Evaluation of power and phase accuracy of the BSD Dodek amplifier for regional hyperthermia using an external vector voltmeter measurement system.
OBJECTIVE
Accurate monitoring of RF (radio frequency) power and phase is a key part of quality assurance (QA) for phased-array hyperthermia systems. In order to assess the steering capability of the BSD 2000 3D facility, an independent measurement system has been implemented, using a vector voltmeter (VVM) as the measuring device.


METHODS
This paper describes the calibration of the RF signal paths from each of the 12 BSD Dodek amplifier outputs to the VVM instrument readout. Periodical network analyser measurements show that the uncertainty of the measured power using the VVM system is <4% for all channels, while the uncertainty of the phase measurements is <0.3 degrees. The values are comparable to those reported for similar monitoring systems and are considered adequate for monitoring of the BSD Dodek steering parameters.


RESULTS
Using the VVM system to investigate the accuracy of the BSD Dodek amplifier power and phase control, systematic differences were observed between the requested and the measured power for all channels: At a requested power level of 25 W per channel, the measured power level was on average 15% lower than nominal, whereas at 100 W it was nearly 20% higher. It was also observed that the absolute phase values are nearly 30 degree higher at 25W per channel than at power levels > or = 50W per channel. Under certain circumstances, these issues may reduce target steering accuracy for the BSD 2000 3D system; on the other hand, the Dodek power and phase control stability is found to be acceptable.


CONCLUSIONS
The results emphasize the need for accurate, independent online power and phase QA during regional hyperthermia treatments using phased array systems.
Kongsli
J
J
Department of Oncology and Medical Physics, Haukeland University Hospital, Bergen, Norway.
Hjertaker
B T
BT
Frøystein
T
T
D011211:Electric Power Supplies / Q000592:standards*; D004869:Equipment Safety; D006801:Humans; D006979:Hyperthermia, Induced / Q000295:instrumentation*; D011785:Quality Assurance, Health Care; D011786:Quality Control