Scanning electron microscopic study of the three-dimensional structure of the collagen sheath surrounding cancer cells after single high-dose irradiation.

The effect of single high-dose irradiation on collagen networks in tumor cells was examined by scanning electron microscopy. MM46 tumor cells were transplanted into C3H/He mice and locally irradiated with a 30 Gy dose (6 MeV) 7-8 days posttransplantation. Mice were killed at various time points postirradiation, and tumor tissues were excised and fixed. After 2 N NaOH maceration, tissues were washed and stained with 1% tannic acid. They were then postfixed with 1% OsO4, dehydrated, and dried. The tissues were coated with gold, and the three-dimensional structure of the collagen fibers was observed using scanning electron microscopy. In the control group, the chambers formed by collagen fibers were larger on days 7 and 14 than those on days 1 and 3. In the irradiated group, the chambers were largest and most irregular in shape on day 7. The chamber size had decreased approximately 50% by day 14, and there was evidence of tumor cell regeneration. In addition, several fenestrations in the chamber wall developed in the irradiated group. Fenestrations in the collagen chamber walls surrounding tumor cells might allow transfer of metabolites that provide nutrition to the tumor cells, leading to their regeneration.