Purpose: Many patients with brain lesions located in or near eloquent regions of the brain are not candidates for surgical resection in order to preserve the function of the affected areas. These patients can be treated with the more noninvasive laser interstitial thermal therapy (LITT). The purpose of this study was to examine the change in lesion size of brain tumors and cerebral radiation necrosis (CRN) before, during, and after treatment with LITT.

Materials and Methods: This single-center retrospective study included 39 patients with primary brain tumors, brain metastases, or CRN and who were treated with LITT. Lesion area was measured in axial T1-weighted post-contrast MR images. Measurements were made at the following timepoints: pretreatment; during treatment; and 3, 6, and 12 months posttreatment. The lesion sizes were compared between three groups: patients who had never undergone radiation therapy to the lesion of interest (Group 1, n=8), patients who had undergone radiation therapy but had no histological evidence of CRN (Group 2, n=24), and patients with histological evidence of CRN (Group 3, n=7).

Results: Overall, mean lesion size increased between the pretreatment and during-treatment timepoints (245 mm^2 vs. 363 mm^2, p=0.009) and decreased between the pretreatment and 12-months-posttreatment timepoints (245 mm^2 vs. 87 mm^2, p=0.0002). Individually, Group 2 also demonstrated an increase in mean lesion size between the pretreatment and during-treatment timepoints (265 mm^2 vs. 399 mm^2, p=0.046) and a decrease between the pretreatment and 12-months-posttreatment timepoints (265 mm^2 vs. 93 mm^2, p=0.003). At the 3-months-posttreatment timepoint, the mean lesion size of Group 1 was significantly smaller than the mean lesion sizes of Group 2 (88 mm^2 vs. 358 mm^2, p=0.008) and Group 3 (88 mm^2 vs. 465 mm^2, p=0.017), but this difference disappeared at both subsequent timepoints.

Conclusion: This study demonstrates that LITT reduces the size of treated brain lesions after an initial increase in size when the treatment is administered.

Clinical Relevance: This study supports the efficacy of LITT on brain lesions and demonstrates expected size change over time. It contributes to developing an understanding of the appropriate follow-up imaging schedule.