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D Baltas

Publications and source records attributed to D Baltas.

51 records · Page 3Linked to original sources
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

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

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↗
PubMed1998

Application of the Monte Carlo integration (MCI) method for calculation of the anisotropy of 192Ir brachytherapy sources.

Source anisotropy is a very important factor in the brachytherapy quality assurance of high-dose rate (HDR) 192Ir afterloading stepping sources. If anisotropy is not taken into account then doses received by a brachytherapy patient in certain directions can be in error by a clinically significant amount. Experimental measurements of anisotropy are very labour intensive. We have shown that within acceptable limits of accuracy, Monte Carlo integration (MCI) of a modified Sievert integral (3D generalization) can provide the necessary data within a much shorter time scale than can experiments. Hence MCI can be used for routine quality assurance schedules whenever a new design of HDR or PDR 192Ir is used for brachytherapy afterloading. Our MCI calculation results are compared with published experimental data and Monte Carlo simulation data for microSelectron and VariSource 192Ir sources. We have shown not only that MCI offers advantages over alternative numerical integration methods, but also that treating filtration coefficients as radial distance-dependent functions improves Sievert integral accuracy at low energies. This paper also provides anisotropy data for three new 192Ir sources, one for the microSelectron-HDR and two for the microSelectron-PDR, for which data are currently not available. The information we have obtained in this study can be incorporated into clinical practice.

Algorithms↗
PubMed1997

[A quality assurance program of simulators in radiation therapy. 2. Extent and results of long-term quality assurance test on a therapy simulator].

BACKGROUND: Since 1990 we follow a quality assurance program with periodical tests of functional performance values of a 16-year-old simulator. MATERIAL AND METHOD: For this purpose we adopted and modified German standards for quality assurance on linear accelerators and international standards elaborated for simulators (International Electrotechnical Commission). The tests are subdivided into daily visual checks (light field indication, optical distance indicator, isocentre-indicating devices, indication of gantry and collimator angles) and monthly and annually tests of relevant simulator parameters. Some important examples demonstrate the small variation of parameters over 6 years: position of the light field centre when rotating the collimator, diameter of the isocentre circle when rotating the gantry, accuracy of the isocentre indication device, and coincidence of light field and simulated radiation field. RESULTS: As an important result we can state, that by these rigid periodic tests it was possible to detect and compensate deteriorations of simulators quality rapidly. CONCLUSIONS: Technical improvements and specific calling-in of maintenance personnel whenever felt appropriate provided performance characteristics of our old simulator which are required by international recommendations as a basis for modern radiotherapy.

Germany↗
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↗
PubMed1996

[A proposal for dosage and volume specification and documentation in HDR brachytherapy].

BACKGROUND: Modern computer-aided brachytherapy techniques and the various clinical and radiobiological methods require a review and standardization of dose specification and documentation in brachytherapy. METHOD: The methods and the extent of the dose specification and documentation have been analysed on the base of known international and national procedure. A new modified report has been prepared for the standardized dose specification for HDR-brachytherapy techniques. RESULT: Brachytherapy treatments are supposed to be documented in 3 different levels (I to III), the extent of which depending on the treated volume, the therapeutic aim and the equipment available. CONCLUSION: The extent of documentation and dose specification proposed in this paper requires the close cooperation of radio-oncologists and medical physicists. It seems to be advantageous to use prepared sheets or computer prints in order to minimize the time and efforts for a sufficient documentation.

Brachytherapy↗
PubMed1995

Prognostic evaluation of oestrogen-regulated protein immunoreactivity in ductal invasive (NOS) breast cancer.

Determination of steroid receptors and several oestrogen-regulated proteins in mammary carcinomas is useful in the prediction of their evolution and of the likely success of endocrine therapy. Cathepsin D (Cat D), pS2 peptide and heat shock protein 27 (Hsp 27) were detected immunohistochemically in 63 infiltrating ductal (NOS) breast carcinomas, and our results were qualitatively correlated with several clinicopathological indicators and patients' overall survival. Cat D immunostaining of tumour cells was strongly associated with axillary nodal involvement (Pf = 0.0005) and so, it is directly connected with the metastatic capacity of malignant cells. pS2 immunoreactivity was correlated with oestrogen and progesterone receptor positivity (Pf = 0.0009 and Pf = 0.05 respectively) and, nonsignificantly, with good differentiation of the tumours (Pf = 0.06). Neoplastic cells expressing this protein are therefore characterised by a highly organised state of cellular physiology. Hsp 27 was expressed predominantly in tumours with one to four infiltrated lymph nodes (Pt = 0.05), and Hsp 27-positive patients were inclined to rather short survival, possibly due to chemotherapy resistance. In future, prognostic estimation of each one of the examined markers should be performed in specific large subgroups of patients. The findings of this study contribute to the establishment of criteria by which these subgroups should be formed.

Adult↗
PubMed1993

[A quality assurance program for simulators in radiotherapy. 1: The universal phantom for quality control of therapy simulators and teletherapy equipment].

A new phantom is described which shall be utilized to check geometric parameters of simulators and therapy units. Because of its mechanical assembly technique construction it is possible to use any part of the system fixed on a base plate which has to be adjusted only once. The application of the different parts of the phantom will be illustrated by some check examples on simulators and linacs. An intercomparison of quality control data referring to therapy simulators in various centres of South Germany has been started whereby the usability and reliability of the phantom also will be tested. The preliminary results give objective reasons for its suitability to study generally the performance tolerances of simulators with regard to quality assurance in radiotherapy.

Computer Simulation↗
PubMed1989

Analysis of late effects data using dose-response models: application to human skin telangiectasia data.

The clinical data for skin telangiectasia from previous prospective studies at the Radiotherapy Department in Gothenborg are reanalyzed using two dose-response models - the general formulations of the well known linear-quadratic (LQ) and NSD isoeffect models. Assuming that essentially no repopulation appears in the vessel endothelium for overall treatment times up to 68 days, the alpha/beta-value of 2.75 Gy is obtained for the LQ-model. The time factor is found not to be significant by the NSD-model for the treatment times used (less than or equal to 68 days) at the 95% level of confidence. The estimated value of the exponent of the number of fractions, A, is 0.321. The obtained values of the alpha/beta-ratio and of A show high sensitivity of the vessel endothelium to changes in the dose per fraction. Our results show that within the interval of the number of fractions used, 10-35 fractions, the NSD-model gives predictions comparable to those of the LQ-model. For number of fractions smaller than 5, a high discrepancy occurs between the two models, the NSD-model predicting higher values of the isoeffective total dose. The maximal deviation between the models appears for N = 1; 25% and 27% at the 5 and 50% level of effect, respectively. For large N and especially at low effect probabilities the NSD-model again predicts higher isoeffective doses: the dose predicted by the NSD-model for a regimen with 40 fractions and for 5% probability of telangiectasia is 7.5%, higher than that predicted by the LQ-model. Based on the estimated dose-response curves, considering the telangiectasia as the decisive late tissue effect, the requirement for the combined uncertainty in the dose delivery is estimated between 3 and 4.5%.

Dose-Response Relationship, Radiation↗
PubMedDate not supplied

Clinical relevance of tumor ploidy and micronucleus formation for oral cavity cancer.

AIMS AND BACKGROUND: To study the clinical relevance of tumor ploidy and micronucleus formation as prognostic factors. METHODS AND STUDY DESIGN: Twenty-eight patients with squamous cell carcinoma of the oral cavity were treated with primary radiochemotherapy consisting of irradiation up to 70 Gy in combination with cisplatin. Cell cycle distribution, micronucleus formation and ploidy were evaluated by flow cytometry of biopsies taken before treatment and after irradiation to 10 Gy (5x2 Gy). Sexteen out of 28 patients relapsed after a minimum follow-up period of two years. RESULTS: Flow cytometry of the recurrence biopsy showed hyperpentaploid (5c exceeding) cells in 13/16 (81%) of the relapsed patients. In 7 patients the hyperploid clone was not present in the flow cytometry of the primary tumors. Ploidy could retrospectively be determined also by image cytometry in archival tumor material of the pretreatment specimens. Patients with a level below 100 5c cells per 10,000 cell nuclei were shown to have a significantly better prognosis than patients with more than 100 hyperpentaploid tumor cells. The micronucleus formation was 2-5 times higher in tumors showing a good response to treatment than in carcinomas relapsing within two years. CONCLUSIONS: The 5c-exceeding ratio measured by image cytometry and micronucleus formation proved to be good prognostic parameters for the clinical outcome of patients with locally advanced head and neck carcinomas.

Chemotherapy, Adjuvant↗
PubMedDate not supplied

Tumor volumetry as predictive and prognostic factor in the management of ovarian cancer.

BACKGROUND: The usefulness of tumor volumetry in ovarian epithelial cancer has never been intensively investigated. The aim of the present study was to determine the value of quantitative analysis of tumor volume as a predictive method for response to treatment and as a prognostic method for disease outcome. MATERIALS AND METHODS: Seventy-five women with advanced ovarian cancer who presented with measurable disease on CT scan prior to chemotherapy were retrospectively studied. The patients were treated with platinum-based chemotherapy. The median follow-up was 113.36 weeks. An independent radiologist identified and delineated tumor contours in each slice of sequential CT scans before and after therapy. Volumetry was measured with a three-dimensional approach by utilizing a digitizer and a specific algorithm on a software computed program. RESULTS: Data were analyzed according to initial and to residual tumor volumes. Patients with low initial volume of <52 cm3 exhibited higher responses (p<0.01), while patients with medium (52-165 cm3) or high (>165 CM3) initial tumor volume had a shorter time to progression (p<0.01). Patients without or with low residual volume of <35 cm3 were found to have a longer time to progression (p<0.05) and longer survival (p<0.01 and p<0.05). In addition, serum CA 125 levels followed precisely tumor volumetry for both initial and residual disease. CONCLUSION: Tumor volumetry in advanced ovarian cancer was found to have predictive value for response to platinum-based chemotherapy. Initial tumor volume has prognostic significance only for the time to progression, whereas residual tumor volume has for both time to progression and survival.

Adult↗