Ultra-early response assessment in lymphoma treatment: [F]FDG PET/MR captures changes in glucose metabolism and cell density within the first 72 hours of treatment.

Purpose: To determine whether, in patients with Hodgkin lymphoma (HL) or non-Hodgkin lymphoma (NHL), [F]FDG PET/MR can capture treatment effects within the first week after treatment initiation, and whether changes in glucose metabolism and cell density occur simultaneously.

Methods: Patients with histologically proven HL or NHL were included in this prospective IRB-approved study. Patients underwent [F]FDG PET/MR before, and then 48-72 h after (follow-up 1, FU-1) and 1 week after (FU-2) initiation of the first cycle of their respective standard chemotherapy (for HL) or immunochemotherapy (for NHL). Standardized [F]FDG uptake values (SUVmax, SUVmean) and apparent diffusion coefficients (ADCmin, ADCmean) based on diffusion-weighted MRI, and metabolic and morphological tumour volumes (MTV, VOL) were assessed at each time-point. Multilevel analyses with an unstructured covariance matrix, and pair-wise post-hoc tests were used to test for significant changes in SUVs, ADCs, MTVs and VOLs between the three time-points.

Results: A total of 58 patients (11 with HL and 47 with NHL) with 166 lesions were analysed. Lesion-based mean rates of change in SUVmax, SUVmean, ADCmin, ADCmean, MTV and VOL between baseline and FU-1 were -46.8%, -33.3%, +20.3%, +14%, -46% and -12.8%, respectively, and between baseline and FU-2 were -65.1%, -49%, +50.7%, +32.4%, -61.1% and -24.2%, respectively. These changes were statistically significant (P < 0.01) except for the change in VOL between baseline and FU-1 (P = 0.079).

Conclusion: In lymphoma patients, [F]FDG PET/MR can capture treatment-induced changes in glucose metabolism and cell density as early as 48-72 h after treatment initiation.