Use of heating rate and specific absorption rate in the hyperthermia clinic.

The specific absorption rate (SAR), which is the mass-normalized rate of energy absorption by a biological body, has been used by hyperthermia researchers to characterize energy deposition and heating patterns in tissues and in biological models. Before thermal diffusion and blood flow alter the temperature distribution, energy deposition and heating rate (HR) are related by constants. Therefore SAR is usually calculated from the initial rate of temperature rise measured during heating. SAR is an appropriate parameter for theoretical calculations or electric field measurement in tissue. However, the ultimate parameter in hyperthermia is temperature. Instead of computing the temperature rise from SAR (W/kg) and specific heat (kcal/kg.degree C) which were originally obtained from temperature measurements, it is simpler and more convenient to use HR (degree C/W-min) directly, especially when heterogeneous tissues are involved. The advantages of using HR instead of SAR in hyperthermia clinics are discussed.