A needle type applicator using heatpipe is proposed for local intracavital or interstitial thermotherapy of malignant neoplasmas. Advantages of heatpipe are as follows : (1) rapid and high heat transfer rate (2) homogenious heating along needle length (3) easy temperature control. Its disadvantages are traumatic and short range of heat transfer in the transaxial direction. But the short range of heating may be a merit to preserve surrounding normal tissues from heat damages and several numbers of heatpipes inserted with appropriate arrdngement may control bulky tumors. Histological studies revealed gradual changes after heat therapy in the trans-axial plane. The tissue close to the heatpipe shows necrosis and between it and viable tumor tissue capillary dilatation with hemorrhage is found. The boundary of tissue damage is so clear that it supports existence of a breaking point in thermal damage in the tissue level.
