Radiobiologia, radiotherapia最新文献

A semi-phenomenological model has been derived, which describes the inactivation effect on individual cells by survival curves. This model is applied to experimental data of pneumopathy in pigs. The corresponding survival curves as well as the relations between cell survival and complication probability are calculated and discussed. Furthermore, dose-response curves for single dose irradiation and different fractionation schemes are derived. The comparison between the response curve for single dose irradiation and similar curves from the literature shows a good agreement.

With irradiation planning for electrons the calculation of dose distribution is very complicated because of dispersion of electrons especially in inhomogeneous medium. Using more efficient computers it is possible to calculate the electron distribution also for clinical application with complicated dose calculation programmes. An arithmetical logarithm according to principle of elementary pencil of rays is described and the correspondence of calculation with measurings at a plexiglass phantom is shown.

Though great advantages will be connected with endoradiotherapy, a lot of problems has still to be overcome, the greatest of them being without doubt the problem of selectivity of the carrier compounds. Some few of them have proved to be able to accumulate in certain cancers by reason of their incorporation as metabolites, especially in melanomas. The other great hope are the monoclonal antibodies or their fragments, and in this field much endeavour has been spent in the last years. Especially the two-step method of loading the radioactive nuclide to the antibodies when their binding to the cancer cells is complete appears very promising. Some other, unspecific vehicles may also prove suitable for accumulation in certain tumor types. For the selection of the nuclides it has to be considered that radiation biophysical experiments demonstrated that the critical targets for radiation action are with high probability the DNA superstructure units, and that the distribution of ionizations within them is decisive for the inactivation of a cell. With sparsely ionizing radiation (e.g. beta-radiation) rather high doses are required for reaching an adequate concentration of ionizations in these DNA units. Densely ionizing radiation with an LET of about 150 keV/microns exhibits the maximum relative biological effectiveness (12-16 referred to X-radiation). Therefore emitters of alpha-particles the LET of which lies actually somewhat lower, near 100 keV/microns, seem to be very suitable for endoradiotherapy. Moreover the short ranges of these particles (about 60 microns in tissue) render an extensive sparing of the surrounding normal tissue possible. The second group of effective nuclides is that of Auger electron emitters. The low-energy proportion of Auger electrons leads to a high ionization density in small volumes. The very short ranges of these electrons (in the nanometer range), however, require an incorporation of the nuclide into the cell nucleus if an effective cell inactivation is to occur. 211At (alpha-emitter) and 125I (Auger electron emitter) already proved their high inactivating effectiveness in cell cultures and their curative action in animal experiments, and studies of binding 211At to monoclonal antibodies are encouraging. Some other approaches proposed for the transport of radionuclides into tumor cells or for generating them within tumor tissue are also aimed in essential at the release of densely ionizing alpha-particles or of Auger electrons.

The aim of curative tumor therapy is healing without complications. Therefore the avoidance of undesirable side-effects in healthy tissue becomes more important to such a degree as the lifespan can be prolonged by therapy: In this review the experiences to cardiac reactions by ionizing radiations are represented from experiments on animals. The former conception of a marked radioresistance of the heart has to be revised to the hitherto presented investigations. Acute inflammatory reactions and late, often progressive alterations can develop in the heart like in other normal tissue. These late-effects especially are reflected at pericardium, myocardium and vessel system (microvessel system and coronaries) and not rarely cause functional injuries of the tissue. Actual investigations give special attention to pathogenesis of acute radioreaction. It is supposed that their explanation gives a better understanding for the process of independence and progress and with that a possibility for prophylactic or therapeutic measures.

Presented is the method of selective decontamination by van der Waaj. It is based on the conception of colonisation resistance deduced from animal experiments. So it means the concurrence of defense mechanisms which prevent the settlement of pathogenic germs and stabilize the normal microflora. First clinical and experimental results are reported.

Acute symptoms have to be noted by the roentgenologist in diagnosis of emergency as direct consequence of irradiation. Above all they pertain to organs of thoracal area (lung, heart) and of abdomen (small intestine, colon). Roentgenologic pictures are presented with exemplary case reports.

To test the radiogenic reaction of normal lung tissue experiments were done in 99 young pigs altogether. The radiation field included the total right lobe of the lung, 5 fractions of photons or neutrons (mean energy 6.2 MeV) were applied in a total treatment of 5 or 35 days. After killing the animals and taking the lungs the examination of tissue samples and others has been done for contents of hydroxyproline (HP) that has been used to register radiogenic injuries where the relation of irradiated and non-irradiated half of the same animal was estimated as measuring value. Above a limit of 1.13 for the HP-quotient (estimated in non-irradiated controls) there was a significant correlation with dose. Between the results of HP-quotients and histopathological findings a very good correlation was found. Calculation of RBE was done from relation of the dose values of photons and neutrons on base of the same level of injuries. In the tested total dose limit (photons: 14.25-38 Gy, neutrons 3.0-8.5 Gy) RBE-values of 3.8-4.5 were reached that correlates well with other tested criteria of the study in young pigs.

Two examples are presented to apply high dose rate afterloading therapy in treatment of tumors in childhood. The AL-therapy can be indicated in tumors in natural or artificial openings of the body that are limited locoregionally or were operated in sano. Applying brachytherapy radiogenic late-effects can be prevented in normal tissue like gonads and skeleton predominantly. On the other hand a tumor dimension greater than the target volume attainable by contact therapy has to be excluded certainly to avoid local recurrences.