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  • Quantitative Volumetric Response After Gamma Knife Radiosurgery For Meningiomas

    Final Number:

    Gillian Harrison BS; Hideyuki Kano MD PhD; L. Dade Lunsford MD; John Flickinger MD; Douglas Kondziolka MD MSc FRCS(C) FACS

    Study Design:

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2012 Annual Meeting

    Introduction: This study attempts to quantitatively define the early radiobiologic response of meningioma following Gamma Knife stereotactic radiosurgery (SRS) and evaluate early tumor response as a predictor of long-term tumor control.

    Methods: We reviewed serial T1-weighted contrast-enhanced MRIs of patients undergoing SRS for meningioma from 2002-2010. Volume percent change from baseline, absolute rate of change, and percent rate of change were compared at 3-month intervals for patients classified by ultimate tumor outcome (progressed, stable, regressed). A total of 252 patients with mean age of 56 years (14-87), baseline tumor volume of 5.8 cm3 (0.2-33.8), and follow-up time of 28.6 months (0.1-106.1) were evaluated.

    Results: Mean regression of -40.2% occurred in 168 (67%) patients, progression of +104% occurred in 17 (7%) patients, and stability (-2.7%) was maintained in 67 (27%) patients (p<0.001). In patients who ultimately regressed, mean shrinkage of -18.2% and maximum rate of change (mean -0.6 cm3/month, -6.4%/month) were observed at 3 months. In patients who ultimately progressed, initial regression was observed in the first 3 months (mean -0.1 cm3/month, -0.9%/month), with progression observed by 6 months. Transient progression was observed in 15 (9%) tumors before eventual decrease and transient regression was observed in 6 (35%) tumors before eventual increase. Skull base tumors regressed significantly more than non-skull base tumors (mean -25% vs. -16%, p=0.036). On multivariable analysis, volume percent change, slope of volume change, and slope of percent change were significant predictors of progression after 6 months.

    Conclusions: Meningioma volume response after SRS is dynamic; early changes may not be indicative of final response. Tumors that ultimately regress often shrink in the first 3 months, whereas tumors that ultimately progress may shrink in this period, then progress by 6 months post-treatment. Tumor rate of change 6-12 months post-SRS is predictive of long-term tumor response.

    Patient Care: A more thorough understanding of meningioma response to radiosurgery will aid clinician decision-making during the early follow-up period. Quantification of volume changes, with characterization of the variable nature of response trends and identification of important time points in the natural history of tumor response, can support post-treatment management decisions

    Learning Objectives: By the conclusion of this session, participants should be able to describe the dynamic volumetric response demonstrated by meningiomas following Gamma Knife radiosurgery.


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