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N K Uzunoglu

Publications and source records attributed to N K Uzunoglu.

17 recordsLinked to original sources
PubMed2006

A four-dimensional computer simulation model of the in vivo response to radiotherapy of glioblastoma multiforme: studies on the effect of clonogenic cell density.

Tumours behave as complex, self-organizing, opportunistic dynamic systems. In an attempt to better understand and describe the highly complicated tumour behaviour, a novel four-dimensional simulation model of in vivo tumour growth and response to radiotherapy has been developed. This paper presents the latest improvements to the model as well as a parametric validation of it. Improvements include an advanced algorithm leading to conformal tumour shrinkage, a quantitative consideration of the influence of oxygenation on radiosensitivity and a more realistic, imaging based description of the neovasculature distribution. The tumours selected for the validation of the model are a wild type and a mutated p53 gene glioblastomas multiforme. According to the model predictions, a whole tumour with larger cell cycle duration tends to repopulate more slowly. A lower oxygen enhancement ratio value leads to a more radiosensitive whole tumour. Higher clonogenic cell density (CCD) produces a higher number of proliferating tumour cells and, therefore, a more difficult tumour to treat. Simulation predictions agree at least semi-quantitatively with clinical experience, and particularly with the outcome of the Radiation Therapy Oncology Group (RTOG) Study 83-02. It is stressed that the model allows a quantitative study of the interrelationship between the competing influences in a complex, dynamic tumour environment. Therefore, the model can already be useful as an educational tool with which to study, understand and demonstrate the role of various parameters in tumour growth and response to irradiation. A long term quantitative clinical adaptation and validation of the model aiming at its integration into the treatment planning procedure is in progress.

Algorithms↗
PubMed2003

A 3D high-resolution gamma camera for radiopharmaceutical studies with small animals.

The results of studies conducted with a small field of view tomographic gamma camera based on a Position Sensitive Photomultiplier Tube are reported. The system has been used for the evaluation of radiopharmaceuticals in small animals. Phantom studies have shown a spatial resolution of 2mm in planar and 2-3mm in tomographic imaging. Imaging studies in mice have been carried out both in 2D and 3D. Conventional radiopharmaceuticals have been used and the results have been compared with images from a clinically used system.

Algorithms↗
PubMed2003

Working memory deficits in multiple sclerosis: a controlled study with auditory P600 correlates.

BACKGROUND: Recently, the P600 component of event related potentials, a waveform that is conceived to be generated and/or modulated by basal ganglia and cingulate area has been considered an index of the completion of any synchronised operation after target detection, having much in common with working memory operation. Moreover, dysfunction of these brain structures as well as working memory deficits have been implicated in the pathophysiology of multiple sclerosis. The aim of this study was to investigate the patterns of P600 elicited during a working memory test in multiple sclerosis patients compared with healthy controls. METHODS: Twenty two definite, chronic progressive multiple sclerosis patients, with recent exacerbation of their illness, and 20 normal subjects matched for age, sex, and educational level, were studied with a computerised version of the digit span test of Wechsler batteries. Auditory P600 were measured during the anticipatory period of this test. RESULTS: The patient group, as compared with healthy controls, showed significantly reduced latencies of P600 at left frontal areas and reduced P600 amplitudes at left temporoparietal region. Moreover, memory performance of patients was significantly more impaired when compared with healthy controls. CONCLUSIONS: These findings may indicate that multiple sclerosis is associated with abnormal features of the completion of synchronised operation after target detection, as they are reflected by P600 amplitudes and latencies. Dysfunction of this mechanism may contribute to the identification of basic cognitive processes that could account for the cognitive deficits in multiple sclerosis.

Adult↗
PubMed2002

Intraoperative hyperthermia and chemoradiotherapy for inoperable pancreatic carcinoma.

The aim of this study was to evaluate the tolerability and the possible clinical benefit of intraoperative hyperthermia combined with multischedule chemotherapy and bypass surgery for the palliative treatment of inoperable pancreatic cancer. Ten patients with unresectable adenocarcinoma of the pancreas received preoperative chemotherapy [5-fluorouracil (5-FU)], bypass surgery and postoperative chemotherapy (5-FU, doxorubicin and cisplatin) plus sandostatin and radiotherapy (45 Gy, 25 fractions, 5 days a week). A single session of intraoperative hyperthermia was performed, by using a waveguide-type applicator (433 MHz). The tumour region was heated to 43-45 degrees C for up to 60 min, while 500 mg 5-FU was infused simultaneously through the gastroduodenal into the splenic artery. Postoperative recovery was uneventful for all patients. A brief instrument was developed for evaluating patients' quality of life. Chemotherapy-related toxicity included myelosuppression, vomiting, alopecia and increase in blood urea nitrogen (BUN), creatinine, SGOT and SGPT. Glucose and amylase determinations remained within normal limits throughout the whole treatment. There was a significant improvement before and 1 month after combined treatment in Eastern Cooperative Oncology Group (ECOG) status (1.8 +/- 0.4), Scott-Huskinsson pain scale (3.2 +/- 0.8) and quality of life score (30.5 +/- 6.7). No progressive disease was noticed and the median overall survival was 11 (SE = 2.4) months. There was also a significant (P = 0.002, Wilcoxon test) decrease in values of both serum carcinoembryonic antigen (CEA) and carbohydrate antigen (CA19-9), from 7.6 +/- 1.3 ng/mL and 875.7 +/- 104.8 U/mL to 3.5 +/- 0.7 ng/mL and 65.3 +/- 14.1 U/mL respectively. The first clinical results suggest a potential advantage of using combined intraoperative hyperthermia, chemotherapy and postoperative radiotherapy in the palliative treatment of the adenocarcinoma of the pancreas. The whole procedure seems to be free of perioperative morbidity, while the chemotherapy toxicity was rather moderate. However, the preliminary nature limits the general applicability of our results.

Adenocarcinoma↗
PubMed2001

Cytoreductive surgery combined with intraoperative chemo-hyperthermia and postoperative radiotherapy in the management of advanced pancreatic adenocarcinoma: feasibility aspects and efficacy.

BACKGROUND/PURPOSE: The aim of our study was to evaluate the feasibility and the efficacy of cytoreductive surgery (CS) with intraoperative chemo-hyperthermia in the management of advanced stage IVA (T4N0M0) pancreatic cancer. METHODS: From August 1995 through March 1996, seven patients with unresectable adenocarcinoma of the pancreas underwent CS, with preoperative chemotherapy (5-fluorouracil [FU] for 96 h), plus 45-Gy external beam postoperative irradiation with a 6-MeV linear accelerator (1.8 Gy per fraction, 5 days per week). A single session of intraoperative hyperthermia was performed with a waveguide-type applicator operating at 433 MHz, and temperature was measured by inserting a flexiguide needle catheter carrying a thermometry probe with three measuring points into the tumor. The tumor region was heated to 43 degrees C-45 degrees C for up to 60 min, while 5-FU 500 mg was injected simultaneously through the gastroduodenal artery into the splenic artery (intraoperative regional chemotherapy). RESULTS: Postoperative recovery was uneventful for all patients. After the combined treatment, there was a significant decrease in the values of both serum carcinoembryonic antigen (CEA; P = 0.017, Wilcoxon test) and carbohydrate antigen (CA)19-9 ( P = 0.016; Wilcoxon test), from 7.6 +/- 1.5 ng/ml CEA and 869.6 +/- 126.9 U/ml CA to 3.5 +/- 0.8 ng/ml CEA and 104.7 +/- 35.4 U/ml CA19-9. Moreover, there was a significant improvement ( P = 0.016; Wilcoxon test) in Eastern Cooperative Oncology Group performance status, pain score, and body mass index. The median overall survival was 18.5 (SE, 1.8) months. CONCLUSIONS: Our preliminary clinical results suggest the tolerability and the considerable potential advantage of using cytoreductive resection with preoperative chemotherapy, intraoperative chemo-hyperthermia, and external beam postoperative radiotherapy for the management of advanced adenocarcinoma of the pancreas.

Adenocarcinoma↗
PubMed2001

Modeling tumor growth and irradiation response in vitro--a combination of high-performance computing and web-based technologies including VRML visualization.

A simplified three-dimensional Monte Carlo simulation model of in vitro tumor growth and response to fractionated radiotherapeutic schemes is presented in this paper. The paper aims at both the optimization of radiotherapy and the provision of insight into the biological mechanisms involved in tumor development. The basics of the modeling philosophy of Duechting have been adopted and substantially extended. The main processes taken into account by the model are the transitions between the cell cycle phases, the diffusion of oxygen and glucose, and the cell survival probabilities following irradiation. Specific algorithms satisfactorily describing tumor expansion and shrinkage have been applied, whereas a novel approach to the modeling of the tumor response to irradiation has been proposed and implemented. High-performance computing systems in conjunction with Web technologies have coped with the particularly high computer memory and processing demands. A visualization system based on the MATLAB software package and the virtual-reality modeling language has been employed. Its utilization has led to a spectacular representation of both the external surface and the internal structure of the developing tumor. The simulation model has been applied to the special case of small cell lung carcinoma in vitro irradiated according to both the standard and accelerated fractionation schemes. A good qualitative agreement with laboratory experience has been observed in all cases. Accordingly, the hypothesis that advanced simulation models for the in silico testing of tumor irradiation schemes could substantially enhance the radiotherapy optimization process is further strengthened. Currently, our group is investigating extensions of the presented algorithms so that efficient descriptions of the corresponding clinical (in vivo) cases are achieved.

Carcinoma, Small Cell↗
PubMed2000

Simulated generation of evoked potentials components using networks with distinct excitatory and inhibitory neurons.

Long latency evoked potentials (EP's) are electrical potentials related to brain information processing mechanisms. In this paper, three-layered neurophysiologically based artificial neural network model is presented whose neurons obey to Dale's law. The first two layers of the network can memorize and recall sparsely coded patterns, oscillating at biologically plausible frequencies. Excitatory low-pass filtering synapses, from the second to the third layer, create evoked current dipoles, when the network retrieves memories related to stimuli. Based on psychophysiological indications, simulated intracranial dipoles are straightforwardly transformed into long latency EP components such as N100 and P300 that match laboratory-measured scalp EP's.

Biomedical Engineering↗
PubMed1998

Optimization of the deposited power distribution inside a layered lossy medium irradiated by a coupled system of concentrically placed waveguide applicators.

A method is proposed for controlling the deposited power distribution in a layered cylindrical lossy model, irradiated by a phased-array hyperthermia system consisting of four waveguide applicators. A rigorous electromagnetic model of the heated tissue, which takes into account coupling phenomena between system elements, is used for predicting the electric field at any point inside tissue. The relative amplitudes and relative phases of the array elements are optimized in order to attain desired specific absorption rate (SAR) distributions inside and outside malignant tissues. A constrained nonlinear optimization problem is solved by using the penalty function method and the resulting unconstrained minimization of the penalty function is carried out by the downhill simplex method. Two practical phased-array hyperthermia systems have been studied and numerical results are presented.

Algorithms↗
PubMed1997

CT-based software for 3-D localization and reconstruction in stepping source brachytherapy.

This paper describes innovative software for catheter localization and three-dimensional (3-D) reconstruction in stepping source brachytherapy applications. Patient information is a set of computed tomography (CT) slices scanned during the implantation of brachytherapy catheters. Catheter geometry and patient anatomy are exported for use with dose calculation software modules. The errors produced by the system are also encouragingly low. Time saving was achieved, in terms of other traditional reconstruction techniques. Various automated procedures, 3-D graphics and a user-friendly GUI, have contributed to providing a powerful, comprehensive software tool, directly useable in the clinical practice.

Brachytherapy↗
PubMed1993

Optimal steady-state temperature distribution for a phased array hyperthermia system.

A method is presented for the evaluation of optimal amplitude and phase excitations for the radiating elements of a phased array hyperthermia system, in order to achieve desired steady-state temperature distributions inside and outside of malignant tissues. Use is made of a detailed electromagnetic and thermal model of the heated tissue in order to predict the steady-state temperature at any point in tissue. Optimal excitations are obtained by minimizing the squared error between desired and model predicted temperatures inside the tumor volume, subject to the constraint that temperatures do not exceed an upper bound outside the tumor. The penalty function technique is used to solve the constrained optimization problem. Sequential unconstrained minima are obtained by a modified Newton method. Numerical results for a four element phased array hyperthermia system are presented.

Electromagnetic Phenomena↗
PubMedDate not supplied

Improving spatial resolution in SPECT with the combination of PSPMT based detector and iterative reconstruction algorithms.

This paper investigates the possibility of developing a SPECT system that combines the high spatial resolution of position sensitive photomultiplier tubes (PSPMTs) with the excellent performance of iterative reconstruction algorithms. A small field of view (FOV) camera based on a PSPMT and a pixelized scintillation crystal made of CsI(Tl) have been used for the acquisition of the projections. With the use of maximum likelihood expectation maximization (ML-EM) and ordered subsets expectation maximization (OSEM) slices of the object are obtained while three-dimensional (3D) reconstruction of the object is carried out using a modified marching cubes (MMC) algorithm. The spatial resolution of tomographic images obtained with the system was 2-3mm. The spatial resolution of a conventional system that uses filtered backprojection (FBP) for slices reconstruction was more than 9 mm.

Algorithms↗
PubMedDate not supplied

Intraoperative hyperthermia in conjunction with multi-schedule chemotherapy (pre-, intra- and post-operative), by-pass surgery, and post-operative radiotherapy for the management of unresectable pancreatic adenocarcinoma.

The aim of this study was to evaluate the potential role of intraoperative hyperthermia (IOHT) in the management of stage IV pancreatic adenocarcinoma. Twenty-seven patients (group A) received pre-operative chemotherapy (5-FU), by-pass surgery with intraoperative bolus infusion of 5-FU and post-operatively multi-agent chemotherapy plus sandostatin and external beam irradiation (45Gy, 25 fractions, 5 days a week). In a non-randomized way, 10 patients (group B) received an additional single session of IOHT (43-45 degrees C, 1h) performed directly on the tumour using a waveguide applicator (433MHz) with interstitial measurements of temperature measured. A brief instrument was developed for evaluating patients' quality of life. No progressive disease (PD) was noticed in group B vs 11% (3/27) of PD in group A. There was also a significant increase of overall survival (OS) in group B vs A patients (p = 0.029, log-rank test). Moreover, there was a significant improvement for group B vs A patients regarding Karnofsky performance status (p < 0.001, Mann-Whitney test), pain score (p < 0.001, Mann-Whitney test) and quality of life score (p = 0.031, Mann-Whitney test). A significant correlation was noticed between OS and thermal parameters such as average T(min) (p = 0.043), average T(max) (p = 0.027) and cumulative minutes T(90) >or= 44 degrees C (p < 0.001). Combined IOHT with chemotherapy (pre-, intra- and post-operative) and external beam post-operative radiotherapy seem to have a potential benefit in the management of unresectable adenocarcinoma of the pancreas, concerning local response, OS and quality of life. Further clinical studies to evaluate the benefit of IOHT suggested in this study are warranted.

Adenocarcinoma↗
PubMedDate not supplied

Optimum excitation of phases and amplitudes in a phased array hyperthermia system.

In order to achieve a desired temperature distribution inside and outside of malignant tissues, optimization techniques could be used in phased array hyperthermia systems to control effectively the amplitude and phase of the radiating elements. The optimization of a four-element phased array hyperthermia system operating at 432 MHz is examined theoretically. The proposed technique is based on a detailed physical model of the tissue medium to be heated in terms of both electromagnetic and thermal properties. A penalty function technique using a Newton method is applied to determine the optimum phases and amplitudes of the array. Several array geometries have been studied and numerical results are presented.

Algorithms↗