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N Zamboglou

Publications and source records attributed to N Zamboglou.

At least 19 recordsLinked to original sources
PubMed2000

Reconstruction and navigation system for intraoperative brachytherapy using the flab technique for colorectal tumor bed irradiation.

PURPOSE: To present the development of a new navigation and reconstruction system based on an electromagnetic free-hand tracker and on CT imaging for treatment planning of intraoperative high-dose-rate brachytherapy (IORT-HDRB) in the sacral region. Our aim is to improve accuracy and to enable individualized treatment planning and dose documentation to be performed for IORT-HDRB using a flab technique. METHODS AND MATERIALS: The material consists of an electromagnetic 3D tracker system, a PC workstation with Microsoft Windows NT 4.0 operating system, and a recognition program for continuous speech. In addition, we designed an external reference system constructed of titanium and Perspex, which is positioned in the pelvis, and a special digitizer pen for reconstruction of the flab geometry. The flab design incorporates a series of silicon 10-mm-diameter spherical pellets. Measurements were made with a pelvic phantom in order to study the accuracy of the system. The reconstruction results are stored and can be exported via network or floppy to our different treatment planning systems. RESULTS: Our results for the reconstruction of a flab with six catheters and a total of 100 spherical pellets give mean errors in the range (2.5 +/- 0.6) mm to (3.5 +/- 0.8) mm depending on the positions of the pelvic phantom and transmitter relative to the operation table. These errors are calculated by comparing the reconstruction results of our system with those using a CT-based reconstruction of the flab geometry. For the accuracy of the navigation system for the pelvic phantom, we obtained mean errors in the range (2.2 +/- 0.7) mm to (3. 1 +/- 1.0) mm. CONCLUSIONS: The new system we have developed enables navigation and reconstruction within the surgical environment with a clinically acceptable level of accuracy. It offers the possibility of individualized treatment planning and effective documentation of the 3D dose distribution in IORT-HDRB using a flab technique.

Brachytherapy↗
PubMed2000

3D interstitial HDR brachytherapy combined with 3D external beam radiotherapy and androgen deprivation for prostate cancer. Preliminary results.

BACKGROUND: Evaluation of feasibility, tolerance and efficiency for a new 3D interstitial HDR brachytherapy technique combined with 3D external beam radiotherapy and androgen deprivation for prostate cancer. PATIENTS AND METHODS: Between January 1997 and August 1998 we treated 35 patients with stage cT1-3 N0 M0 prostate cancer. Thirty-two patients with a follow-up of 12 to 28 months (median: 18 months) were evaluated. After ultrasound-guided transrectal implantation of 4 non-parallel needles, CT based 3D brachytherapy treatment planning ("Offenbach system") was performed. All patients received 4 fractions brachytherapy using a fractional dose of 5 or 7 Gy. Time between each fraction was 14 days. After brachytherapy 3D external irradiation followed up to 39.6 or 45.0 Gy. All patients received androgen deprivation, starting 2 to 19 months before brachytherapy, ending 3 months after 3D external radiotherapy. RESULTS: Posttreatment PSA levels dropped to < 1.5 ng/ml in 29/32 patients (91%). In 25 patients PSA levels were < 0.5 ng/ml, in 4 patients 0.5 to 1.5 ng/ml. In 2 patients we noted biochemical relapse. Transrectal implantation was very well tolerated. Grade 3 acute urinary toxicity occurred in 1 patient. We noted no Grade 2 or higher acute gastrointestinal toxicity. One patient developed a Grade 3 late urinary toxicity. No patient showed late gastrointestinal side effects. All 140 dose-volume histograms for 3D HDR brachytherapy were analyzed. CONCLUSIONS: The new 3D HDR brachytherapy technique, combined with 3D external irradiation and androgen deprivation, is a feasible, so far well-tolerated and effective treatment in the short-time follow-up of median 18 months.

Adenocarcinoma↗
PubMed2000

Navigation system for interstitial brachytherapy.

PURPOSE: To develop a computed tomography (CT) based electromagnetic navigation system for interstitial brachytherapy. This is especially designed for situations when needles have to be positioned adjacent to or within critical anatomical structures. In such instances interactive 3D visualisation of the needle positions is essential. METHODS AND MATERIALS: The material consisted of a Polhemus electromagnetic 3D digitizer, a Pentium 200 MHz laptop and a voice recognition for continuous speech. In addition, we developed an external reference system constructed of Perspex which could be positioned above the tumour region and attached to the patient using a non-invasive fixation method. A specially designed needle holder and patient bed were also developed. Measurements were made on a series of phantoms in order to study the efficacy and accuracy of the navigation system. RESULTS: The mean navigation accuracy of positioning the 20.0 cm length metallic needles within the phantoms was in the range 2.0-4.1 mm with a maximum of 5.4 mm. This is an improvement on the accuracy of a CT-guided technique which was in the range 6.1-11.3 mm with a maximum of 19.4 mm. The mean reconstruction accuracy of the implant geometry was 3.2 mm within a non-ferromagnetic environment. We found that although the needles were metallic this did not have a significant influence. We also found for our experimental setups that the CT table and operation table non-ferromagnetic parts had no significant influence on the navigation accuracy. CONCLUSIONS: This navigation system will be a very useful clinical tool for interstitial brachytherapy applications, particularly when critical structures have to be avoided. It also should provide a significant improvement on our existing technique.

Brachytherapy↗
PubMed2000

CT imaging based digitally reconstructed radiographs and their application in brachytherapy.

The aim of our study was to develop an algorithm to simulate the digitally reconstructed radiograph (DRR) calculation process for different beam qualities (photon energies) in the range 50 keV to 12 MeV. This was achieved using volumetric anatomical data for the patient obtained from three-dimensional diagnostic CT images. These DRR images can be used in three-dimensional treatment planning for external beam radiotherapy as well as for brachytherapy in the same way as conventional radiographic films. The advantages of using such DRRs in modern 3D brachytherapy treatment planning are shown. A number of tools are described, illustrating that the application of DRRs in brachytherapy is very useful.

Algorithms↗
PubMed2000

Optimized bounding boxes for three-dimensional treatment planning in brachytherapy.

It is sometimes necessary to determine the optimal value for a direction dependent quantity. Using a search technique based on Powell's quadratic convergent method such an optimal direction can be approximated. The necessary geometric transformations in n-dimensional space are introduced. As an example we consider the approximation of the minimum bounding box of a set of three-dimensional points. Minimum bounding boxes can significantly improve accuracy and efficiency of the calculations in modern brachytherapy treatment planning of the volumes of objects or the dose distribution inside an object. A covariance matrix based approximation method for the minimum bounding box is compared with the results of the search method. The benefits of the use of optimal oriented bounding boxes in brachytherapy treatment planning systems are demonstrated and discussed.

Algorithms↗
PubMed2000

Dose-volume histograms computation comparisons using conventional methods and optimized fast Fourier transforms algorithms for brachytherapy.

In anatomy based optimization procedures for large volume implants the calculation of dose-volume histograms (DVH) accounts for the major part of the time involved and can be as long as a few hours. This time is proportional to the number of seeds or source dwell positions required for the implant. A procedure for the calculation of brachytherapy seed dose distribution calculation employing fast Fourier transforms (FFT) and the convolution theorem has been described by others and was supposed to significantly improve the speed of the dose distribution computation. Using new significantly improved FFT algorithms and various other optimization techniques we have compared the calculated differential and integral DVHs in high dose rate (HDR) brachytherapy with a single stepping source using actual clinical implants. This is so that we could assess the efficiency and accuracy of the FFT method with that of conventional methods. Our results showed that the FFT based method of calculating DVHs in brachytherapy is comparable in speed with conventional dose calculation methods, but only for implants with more than 287 sources. It is therefore of limited practical use even for large implants. This result is in direct opposition to the claim by other authors.

Algorithms↗
PubMed2000

Generation of uniformly distributed dose points for anatomy-based three-dimensional dose optimization methods in brachytherapy.

We have studied the accuracy of statistical parameters of dose distributions in brachytherapy using actual clinical implants. These include the mean, minimum and maximum dose values and the variance of the dose distribution inside the PTV (planning target volume), and on the surface of the PTV. These properties have been studied as a function of the number of uniformly distributed sampling points. These parameters, or the variants of these parameters, are used directly or indirectly in optimization procedures or for a description of the dose distribution. The accurate determination of these parameters depends on the sampling point distribution from which they have been obtained. Some optimization methods ignore catheters and critical structures surrounded by the PTV or alternatively consider as surface dose points only those on the contour lines of the PTV. D(min) and D(max) are extreme dose values which are either on the PTV surface or within the PTV. They must be avoided for specification and optimization purposes in brachytherapy. Using D(mean) and the variance of D which we have shown to be stable parameters, achieves a more reliable description of the dose distribution on the PTV surface and within the PTV volume than does D(min) and D(max). Generation of dose points on the real surface of the PTV is obligatory and the consideration of catheter volumes results in a realistic description of anatomical dose distributions.

Algorithms↗
PubMed2000

Catheter autoreconstruction in computed tomography based brachytherapy treatment planning.

The aim of this study is to develop an automatic reconstruction of brachytherapy catheters using CT (computed tomography) data. Previously no such automatic facility has existed in any treatment planning software. To achieve this facility we have developed tools for the automatic reconstruction (which we term autoreconstruction) of plastic and metallic catheters. These algorithms overcome a number of difficulties which arise when a large number of catheters are present. These include situations with intersecting catheters and with loop techniques. The time required for the catheter reconstruction process using our autoreconstruction method is significantly reduced. The accuracy of our autoreconstruction is at least as high as the classical manual slice-by-slice method.

Algorithms↗
PubMed2000

[Radiotherapy in Langerhans-cell histiocytosis. 2 case reports and review of the literature].

The use of radiotherapy in the treatment of Langerhans' cell histiocytosis was first reported in the literature in 1930 and has been proven as effective in numerous studies. We present the results of two female adults with eosinophilic granuloma of bone who underwent conventionally fractionated radiation therapy with total doses of 7 x 1.8 Gy and 7 x 2.0 Gy in four different sites. After observation periods raging from three months to six years local control of the disease was achieved in all treated locations. A review of 18 previously published studies include a total of 310 sites of eosinophilic granuloma of bone in 216 patients. It was demonstrated in 13 studies that the patients had complete relief of symptoms. An average of 94.3% had local control of the symptoms. Furthermore, in 12 studies for a total of 344 cases with involvement of other organs local control was reported in an average of 64.8% (range: 14.3-100%). Based on our own observations and on the literature review we conclude that low dose radiation therapy plays an important role in the management of localised Langerhans' cell histiocytosis. In order to minimise the risk of radiation induced neoplasms an accurate and precise radiation technique is required.

Adult↗
PubMed1999

Comparison of calibration procedures for 192Ir high-dose-rate brachytherapy sources.

PURPOSE: To compare the efficacy of different calibration procedures for 192Ir high-dose-rate (HDR) brachytherapy sources and to determine their suitability in clinical practice. In addition the manufacturer's calibration is compared with our experimental measurements so that the accuracy of the source strength on the manufacturer certificate which is supplied with each new 192Ir source can be accessed. METHODS AND MATERIALS: We compared three types of calibration system: well-type chambers (HDR-1000 and SDS), cylindrical phantom, and plate phantom. The total number of measurements we obtained was 365. The number of sources used for the calibration procedure comparison was 20 and the number used for comparison with the manufacturer's calibration was 46. This study was made during the period 1989-1997. Also, Physikalisch-Technische Bundesanstalt (PTB) calibrated one of our sources using their PTB protocol so that the results could be compared with our own. RESULTS: The sensitivity of each system on scattering from the room walls was studied. It was found that different minimum lateral distances from the walls were required for the different systems tested: 15 cm and 25 cm for the well-type chambers, 75 cm for the cylindrical phantom, and 13 cm for the plate phantom. The minimum thickness required to reach phantom scattering saturation for the plate phantom setup is 24 cm. The influence of the applicator material used in the calibration setup was found to be 1.7% for the stainless steel dosimetry applicator compared to the plastic 5F applicator. The accuracy of source positioning within the applicator can lead to dosimetric errors of +/-1.2% for the radial distance of 8.0 cm used with both solid phantoms. The change in the response for both well-type chambers was only 0.1% for changes in the source position within +/-7.5 mm around the response peak. Good agreement was found between all dosimetry systems included in our study. Taking the HDR-1000 well-type chamber results as a reference, we observed percentage root mean square (RMS) values of 0.11% for the SDS well-type chamber, 0.44% for the cylindrical, and 0.60% for the plate phantom setup. A comparison of our results using the cylindrical phantom with those of the manufacturer showed a percentage RMS value of 3.3% with a percentage fractional error range of -13.0% to +6.0%. The comparison of our calibration results with those of PTB gave deviations less than 0.4% for all systems. CONCLUSIONS: Our results have shown that with careful use of all calibration system protocols an accurate determination of source strength can be obtained. However, the manufacturer's calibration is not accurate enough on its own, and it should be mandatory for clinics to always measure the source strength of newly delivered 192Ir brachytherapy sources. The influence of the applicator material, metal or plastic, should always be taken into account.

Brachytherapy↗
PubMed1999

CT-Based interstitial HDR brachytherapy.

PURPOSE: Development, application and evaluation of a CT-guided implantation technique and a fully CT-based treatment planning procedure for brachytherapy. METHODS AND MATERIALS: A brachytherapy procedure based on CT-guided implantation technique and CT-based treatment planning has been developed and clinical evaluated. For this purpose a software system (PROMETHEUS) for the 3D reconstruction of brachytherapy catheters and patient anatomy using only CT scans has been developed. An interface for the Nucletron PLATO BPS treatment planning system for optimization and calculation of dose distribution has been devised. The planning target volume(s) are defined as sets of points using contouring tools and are used for optimization of the 3D dose distribution. Dose-volume histogram based analysis of the dose distribution (COIN analysis) enables a clinically realistic evaluation of the brachytherapy application to be made. The CT-guided implantation of catheters and the CT-based treatment planning procedure has been performed for interstitial brachytherapy and for different tumor sites in 197 patients between 1996 and 1997. RESULTS: The accuracy of the CT reconstruction was tested using first a quality assurance phantom and second, a simulated interstitial implant of 12 needles. These were compared with the results of reconstruction using radiographs. Both methods gave comparable results with regard to accuracy, but the CT based reconstruction was faster. Clinical feasibility was proved in pre-irradiated recurrences of brain tumors, in pretreated recurrences or metastatic disease, and in breast carcinomas. The tumor volumes treated were in the range 5.1 to 2,741 cm3. Analysis of implant quality showed a slightly significant lower COIN value for the bone implants, but no differences with respect to the planning target volume. CONCLUSIONS: The Offenbach system, incorporating the PROMETHEUS software for interstitial HDR brachytherapy has proved to be extremely valuable in routine clinical practice for many tumor sites. Our CT-guided implantation technique together with a fully CT-based planning system has enabled conformal brachytherapy treatment to become routine.

Brachytherapy↗
PubMed1999

[In Process Citation]

Intraoperative radiotherapy (IORT) is a new concept in the treatment of recurrent and primary advanced colorectal tumors. Between October 1994 and December 1997 27 patients (primary tumor: 8, first recurrent tumor: 12, second recurrent tumor: 7) received IORT (32 applications). Chemotherapy and percutaneous radiotherapy had already been given to all patients with advanced and recurrent colorectal tumors. The intraoperative irradiation was performed through HDR iridium afterloading. A flexible flab--individually adapted to the "tumor bed"--was used as applicator. The contact dose ranged from 10 to 15 Gy. The mean operation time (rectum resection: 5, rectum amputation: 14, debulking: 8) increased by 30 min on average. Eight patients had postoperative complications: perianal wound infections (3), sacrovesical fistulas (3), leakage of anastomosis (1) and neural ureter dysfunction (1). To date--on average 17.1 months (range: 3-33) after operation--13 patients are free of tumor recurrence or show stable disease. Ten patients--all of them had macroscopic residual tumor--have local tumor progression combined with good quality of life. Only 4 patients died (acute kidney failure, stroke, marasmus, systemic progression). The afterloading flab technique represents a technically simple, minimally harmful procedure in the therapy of colorectal tumor. Even when IORT with electrons is not feasible or the patients have already been irradiated, a higher radiation dose is possible. Given the demonstrated rate of local tumor recurrence, the afterloading flab technique seems to be a valuable treatment alternative to extended, high-risk resections. Long-term follow-ups will be necessary.

Journal Article↗
PubMed1999

New interstitial HDR brachytherapy technique for prostate cancer: CT based 3D planning after transrectal implantation.

We have developed a new interstitial HDR brachytherapy technique for the treatment of prostate cancer using CT based 3D planning after transrectal implantation of four non-parallel needles. CT based needle reconstruction, target definition, evaluation and documentation, including DVHs and 3D imaging, is a feasible, safe and well tolerated treatment concept.

Adenocarcinoma↗
PubMed1999

Radiation and concomitant weekly administration of paclitaxel in patients with glioblastoma multiforme. A phase II study.

The present study was conducted to evaluate the activity and toxicity profile of radiation (RT) and concomitant chemotherapy in patients with glioblastoma multiforme (GBM). Thirty-nine patients were treated postoperatively with RT and concomitant administration of paclitaxel. Cranial irradiation was initiated 2-3 weeks postoperatively and was administered in 2.0 fractions, one fraction per day, for 5 consecutive days per week, to a total of 60 Gy. Paclitaxel was delivered at a dose of 100 mg/m2 over 3-h once weekly for 6 weeks. Thirty-three patients received all 6 cycles of paclitaxel according to the protocol. Totally, 217 cycles were delivered all of them at full dose. The median relative dose intensity of paclitaxel was 1 (range 0.88-1.1). Three (7.5%) patients achieved complete and 9 (23%) partial response, while 12 (30.5%) patients demonstrated stabilization of the disease. Side effects from combined chemoradiotherapy were mainly mild. Grade III toxicity included infection (7.5%) and alopecia (5%). Median time to progression was 6 (range 0.9-27) months and median survival 10.7 (range 0.9-39.5+) months. The present study has clearly shown that 100 mg/m2 of paclitaxel in 1-h infusion weekly can be safely given concomitantly with RT in patients with GBM with manageable toxicity. However, the efficacy of this combined modality treatment does not appear to be superior to that of RT alone.

Adult↗
PubMed1999

Anatomy-based three-dimensional dose optimization in brachytherapy using multiobjective genetic algorithms.

In conventional dose optimization algorithms, in brachytherapy, multiple objectives are expressed in terms of an aggregating function which combines individual objective values into a single utility value, making the problem single objective, prior to optimization. A multiobjective genetic algorithm (MOGA) was developed for dose optimization based on an a posteriori approach, leaving the decision-making process to a planner and offering a representative trade-off surface of the various objectives. The MOGA provides a flexible search engine which provides the maximum of information for a decision maker. Tests performed with various treatment plans in brachytherapy have shown that MOGA gives solutions which are superior to those of traditional dose optimization algorithms. Objectives were proposed in terms of the COIN distribution and differential volume histograms, taking into account patient anatomy in the optimization process.

Algorithms↗
PubMed1999

CT guided interstitial high dose rate brachytherapy for recurrent malignant gliomas.

This paper describes the technique and preliminary results of high dose rate (HDR) interstitial brachytherapy for recurrent grade III and grade IV gliomas. Although in the initial treatment of malignant gliomas brachytherapy has been shown to give better results than external beam therapy, this has previously always been with low dose rate (LDR) brachytherapy. Stereotactic frames are used for interstitial LDR brachytherapy but a CT image-guided technique does not require such a frame. The survival rates for our initial 53 patients do not significantly differ from LDR results. However, using HDR there are several advantages, including a much shorter treatment time with HDR than LDR and better patient comfort. HDR also allows better individualized optimization of the treatment than LDR.

Adult↗
PubMed1998

A conformal index (COIN) to evaluate implant quality and dose specification in brachytherapy.

PURPOSE: To propose a new index (COIN) that can be easily understood and computed to assess high dose rate (HDR) brachytherapy interstitial implant quality and dose specification and is an improvement on existing indexes. METHODS AND MATERIALS: The COIN index is based on an extension of dose-volume histograms and employs an analogous concept to that of cost-benefit analysis, which has already been applied to quality-of-life assessments for two alternative treatment protocols. The COIN index calculation methodology is shown for two cases: with and without critical structures. An analysis is given of dose distributions for two planning treatment volumes (PTV) of simple geometrical shape, applying both the rules of the Paris system and that of the "Offenbach" system. 40 patients who have received interstitial implants form the clinical material. With current HDR brachytherapy technology both for dose delivery, using remote afterloaders, and for three-dimensional (3D) treatment planning, it is now possible to relatively easily plan conformal brachytherapy treatments that would have been impossible with manual afterloading techniques and two-dimensional (2D) treatment planning. RESULTS: Examples of the use of the COIN index are presented for experimental and clinical data. CONCLUSIONS: The results show that COIN is a useful and practical index to improve the quality of treatment of interstitial brachytherapy implants. Further work will be undertaken with a larger population of implanted cancer patients and a subdivision of the results by treatment site.

Algorithms↗