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

Abstract

Introduction 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. Materials and methods In this retrospective french multicentric study (Clermont-Ferrand, Montpellier, Rennes), we evaluated 45\xa0patients 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\xa0months after the last SRS session. Dual-PET included both an “early” and a “delayed” acquisition, respectively 30\xa0to 60\xa0minutes and 4\xa0to 5\xa0hours 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\xa0=\xa0[(Delayed-Early)/Early]). Visual analysis was also conducted using a subjective 6\xa0points 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\xa0months. Results Final diagnoses were TR for 24\xa0patients and RN for 21\xa0patients. There was no statistically significant difference regarding AUC between the different interpretation methods. AUC ranged from 0,78 [95\xa0%CI 0,63; 0,89] with the L1/GM1\xa0Ratio, to 0.85 [95\xa0%CI 0.72; 0.94] with the L2/GM2\xa0ratio. Visual analyses AUC were excellent at both early (0.835 [95\xa0%CI 0.7; 0.93]) and delayed acquisitions (0.83 [95\xa0%CI 0.69; 0.92]). There was no statistically significant difference between accuracies (p\xa0=\xa00.87) ranging from 0.71\xa0with the RI ratio to 0.80\xa0with both the “delayed” visual and quantitative analyses. Conclusion Dual-PET protocol distinguishes RN and TR after SRS with robust diagnostic performances in case of doubtful MR, with an accuracy up to 80\xa0%.