Physical predictors of adequate hyperthermia with the annular phased array

One hundred and fifty-two hyperthermia sessions in 36 consecutive patients treated with the BSD 1000 annular phased array system (APAS) are reviewed with regard to physical predictors of quality of hyperthermia. Although central tumour temperatures exceeding 42°C were momentarily obtained in 62% of the sessions, it frequently proved difficult to maintain the patient at temperature for prolonged periods of time. The time to reach target temperature was negatively associated with quality of hyperthermia. Thus, of 25 sessions which required over 25 min to attain a temperature of 42°C, only one was adequate (defined as central tumour temperature ± 42°C maintained for at least 30 min) as opposed to 28/69 adequate sessions when 42 °C was reached in less than 25 min. Physical parameters measured in the first 3 min of the session found to be associated with adequate hyperthermia include an initial rate of temperature rise at the tumour site exceeding 0.4°C/min achieved with a net forward power less than 1500 W. Only three of 57 sessions not meeting these criteria were adequate. Treatment policy recommendations and recommendations for future research are made.