NIMG-14. RADIOLOGIC ASSESSMENT OF BRAIN METASTASES UNDERGOING LASER INTERSTITIAL THERMAL THERAPY (LITT)

Abstract

Abstract BACKGROUND Laser Interstitial Thermal Therapy (LITT) is a novel treatment for brain metastases (BMs), and data regarding radiologic changes and long-term efficacy is sparse. This study explored volumetric changes in responding and non-responding BMs and their associations with lesion-specific progression-free survival (PFS-L). METHODS Patients with BMs treated with LITT were retrospectively enrolled. 3D volumes-of-interest of the contrast-enhancing BM tissue (CE) on pre-, post-LITT, and follow-up MRI scans were obtained. BMs were followed until progression or censoring. PFS-L was determined using the modified RANO criteria to assess treatment efficacy on each lesion. RESULTS Thirty-one BMs (from 30 patients) were preliminarily analyzed. 2 BMs had no follow-up scans. Median follow-up for 29 BMs was 248 days (range 28-2200). Median time to response was 430 days (responders n=7/29), median time to progression was 176 days (progressive disease n=7/29). Pre-LITT CE volume was a predictor of PFS-L (p=0.001), with BMs> 2.5 cc being 14 times more likely to undergo progression. Differences in age and primary tumor site did not impact PFS-L, whereas PFS-L tended to be longer in females (p=0.059), and in frontal and deep grey matter BMs (p=0.11). Post-LITT CE volume was higher than pre-LITT (p< 0.0001, median increase 59%), with no significant differences among responders, stable disease, and progressive disease. In each responding BM, the CE volume shrinkage over time was described by an exponential decay (R2 ranging 0.92-1.0 and half-life ranging 16.55-204 days). All responding BMs showed a pooled exponential decay with R2=0.88 and half-life=75.6 days. CONCLUSIONS Our data suggest that smaller BMs may have improved outcomes from LITT treatment. CE volumes may increase in the early post-procedural scans, possibly due to both inflammatory changes and thermal damage. The characterization of the volumetric changes across time for responding lesions may be useful for an early detection of BMs at risk for progression.