Influence of thorax irradiation on the survival of mice with spontaneous or artificial lung metastases from a transplantable mammary adenocarcinoma

Residual late radiation damage in mouse stromal tissue assessed by the tumor bed effect

Irradiation of murine subcutaneous stroma before implantation of tumor cells leads to retarded tumor growth. This effect is called Tumor Bed Effect (TBE) and can be used to assess the sensitivity of stromal tissue to radiation. We tested the ability of stromal tissue to recover from X-ray-induced damage as a function of the time interval between X-irradiation and implantation of tumor cells over a period of 195 days. We also assessed the effects of a second test treatment of X-irradiation before implantation to assess residual damage by the first radiation treatment. The tumor bed effect in C57Bl10xDBA2 mice observed after X-ray treatment and implantation of M8013 cells (from a transplantable mouse mammary carcinoma) declines with the time that elapses between X-rays and implantation. Implantation of tumor cells 195 days after initial irradiation of 10 or 20 Gy resulted in a considerably smaller TBE. The half-time of the decay is estimated as about 50 days. The extent of the recovery was then tested in two-fraction experiments, with radiation fractions separated by intervals of 30 or 180 days. In the experiment with re-irradiation at an interval of 30 days after the first radiation dose of 20 Gy hardly any recovery was observed, whereas at an interval of 180 days a considerable recovery was observed. We presume that the recovery in TBE that was observed a long time after the irradiation results from a proliferative stimulus to endothelial cells which takes place during the post-irradiation period. The proliferative response leads to cell death of the X-ray damaged endothelial cells and thereafter these are replaced by healthy cells.

Radiobiological determination of growth kinetics and radiosensitivity of pulmonary micrometastases of the R1H tumour

The aim of the study was to determine the radiosensitivity and the growth kinetics of pulmonary micrometastases of the R1H tumour of the rat. Lung metastases were induced by intravenous injection of viable tumour cells. At different time intervals (3-32 days) after injection, lungs were locally irradiated with 200 kVp X-rays, using 1.5 Gy/fraction. Total doses of 6-33 Gy were administered within 11 days. Endpoints used were survival time, local control rate, and number of metastases in the lungs at autopsy. The data were evaluated using the multi-target model. Beginning in the fifth week after tumour cell inoculation the animals started to exhibit a pronounced dyspnoea and were sacrificed. Sections revealed an extensive metastatic infiltration of the lungs. With increasing total dose a prolongation of survival time as well as an increase in cure rate was observed. The number of metastases found in the lungs decreased with increasing total dose. It is concluded that metastatic growth does not start earlier than 3 days after tumour cell inoculation and accelerates continuously. The doubling time of the tumour cells in the micrometastases decreases continuously and from 5.2 to 1.2 days between day 3 and 40, whereas larger metastases containing more than 10(6) cells show gompertzian growth kinetics. The cell doubling time in this stage of metastatic growth is longer than 5 days. During the first 4 weeks of metastatic growth the radiosensitivity of metastatic R1H cells in the lungs is the same as in vitro.

The lymphnodal clonogenicity and kinetics of metastatic cells disseminated by a transplanted rat carcinoma

We report data on the transplantation of primary tumour cells and of lymph nodes containing metastatic cells disseminated by a mammary carcinoma (LMC1) implanted s.c. in the Johns' Strain Wistar rat. A new method is described for deriving the TD50 of metastatic cells and for comparing their lymphnodal clonogenicity in the transplanted and the original, i.e. 'primary' tumour host. The TD50 for transplanted primary LMC1 cells was approximately 12 (fiducial limits 8-20 cells), and the latency of the 8-10mm tumours formed (T8-10) after inocula of 10(2) to 10(5) cells decreased linearly with the logarithmic increase in the number of cells injected. From the T8-10 and tumour incidence data for transplanted inguinal, axillary and para-aortic nodes, the TD50 for metastatic cells was calculated to be 1120 cells (fiducial limits 790-1603 cells) indicating that the clonogenicity of naturally disseminated metastatic cells was about a 100 fold lower than that determined for transplanted primary tumour cells. The incidence and T8-10 data for axillary, inguinal and para-aortic lymph node metastases in primary-tumour-excised hosts suggests that, although metastatic cells may continue translymphnodal dissemination in situ, their TD50 is still consistent with that determined by node transplantation.

Effects of hyperthermia and X-irradiation on mouse stromal tissue

The sensitivity of normal stroma to heat, irradiation and heat combined with irradiation has been studied using the tumour bed effect (TBE) assay. Irradiation before implantation led to a TBE. This TBE was dose dependent below 15 Gy, the TBE remaining relatively constant above 15 Gy. The interval (0-90 days) between irradiation and tumour implantation did not influence the magnitude of the TBE. Hyperthermia with large heat doses (45-60 min at 44 degrees C) before implantation may lead to a TBE. The interval between hyperthermia and tumour implantation proved to be very important. Our results show that the recovery from heat-induced stromal damage is very rapid. When the interval between hyperthermia and tumour implantation is 10 days or longer, no TBE could be observed. Irradiation combined with large heat doses (30-60 min at 44 degrees C) decreased the radiation-induced TBE. However, the combination of irradiation with mild heat treatments (15 min at 44 degrees C) could lead to a larger TBE than after irradiation alone. When hyperthermia was given prior to irradiation, the interval between heat and irradiation proved to be very important. With large intervals (21 days or longer) the TBE values were about the same as with irradiation alone. When heat was given after irradiation it always reduced the irradiation-induced TBE.