Purpose: To correlate patient-, tumor-, and treatment-related factors with subsequent local tumor control. Methods and Materials: From 1977 to 1990, 196 subcutaneous/superficial lesions (179 measurable, 17 microscopic) in 151 patients with recurrent breast carcinoma of the chest wall were treated with superficial 915-MHz microwave hyperthermia and irradiation. The definition of min t(43) greater than or equal to 10 min is that all monitored tumor catheters had a minimum of 1 hyperthermia session with temperatures >43 degrees C for at least 10 min. Results: Factors correlating with local control on univariate analysis included length of survival (greater than or equal to 1 year vs. <1 year) (p < 0.0001), specific absorption rate (SAR) (greater than or equal to 25% vs. <25%) (p = 0.0001), minimum t(43) > 10 min (p < 0.0001), tumor volume (p < 0.0001), tumor surface area (p < 0.0001), tumor depth (p = 0.0002), number of hyperthermia sessions (p = 0.0003), and current radiation dose (p = 0.0012). On multivariate analysis, the factors best correlated with ultimate local control were SAR (p < 0.001) and number of hyperthermia sessions (p = 0.003). Conclusions: Multivariate analysis supports the importance of adequate specific absorption rate (SAR) coverage as a better predictor of local control than tumor volume, surface area, or depth. The explanation is that SAR can be correlated with the tumor surface area and depth, depending on the hyperthermia applicator characteristics. It is recommended that future clinical trials stratify study lesions into either SAR greater than or equal to 25% or <25% because this can be readily estimated prior to initiating treatment, It is also recommended that future clinical trials attempt to have adequate lengths of follow-up after therapy to assess the results in long-term survivors. (C) 1998 Elsevier Science Inc.
