The postoperative period after laser interstitial thermal therapy (LITT) is marked by a temporary increase in volume, which can impact the accuracy of radiographic assessment. The current criteria for progressive disease (PD) suggest that a 20% increase in size of brain metastasis (BM) assessed in 6-12 weeks intervals should be considered as local progression (LP). However, there is no agreement on how LP should be defined in this context. In this study, we aimed to statistically analyze which tumor volume variations were associated with LP.

We analyzed 40 BM that underwent LITT between 2013 and 2022. For this study, LP was defined following radiographic features. A ROC curve was generated to evaluate volume change as a predictor of LP and find the optimal cutoff point. A logistic regression analysis and Kaplan Meier curves were performed to assess the impact of various clinical variables on LP.

Out of 40 lesions, 12 (30%) had LP. An increase in volume of 25.6% from baseline within 120-180 days after LITT presented a 70% sensitivity and 88.9% specificity for predicting LP (AUC: 0.78, p = 0.041). The multivariate analysis showed a 25% increase in volume between 120 and 180 days as a negative predictive factor (p = 0.02). Volumetric changes within 60-90 days after LITT did not predict LP (AUC: 0.57; p = 0.61).

Volume changes within the first 120 days after the procedure are not independent indicators of LP of metastatic brain lesions treated with LITT.