Long-Term Results of PET-Guided Radiation in Advanced-Stage Diffuse Large B-Cell Lymphoma Patients Treated with R-CHOP.

Consolidative radiation therapy (RT) for advanced-stage diffuse large B-cell lymphoma (DLBCL) remains controversial with routine practice continuing to include RT in patients with initial bulky disease or residual masses. PET-CT is a sensitive modality for detecting the presence of residual disease at end-of-treatment (EOT). A PET-guided approach to selectively administer RT has been policy in BC since 2005. Patients with advanced-stage DLBCL diagnosed between January 2005 - March 2017 treated with at least 6 cycles of R-CHOP that underwent EOT-PET were included in this analysis. Those with complete metabolic response (PET-NEG) were observed; those with PET-positive scans (PET-POS) were offered consolidative RT, when feasible. 723 patients were identified with median follow-up of 4.3 years: 517 (72%) were PET-NEG; 206 (28%) were PET-POS. Time-to-progression (TTP) and overall survival (OS) at 3 years were 83% v 56% and 87% v 64%, for PET-NEG and PET-POS patients, respectively. Non-progressing PET-POS patients treated with consolidative RT (109/206, 53%) had outcomes approaching those of PET-NEG patients, with 3-year estimates of 76% and 80% for TTP and OS. PET-NEG patients with bulky disease (≥10 cm) at diagnosis, had outcomes indistinguishable from those without bulk, despite omitting RT. These data suggest that patients with advanced-stage DLBCL that are PET-NEG at EOT and receive no RT have excellent outcomes. FDG-PET can reliably guide selective administration of consolidative RT, even for patients with initially bulky disease.