Regrowth, tumor cell proliferation and morphological alterations of the adenocarcinoma EO 771 following a single dose of 30 Gy 60Co gamma-rays.

The effect of irradiation with 30 Gy 60Co gamma-rays on the adenocarcinoma EO 771 has been studied by simultaneously evaluating the effect on tumor growth, on tumor cell proliferation and on the histological structure of the tumor. Inspite of a drastic decrease of tumor cell density by a factor of 2 within one day after irradiation there is practically no tumor regression but only a growth delay lasting about five to six days. The lack of decrease in tumor volume is due to hemorrhages and interstitial oedemas. Regrowth of the tumor starting after about five days concomitantly with the removal of necrotic tissue is followed by a second wave of growth delay. Following the release of the G2 block of the cells tumor cell proliferation is reduced to about half the normal proliferative activity for further three days. Tumor cell proliferation reaches its maximum about eight days after irradiation and then decreases again although higher proliferative activity should be expected comparing the size of the tumor with that in untreated animals. The proliferative activity is much higher in the tumor periphery than in the center suggesting that radiation damage is more rapidly compensated in the tumor periphery. These studies confirm that tumor volume changes are not representative for radiation effects but that there are many processes as damage to the vascular system or the tumor bed effect that influence the effect of irradiation on the tumor.