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Phase stability of a clinical phased array system for deep regional hyperthermia
W L Straube1, E G Moros, R J Myerson
1Washington University School of Medicine, Mallinckrodt Institute of Radiology, Radiation Oncology Center, St Louis, MO 63110.
Summary
Phased array system amplifiers show significant phase shifts with frequency, impacting treatment accuracy. These phase variations, up to 30 degrees, exceed acceptable limits, potentially altering specific absorption rate distributions during clinical use.
Area of Science:
- Medical Physics
- Biomedical Engineering
- Electromagnetics
Background:
- Phased array systems are crucial for targeted therapies.
- Accurate phase control is essential for effective treatment planning and delivery.
- Previous studies highlight the need for precise phase relationships (within 20 degrees).
Purpose of the Study:
- To evaluate the frequency dependence of phase in phased array system amplifiers.
- To assess the accuracy of phase measurements and system-displayed values.
- To determine the potential impact of phase inaccuracies on treatment outcomes.
Main Methods:
- Measurements of amplifier phase were conducted on a phased array system.
- Power was terminated into a 50 ohm load at the antenna connection point.
- Phase relationships between amplifier channels were determined by power sampling.
Main Results:
- Phase differences between amplifier channels varied up to 20 degrees with frequency.
- Measured phase differences deviated up to 12 degrees from the prescribed phase.
- System-displayed phase values differed from actual measurements by up to 30 degrees.
Conclusions:
- Observed phase variations exceed the 20-degree tolerance required for accurate treatment planning.
- Inaccurate system-reported phases may prevent operators from compensating for deviations under clinical loading conditions.
- These findings necessitate quality assurance procedures to ensure safe and effective utilization of phased array systems for power steering.