Positive Predictive Value of PET CT in HPV Associated Oropharyngeal Cancers Treated with Definitive Proton Therapy

PET/CT for post-treatment evaluation of patients treated with PT had an expectedly high NPV of 98% for residual/locoregionally recurrent disease; however, the PPV was 9% (1/11) which is much lower than would be expected with photon-based treatment. These findings may be the result of lingering acute inflammation caused by RBE differences at the distal end of the Bragg peak. Our findings are hypothesis generating and require validation with larger well-matched patient cohorts.