Performance of binary MLC using real-time optical sensor feedback system

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• The Radixact system, based on TomoTherapy technology, is the latest radiotherapy platform.
• It incorporates a Multi-Leaf Collimator (MLC) with optical sensors for real-time Leaf Open Time (LOT) monitoring and correction.
• Unlike previous systems, it does not use a post-optimization latency model correction.

Purpose of the Study:

• To evaluate the performance and accuracy of the Radixact MLC system with real-time latency correction.
• To assess the reliability and repeatability of the MLC feedback system in daily radiotherapy delivery.
• To determine the clinical impact of MLC latency deviations on patient target dosimetry.

Main Methods:

• Statistical analysis of MLC LOT errors from 290 plan-specific quality assurance (PSQA) measurements.
• Repeatability testing using over 1300 delivered treatment fractions to quantify feedback system uncertainty.
• Estimation of dose differences in patient targets resulting from measured plan latencies.

Main Results:

• An average plan latency of 2.0 ± 0.4 ms (0.6% ± 0.2%) was measured across 290 PSQAs.
• Repeatability tests revealed a mean standard deviation in plan latencies of 0.05 ms (0.02%).
• The estimated deviation in mean target dose due to latencies was minimal (0.0% ± 0.2%, range: -0.7% to 1.1%).

Conclusions:

• The Radixact MLC system with real-time optical feedback accurately delivers Treatment Planning System (TPS)-generated sinograms.
• The system demonstrates high reliability for daily sinogram delivery, confirmed by repeatability testing.
• MLC latency deviations have a clinically insignificant impact on overall target dosimetry.