance measure, the distance discordance metric (DDM). To sample the distribution of possible true, predicted dose distributions (Dpred), we resampl...
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 2017
Segmentation of prostate Cone Beam CT (CBCT) images is an essential step towards real-time adapti... more Segmentation of prostate Cone Beam CT (CBCT) images is an essential step towards real-time adaptive radiotherapy (ART). It is challenging for Calypso patients, as more artifacts generated by the beacon transponders are present on the images. We herein propose a novel wavelet-based segmentation algorithm for rectum, bladder, and prostate of CBCT images with implanted Calypso transponders. For a given CBCT, a Moving Window-Based Double Haar (MWDH) transformation is applied first to obtain the wavelet coefficients. Based on a user defined point in the object of interest, a cluster algorithm based adaptive thresholding is applied to the low frequency components of the wavelet coefficients, and a Lee filter theory based adaptive thresholding is applied on the high frequency components. For the next step, the wavelet reconstruction is applied to the thresholded wavelet coefficients. A binary (segmented) image of the object of interest is therefore obtained. 5 hypofractionated Calypso prostate patients with daily CBCT were studied. DICE, Sensitivity, Inclusiveness and ∆V were used to evaluate the segmentation result.
Physics and Imaging in Radiation Oncology, 2017
Background and purpose: In this study we investigated the ability of textures from T1-weighted MR... more Background and purpose: In this study we investigated the ability of textures from T1-weighted MRI scans post-contrast (T1w post ) to identify the critical muscle(s) for radiation-induced trismus. The study included ten cases (Trismus: !Grade 1), and ten age-sex-tumor-loca tion-and-stage-matched controls treated with intensity-modulated radiotherapy to 70 Gy@2.12 Gy in 2005-2009. Trismus status and T1w Post were conducted within one year post-radiotherapy. For the masseter, lateral and medial pterygoids, and temporalis (M/LP/MP/T), 24 textures were extracted (Grey Level Co-Occurrence (GLCM), Histogram, and Shape). Univariate logistic regression with Bootstrapping (1000 populations) was applied to compare the muscle mean dose (Dmean) and textures between cases and controls (ipsilateral muscles); candidate predictors were suggested by an average p 0.20 across all Bootstrap populations. Results: Dmean to M/LP/MP (p = 0.03/0.14/0.09), one MP/T (p = 0.12/0.17), and three M (p = 0.14-0.19) textures were candidate predictors. Three of these textures were GLCM-and two Histogram textures with the former being generally higher and the latter lower for cases compared to controls. The Dmean to M and MP, and Haralick Correlation (GLCM) of MP presented with the best discriminative ability (area under the receiver-operating characteristic curve: 0.85, 0.77, and 0.78), and the correlation between Dmean and this texture was weak (Spearman's rank correlation coefficient: 0.26-0.27). Conclusions: Our exploratory study points towards an interplay between the dose to the masseter, and the medial pterygoid together with the local relationship between the mean MRI intensity relative to its variance of the medial pterygoid for radiation-induced trismus. This opens up for exploration of this interplay within the radiation-induced trismus etiology in the larger multi-institutional setting.
Physics in medicine and biology, Jan 21, 2016
Deformable image registration (DIR) is essential for adaptive radiotherapy (RT) for tumor sites s... more Deformable image registration (DIR) is essential for adaptive radiotherapy (RT) for tumor sites subject to motion, changes in tumor volume, as well as changes in patient normal anatomy due to weight loss. Several methods have been published to evaluate DIR-related uncertainties but they are not widely adopted. The aim of this study was, therefore, to evaluate intra-patient DIR for two highly deformable organs-the bladder and the rectum-in prostate cancer RT using a quantitative metric based on multiple image registration, the distance discordance metric (DDM). Voxel-by-voxel DIR uncertainties of the bladder and rectum were evaluated using DDM on weekly CT scans of 38 subjects previously treated with RT for prostate cancer (six scans/subject). The DDM was obtained from group-wise B-spline registration of each patient's collection of repeat CT scans. For each structure, registration uncertainties were derived from DDM-related metrics. In addition, five other quantitative measures,...
Radiotherapy and Oncology, 2011
Acta Oncologica, 2015
Background. To investigate the dose-volume factors in mastication muscles that are implicated as ... more Background. To investigate the dose-volume factors in mastication muscles that are implicated as possible causes of trismus in patients following treatment with intensity-modulated radiotherapy (IMRT) and concurrent chemotherapy for head and neck cancers. Material and methods. All evaluable patients treated at our institution between January 2004 and April 2009 with chemotherapy and IMRT for squamous cell cancers of the oropharynx, nasopharynx, hypopharynx or larynx were included in this analysis (N ϭ 421). Trismus was assessed using CTCAE 4.0. Bi-lateral masseter, temporalis, lateral pterygoid and medial pterygoid muscles were delineated on axial computed tomography (CT) treatment planning images, and dose-volume parameters were extracted to investigate univariate and multimetric correlations. Results. Forty-six patients (10.9%) were observed to have chronic trismus of grade 1 or greater. From analysis of baseline patient characteristics, toxicity correlated with primary site and patient age. From dose-volume analysis, the steepest dose thresholds and highest correlations were seen for mean dose to ipsilateral masseter (Spearman ' s rank correlation coeffi cient Rs ϭ 0.25) and medial pterygoid (Rs ϭ 0.23) muscles. Lyman-Kutcher-Burman modeling showed highest correlations for the same muscles. The best correlation for multimetric logistic regression modeling was withV 68Gy to the ipsilateral medial pterygoid (Rs ϭ 0.29). Conclusion. Chemoradiation-induced trismus remains a problem particularly for patients with oropharyngeal carcinoma. Strong dose-volume correlations support the hypothesis that limiting dose to the ipsilateral masseter muscle and, in particular, the medial pterygoid muscle may reduce the likelihood of trismus.
Atmospheric Science-L22813-Runaway breakdown in the Jovian atmospheres (DOI 10.1029/2006GL027633)
A Ground-Based Campaign in Search of Terrestrial Gamma-ray Flashes Associated with Thunderclouds and Lightning
Terrestrial Gamma-ray Flashes (TGFs) are intense bursts of gamma-rays first observed from space u... more Terrestrial Gamma-ray Flashes (TGFs) are intense bursts of gamma-rays first observed from space using the BATSE instrument onboard the Compton Gamma Ray Observatory. Recent measurements from the RHESSI spacecraft, along with modeling, show that these flashes most likely originate from altitudes between 15 and 21 km, making it difficult to detect such events on the ground due to atmospheric attenuation. However, in 2004, Dwyer et al. reported a gamma-ray burst at ground level during the initial stage of a rocket-triggered lightning that had a similar energy spectrum and time duration to TGFs. These results suggest that the processes that produce TGFs may also occur at lower altitudes within thunderclouds, beamed downwards instead of upwards like TGFs observed from space, making it possible to observe such events on the ground. In 2009, we launched a ground campaign to search for such TGF-like gamma-ray events during thunderstorms in coordination with ADELE (Airborne Detector for Ener...
Physics in Medicine and Biology, 2014
Previous methods to estimate the inherent accuracy of deformable image registration (DIR) have ty... more Previous methods to estimate the inherent accuracy of deformable image registration (DIR) have typically been performed relative to a known ground truth, such as tracking of anatomic landmarks or known deformations in a physical or virtual phantom. In this study, we propose a new approach to estimate the spatial geometric uncertainty of DIR using statistical sampling techniques that can be applied to the resulting deformation vector fields (DVFs) for a given registration. The proposed DIR performance metric, the distance discordance metric (DDM), is based on the variability in the distance between corresponding voxels from different images, which are co-registered to the same voxel at location (X) in an arbitrarily chosen "reference" image. The DDM value, at location (X) in the reference image, represents the mean dispersion between voxels, when these images are registered to other images in the image set. The method requires at least four registered images to estimate the uncertainty of the DIRs, both for inter-and intra-patient DIR. To validate the proposed method, we generated an image set by deforming a software phantom with known DVFs. The registration error was computed at each voxel in the "reference" phantom and then compared to DDM, inverse consistency error (ICE), and transitivity error (TE) over the entire phantom. The DDM showed a higher Pearson correlation (R p ) with the actual error (R p ranged from 0.6 to 0.9) in comparison with ICE and TE (R p ranged from 0.2 to 0.8). In the resulting spatial DDM map, regions with distinct intensity gradients had a lower discordance and therefore, less variability relative to regions with uniform intensity. Subsequently, we applied DDM for intra-patient DIR in an image set of 10 longitudinal computed tomography (CT) scans of one prostate cancer patient and for inter-patient DIR in an image set of 10 planning CT scans of different head and neck cancer patients. For both intra-and inter-patient DIR, the spatial DDM map showed large
Medical Physics, 2012
Right: Perfect Registration, Left: Gridded MirrorScope -Notice that each circular region within t... more Right: Perfect Registration, Left: Gridded MirrorScope -Notice that each circular region within the grid is symmetric about the vertical axis. Right: Imperfect Registration, Left: Gridded MirrorScope -Notice that each circular region within the grid is NOT symmetric about the vertical axis. Since the moving image was systematically shifted, all circular regions show asymmetry.
SU-C-BRB-02: Exploring the Correlation Between 3D Spatial Dose Distribution and Toxicity in Normal Tissue
Medical Physics, 2012
ABSTRACT Purpose: To explore the correlation between spatial dose distribution and toxicity of no... more ABSTRACT Purpose: To explore the correlation between spatial dose distribution and toxicity of normal tissue by mapping 3D dose distribution onto a reference patient. Methods: In order to facilitate the direct correlation between dose to a certain tissue sub-volume and toxicity, 3D dose distributions of a patient cohort are deformed onto a single reference patient using deformable image registration. Spatial Spearman rank correlations between warped dose and toxicity are then computed on a point-by-point basis over the entire voxel space of the reference patient. We illustrate this approach using a cohort of 37 right-sided H&N cancers of the oropharynx regarding the endpoint of trismus. Patients were treated with definitive IMRT and concurrent chemotherapy with a prescription dose of 70 Gy between Jan. 2004 and April 2009 at MSKCC with a median follow-up time of 34 months (range, 6-68). 12 patients developed trismus (Grade >=1). Dose volume histograms (DVH) of the mastication muscles were also exported to perform logistic regression. Results: The standard logistic regression model based on DVH derived parameters for contoured muscles provided a moderate Spearman correlation (Rs=0.45, p<0.05). Meanwhile, examining the 3D Spearman map reveals a region with high correlation (Rs=0.58, p<0.001). Interestingly, a close up view shows that this potentially 'radio-sensitive' region is located on the contralateral side at the attachment point of the medial and lateral pterygoid muscles with the pterygoid plate. Conclusions: This study demonstrates the feasibility of studying the spatial correlation between dose and toxicity in normal tissues. The validity of this method was demonstrated in H&N patients. This technique preserves the spatial information of the dose distribution and provides an unbiased approach to identify critical anatomic structures since it does not require prior assumptions about the organs at risk. In addition, this method is generic and can be extended to study other complication endpoints. Partially supported by NIH grant ROI CA85181.
Journal of Geophysical Research: Atmospheres, 2010
Using an eight‐station array of electric field derivative (dE/dt) sensors and colocated NaI X‐ray... more Using an eight‐station array of electric field derivative (dE/dt) sensors and colocated NaI X‐ray detectors, we have obtained 3‐D RF source locations during the leaders and attachment processes of three first strokes initiated by stepped leaders in natural cloud‐to‐ground lightning and one stroke initiated by a dart‐stepped leader in a rocket‐and‐wire triggered flash. Stepped leader and dart‐stepped leader dE/dt pulses are tracked from a few hundred meters to a few tens of meters above ground, after which pulses of different characteristics than the step pulses are observed to occur at lower altitudes. These postleader pulses include: (1) the “leader burst,” a group of pulses in the dE/dt waveform occurring just prior to the slow front in the corresponding return‐stroke electric field waveform; (2) dE/dt pulses occurring during the slow front; and (3) the fast‐transition or dominant dE/dt pulse that is usually associated with the rapid transition to peak in the return‐stroke electri...
Journal of Geophysical Research: Atmospheres, 2009
The Thunderstorm Energetic Radiation Array (TERA) is located at the University of Florida, Florid... more The Thunderstorm Energetic Radiation Array (TERA) is located at the University of Florida, Florida Tech International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida. The array includes forty‐five 7.6‐cm‐diameter NaI/photomultiplier tube detectors enclosed in 24 separate aluminum boxes that shield the detectors from light, moisture, and RF noise. The array covers the ∼1 km2 ICLRT facility, centered on the rocket launch tower, used to trigger lightning. From 2005 to 2007, TERA recorded seven rocket‐triggered lightning flashes. In this paper we present an analysis of the X‐ray emission of three of these flashes. The X‐ray emission is observed to occur during the dart leader phase of each stroke, just prior to the time of the return stroke. Significant X‐rays are observed on all the detectors to a distance of 500 m from the lightning channel for times up to 200 μs prior to the start of the return stroke. Using Monte Carlo simulations to model the X‐ray propa...
Journal of Geophysical Research, 2008
We present a detailed investigation of X-ray emission from long laboratory sparks in air at atmos... more We present a detailed investigation of X-ray emission from long laboratory sparks in air at atmospheric pressure. We studied 231 sparks of both polarities using a 1-MV Marx generator with gap lengths ranging from 10 to 140 cm. The X rays generated by the discharges were measured using five NaI/PMT detectors plus one plastic scintillator/PMT detector, all enclosed in 0.32-cm-thick aluminum boxes. X-ray emission was observed to accompany about 70% of negative polarity sparks and about 10% of positive polarity sparks. For the negative sparks, X-ray emission was observed to occur at two distinct times during the discharge: (1) near the peak voltage, specifically, about 1 ms before the voltage across the gap collapsed, and (2) near the time of the peak current through the gap, during the gap voltage collapse. Using collimators we determined that the former emission emanated from the gap, while the latter appeared to originate from above the gap in the space over the high-voltage components. During individual sparks, the total energy of the X rays that was deposited in a single detector sometimes exceeded 50 MeV, and the maximum energy of individual photons in some cases exceeded 300 keV. X-ray emission near the peak voltage was observed for a wide range of electrode geometries, including 12-cm-diameter spherical electrodes, a result suggesting that the X-ray emission was the result of processes occurring within the air gap and not just due to high electric fields at the electrode.
Journal of Geophysical Research, 2011
On 21 August 2009, the Airborne Detector for Energetic Lightning Emissions (ADELE), an array of s... more On 21 August 2009, the Airborne Detector for Energetic Lightning Emissions (ADELE), an array of six gamma-ray detectors, detected a brief burst of gamma rays while flying aboard a Gulfstream V jet near two active thunderstorm cells. The duration and spectral characteristics of the event are consistent with the terrestrial gamma ray flashes (TGFs) seen by instruments in low Earth orbit. A long-duration, complex +IC flash was taking place in the nearer cell at the same time, at a distance of ∼10 km from the plane. The sferics that are probably associated with this flash extended over 54 ms and included several ULF pulses corresponding to charge moment changes of up to 30 C km, this value being in the lower half of the range of sferics associated with TGFs seen from space. Monte Carlo simulations of gamma ray propagation in the Earth's atmosphere show that a TGF of normal intensity would, at this distance, have produced a gamma ray signal in ADELE of approximately the size and spectrum that was actually observed. We conclude that this was the first detection of a TGF from an aircraft. We show that because of the distance, ADELE's directional and spectral capabilities could not strongly constrain the source altitude of the TGF but that such constraints would be possible for TGFs detected at closer range.
Journal of Geophysical Research: Atmospheres, 2010
Using recent X‐ray and gamma‐ray observations of terrestrial gamma‐ray flashes (TGFs) from spacec... more Using recent X‐ray and gamma‐ray observations of terrestrial gamma‐ray flashes (TGFs) from spacecraft and of natural and rocket‐triggered lightning from the ground, along with detailed models of energetic particle transport, we calculate the fluence (integrated flux) of high‐energy (million electronvolt) electrons, X rays, and gamma rays likely to be produced inside or near thunderclouds in high electric field regions. We find that the X‐ray/gamma‐ray fluence predicted for lightning leaders propagating inside thunderclouds agrees well with the fluence calculated for TGFs, suggesting a possible link between these two phenomena. Furthermore, based on reasonable meteorological assumptions about the magnitude and extent of the electric fields, we estimate that the fluence of high‐energy runaway electrons can reach biologically significant levels at aircraft altitudes. If an aircraft happened to be in or near the high‐field region when either a lightning discharge or a TGF event is occur...
International Journal of Radiation Oncology*Biology*Physics, 2012
Purpose-The severe reduction of salivary function (xerostomia) is a common complication following... more Purpose-The severe reduction of salivary function (xerostomia) is a common complication following radiation therapy for head and neck cancer. Consequently, guidelines to ensure adequate function based on parotid gland tolerance dose-volume parameters have been suggested by the QUANTEC group (1) and by Ortholan et al. (2). We perform a validation test of these guidelines against a prospectively collected dataset and compared to a previously published dataset. Method and Materials-Whole-mouth stimulated salivary flow data from 66 head and neck cancer patients treated with radiotherapy at the British Columbia Cancer Agency (BCCA) were measured, and treatment planning data were abstracted. Flow measurements were collected from 50 patients at 3 months, and 60 patients at 12 month follow-up. Previously published data from a second institution (WUSTL) were used for comparison. A logistic model was used to describe the incidence of grade 4 xerostomia as a function of the mean dose of the spared parotid gland. The rate of correctly predicting the lack of xerostomia (negative predictive value, NPV) was computed for both the QUANTEC constraints and Ortholan et al. (2) recommendation to constrain the total volume of both glands receiving more than 40 Gy to less than 33%. Results-Both data sets showed a rate of xerostomia < 20 % when the mean dose to the leastirradiated parotid gland is kept below 20 Gy. Logistic model parameters for the incidence of xerostomia at 12 months after therapy, based on the least-irradiated gland, were D 50 =32.4 Gy and and γ=0.97. NPVs for QUANTEC guideline were 94% (BCCA data), 90% (WUSTL data). For Ortholan et al. (2) guideline NPVs were 85% (BCCA), and 86% (WUSTL).
Dosimetric Evaluation of Trismus in Head and Neck Cancer Patients following Intensity Modulated Radiation Therapy and Chemotherapy
International Journal of Radiation Oncology*Biology*Physics, 2011
Journal of Contemporary Brachytherapy, 2020
Purpose AccuBoost is a complex non-invasive brachytherapy procedure for breast treatment. This te... more Purpose AccuBoost is a complex non-invasive brachytherapy procedure for breast treatment. This technique requires a radiation oncologist to manually select applicator grid position and size by overlaying transparencies over a mammographic image to encompass surgical clips and resected tumor bed. An algorithm was developed in MATLAB™ to automate the selection of round applicators based on surgical clip position. Material and methods A total of 42 mammograms belonging to 10 patients were retrospectively analyzed. Images were pre-processed by masking imprinted localization grid and regions around the grid. A threshold was applied to isolate high-intensity pixels and generate a binary image. A set of morphological operations including region dilation, filling, clearing border structures, and erosion were performed to segment the different regions. A support vector machine classification model was trained to categorize segmented regions as either surgical clips or miscellaneous objects b...
Journal of applied clinical medical physics, Jan 13, 2018
The deep inspiration breath hold (DIBH) and prone (P) position are two common heart-sparing techn... more The deep inspiration breath hold (DIBH) and prone (P) position are two common heart-sparing techniques for external-beam radiation treatment of left-sided breast cancer patients. Clinicians select the position that is deemed to be better for tissue sparing based on their experience. This approach, however, is not always optimum and consistent. In response to this, we develop a quantitative tool that predicts the optimal positioning for the sake of organs at risk (OAR) sparing. Sixteen left-sided breast cancer patients were considered in the study, each received CT scans in the supine free breathing, supine DIBH, and prone positions. Treatment plans were generated for all positions. A patient was classified as DIBH or P using two different criteria: if that position yielded (1) lower heart dose, or (2) lower weighted OAR dose. Ten anatomical features were extracted from each patient's data, followed by the principal component analysis. Sequential forward feature selection was imp...
SU‐E‐J‐62: Estimating Plausible Treatment Course Dose Distributions by Accounting for Registration Uncertainty and Organ Motion
Medical Physics, 2014
Purpose:Dose accumulation following deformable image registration (DIR) is challenging. In this s... more Purpose:Dose accumulation following deformable image registration (DIR) is challenging. In this study, we used a statistical sampling approach, which takes into account both DIR uncertainties and patient‐specific organ motion, to study the distribution of possible true dose distributions.Methods:The study included ten patients (six CT scans/patient) treated with radiotherapy for prostate cancer. For each patient, the planned dose was re‐calculated on the repeated geometries, following rigid registration based on fiducial markers. The dose re‐calculated on the first CT served as our snapshot dose distribution (D1) and the average of the first five repeat scans as our treatment course reference dose distribution (Dref). Patient‐specific motion and DIR‐uncertainties, at each voxel in CT1, were assessed using a previously developed DIR performance measure, the distance discordance metric (DDM). To sample the distribution of possible true, predicted dose distributions (Dpred), we resampl...
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 2017
Segmentation of prostate Cone Beam CT (CBCT) images is an essential step towards real-time adapti... more Segmentation of prostate Cone Beam CT (CBCT) images is an essential step towards real-time adaptive radiotherapy (ART). It is challenging for Calypso patients, as more artifacts generated by the beacon transponders are present on the images. We herein propose a novel wavelet-based segmentation algorithm for rectum, bladder, and prostate of CBCT images with implanted Calypso transponders. For a given CBCT, a Moving Window-Based Double Haar (MWDH) transformation is applied first to obtain the wavelet coefficients. Based on a user defined point in the object of interest, a cluster algorithm based adaptive thresholding is applied to the low frequency components of the wavelet coefficients, and a Lee filter theory based adaptive thresholding is applied on the high frequency components. For the next step, the wavelet reconstruction is applied to the thresholded wavelet coefficients. A binary (segmented) image of the object of interest is therefore obtained. 5 hypofractionated Calypso prostate patients with daily CBCT were studied. DICE, Sensitivity, Inclusiveness and ∆V were used to evaluate the segmentation result.
Physics and Imaging in Radiation Oncology, 2017
Background and purpose: In this study we investigated the ability of textures from T1-weighted MR... more Background and purpose: In this study we investigated the ability of textures from T1-weighted MRI scans post-contrast (T1w post ) to identify the critical muscle(s) for radiation-induced trismus. The study included ten cases (Trismus: !Grade 1), and ten age-sex-tumor-loca tion-and-stage-matched controls treated with intensity-modulated radiotherapy to 70 Gy@2.12 Gy in 2005-2009. Trismus status and T1w Post were conducted within one year post-radiotherapy. For the masseter, lateral and medial pterygoids, and temporalis (M/LP/MP/T), 24 textures were extracted (Grey Level Co-Occurrence (GLCM), Histogram, and Shape). Univariate logistic regression with Bootstrapping (1000 populations) was applied to compare the muscle mean dose (Dmean) and textures between cases and controls (ipsilateral muscles); candidate predictors were suggested by an average p 0.20 across all Bootstrap populations. Results: Dmean to M/LP/MP (p = 0.03/0.14/0.09), one MP/T (p = 0.12/0.17), and three M (p = 0.14-0.19) textures were candidate predictors. Three of these textures were GLCM-and two Histogram textures with the former being generally higher and the latter lower for cases compared to controls. The Dmean to M and MP, and Haralick Correlation (GLCM) of MP presented with the best discriminative ability (area under the receiver-operating characteristic curve: 0.85, 0.77, and 0.78), and the correlation between Dmean and this texture was weak (Spearman's rank correlation coefficient: 0.26-0.27). Conclusions: Our exploratory study points towards an interplay between the dose to the masseter, and the medial pterygoid together with the local relationship between the mean MRI intensity relative to its variance of the medial pterygoid for radiation-induced trismus. This opens up for exploration of this interplay within the radiation-induced trismus etiology in the larger multi-institutional setting.
Physics in medicine and biology, Jan 21, 2016
Deformable image registration (DIR) is essential for adaptive radiotherapy (RT) for tumor sites s... more Deformable image registration (DIR) is essential for adaptive radiotherapy (RT) for tumor sites subject to motion, changes in tumor volume, as well as changes in patient normal anatomy due to weight loss. Several methods have been published to evaluate DIR-related uncertainties but they are not widely adopted. The aim of this study was, therefore, to evaluate intra-patient DIR for two highly deformable organs-the bladder and the rectum-in prostate cancer RT using a quantitative metric based on multiple image registration, the distance discordance metric (DDM). Voxel-by-voxel DIR uncertainties of the bladder and rectum were evaluated using DDM on weekly CT scans of 38 subjects previously treated with RT for prostate cancer (six scans/subject). The DDM was obtained from group-wise B-spline registration of each patient's collection of repeat CT scans. For each structure, registration uncertainties were derived from DDM-related metrics. In addition, five other quantitative measures,...
Radiotherapy and Oncology, 2011
Acta Oncologica, 2015
Background. To investigate the dose-volume factors in mastication muscles that are implicated as ... more Background. To investigate the dose-volume factors in mastication muscles that are implicated as possible causes of trismus in patients following treatment with intensity-modulated radiotherapy (IMRT) and concurrent chemotherapy for head and neck cancers. Material and methods. All evaluable patients treated at our institution between January 2004 and April 2009 with chemotherapy and IMRT for squamous cell cancers of the oropharynx, nasopharynx, hypopharynx or larynx were included in this analysis (N ϭ 421). Trismus was assessed using CTCAE 4.0. Bi-lateral masseter, temporalis, lateral pterygoid and medial pterygoid muscles were delineated on axial computed tomography (CT) treatment planning images, and dose-volume parameters were extracted to investigate univariate and multimetric correlations. Results. Forty-six patients (10.9%) were observed to have chronic trismus of grade 1 or greater. From analysis of baseline patient characteristics, toxicity correlated with primary site and patient age. From dose-volume analysis, the steepest dose thresholds and highest correlations were seen for mean dose to ipsilateral masseter (Spearman ' s rank correlation coeffi cient Rs ϭ 0.25) and medial pterygoid (Rs ϭ 0.23) muscles. Lyman-Kutcher-Burman modeling showed highest correlations for the same muscles. The best correlation for multimetric logistic regression modeling was withV 68Gy to the ipsilateral medial pterygoid (Rs ϭ 0.29). Conclusion. Chemoradiation-induced trismus remains a problem particularly for patients with oropharyngeal carcinoma. Strong dose-volume correlations support the hypothesis that limiting dose to the ipsilateral masseter muscle and, in particular, the medial pterygoid muscle may reduce the likelihood of trismus.
Atmospheric Science-L22813-Runaway breakdown in the Jovian atmospheres (DOI 10.1029/2006GL027633)
A Ground-Based Campaign in Search of Terrestrial Gamma-ray Flashes Associated with Thunderclouds and Lightning
Terrestrial Gamma-ray Flashes (TGFs) are intense bursts of gamma-rays first observed from space u... more Terrestrial Gamma-ray Flashes (TGFs) are intense bursts of gamma-rays first observed from space using the BATSE instrument onboard the Compton Gamma Ray Observatory. Recent measurements from the RHESSI spacecraft, along with modeling, show that these flashes most likely originate from altitudes between 15 and 21 km, making it difficult to detect such events on the ground due to atmospheric attenuation. However, in 2004, Dwyer et al. reported a gamma-ray burst at ground level during the initial stage of a rocket-triggered lightning that had a similar energy spectrum and time duration to TGFs. These results suggest that the processes that produce TGFs may also occur at lower altitudes within thunderclouds, beamed downwards instead of upwards like TGFs observed from space, making it possible to observe such events on the ground. In 2009, we launched a ground campaign to search for such TGF-like gamma-ray events during thunderstorms in coordination with ADELE (Airborne Detector for Ener...
Physics in Medicine and Biology, 2014
Previous methods to estimate the inherent accuracy of deformable image registration (DIR) have ty... more Previous methods to estimate the inherent accuracy of deformable image registration (DIR) have typically been performed relative to a known ground truth, such as tracking of anatomic landmarks or known deformations in a physical or virtual phantom. In this study, we propose a new approach to estimate the spatial geometric uncertainty of DIR using statistical sampling techniques that can be applied to the resulting deformation vector fields (DVFs) for a given registration. The proposed DIR performance metric, the distance discordance metric (DDM), is based on the variability in the distance between corresponding voxels from different images, which are co-registered to the same voxel at location (X) in an arbitrarily chosen "reference" image. The DDM value, at location (X) in the reference image, represents the mean dispersion between voxels, when these images are registered to other images in the image set. The method requires at least four registered images to estimate the uncertainty of the DIRs, both for inter-and intra-patient DIR. To validate the proposed method, we generated an image set by deforming a software phantom with known DVFs. The registration error was computed at each voxel in the "reference" phantom and then compared to DDM, inverse consistency error (ICE), and transitivity error (TE) over the entire phantom. The DDM showed a higher Pearson correlation (R p ) with the actual error (R p ranged from 0.6 to 0.9) in comparison with ICE and TE (R p ranged from 0.2 to 0.8). In the resulting spatial DDM map, regions with distinct intensity gradients had a lower discordance and therefore, less variability relative to regions with uniform intensity. Subsequently, we applied DDM for intra-patient DIR in an image set of 10 longitudinal computed tomography (CT) scans of one prostate cancer patient and for inter-patient DIR in an image set of 10 planning CT scans of different head and neck cancer patients. For both intra-and inter-patient DIR, the spatial DDM map showed large
Medical Physics, 2012
Right: Perfect Registration, Left: Gridded MirrorScope -Notice that each circular region within t... more Right: Perfect Registration, Left: Gridded MirrorScope -Notice that each circular region within the grid is symmetric about the vertical axis. Right: Imperfect Registration, Left: Gridded MirrorScope -Notice that each circular region within the grid is NOT symmetric about the vertical axis. Since the moving image was systematically shifted, all circular regions show asymmetry.
SU-C-BRB-02: Exploring the Correlation Between 3D Spatial Dose Distribution and Toxicity in Normal Tissue
Medical Physics, 2012
ABSTRACT Purpose: To explore the correlation between spatial dose distribution and toxicity of no... more ABSTRACT Purpose: To explore the correlation between spatial dose distribution and toxicity of normal tissue by mapping 3D dose distribution onto a reference patient. Methods: In order to facilitate the direct correlation between dose to a certain tissue sub-volume and toxicity, 3D dose distributions of a patient cohort are deformed onto a single reference patient using deformable image registration. Spatial Spearman rank correlations between warped dose and toxicity are then computed on a point-by-point basis over the entire voxel space of the reference patient. We illustrate this approach using a cohort of 37 right-sided H&N cancers of the oropharynx regarding the endpoint of trismus. Patients were treated with definitive IMRT and concurrent chemotherapy with a prescription dose of 70 Gy between Jan. 2004 and April 2009 at MSKCC with a median follow-up time of 34 months (range, 6-68). 12 patients developed trismus (Grade >=1). Dose volume histograms (DVH) of the mastication muscles were also exported to perform logistic regression. Results: The standard logistic regression model based on DVH derived parameters for contoured muscles provided a moderate Spearman correlation (Rs=0.45, p<0.05). Meanwhile, examining the 3D Spearman map reveals a region with high correlation (Rs=0.58, p<0.001). Interestingly, a close up view shows that this potentially 'radio-sensitive' region is located on the contralateral side at the attachment point of the medial and lateral pterygoid muscles with the pterygoid plate. Conclusions: This study demonstrates the feasibility of studying the spatial correlation between dose and toxicity in normal tissues. The validity of this method was demonstrated in H&N patients. This technique preserves the spatial information of the dose distribution and provides an unbiased approach to identify critical anatomic structures since it does not require prior assumptions about the organs at risk. In addition, this method is generic and can be extended to study other complication endpoints. Partially supported by NIH grant ROI CA85181.
Journal of Geophysical Research: Atmospheres, 2010
Using an eight‐station array of electric field derivative (dE/dt) sensors and colocated NaI X‐ray... more Using an eight‐station array of electric field derivative (dE/dt) sensors and colocated NaI X‐ray detectors, we have obtained 3‐D RF source locations during the leaders and attachment processes of three first strokes initiated by stepped leaders in natural cloud‐to‐ground lightning and one stroke initiated by a dart‐stepped leader in a rocket‐and‐wire triggered flash. Stepped leader and dart‐stepped leader dE/dt pulses are tracked from a few hundred meters to a few tens of meters above ground, after which pulses of different characteristics than the step pulses are observed to occur at lower altitudes. These postleader pulses include: (1) the “leader burst,” a group of pulses in the dE/dt waveform occurring just prior to the slow front in the corresponding return‐stroke electric field waveform; (2) dE/dt pulses occurring during the slow front; and (3) the fast‐transition or dominant dE/dt pulse that is usually associated with the rapid transition to peak in the return‐stroke electri...
Journal of Geophysical Research: Atmospheres, 2009
The Thunderstorm Energetic Radiation Array (TERA) is located at the University of Florida, Florid... more The Thunderstorm Energetic Radiation Array (TERA) is located at the University of Florida, Florida Tech International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida. The array includes forty‐five 7.6‐cm‐diameter NaI/photomultiplier tube detectors enclosed in 24 separate aluminum boxes that shield the detectors from light, moisture, and RF noise. The array covers the ∼1 km2 ICLRT facility, centered on the rocket launch tower, used to trigger lightning. From 2005 to 2007, TERA recorded seven rocket‐triggered lightning flashes. In this paper we present an analysis of the X‐ray emission of three of these flashes. The X‐ray emission is observed to occur during the dart leader phase of each stroke, just prior to the time of the return stroke. Significant X‐rays are observed on all the detectors to a distance of 500 m from the lightning channel for times up to 200 μs prior to the start of the return stroke. Using Monte Carlo simulations to model the X‐ray propa...
Journal of Geophysical Research, 2008
We present a detailed investigation of X-ray emission from long laboratory sparks in air at atmos... more We present a detailed investigation of X-ray emission from long laboratory sparks in air at atmospheric pressure. We studied 231 sparks of both polarities using a 1-MV Marx generator with gap lengths ranging from 10 to 140 cm. The X rays generated by the discharges were measured using five NaI/PMT detectors plus one plastic scintillator/PMT detector, all enclosed in 0.32-cm-thick aluminum boxes. X-ray emission was observed to accompany about 70% of negative polarity sparks and about 10% of positive polarity sparks. For the negative sparks, X-ray emission was observed to occur at two distinct times during the discharge: (1) near the peak voltage, specifically, about 1 ms before the voltage across the gap collapsed, and (2) near the time of the peak current through the gap, during the gap voltage collapse. Using collimators we determined that the former emission emanated from the gap, while the latter appeared to originate from above the gap in the space over the high-voltage components. During individual sparks, the total energy of the X rays that was deposited in a single detector sometimes exceeded 50 MeV, and the maximum energy of individual photons in some cases exceeded 300 keV. X-ray emission near the peak voltage was observed for a wide range of electrode geometries, including 12-cm-diameter spherical electrodes, a result suggesting that the X-ray emission was the result of processes occurring within the air gap and not just due to high electric fields at the electrode.
Journal of Geophysical Research, 2011
On 21 August 2009, the Airborne Detector for Energetic Lightning Emissions (ADELE), an array of s... more On 21 August 2009, the Airborne Detector for Energetic Lightning Emissions (ADELE), an array of six gamma-ray detectors, detected a brief burst of gamma rays while flying aboard a Gulfstream V jet near two active thunderstorm cells. The duration and spectral characteristics of the event are consistent with the terrestrial gamma ray flashes (TGFs) seen by instruments in low Earth orbit. A long-duration, complex +IC flash was taking place in the nearer cell at the same time, at a distance of ∼10 km from the plane. The sferics that are probably associated with this flash extended over 54 ms and included several ULF pulses corresponding to charge moment changes of up to 30 C km, this value being in the lower half of the range of sferics associated with TGFs seen from space. Monte Carlo simulations of gamma ray propagation in the Earth's atmosphere show that a TGF of normal intensity would, at this distance, have produced a gamma ray signal in ADELE of approximately the size and spectrum that was actually observed. We conclude that this was the first detection of a TGF from an aircraft. We show that because of the distance, ADELE's directional and spectral capabilities could not strongly constrain the source altitude of the TGF but that such constraints would be possible for TGFs detected at closer range.
Journal of Geophysical Research: Atmospheres, 2010
Using recent X‐ray and gamma‐ray observations of terrestrial gamma‐ray flashes (TGFs) from spacec... more Using recent X‐ray and gamma‐ray observations of terrestrial gamma‐ray flashes (TGFs) from spacecraft and of natural and rocket‐triggered lightning from the ground, along with detailed models of energetic particle transport, we calculate the fluence (integrated flux) of high‐energy (million electronvolt) electrons, X rays, and gamma rays likely to be produced inside or near thunderclouds in high electric field regions. We find that the X‐ray/gamma‐ray fluence predicted for lightning leaders propagating inside thunderclouds agrees well with the fluence calculated for TGFs, suggesting a possible link between these two phenomena. Furthermore, based on reasonable meteorological assumptions about the magnitude and extent of the electric fields, we estimate that the fluence of high‐energy runaway electrons can reach biologically significant levels at aircraft altitudes. If an aircraft happened to be in or near the high‐field region when either a lightning discharge or a TGF event is occur...
International Journal of Radiation Oncology*Biology*Physics, 2012
Purpose-The severe reduction of salivary function (xerostomia) is a common complication following... more Purpose-The severe reduction of salivary function (xerostomia) is a common complication following radiation therapy for head and neck cancer. Consequently, guidelines to ensure adequate function based on parotid gland tolerance dose-volume parameters have been suggested by the QUANTEC group (1) and by Ortholan et al. (2). We perform a validation test of these guidelines against a prospectively collected dataset and compared to a previously published dataset. Method and Materials-Whole-mouth stimulated salivary flow data from 66 head and neck cancer patients treated with radiotherapy at the British Columbia Cancer Agency (BCCA) were measured, and treatment planning data were abstracted. Flow measurements were collected from 50 patients at 3 months, and 60 patients at 12 month follow-up. Previously published data from a second institution (WUSTL) were used for comparison. A logistic model was used to describe the incidence of grade 4 xerostomia as a function of the mean dose of the spared parotid gland. The rate of correctly predicting the lack of xerostomia (negative predictive value, NPV) was computed for both the QUANTEC constraints and Ortholan et al. (2) recommendation to constrain the total volume of both glands receiving more than 40 Gy to less than 33%. Results-Both data sets showed a rate of xerostomia < 20 % when the mean dose to the leastirradiated parotid gland is kept below 20 Gy. Logistic model parameters for the incidence of xerostomia at 12 months after therapy, based on the least-irradiated gland, were D 50 =32.4 Gy and and γ=0.97. NPVs for QUANTEC guideline were 94% (BCCA data), 90% (WUSTL data). For Ortholan et al. (2) guideline NPVs were 85% (BCCA), and 86% (WUSTL).
Dosimetric Evaluation of Trismus in Head and Neck Cancer Patients following Intensity Modulated Radiation Therapy and Chemotherapy
International Journal of Radiation Oncology*Biology*Physics, 2011