3 years ago

A concept study on real-time adaptive radiation therapy optimization.

Rodney D. Wiersma, Xinmin Liu

A central problem in the field of radiation therapy is how to optimally deliver dose to a patient in a way that fully accounts for anatomical changes due to motion. Adaptive radiation therapy (ART) is a motion management modality where dose re-planning is performed before the start of each treatment fraction. However, ART cannot address real-time tumor motion, or other volumetric anatomy changes, that may take place during actual radiation delivery. To overcome these limitations, we present a concept study on a novel approach to perform real-time ART (RT-ART) based on voxel dose history tracking and fast beamlet delivery.

The conceptual RT-ART system had radiation beamlets arranged 360 degrees around the patient in a ring configuration and fast gantry and MLC speeds that allow real-time access to the entire beamlet space. It was assumed that there exists a suitable image tracking system that can monitor the real-time position of all voxels forming targets and organs-at-risk. The voxel dose history was calculated at any point during delivery based on the tracked voxel position and beam on/off history. During delivery, if patient motion remains under a predefined threshold, beamlet intensities were delivered as according to the initial RT plan. However, if motion exceeds threshold, a time dependent objective function was solved using fast optimization methods to calculate new beamlet intensities that were then delivered to the patient. To evaluate the effectiveness of the system, dynamical CT input data was simulated using a TG-119 phantom for recorded patient motion. The RT-ART method was compared against the ideal static case (no patient motion) as well as to the dynamic case without the use of RT-ART. Dose-volume-histograms showed that the RT-ART plan quality was approximately the same as the static case, whereas, the dynamic case showed reduced PTV-D95 by 10-20%.

Publisher URL: http://arxiv.org/abs/1811.03665

DOI: arXiv:1811.03665v1

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