Effect of insertion depth on helical antenna performance in a muscle-equivalent phantom

Preliminary findings from tests of a microwave applicator designed to treat Barrett's oesophagus

Barrett's oesophagus is considered to increase the risk of cancer 30-fold. Helical microwave antennas have been developed for ablative treatment of Barrett's. A microwave balloon applicator was tested in an initial animal study using adult white pigs. For treatment, a balloon filled with tissue-equivalent material encapsulated the antenna. A range of different treatment temperatures and durations was used to investigate a range of thermal ablations of the oesophageal epithelium. Eight animals were investigated, five non-survival and three with a 1-week survival period. The balloon was fitted with an array of temperature sensors, which gave an indication of the treatment in situ and allowed modifications to be performed in real time. Temperature data were recorded from all four quadrants of the balloon throughout and test sites were collected and analysed histologically. All experiments were successfully completed without perforation, serious adverse effects or death. Sites of discrete ulceration were induced in the survival tests, whereas the non-survival tests yielded little reproducible tissue modification. Results suggested that an activation temperature of approximately 55 degrees C needed to be reached during the treatment for tissue damage to be induced. Once damage had been triggered the severity was related to the mean temperature attained during the treatment period. A mean temperature of 52 degrees C or more resulted in substantial damage, whilst a mean temperature of approximately 50 degrees C resulted in the desired surface damage with sparing of subjacent tissues.