Medical Student Virginia Commonwealth University Department of Neurosurgery Richmond, Virginia, United States
Introduction: Radiation therapy is a common treatment for meningiomas. Long-term volume changes of meningiomas in response to radiation are not well-characterized. We analyzed and modeled the volumetric change of meningiomas following treatment with radiation.
Methods: Data were collected from a retrospective single-institution database of patients who presented between 2005 and 2015. Tumors were measured using T1-weighted post-contrast images. Volumes were calculated using the ABC/2 ellipsoidal approximation method. In patients whose tumors responded to radiation, tumor volume change was best modeled as an exponential decay process approaching an asymptotic final volume.
Results: 48 patients with meningioma were considered for inclusion. 5 (10%) had tumors that saw growth following radiation. The remaining 43 subjects had maximum follow-up times ranging from 0.3 to 14.9 years. Over three-quarters of the sample had a total volume decrease of at least 50% and a decrease of at least 67% of the predicted volume change. Decay rates were calculated with a median decay rate of 0.81 (IQR: 0.68, 0.98). After 0.35 years, three quarters of these patients’ tumors were reduced by half and, after 1.17 years, 90% of the total reduction was achieved. Predicted and actual tumor volumes had a mean difference of 0.009cc (SD=0.347), with actual volumes being slightly larger. Similar results were obtained when predicting volume in the last MRI for each subject, with the model underestimating the actual volume by -0.062cc (SD=0.689).
Conclusion : 90% of intracranial meningiomas treated with radiation decreased with final tumor volume that strongly correlates to initial tumor volume. Over three quarters had a decrease of at least 50% of their total volume and 67% of their asymptotic volume change, and a 90% final volume decrease by 1.17 years after treatment. WHO grade I and II meningiomas have a radiation response that can be accurately predicted by through mathematical modeling with an asymptotic decay curve.
