SU‐GG‐J‐03: Emission Guided Radiation Therapy System: A Feasibility Study

Abstract

Purpose: To evaluate the feasibility of a combined PET‐Linac system for real‐time guidance of radiation therapy for tumors that move due to respiration. Method and Materials: We are developing a treatment system that will simultaneously deliver radiation during PET acquisition. A method to compensate for respiratory motion will be to deliver radiation beam‐lets along individual PET lines‐of‐response (LOR's) as they are detected. The system involves rotating a radiation source and PET detectors on a gantry while dynamically controlling a binary multi‐leaf collimator to deliver the beam‐let responses in a 2D helical mode. Simulations were conducted using GATE to model 300 seconds of PET list‐mode acquisition of a ‘hot’ 3 cm diameter tumor exhibiting 3.7 second periodic 2 cm peak‐to‐peak motion in a ‘warm’ background. A 5 cm planning target volume (PTV) was used as a filter to reject LOR's that did not intersect this volume. LOR's that intersected the PTV and whose timestamps were within a 500 ms cutoff window were responded to. A voxel‐based Monte Carlo simulation package was used to model the resultant dose distributions comparing the emission guided (EGRT) method with uniform coverage of the PTV. Results: Composite dose volume histograms were calculated using 10 phases of the motion cycle. Dose to the non‐tumor volume was normalized to the same mean value for both scenarios. The EGRT approach exhibited a non‐uniform dose distribution to the tumor compared to uniform PTV coverage. However, even with the non‐uniformity, there was a 30% relative increase in minimum dose to the tumor volume for the EGRT approach. Conclusion: Although non‐uniform dose delivery to the tumor volume needs to be addressed, the feasibility of using PET to guide radiation delivery in real‐time has been demonstrated.Conflict of Interest: SRM and ASN are co‐founders of a company commercializing emission guided radiation therapy.