Guidelines For Limiting Radiofrequency Exposure - Short Wave Diathermy - Safety Code 25

6. RF Radiation Measurements

The need to measure stray RF fields around a short-wave diathermy device may arise when new electrodes or even complete devices are introduced, especially when the devices operate at high power (above 500 W). For instance, some RF diathermy devices used for cancer treatment operate at such high powers, and the design of the applicators may be such that intense stray fields are produced at greater distances(13). In such cases, an RF survey should be carried out to determine a safe working distance for the operator.

The following general recommendations on RF radiation surveys should be followed:

1. The electrode should be positioned over a test treatment area of an appropriate phantom, e.g., a manikin filled with saline solution, or a patient receiving a prescribed treatment.
2. If an output power indicator is provided, a low power setting should be used and the measurement results extrapolated to higher power settings assuming the power setting control operates linearly. For instance, if for a power setting of 100 W the electric field intensity at 1 m from the applicator is 15 V/m, and the treatment power setting is 400 W, then the electric field intensity at 1 m
   
   will be
   
   15 = 30 V/m.(This level should be compared with the recommended maximum exposure of 60 V/m. In this case the operator is within safe limits at a distance of 1 m from the applicator).

c. When an RF survey is performed, the electric and the magnetic field should be measures and their intensities compared against the standard.

d. Instruments having isotropic sensing elements should be used for RF surveys, as the field direction is not known. Examples of suitable instruments include(1): for the electric field, Holaday, model HI3001, HI3002, HI3004, Narda, model 8609, for the magnetic field, Holaday, model HI-3002, Narda, model 8602, 8603, 8607 or 8608 with probe 8631 or 8633, or model 8609.

e. The measurements should be done in the plane of the applicator and the plane of the cables.

(1) This does not constitute a statement of an official recommendation or endorsement of the products mentioned.