A method for the quantitative evaluation of SAR distribution in deep regional hyperthermia

The Specific Absorption Rate (SAR) distribution pattern visualization by a matrix of E-field light-emitting sensors has demonstrated to be a useful to ol to evaluate the characteristics of the applicators used in deep regional hyperthermia and to perform a quality assurance programme. A method to qua ntify the SAR from photographs of the sensor array-the so-called 'Power Ste pping Technique'-has already been proposed. This paper presents a new appro ach to the quantitative determination of the SAR profiles in a liquid phant om exposed to electromagnetic fields from the Sigma-60 applicator (BSD-2000 system for deep regional hyperthermia). The method is based on the constru ction of a 'calibration curve' modelling the light-output of an E-field sen sor as a function of the supplied voltage and on the use of a reference lig ht source to 'normalize' the light-output readings from the photos of the s ensor array, in order to minimize the errors introduced by the non-uniformi ty of the photographic process. Once the calibration curve is obtained, it is possible, with only one photo, to obtain the quantitative SAR distributi on in the operating conditions. For this reason, this method is suitable fo r equipment characterization and also for the control of the repeatability of power deposition in time.