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F Würschmidt

Publications and source records attributed to F Würschmidt.

27 records · Page 2Linked to original sources
PubMed1992

Radiotherapy of the rhabdomyosarcoma R1H of the rat: recovery from radiation injury in tumour and skin.

The response of the rhabdomyosarcoma R1H of the rat to fractionated irradiation has been reported to be almost independent of the dose per fraction in the range from 0.43 to 10 Gy. To elucidate whether recovery from radiation injury is impaired in fractionated irradiation or not, tumours were exposed on 5 days per week over 6 weeks either to a single daily dose or to two daily fractions separated by an interfraction interval of 2 h. Tumour response was assessed by net growth delay. Skin damage was scored for comparison. A significant reduction in tumour response (p less than 0.009) and skin damage (p less than 0.001) was observed when the daily dose was administered in a twice daily irradiation regimen, indicating that recovery from radiation injury does occur in the course of fractionated irradiation in our tumour system. A tumour response was almost independent of the dose per fraction for time intervals between fractions of at least 8 h, a possible explanation might be that recovery is compensated by improved reoxygenation.

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PubMed1991

Influence of treatment time on the response of rat rhabdomyosarcoma R1H to fractionated irradiation.

The aim of this work was to study influence of overall treatment time on response of an experimental tumour to fractionated radiotherapy. Rhabdomyosarcoma R1H of the rat was treated by fractionated irradiation applying 30 fractions in different overall treatment times of 10, 18.5, 29, 39, and 67 days. The doses per fraction ranged from 1.50 to 2.67 Gy. Tumour response was assessed by net growth delay and by an in vitro colony assay. The results indicate that repopulation of the tumour with clonogenic tumour cells slowed down during treatment leading to an average doubling time of clonogenic tumour cells of 8 +/- 1 days, which is considerably longer than that of unirradiated tumours (3 days). The repopulation rate seemed to increase after about 3 weeks of treatment with a doubling time of tumour clonogens of 5 +/- 1 days, which was still lower than in control tumours.

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PubMed1991

Radiotherapy of the rhabdomyosarcoma R1H of the rat: split-course versus continuous fractionation.

Fractionated split-course treatments were given with gaps of different length and the effects on tumor response was studied using the rhabdomyosarcoma R1H of the rat. Total doses of 68, 75 and 82 Gy were applied in 30 fractions (five fractions per week). After four weeks, that is after 20 fractions, treatment was interrupted for one or two weeks followed by another ten fractions. The results were compared to those of continuous treatment given in six consecutive weeks. Tumor response was quantified by TCD37% and net growth delay. The TCD37% increased with increasing duration of the gap. A mean repopulated dose of 0.72 Gy per day was obtained. This corresponds to a doubling time of tumor clonogens of 4.2 days during the gap, which is somewhat slower than the volume doubling time of unperturbed tumors (2.5 days) of the same size. The results obtained for the net growth delay support the results of the TCD37% data. It is concluded that a gap during fractionated radiotherapy leads to poorer results since the dose required for tumor control is enhanced and sparing of normal tissue can only be expected for early but not for late reacting tissues.

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PubMed1990

Radiobiology of the rhabdomyosarcoma R1H of the rat: influence of the size of irradiation field on tumor response, tumor bed effect, and neovascularization kinetics.

R1H tumors were irradiated with a single dose of 15 Gy X rays using varying sizes of treatment fields. Damage to tumor cells and tumor stroma was determined separately by analysis of growth delay to ten times treatment volume (GD10vo) and net growth delay. GD10vo comprises irradiation effects on tumor parenchymal cells and on tumor stroma, whereas net growth delay only measures effects on tumor parenchymal cells. Stromal damage was observed to increase with increasing field size; the effect on the tumor parenchymal cells, however, was independent of the field size. An increase of GD10vo of 13 days per cm increase of field size diameter was observed. From this the velocity of neovascularization of the irradiated tumor bed was calculated to be 0.30 to 0.38 mm per day.

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PubMed1990

A simple experimental technique for interstitial iridium-192 high dose-rate afterloading.

A simple experimental technique for interstitial iridium-192 high dose-rate afterloading is described which allows to perform experimental brachytherapy on a rat tumor model. To illustrate the possibilities and limitations of the technique, rhabdomyosarcoma R1H of the rat were subjected to a combined brachy- and teletherapy treatment applying a total dose of 60 Gy in fractions of 2 Gy. The results show that the surgical procedure had no influence on tumor response. However, would healing was considerably disturbed in animals which received afterloading treatment.

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PubMed1989

Radiotherapy of the rhabdomyosarcoma R1H of the rat: hyperfractionation--126 fractions applied within 6 weeks.

The effect of a hyperfractionated irradiation treatment on the response of the rhabdomyosarcoma R1H of the rat was studied. Tumors were irradiated under ambient conditions with 126 fractions of X rays, applied in 3 fractions per day with a time interval of 8 +/- 1 hr between fractions on 7 days per week during 6 weeks. The total dose ranged from 54 to 90 Gy, that is the dose per fraction ranged from 0.43 to 0.71 Gy. Tumor response was assessed by tumor control probability and tumor net growth delay. The tumor response to the hyperfractionated treatment was found to be slightly more effective compared to the results obtained in a previous study where treatments with 6, 18, 30, and 42 fractions were applied. Since normal tissues are considerably spared with increased numbers of fractions, clinical studies with hyperfractionation seem to be very promising.

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PubMed1988

Radiotherapy of the rhabdomyosarcoma R1H of the rat: the influence of the number of fractions on tumor and skin response.

The influence of the number of fractions on tumor and skin response to fractionated irradiation was studied. R1H rhabdomyosarcomas of the rat (volume doubling time 3 days) were irradiated with 6, 18, 30, or 42 fractions in 6 weeks. Total doses of 45, 60, or 75 Gy were applied in each fractionation scheme, that is, the dose per fraction ranged from 1.07 to 12.5 Gy. Tumor response was assessed by tumor control probability and tumor net growth delay. A clearcut reduction of skin damage was observed with increasing number of fractions, whereas the tumor response was found to be the same whether the dose was given in 6, 18, 30, or 42 fractions. Thus, the fractionation regimens were more effective than expected from calculations based on single-dose in situ survival curves. This result can be explained by assuming that the clonogenic tumor cells become less hypoxic with increasing number of fractions. Since normal tissue damage decreases with increasing number of fractions, the therapeutic gain may be improved by applying a greater number of fractions.

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PubMed1987

Net growth delay: a novel parameter derived from tumor growth curves.

Growth delay does not only reflect the effect of treatment on the tumor parenchymal cells but also on the stroma. Due to tumor bed effect, the extent of growth delay determined from tumor growth curves is highly dependent on the end volume chosen. It was aimed to minimize the influence of the tumor bed effect on the growth delay calculated by choosing a smaller size and essentially an earlier time for regrowth. Net growth delay is a novel parameter derived from the tumor growth curves, allowing a better comparison of the results with colony assay and tumor control data.

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