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Design and test of a new multi-amplifier system with phase and amplitude control
1Department of Radiology, Charité Medical School-Campus Virchow-Klinikum, Humboldt University at Berlin, Germany.
Summary
This study presents a new radiofrequency regional hyperthermia amplifier system that achieves high phase and power accuracy for improved cancer therapy. The advanced digital control system offers enhanced stability and efficiency compared to existing clinical systems.
Area of Science:
- Biomedical Engineering
- Medical Physics
- Oncology
Background:
- Radiofrequency regional hyperthermia (RF-RHT) is an increasingly relevant adjuvant cancer therapy.
- Optimizing RF-RHT requires improved power deposition patterns, necessitating higher phase accuracy and amplitude stability than current systems provide.
- Existing clinical systems like BSD-2000 exhibit significant phase inaccuracies and power registration errors, exacerbated by load mismatching and thermal instabilities.
Purpose of the Study:
- To develop a novel amplifier system for RF-RHT that achieves superior phase accuracy and long-term stability.
- To overcome the limitations of current clinical systems in delivering precise RF energy for hyperthermia treatment.
- To enhance the efficiency and reduce the physical size of RF-RHT amplifier systems.
Main Methods:
- Implementation of single-sideband (SSB) mixing with direct digital synthesizers (DDS) for real-time phase calculation.
- Utilizing in-phase and quadrature-phase (IQ) processing and phase-lock loop (PLL) for precise frequency and phase control.
- Employing digital PLL structures and look-up tables for stability control, with test signals coupled via directional couplers for sensitive phase comparison.
Main Results:
- Achieved long-term output power accuracy of +/- 1-3 W (95% confidence interval) for power levels from 10-100 W.
- Demonstrated phase difference accuracy of +/- 1 degree between channels at constant power and +/- 1.5 degrees at variable power levels (10-100 W).
- The new amplifier system is notably smaller and more efficient than commercially available systems.
Conclusions:
- The developed amplifier system successfully meets the stringent requirements for phase accuracy and stability in RF-RHT.
- The digital control architecture eliminates thermal drift issues associated with analog systems.
- This advancement holds significant potential for improving the efficacy and applicability of hyperthermia as an adjuvant cancer therapy.