[en] Purpose/Objective: The purpose of this study was to elucidate the changes in tumor blood flow, tumor pO₂ and the radiation response of the tumors caused by mild temperature hyperthermia (MTH). Materials And Methods: Experiments were carried out using the R3230 Adenocarcinoma (R3230 AC tumor), grown subcutaneously in the right hind limbs of male Fischer rats. Tumors were heated once at 40.5 deg.to 43.5 deg.C for 30 or 60 min, or twice at a 24 hr interval. Tumor blood flow and tumor pO₂ were measured immediately after the hyperthermic treatments or after 24 hr using a radioactive microsphere method and by an Eppendorf pO₂ Histograph, respectively. The influence of MTH on the effect of X-irradiation (250 kVp) on this tumor was investigated with tumor growth delay and the in vivo/in vitro excision assay for surviving tumor cell fraction. Results: Tumor blood flow and pO₂ increased upon heating for 30 min at 40.5 deg.C to 43.5 deg.C, but following 60 min heating, the pO₂ was similar to that in control tumors. The tumor blood flow increased about 1.4-fold and the tumor pO₂ increased more than 3 times after 30 min heating at 42.5 deg.C. Therefore, the in vivo/in vitro assay and the growth delay were carried out following treatment with 42.5 deg.C for 30 min. As shown in Table 1, the reduction in surviving fraction by MTH before radiation was markedly greater than that by MTH after radiation. Table 1 also shows that MTH alone caused no growth delay compared to control and while heat after radiation increased the growth delay by 2 days, MTH before radiation increased the growth delay by 5 days compared to radiation alone. Conclusion: The results indicate that MTH is effective in increasing tumor blood flow and oxygenation and that MTH for 30 min at 42.5 deg.C, applied before radiation, significantly improves the radiation response of R3230 AC tumors

[en] Purpose/Objective: We have studied the effect of mild temperature hyperthermia (MTH) on pO₂ with or without carbogen breathing and the radio response in three different rodent tumors. Materials and Methods: SCK mammary carcinoma of A/J mice, FSall fibrosarcoma of C3H mice, and R3230 AC mammary carcinoma of Fischer rats were used. The changes in pO₂ in these tumors by MTH alone or in combination with carbogen (95% O₂ + 5% CO₂) breathing were studied. The MTH was done by immersing the legs bearing s.c. tumors into a water bath and the pO₂ was measured using an Eppendorf pO₂ Histograph machine. The influence of MTH on the effect of X-irradiation (250 kVp) on tumors was investigated with tumor growth delay and the in vivo-in vitro excision assay for hypoxic cell fraction. Results: The pO₂ in all three tumor types was increased significantly by MTH. The most effective heating conditions were 60 min at 41.5 deg. C for SCK and FSall, and 30 min at 42.5 deg. C for R3230 AC. Carbogen breathing alone increased the pO₂, but the effect of carbogen was dramatically enhanced when combined with heating. FSall tumors heated at 41.5 deg. C for 60 min before receiving a dose of 20 Gy took an average of 3 days longer than tumors receiving heat after irradiation to grow to four times their original volume. The identical conditions in SCK tumors heated before irradiation caused a 5 day growth delay. Effect of heating before or after irradiation on cell survival in tumor was determined using in vivo-in vitro excision assay method. Heating FSall tumors before irradiation for 30 min at 41.5 deg. C caused marked reduction in the hypoxic cell fraction. Cell survival studies in the SCK and R3230 AC tumors are currently being studied as well as the radiation response of all three tumors after heating combined with carbogen breathing. Conclusion: These results indicate that MTH is very effective in increasing the tumor oxygenation and the response of human tumors to radiotherapy. The combination of MTH and carbogen breathing was far more effective than MTH alone in increasing tumor pO₂