Nirl-12 Understanding Lesion Response on Mri After Laser Interstitial Thermal Therapy (Litt) in Metastatic Brain Tumor Patients

Laser-interstitial thermal therapy (LITT) at the time of radiographic regrowth after stereotactic radiosurgery (SRS) of brain metastases allows lesions to be biopsied and treated simultaneously. While excellent post-LITT responses have been reported, indications for use remain unclear. This study describes the variability seen in post-LITT imaging changes, especially FLAIR, reflecting perilesional edema, and examines clinical and treatment variables that may affect post-LITT response. Using a novel 3D-segmentation tool created at our institution, we analyzed volumetric changes in both FLAIR and contrast-enhancing lesions before and for 12-months post-LITT across 23 patients. Over half (57%, 13/23) of patients demonstrated an initial increase in FLAIR volume at 2 weeks post-LITT and 43% demonstrated stable or decreased FLAIR. For those with an initial decrease, their percentage volume change from 0 to 0.5 months ranged from 21% to 67%, while those with an initial increase, percentage volume change varied from 2.6% to 254%. Of the 13 patients with an initial increase in FLAIR, 6 had FLAIR resolution over the subsequent 6-12 weeks. Four patients did not show FLAIR resolution until 12 months. Of the 10 patients with initial decrease, 6 had resolution of FLAIR signal abnormality by 3 months and 9 by 6 months. At 12 months, in those patients with an initial FLAIR increase, only 54% showed a decrease in enhancing lesion volume compared to 70% of patients with an initial decrease in FLAIR. No clinical or treatment factors were statistically associated with any pattern of lesional change although trends were seen with pre-LITT size and immunotherapy use. Survival was found to be associated with biopsy pathology. This study demonstrates FLAIR changes after LITT can be even more variable than for contrast enhancing lesion volumes. A larger study is needed to determine clinical and treatment factors that contribute to early favorable responses to LITT.