  We analyze the necrosis growth due to thermal coagulation induced by laser
light absorption and limited by heat diffusion into the surrounding live
tissue. The tissue is assumed to contain a certain tumor in the undamaged
tissue whereof the blood perfusion rate does not change during the action. By
contrast, the normal tissue responds strongly to increase in the tissue
temperature and the blood perfusion rate can grow by tenfold. We study in
detail the necrosis formation under conditions typical for a real course of
thermal therapy treatment, the duration of the action is taken about 5 minutes
when a necrosis domain of size about or above 1 cm is formed. In particular, if
the tumor size is sufficiently large, it exceeds 1 cm, and the tissue response
is not too delayed, the delay time does not exceed 1 min, then there are
conditions under which the relative volume of the damaged normal tissue is
small in comparison with the tumor volume after the tumor is coagulated
totally.
