Abstract
Purpose: Emission guided radiation therapy (EGRT) is a new concept that allows for online biological targeting with radioactive tracers. The concept was previously demonstrated in phantom experiments involving free breathing trajectories. This study involves the first patient imaging data to assess feasibility and estimate performance in a more realistic context. Methods: A proposed EGRT geometry involves rotating two PET detector arcs with a linear accelerator and binary multi‐leaf collimator on a CT gantry to deliver beamlets of radiation dynamically along detected PET emission paths. A lung cancer patient underwent PET‐CT as part of radiotherapy planning. PET list‐mode data were retrospectively used as an input to simulate the EGRT system's response and Monte Carlo simulations were used to calculate the dose to the patient. The gross target volume (GTV) was contoured based on the PET‐CT images and the planning volume (PTV) was defined as a 10 mm extension of the GTV in all directions. The EGRT method was compared to uniformly irradiating the same PTV (IMRT), with both methods normalized for the same integral dose to the chest wall. Physiologic motion was ignored during the dose calculations as the tumor exhibited < 2 mm motion. Results: The dose peaks towards the center of the GTV with the EGRT method. However, even in the presence of this inhomogeneity, the EGRT method resulted in 18% relative increase in dose to 95% of the GTV, and 45% increase in dose to 50% of the GTV, compared to the IMRT method. Both methods were normalized for the same integral dose to the chest wall. Conclusions: The feasibility of EGRT has been demonstrated with PET data from a lung cancer patient. Future work will analyze the ability of EGRT to compensate for motion in PET‐CT patient studies which will include breathing traces to estimate ground truth. RefleXion Medical is a company commercializing PET‐guided radiotherapy. SRM and ASN have financial interest in the company.
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