Dual-time point brain FDG PET to differentiate tumor progression from radionecrosis after stereotactic radiotherapy for brain metastases

Abstract

Dual phase 18[F]-FDG brain PET (dual-PET) is useful to distinguish tumor recurrence (TR) from radionecrosis (RN) after stereotaxic radiosurgery (SRS) of brain metastases, when contrast-enhanced MRI is inconclusive. We aimed to compare six different visual and quantitative interpretation criteria to enhance diagnostic performances. In this retrospective french multicentric study (Clermont-Ferrand, Montpellier, Rennes), we evaluated 45 patients previously treated with SRS for BM, addressed for a dual-PET by the local neuro-oncological committees for an evolving lesion on MRI inconclusive between TR and RN, at least 3 months after the last SRS session. Dual-PET included both an “early” and a “delayed” acquisition, respectively 30 to 60 minutes and 4 to 5 hours after 18[F]-FDG injection. After measuring SUVmax values of both lesion (L) and mirror contralateral grey matter (GM) at early (1) and delayed (2) acquisitions, three quantitative metrics were calculated: ratios of L SUVmax to GM SUVmax at “early” (L1/GM1) and “delayed” (L2/GM2) acquisitions and the retention index which is the variation over time of the standardized SUVmax ratio (RI = [(Delayed-Early)/Early]). Visual analysis was also conducted using a subjective 6 points visual scale of the lesion uptake at both acquisitions. The five interpretation criteria were compared according to their area under the ROC curve (AUC), and to their diagnostic accuracy applying the best cut off value (maximizing the Youden's index) by the Cochran Q test. The final diagnosis was based on pathology, or by default radiological and clinical follow-up criteria after at least 6 months. Final diagnoses were TR for 24 patients and RN for 21 patients. There was no statistically significant difference regarding AUC between the different interpretation methods. AUC ranged from 0,78 [95 %CI 0,63; 0,89] with the L1/GM1 Ratio, to 0.85 [95 %CI 0.72; 0.94] with the L2/GM2 ratio. Visual analyses AUC were excellent at both early (0.835 [95 %CI 0.7; 0.93]) and delayed acquisitions (0.83 [95 %CI 0.69; 0.92]). There was no statistically significant difference between accuracies ( p = 0.87) ranging from 0.71 with the RI ratio to 0.80 with both the “delayed” visual and quantitative analyses. Dual-PET protocol distinguishes RN and TR after SRS with robust diagnostic performances in case of doubtful MR, with an accuracy up to 80 %.