Histology as a method for determining thermal gradients in heated tumours.

It is proposed that histological assessment of tumours may be a useful biological thermal dosimeter. Assessment of nodules may give information about thermal gradients, and biopsies of treated tumours may serve as a prognostic indicator in clinical hyperthermia. Cell death after hyperthermia occurs rapidly and surviving cells are readily recognizable as small foci within 24 h. This contrasts with the delayed cell death and the more random distribution of survivors amongst killed cells after ionizing radiation. By 24 h, sections of tumours can demonstrate islands of apparently viable cells in a sea of necrosis after 44.8 degrees C/1 h. This technique has been used to identify regions of poor heating in mouse tumours treated by water immersion. Cells surrounding blood vessels and cells adjacent to underlying normal tissue were seen to be protected from thermal damage.