Recent developments have reinvigorated clinical investigations of hyperthermia (HT) as a viable adjuvant treatment in the fight against cancer. Researchers are placing a greater emphasis on multi-modal approaches that include mild temperatures (40°C - 43°C) and standard therapies like radiation and chemotherapy than on achieving higher temperature treatments (43°C-45°C) which were pursued in the past. The emergence of robust computer simulation tools for accurate hyperthermia treatment planning has aided this resurgence by helping improve the quality of heating. This article outlines a recent collaborative study at Duke University to demonstrate the capabilities of a new suite of 3D electromagnetic and thermodynamic simulation tools for treatment planning of external hyperthermia treatments with a radio frequency (RF) phased array heat applicator. Following a brief introduction to the rationale for moderate temperature hyperthermia and current methodology for heating tissue at depth in the body, the article will present a new approach for improved heating based on treatment planning with electromagnetic simulation software tools. Procedures, benefits, and a comparison of simulated heating patterns with those measured in two clinical hyperthermia treatments of advanced fibrous histiocytoma (soft-tissue sarcoma) tumors will be presented.