Introduction: Our group has utilized MRgLITT for the treatment of recurrent metastatic brain tumors after GammaKnife radiosurgery (GKS) intervention. However, volumetric trends associated with recurrent tumor growth preceding MRgLITT have not been well-studied.
Methods: Nineteen recurrent tumors from thirteen patients were retrospectively tracked from the post-GKS nadir to the day of MRgLITT using OsiriX software. Volume over time was analyzed by plotting individual tumor trends. Three-parameter exponential decay regressions were fit to the data for each recurrent tumor, which were then aggregated together and fitted again to obtain the exponential decay parameters from the mean regression. Asymptotic and intercept values were estimated based on measured volumes at the nadir and time of laser ablation. Finally the decay coefficient was converted to a half-life value and reported as a doubling factor.
Results: Tumors consistently demonstrated trends of non-linear slow growth followed by rapid growth. Regression estimates and measured average values showed good concordance. Mean volume at the time of MRgLITT from the measured data was 3.19cm3(sem=0.67,n=19) compared to the mean regression estimate of 3.09cm3(sem=0.64,n=19). The mean nadir volume, measured at an average of 487 days(sem=65,n=19) days before MRgLITT, was 0.29cm3(sem=0.167,n=19), while the regression estimate at a similar time point was 0.576cm3(sem=0.314,n=19). The half-life estimate from the mean regression was 113.6 days(n=19), conversely interpreted as a doubling factor.
Conclusions: Our preliminary results demonstrate that regression estimates can be used to accurately estimate tumor growth. Such a standard method of predicting growth may help determine optimal time window for MRgLITT intervention for metastatic tumors exhibiting growth after radiosurgery, leading to more effective interventions and better patient outcomes.
Patient Care: As a new technology, much remains to be defined about MRgLITT; not least of these is the important question of when it should be utilized. One of its chief indications presently is the treatment of post-GK recurrent brain tumors. By approaching a standard method of predicting growth of these recurrent brain tumors, we aim to provide a measure by which optimal timing for MRgLITT can be determined on an individualized basis. That is, for a given patient, where does their pattern of recurrent tumor growth fall on a standard curve defining MRgLITT treatment? Are they in an ideal time window for treatment? Our research thus strives to optimize patient outcomes by informing surgical planning with individual volumetric trends.
Learning Objectives: By the conclusion of this session, participants should be able to:
1) Describe the utility of MR-guided laser-induced interstitial therapy (MRgLITT) for recurrent brain tumors.
2) Understand the approach to refining timing of MRgLITT intervention for recurrent tumors following Gamma Knife radiosurgery.