M.K. Khan
Cleveland Clinic
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Featured researches published by M.K. Khan.
The Annals of Thoracic Surgery | 2003
Joseph F. Sabik; Bruce W. Lytle; Eugene H. Blackstone; M.K. Khan; Penny L. Houghtaling; Delos M. Cosgrove
BACKGROUND In coronary arteries with moderate stenosis, competitive flow may lead to internal thoracic artery (ITA) graft occlusion. The goals of this study were to determine if competitive flow reduces ITA patency, and if there is a degree of coronary stenosis below which ITAs should not be used. METHODS From 1972 to 1999, 50,278 patients underwent primary coronary artery bypass grafting (CABG). Of these, 2,002 had at least one ITA graft and postoperative angiography before coronary reintervention; 2,999 angiograms of 2,121 ITAs were made. Time-related ITA occlusion was modeled using longitudinal analysis to identify its risk factors while accounting for lack of independence introduced by repeated angiography and multiple ITA anastomoses per patient. Proximal coronary stenosis (maximum preoperative stenosis between ITA anastomosis and aorta) was the surrogate for competitive flow. RESULTS Unadjusted ITA patency was 93%, 89%, 90%, and 92% at 1, 5, 10, and 15 years after CABG. Risk factors associated with ITA occlusion were lesser degree of proximal coronary stenosis (p < 0.0001); longer time from CABG in grafts to non-left anterior descending coronary arteries (p < 0.0001); female sex (p = 0.0003); later date of CABG (p = 0.01); right ITA (p < 0.0001); and smoking (p < 0.0001). In all arteries, as preoperative proximal coronary stenosis decreased, ITA patency declined; however, at no degree of stenosis was there a sharp decline. CONCLUSIONS Internal thoracic artery patency decreases as coronary competitive flow increases. However, the nature of this relationship indicates ITAs should not be abandoned at moderate grades of stenosis.
International Journal of Radiation Oncology Biology Physics | 2011
Niloufer Khan; M.K. Khan; Alex Almasan; Arun D. Singh; Roger M. Macklis
The incidence of melanoma is rising in the United States, leading to an estimated 68,720 new diagnoses and 8,650 deaths annually. The natural history involves metastases to lymph nodes, lung, liver, brain, and often to other sites. Primary treatment for melanoma is surgical excision of the primary tumor and affected lymph nodes. The role of adjuvant or definitive radiation therapy in the treatment of melanoma remains controversial, because melanoma has traditionally been viewed as a prototypical radioresistant cancer. However, recent studies suggest that under certain clinical circumstances, there may be a significant role for radiation therapy in melanoma treatment. Stereotactic radiosurgery for brain metastases has shown effective local control. High dose per fraction radiation therapy has been associated with a lower rate of locoregional recurrence of sinonasal melanoma. Plaque brachytherapy has evolved into a promising alternative to enucleation at the expense of moderate reduction in visual acuity. Adjuvant radiation therapy following lymphadenectomy in node-positive melanoma prevents local and regional recurrence. The newer clinical data along with emerging radiobiological data indicate that radiotherapy is likely to play a greater role in melanoma management and should be considered as a treatment option.
International Journal of Radiation Oncology Biology Physics | 2013
William Curtis; M.K. Khan; A. Magnelli; K.L. Stephans; Rahul D. Tendulkar; P. Xia
PURPOSE Correction for intrafraction prostate motion becomes important for hypofraction treatment of prostate cancer. The purpose of this study was to estimate an ideal planning margin to account for intrafraction prostate motion as a function of imaging and repositioning frequency in the absence of continuous prostate motion monitoring. METHODS AND MATERIALS For 31 patients receiving intensity modulated radiation therapy treatment, prostate positions sampled at 10 Hz during treatment using the Calypso system were analyzed. Using these data, we simulated multiple, less frequent imaging protocols, including intervals of every 10, 15, 20, 30, 45, 60, 90, 120, 180, and 240 seconds. For each imaging protocol, the prostate displacement at the imaging time was corrected by subtracting prostate shifts from the subsequent displacements in that fraction. Furthermore, we conducted a principal component analysis to quantify the direction of prostate motion. RESULTS Averaging histograms of every 240 and 60 seconds for all patients, vector displacements of the prostate were, respectively, within 3 and 2 mm for 95% of the treatment time. A vector margin of 1 mm achieved 91.2% coverage of the prostate with 30 second imaging. The principal component analysis for all fractions showed the largest variance in prostate position in the midsagittal plane at 54° from the anterior direction, indicating that anterosuperior to inferoposterior is the direction of greatest motion. The smallest prostate motion is in the left-right direction. CONCLUSIONS The magnitudes of intrafraction prostate motion along the superior-inferior and anterior-posterior directions are comparable, and the smallest motion is in the left-right direction. In the absence of continuous prostate motion monitoring, and under ideal circumstances, 1-, 2-, and 3-mm vector planning margins require a respective imaging frequency of every 15, 60, and 240 to account for intrafraction prostate motion while achieving adequate geometric target coverage for 95% of the time.
Thrombosis Research | 2015
Shruti Chaturvedi; Erin Cockrell; Ricardo Espinola; Linda Hsi; Stacey Fulton; M.K. Khan; Liang Li; Fabio V. Fonseca; Suman Kundu; Keith R. McCrae
The antiphospholipid syndrome is characterized by venous or arterial thrombosis and/or recurrent fetal loss in the presence of circulating antiphospholipid antibodies. These antibodies cause activation of endothelial and other cell types leading to the release of microparticles with procoagulant and pro-inflammatory properties. The aims of this study were to characterize the levels of endothelial cell, monocyte or platelet derived, and tissue factor-bearing microparticles in patients with antiphospholipid antibodies, to determine the association of circulating microparticles with anticardiolipin and anti-β2-glycoprotein antibodies, and to define the cellular origin of microparticles that express tissue factor. Microparticle content within citrated blood from 47 patients with antiphospholipid antibodies and 144 healthy controls was analyzed within 2hours of venipuncture. Levels of Annexin-V, CD105 and CD144 (endothelial derived), CD41 (platelet derived) and tissue factor positive microparticles were significantly higher in patients than controls. Though levels of CD14 (monocyte-derived) microparticles in patient plasma were not significantly increased, increased levels of CD14 and tissue factor positive microparticles were observed in patients. Levels of microparticles that stained for CD105 and CD144 showed a positive correlation with IgG (R=0.60, p=0.006) and IgM anti-beta2-glycoprotein I antibodies (R=0.58, p=0.006). The elevation of endothelial and platelet derived microparticles in patients with antiphospholipid antibodies and their correlation with anti-β2-glycoprotein I antibodies suggests a chronic state of vascular cell activation in these individuals and an important role for β2-glycoprotein I in development of the pro-thrombotic state associated with antiphospholipid antibodies.
Medical Physics | 2010
T. Djemil; S Gajdos; M Ouzidane; Rahul D. Tendulkar; M.K. Khan; P. Xia
Purpose:Ultrasound,CBCT, and Electro‐Magnetic image‐guidedradiotherapy(IGRT) techniques are widely used in prostate localization. Using a single phantom, our aim is to investigate the accuracy of these technologies. Method and Materials: A CT scan (1 mm slice) of an ultrasound phantom with three implanted transponders was acquired for this study. Ten treatment plans with 10 different isocenters within a range of 5 cm from the origin of the phantom were created. The contoured cavity and coordinates of the isocenters were exported to the three systems. The origin of the phantom was aligned to the lasers and the isocenters were localized by the three techniques. During the 30 localization experiments, the phantom was not moved. The measured shifts from each localization method were compared with the known shifts from the treatment plans. The differences between these shifts were analyzed. Results: The mean vector differences are 2.7 ± 0.5 mm, 0.9 ± 0.3 mm and 0.3 ± 0.1 mm for Clarity, CBCT, and Calypso system, respectively. Specifically, the mean differences in the lateral direction are 2.1 ± 0.4 mm, 0.3 ± 0.3 mm, and −0.17 ± 0.09 mm, respectively. In the longitudinal direction, the mean differences are −1.6 ± 0.2 mm, 0.6 ± 0.2 mm, and −0.1 ±0.1 mm, respectively inthe 0.4 ± 0.2 mm, 0.6 ± 0.2 mm, and −0.1 ±0.1 mm, respectively in the vertical direction. The maximum deviation from the known shifts is 3.1 mm for Clarity, followed by 0.9 mm for CBCT, and 0.3 mm for Calypso. These shifts are independent of the distances from each isocenter to the origin of the phantom. Conclusion: The three IGRT systems achieve different accuracy and it is important to understand the limitation of each system. Further studies for the impact of rotation on localization are warranted.
Medical Physics | 2008
A. Mahadevan; M.K. Khan; Qin-Sheng Chen
Purpose: The use of intraprostatic fiducials as surrogates for prostate gland position assumes that the markers are rigidly positioned within the prostate. To test this assumption, the intermarker distances (IMD) of implanted Calypso® beacon transponders were monitored during radiation therapy to determine marker stability within the prostate gland. Method and Materials: The analysis is performed on 4 patients treated with intensity‐modulated radiotherapy. A total of 12 markers (3 transponders per patient) were implanted. Each of the three transponder locations are continuously measured using the Calypso® 3D Localization and Real Time Tracking system at a rate of 10 Hz. A total of 110,265 sampling points were available for analysis. Each sampling point allows the computation of the 3 IMDs. To study variations in marker position, daily IMDs were compared with the IMD that was observed during the first alignment. We defined the variation in the IMD as the important measure of intrinsic marker position variation. The standard deviation (SD) of IMD variations was studied as a measure of the extent of marker position variation. Results: The maximum deformation as measured by analysis of IMDs with a 95% confidence interval was +/− 2.8 mm across all 4 patients with the minimum deformation of +/− 0.28 mm. The average deformation with a 95% confidence interval was +/− 2 mm. The maximum relative variation of all the IMDs was 7.7% in the worse case scenario and represents at least a 92.7% confidence in the data. Conclusion: IMDs varied minimally, which indicated relatively little deformation of the gland as well as the absence of significant marker migration. Intraprostatic implanted Calypso ® beacon transponders in the prostate allow for a reliable localization of the prostate gland.
Journal of Pediatric Surgery | 2005
Max Olesevich; Frederick Alexander; M.K. Khan; Kathy Cotman
International Journal of Radiation Oncology Biology Physics | 2011
N. Khan; M.K. Khan; V. Torres; Arun D. Singh; Roger M. Macklis
International Journal of Radiation Oncology Biology Physics | 2010
M. Howard; M.K. Khan; L. Miller; P. Xia
International Journal of Radiation Oncology Biology Physics | 2009
M.K. Khan; Shlomo A. Koyfman; G.H. Hunter; C.A. Reddy; Jerrold P. Saxton