Mechanisms of Synergism between Arteriolar Embolization and Hyperthermia in a Rabbit V-2 Model of Solitary Hepatic Metastasis1

In a V-2 model of solitary hepatic metastasis, residual tumor was histologically identified in the treatment field in only three of 14 (21%) animals subjected to microsphere embolization of tumor arterioles plus focal (43°C, 40 min) hyperthermia compared with seven of ten (70%) subjected to focal (43°C, 40 min) hyperthermia alone (/' < 0.05), five of seven (71%) (P < 0.05) treated by occlusion plus sham heating, and five of five (100%) (/' 0.01) sham-treated controls. Prior occlusion tended to reduce the radiofrequency power required for heat up and steady-state temperature maintenance of tumors (/' < 0.09 and /' < 0.06, respectively) and reduced the cooling rate after heating compared to unoccluded tumors (/' 0.02) but did not affect mean time to temperature, maximum and minimum temperature measured at the tumor-normal tissue interface, and animal core temperature compared with that of the hyperthermia alone treatment group. In ten other animals with hepatic V-2 tumors of comparable size subjected to focal hyperthermia plus or minus arteriolar embolization, temperatures were continuously monitored at four addi tional inirui unior sites in a fixed geometric orientation around the heating probe. No significant differences were noted in maximum and minimum temperatures in comparably oriented probes over a 40-min heating period between the hyperthermia and the occlusion-hyperthermia treatment groups. In five other animals with solitary V-2 hepatic implants, com parable microembolization plus or minus focal tumor heating to 43°C, 40 min, did not significantly reduce tumor interstitial pH compared with pretreatment values. This study reproduces previously observed synergism between arteriolar embolization and hyperthermia but suggests the mechanism may be unrelated to observable differences in intratumor pH and thermal profile and may result from other mechanisms, perhaps by mimicking the angioocclusive effects of hyperthermia itself.