Purpose: IMRT delivery follows planned leaf sequences, which are optimized before treatment delivery. Real‐time variations, such as respirations, are hardly to be modeled in planning procedure. We developed a real‐time Motion‐Adapted‐Optimization (MAO)‐guided delivery technique in TomoTherapySM treatments. This technique models the radiation delivery with the real‐time motion as a negative feedback system. It updates the motion‐encoded cumulative dose and optimizes the leaf sequence in real‐time, right before the delivery of each projection. Method and Materials: TomoTherapySM treatment delivery consists of thousands of projections with projection time around 200–500 ms. The leaf latency plus transition of TomoTherapy® binary MLC takes less than 50 ms. Real‐time MAO is to optimize leaf sequence of the coming projection right before its execution. It consists of several real‐time procedures including “motion detection and prediction”, “motion‐encoded dose accumulation” and “leaf sequence optimization” for the coming projection. To update leaf sequence in real‐time, all above procedures must be executed within 150 ms. We developed ultra‐fast algorithms and codes to approach such critical goal. We implemented and tested this technique with the TomoTherapy® research system. The integrated system includes a real time camera system and a programmable motor‐driven phantom. We tested different TomoTherapySM plans with various simulated and real respiration traces. We used film dosimetry to verify and validate the final results. Results: MAO‐guided delivery runs smoothly in the integrated TomoTherapy® system. The whole MAO procedure takes less 100 ms per projection. Both simulated motion and real respiration of ∼2cm amplitude, the real‐time MAO‐guided delivery doses matched with the planning dose within 3% and 3mm criteria, for a typical TomoTherapySM treatment configuration. No hot and cold spots are noticeable. Conclusion: We present a novel technique for real‐time MAO‐guided delivery within current TomoTherapy® hardware. Simulations and experiments conceptually proved this technique. Further validation and clinical implementation are underway.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging