Quantitative colorimetric analysis of liquid crystal films (LCF) for phantom dosimetry in microwave hyperthermia

Quality assurance guidelines for interstitial hyperthermia

Quality assurance (QA) guidelines are essential to provide uniform execution of clinical hyperthermia treatments and trials. This document outlines the clinical and technical consequences of the specific properties of interstitial heat delivery and specifies recommendations for hyperthermia administration with interstitial techniques. Interstitial hyperthermia aims at tumor temperatures in the 40-44 °C range as an adjunct to radiation or chemotherapy. The clinical part of this document imparts specific clinical experience of interstitial heat delivery to various tumor sites as well as recommended interstitial hyperthermia workflow and procedures. The second part describes technical requirements for quality assurance of current interstitial heating equipment including electromagnetic (radiative and capacitive) and ultrasound heating techniques. Detailed instructions are provided on characterization and documentation of the performance of interstitial hyperthermia applicators to achieve reproducible hyperthermia treatments of uniform high quality. Output power and consequent temperature rise are the key parameters for characterization of applicator performance in these QA guidelines. These characteristics determine the specific maximum tumor size and depth that can be heated adequately. The guidelines were developed by the ESHO Technical Committee with participation of senior STM members and members of the Atzelsberg Circle.

Infrared thermographic SAR measurements of interstitial hyperthermia applicators: errors due to thermal conduction and convection

Thermal conduction and convection were examined as sources of error in thermographically measured SAR patterns of an interstitial microwave hyperthermia applicator. Measurements were performed in a layered block of muscle-equivalent phantom material using an infrared thermographic technique with varying heating duration. There was a 52.7% reduction in maximum SAR and 75.5% increase in 50% iso-SAR contour area for a 60-s heating duration relative to a 10-s heating duration. A finite element model of heat transfer in an homogeneous medium was used to model conductive and convective heat transfer during the thermographic measurement. Thermal conduction artefacts were found to significantly distort thermographically measured SAR patterns. Convective cooling, which occurs when phantom layers are exposed for thermal image acquisition, was found to significantly affect the magnitude, but not the spatial distribution, of thermographically measured SAR patterns. Results from this investigation suggest that the thermal diffusion artefacts can be minimized if the duration of the applied power pulse is restricted to 10 s or less.

Radio frequency electromagnetic exposure: tutorial review on experimental dosimetry

Radio frequency (RF) dosimetry is the quantification of the magnitude and distribution of absorbed electromagnetic energy within biological objects that are exposed to RF fields. At RF, the dosimetric quantity, which is called the specific absorption rate (SAR), is defined as the rate at which energy is absorbed per unit mass. The SAR is determined not only by the incident electromagnetic waves but also by the electrical and geometric characteristics of the irradiated subject and nearby objects. It is related to the internal electric field strength (E) as well as to the electric conductivity and the density of tissues; therefore, it is a suitable dosimetric parameter, even when a mechanism is determined to be "athermal." SAR distributions are usually determined from measurements in human models, in animal tissues, or from calculations. This tutorial describes experimental techniques that are used commonly to determine SAR distributions along with the SAR limitations and unresolved problems. The methods discussed to obtain point, planar, or whole-body averaged SARs include the use of small E-field probes or measurement of initial rate of temperature rise in an irradiated object.