The Effect of Radiation on Meningioma Volume Change.

Background: Radiation therapy is a common treatment for meningiomas. Volume changes of meningiomas in response to radiation are not well characterized. This study seeks to quantify the volume change of meningiomas following radiation.

Methods: Data were collected from a retrospective single-institution database of cases from 2005-2015. Tumors were measured using T1-weighted post-contrast magnetic resonance imaging. Volumes were calculated using the ABC/2 ellipsoidal approximation.

Results: A total of 63 patients fit the inclusion criteria; 37 patients (59%) received radiation following resection, 19 (30%) received radiation alone, 4 (6%) received radiation following a biopsy, and 3 (5%) had unknown surgical status. A total of 39 patients (62%) had skull base meningiomas; 43 tumors were World Health Organization (WHO) grade I, and 12 tumors were WHO grade II. Thirteen patients received radiosurgery, 43 received radiotherapy, and 7 received an unknown number of treatments. Eight patients did not attain local control and were excluded from volume analyses. WHO grade I meningiomas saw an average of 33% ± 19% decrease in tumor volume; WHO grade II tumor volumes decreased by an average 30% ± 23%. Radiosurgery saw an average volume decrease of 34% ± 13%, while radiotherapy resulted in volume decrease of 31% ± 21%. For those who achieved local control, there was an average decrease in tumor size of 30% ± 19%, 30% ± 22%, and 41% ± 19% over 0.5-1.5, 2.5-3.5, and >5 years, respectively.

Conclusions: Meningiomas treated with radiation exhibit nonlinear decrease in size over time. The greatest decrease in tumor volume occurs within the first year and begins to plateau 5 years post-radiation treatment.