Meningioma

1.Who gets radiosurgery

Radiosurgery is well suited to small-to-moderate, presumed grade I meningiomas that are growing or symptomatic, especially at surgically difficult sites (cavernous sinus, petroclival, tentorial), as well as to residual or recurrent tumor after subtotal resection and to tumors in elderly or comorbid patients. Imaging is contrast-enhanced MRI; somatostatin-receptor (DOTATATE) PET can aid delineation and confirm meningiomatous identity in ambiguous cases. Asymptomatic, non-growing meningiomas are often simply observed. Surgery remains preferred when there is significant mass effect or edema, when tissue diagnosis is needed, or for larger tumors amenable to safe resection.

2.Grade I dose and control

For presumed grade I meningioma, single-fraction marginal doses of roughly 12–16 Gy (commonly 13–15 Gy, prescribed at the 50% isodose line with Gamma Knife) achieve durable control, and the large series agree. The Pittsburgh experience (Kondziolka 2008, 972 patients, mean ~14 Gy) reported ~93% grade I control; the multicenter Santacroce series (~3,768 meningiomas, median 14 Gy) found 5- and 10-year progression-free survival of ~95% and ~89% overall, ~93%/83% for histologically confirmed grade I, and ~97%/93% for benign-imaging tumors treated without biopsy; and Pollock (416 grade I, median 16 Gy) reported 5- and 10-year local control of 96% and 89%. Reported associations between tumor volume and control are inconsistent: several large series found no significant volume effect, while Kondziolka, Pollock, and the Marchetti meta-analysis found larger volume predicted both worse control and higher complication risk. Grade remains the strongest single predictor, but volume and location matter, and convexity, parasagittal, and parafalcine tumors control less well than skull-base tumors. Cavernous-sinus meningiomas control well, with 5-year PFS of 86–99% and 10-year PFS of 69–97% across the ISRS systematic review, and new cranial neuropathy directly attributable to SRS in about 6–9%. The dominant constraint is the optic apparatus: for perioptic or juxta-optic tumors (cavernous sinus extending to the optic nerve/chiasm, optic-nerve-sheath meningioma), the single-fraction optic constraint is often incompatible with a tumoricidal margin dose. Current HyTEC guidance for a previously unirradiated optic apparatus is a maximum point dose of 10 Gy in one fraction for about 1% risk, with D0.2cc under 8 Gy, and risk rises steeply above 12 Gy; fractionating relaxes this to roughly 20 Gy maximum in 3 fractions or 25 Gy in 5, so these are treated with fractionated SRT (or hypofractionation) to deliver adequate tumor dose within optic tolerance.

Toxicity is modest but not negligible. New or worsening peritumoral edema is the most common adverse event, reported in 8–25% of treated tumors, symptomatic in roughly 4–8%, and reaching about 40% in parasagittal and parafalcine locations. Predictors are parasagittal location, volume above 10 cc, venous sinus compression or invasion, higher margin dose, and pre-existing edema; extensive perilesional edema before treatment is a relative contraindication to single-fraction SRS. Permanent morbidity was 6.6% in the Santacroce series, and complication rates rise above about 16 Gy at the 50% isodose line. New cranial neuropathy attributable to SRS runs about 6–9% for cavernous-sinus tumors.

3.Higher-grade meningioma is a different disease

Atypical (WHO grade II) and anaplastic (WHO grade III) meningiomas recur far more readily and have infiltrative margins; single-fraction SRS to a tight margin is generally inadequate (5-year control falls to roughly 50–65% for grade II and lower for grade III, even at higher margin doses of ~16–18 Gy). These are managed with maximal safe resection and fractionated radiotherapy, typically 54–59.4 Gy for grade II after gross-total resection, 59.4–66 Gy for grade II after subtotal resection, and 60–66 Gy for grade III to generous margins, with the risk-adapted approach studied in RTOG 0539 and adjuvant grade II radiotherapy tested in EORTC 22042; SRS has a more limited, often salvage or boost, role for focal nodular recurrence. Recognizing that a "meningioma" may be higher grade (rapid growth, marked edema, bone invasion, atypical imaging) should prompt consideration of resection for diagnosis rather than empiric radiosurgery.

4.The evidence base, and the grade II problem

Meningioma radiosurgery rests on large prospective cohorts rather than randomized trials for grade I disease; the prospective trials concentrate on higher-grade tumors, where the real debates live.

Open controversies:

• Adjuvant timing for grade II. Whether to irradiate immediately after gross-total resection or reserve radiation for documented recurrence remains unresolved. Two randomized trials address it: ROAM/EORTC-1308 randomized observation versus 60 Gy in 30 fractions after Simpson 1 to 3 resection of atypical meningioma and closed to accrual in 2021, and NRG-BN003 is the phase III North American counterpart randomizing observation versus 59.4 Gy after gross-total resection of grade 2 disease. Practice-changing outcome data are awaited.
• SRS versus fractionated RT for atypical disease. Single-fraction SRS is limited for grade II/III tumors, which are infiltrative and larger; fractionated higher-dose RT (~54–60 Gy) is generally preferred, with SRS reserved for small, well-defined recurrences.
• Grading and the imaging diagnosis. Many SRS-treated meningiomas are never biopsied, so an unrecognized higher grade can masquerade as a benign-imaging tumor; WHO CNS5 (2021) is largely subtype-agnostic and defines grade 3 by a TERT promoter variant or homozygous CDKN2A/B deletion regardless of histology, and cIMPACT-NOW update 8 (2025) proposes grade 2 for otherwise-benign tumors carrying 1p deletion with monosomy 22q or an NF2 variant and endorses methylation profiling for borderline cases. None of that is available for an imaging-only diagnosis, which is the real limitation of treating a presumed grade 1 tumor without tissue.
• Perioptic and large tumors. When a meningioma abuts the optic apparatus, the single-fraction optic limit forces fractionation: the same perioptic logic as the sellar region.