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Biomedical subjects

M Bleher

Publications and source records attributed to M Bleher.

5 recordsLinked to original sources
PubMed1999

Comparative study of the PARK and ASTRAL post-accidental decision support software.

The French radioecological assessment model ASTRAL and the German model PARK have been developed to evaluate the radiological situation in the case of an accidental release of radionuclides and a widespread contamination of the environment. For decision makers it is of importance that the results on foodstuff contamination and on dose to humans are in fairly good agreement, when areas of the common border are affected. Therefore a comparative study has been done for two scenarios, assuming accidental releases on 1 June and 1 October. The study indicates that the models' structures and the transfer parameters are in good agreement. Only model principles for root vegetables are different in both models. Significant differences in results on the contamination of foodstuff and on dose to humans by ingestion are caused by different assumptions on dates of harvest and feeding methods of animals. A corresponding harmonization is essential with respect to decision making.

Animal Feed↗
PubMed1992

The use of isodose curves on radiographs and on CT scans in interstitial brachytherapy.

In brachytherapy an accurate dose distribution is usually not definable, and therefore not required. If flexible catheters are implanted, such as in head and neck cancer, resulting isodose curves only rarely fit exactly to radiographic films, and the target volume is not easily reconstructed. Usually no clear relationship exists between the three-dimensional (3D) dose distribution and target volume on the one hand and the two-dimensional (2D) radiographic films on the other. Dose distributions on radiographs are not sufficient to define the target absorbed dose and doses that critical areas will receive. A 3D imaging system, like computed tomographic (CT) scans, is needed in order to visualize underdosage inside the target volume and non-tolerable hot spots outside the tumour. Large-scale and expensive techniques exist to tackle these problems. Our inexpensive and verifiable approach to solve these problems combines localization radiographs with CT scans. Whereas tumour and critical areas are displayed on CT scans, flexible catheters loaded with dummy sources are best seen on radiographic films. With the help of a self-developed computer program, dose distributions are superimposed on CT scans. Doses to the target and critical organs are easily read and verified by external and internal detectors.

Brachytherapy↗
PubMed1991

[Assessment of radiotherapy plans: dose-volume histograms, integral effects and tumor control].

Suitable criteria are necessary for judgement and for comparison of treatment plans. These criteria must take into account radiobiological effects, i.e. tumor control and treatment complications. Quantitative evaluation of dose volume histograms gives helpful criteria for radiation treatment planning and for the choice between different treatment plans. For normal tissue and organs at risk it is shown, how to assign integral dose effect to inhomogeneous dose distribution. The evaluation algorithm is based on the assumption of a power law for volume dependence of dose effect. The algorithm is discussed for arbitrary form of dose effect function. Explicit evaluation is given in terms of the linear quadratic model. Hot spots influence integral dose effect much stronger than low dose level irradiation. For judgement of treatment plans, the significance of mean organ dose is only poor. Higher moments of dose distribution are more suitable. An effective tumor control probability is derived for judgement of tumor dose distribution. It is shown that tumor control is determined by mean dose and dose inhomogeneity in tumor volume. Control probability falls with increasing dose inhomogeneity in tumor region-in first order approximation characterized by variance of dose distribution. Using a clinical example, the evaluation rules for normal and tumor tissue are demonstrated. Two different treatment techniques are analyzed and discussed. Only numerical evaluation of dose volume histograms for lung region shows the better technique.

Algorithms↗
PubMed1991

[Quality assurance in dynamic radiotherapy techniques].

Compared with conventional radiation treatment techniques, quality assurance for dynamic techniques has to consider additionally the variability of the movement parameters of the treatment unit. In this context the exactness and the reliability of the computer control are of special interest. In this paper the results of quality assurance for dynamic treatment techniques are reported. At first investigations concerning the reproducibility are carried out. Another test is the simulation of conventional moving beam techniques by external computer control. Further the differences between measured dose distributions of dynamic techniques and the distributions resulting from the sequence of fixed fields approximating these techniques are determined. Finally we compared measured and calculated dose distributions. The results of the investigations justify the introduction of dynamic radiation treatment techniques into clinical use.

Humans↗