Interim 18F-FDG-PET based response-adaptive dose escalation of proton therapy for head and neck cancer: a treatment planning feasibility study

Abstract

Abstract Background Image-driven dose escalation to tumor subvolumes has been proposed to improve treatment outcome in head and neck cancer (HNC). We used 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) acquired at baseline and two-three weeks into treatment (interim) to identify biologic target volumes (BTV). We assessed the feasibility of interim dose escalation to the BTV with proton therapy by simulating the effects to organs at risk (OARs). Methods We used the semiautomated just-enough-interaction (JEI) method to semi-automatically identify BTVs from 18F-FDG-PET images from nine HNC patients. Between baseline and interim FDG-PET all patients received photon radiotherapy. BTV was defined by assuming that lasting standardized uptake value (SUV) at interim reflects tumor radioresistance. Using Eclipse (Varian Medical Systems), we simulated the effects of a 10% (6.8 Gy(RBE1.1)) dose escalation to the BTV with protons and compared results with proton plans without dose escalation. Results At interim 18F-FDG-PET, radiotherapy resulted in reduced SUV compared to baseline. However, there was a spatial overlap between high-SUV regions at baseline and interim that allowed definition of the BTV. Proton therapy planning demonstrated that dose escalation to the BTV was feasible while the increases in median and max dose to OARs remained below 2.0 Gy(RBE1.1) and 1.0 Gy(RBE1.1), respectively. Conclusion Our in silico analysis demonstrated the potential for response-adaptive dose escalation to the BTV with proton therapy based on interim 18F-FDG-PET. This approach may give more efficient treatment to HNC with radioresistant tumor subvolumes without increasing normal tissue toxicity. Further studies in larger cohorts are required to determine the full potential for interim 18F-FDG-PET-guided dose escalation of proton therapy in HNC.