Volumetric response of progressing post-SRS lesions treated with laser interstitial thermal therapy.

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We analyzed volumetric response of metastatic brain tumors that progressed despite treatment with stereotactic radiosurgery (SRS) after treatment with laser interstitial thermal therapy (LITT). We retrospectively reviewed consecutive patients treated from 1/2012 to 10/2015 with LITT for metastatic brain tumors demonstrating progression after SRS. Volumes were quantified using MRI with contrast-enhanced T1-weighted (T1W) and fluid-attenuated inversion recovery (FLAIR). Fifty lesions from 36 patients were studied. Lesions were assessed prior to LITT, immediately after LITT, 0-90 days after LITT, 90-180 days after LITT, 180-270 days after LITT, and 270-360 days after LITT. The median T1W volume was 5.05cc (range 0.54-23.31cc) before LITT treatment (n = 50), 7.70cc (range 1.72-38.76cc) 0-90 days after LITT (n = 47), and 3.68cc (range 1.282-48.31cc) 180-270 days after LITT (n = 21). The median FLAIR volume was 43.36cc (range 3.09-233.01cc) before LITT treatment (n = 50), 37.13cc (range 3.48-244.23cc) 0-90 days after LITT (n = 43), 31.68cc (range 1.6-248.75cc) 180-270 days after LITT (n = 18). The 6-month FLAIR volume showed a statistically significant reduction compared to pretreatment (p = 0.04). After selecting for cases where patients had two or more post-operative MRIs, we found that 24 lesions (63%) demonstrated an overall downward trend and 14 lesions (37%) demonstrated an upward trend. The median pre-treatment T1W volume for the patients whose lesions demonstrated volumetric reduction after LITT was 3.54cc (range 0.539-10.06cc) and for those who did not demonstrate volumetric reduction after LITT it was 8.81cc (range 0.926-23.313cc). The pre-treatment tumor volume plays a significant role in determining response to LITT with smaller tumor volumes responding better to LITT than tumors with larger volumes.