Tumor control in long-term survivors following superficial hyperthermia

Sixty tumors with a minimum of 1-year follow-up were treated with radiation and superficial microwave hyperthermia (915 MHz). The overall local control rate was 50% ( 30 60). The most important factor in outcome was appropriateness of the hyperthermia applicator. Tumors covered by at least the 25% iso-SAR contour achieved 65% local control versus 21% local control with less than 25% SAR coverage (p < 0.01). Several measures of adequate minimum monitored tumor temperature and duration were considered. The measure best correlated with outcome was best single session time at or above 43°C (t₄₃). If each monitored tumor catheter achieved t₄₃ ≥ 30 minutes in at least one session, then tumor control was significantly (p < 0.01) improved (63% with Min t₄₃ ≥ 30 versus 25% with Min t₄₃ < 30). Although there was considerable overlap between tumors with SAR ≥ 25% and those achieving Min t₄₃ ≥ 30, a statistically significant (p = 0.02) difference could be demonstrated between the group meeting both the SAR and the minimum tumor time/duration standards as opposed to those meeting only one standard. The actuarial local progression-free survival for tumors most likely to have had adequate hyperthermia (defined as SAR ≥ 25% and Min t₄₃ > 30) and all other tumors did not begin to separate significantly until 8 to 12 months after treatment. Implications for future randomized studies are discussed.