Professor of Neurosurgery University of Chicago Chicago, Illinois, United States
Introduction: MRI-guided laser interstitial thermal therapy (LITT) for secondary brain tumors is a rising non-invasive, low-risk treatment option compared to traditional craniotomies. However, unlike previous studies using PFS and overall survival (OS) to assess the efficacy of LITT, our study directly quantifies its effects on the capillary bed of the tumor region and its success in reducing vasogenic edema, or peritumoral fluid build-up . This study has two specific aims: 1) to establish the physical response of capillaries in the tumor region to LITT and 2) to study chemotherapeutic drug delivery via pharmacokinetic modeling.
Methods: To test these, we analyzed permeability statistics before and after the LITT procedure in a consecutive series of 5 patients by calculating regional K1 (blood-to-tissue transfer constant), k2 (tissue-to-blood efflux), Vp (tissue plasma vascular space), and Ve (tumor extracellular space) using a two-compartment Patlak model following a Gadolinium-based MRI contrast-agent. To determine if the expected increase in regional cerebral blood flow (rCBF) occurred after restoring the BBB with LITT, we conducted perfusion studies using a standard deconvolution process of the arterial input function.
Results: Regions-of-interest (ROI) analysis and contralateral brain matter studies in patients have shown a decrease in the K1 statistic, representing decreased tumor permeability post-surgery already within less than 24 hours. A medium reduction of 56.4% of capillary permeability (K1) was seen and consecutively an increase in rCBF and reduction in extracellular space. Also k2 the efflux constant was significantly reduced.
Conclusion : With defined relationships between LITT, rCBF, and permeability, we can better understand the vasculature of the tumor region post-LITT and verify pharmacokinetic modeling as a viable tumor MRI-analysis technique. This knowledge could optimize chemotherapy and radiation strategies, which likewise hold a vascular dynamic in the tumor region. In future work, we hope to use quantitative changes in tumor physiology as a biomarker.
