Abstract
Hyperthermia has been applied for the treatment of oral cancers, in combination with radiation and chemotherapy. However, hyperthermia apparently affects normal tissues, such as the salivary glands, which lie adjacent to tumors.
In the present study, damage to the submandibular salivary glands resulting from hyperthermal therapy was investigated in the rat. The glands were heated at 40°C (maximum temperature in glands=40.43°C ±0.31°C), 41°C (41.68°C ± 0.44°C), 42°C (42.30°C ± 0.25°C), 43°C (43.38°C ± 0.50°C), and 44°C (44.51°C ± 0.34°C), respectively. Heat was applied for 40 minutes using 13.56 MHz RF hyperthermia (NOVATHARM IH 500). Histopathology, angiography, and the uptake and excretion of 99mTcO4-were employed to evaluate the severity of the damage. It was found that heat below 42.30°C ± 0.25°C caused no serious damage either morphologically or functionally. At 43°C, some of the glands changed irreversibly, while others did not. All of the glands which were heated to 44°C suffered irreversible changes. The maximum tolerated temperature was, therefore, assessed as 43.38°C ±0.50°C.
To examine the process of regeneration of glands which had been damaged by heating to 44°C, BrdU was employed. Staining was positive from the 1st day until 4 weeks after heating. Coagulation necrosis was seen on the 3rd day after heating, and squamous cell metaplasia was observed on 7th day. Regenerated acinous cells that were stained by BrdU and PAS were seen 3 weeks after heating just next to the remaining normal cells. 8 weeks after heating, the borders between normal and damaged tissues had become indistinct.
