Stromal sensitivity to radiation and hyperthermia.

The influence on stroma of heat alone, X-rays alone or the combined treatment, has been studied using the tumour bed effect (TBE) as an assay. Ca NT cells have been implanted into previously treated subcutaneous sites as an angiogenic stimulus. The vascular damage is then assessed by the reduced tumour growth rate, which results from inadequate vascular proliferation. A range of X-ray doses was used and large alterations in latent period for growth to 2 mm diameter were followed by smaller alterations in the growth rate of established tumours. A dose response relationship was seen for latency (0-20 Gy) and for growth rate (0-16 Gy). A range of subcutaneous temperatures was obtained by immersion in a water bath for 60 minutes at 40 degrees, 41.5 degrees, 43 degrees or 44.5 degrees C. A slight retardation of tumour growth was seen after 41.5 degrees C, but an unexpected acceleration resulted from the highest heat treatment. Combined heat and X-ray treatments showed thermal sensitization of the X-ray induced TBE at 41.5 degrees C, with a reversal at higher temperatures. At 43 degrees C and 44.5 degrees C a mild thermal burn was induced and this appeared to elicit neovascularisation that could be utilized by the implanted tumour cells. Delayed implantation of tumour cells (at 4 weeks instead of 1 day) abolished this effect.