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Long-term dosimetric stability of multiple TomoTherapy delivery systems
Jennifer B Smilowitz1,2, David Dunkerley2, Patrick M Hill1
1Department of Human Oncology, University of Wisconsin - Madison, Madison, WI, USA.
Journal of Applied Clinical Medical Physics
|May 3, 2017
Summary
TomoTherapy units demonstrate excellent dosimetric stability over time and system upgrades. Newer systems with Dose Control Stability (DCS) show significantly improved output consistency compared to older models.
Area of Science:
- Medical Physics
- Radiation Oncology
- Quality Assurance
Background:
- TomoTherapy systems have evolved, incorporating upgrades like Dose Control Stability (DCS) and Fixed Target Linear Accelerators (FTL).
- Long-term performance monitoring is crucial for ensuring consistent radiation delivery in clinical practice.
- Understanding the dosimetric stability of these systems over time and across different models is essential for reliable cancer treatment.
Purpose of the Study:
- To evaluate the dosimetric stability of six TomoTherapy units, including Hi-Art, TomoHDA, and Radixact models, over extended clinical use.
- To investigate the impact of system upgrades, such as DCS and FTL, on output and energy stability.
- To compare the performance of the newer Radixact system with established TomoHDA units.
Main Methods:
- Tracking energy and output using monitor chamber signals, onboard megavoltage computed tomography (MVCT) detector profiles, and external ion chamber measurements.
- Analyzing data from three Hi-Art, two TomoHDA, and one Radixact unit, with monitoring periods ranging from 11 to 67 months.
- Assessing output stability via deviation from reference monitor chamber signals and/or external chamber signals; energy stability was monitored using MVCT detector profiles and ion chamber depth ratios.
Main Results:
- All TomoTherapy systems exhibited very stable beam energy.
- Non-DCS systems showed output stability with a standard deviation of 0.94-1.52%, while DCS systems demonstrated significantly improved stability (0.004-0.06%).
- Profile flatness standard deviation was 0.23-0.62% for rotating target systems and 0.04-0.09% for FTL systems, with consistent results across measurement tools.
Conclusions:
- TomoTherapy units, particularly those with DCS, maintain high dosimetric stability over extended operational periods and through system upgrades.
- The results validate the reliability of these systems for precise radiation therapy delivery.
- Multiple measurement techniques confirm the stability, underscoring the robustness of quality assurance protocols in radiation oncology.
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