Benign CNS tumors
Meningioma
The most common benign brain tumor, where radiation controls growth after subtotal resection or replaces surgery at critical skull-base locations.
Definition
A meningioma is a benign (WHO grade 1 in the great majority) tumor arising from arachnoid cap cells of the meninges. It grows slowly, compressing rather than invading the brain, and presents with seizures, focal deficits, or is found incidentally. Location matters more than size: skull-base, parasagittal, and cavernous sinus lesions abet critical neurovascular structures and are frequently unresectable without substantial morbidity.
How radiation treats it
Radiation arrests meningioma cell proliferation, leading to slow involution of the tumor and, in many cases, durable lifelong growth control. Because complete resection (Simpson grade 1) is curative, radiation is reserved for residual or recurrent tumor, unresectable skull-base locations, and patients who are poor surgical candidates. For benign meningiomas, radiation is frequently used as the only treatment, avoiding a craniotomy entirely.
Side effects
- Acute fatigue, mild headache, and transient alopecia over the treatment field.
- Temporary worsening of neurologic deficits from peritumoral edema, sometimes managed with corticosteroids.
- Late risks include cognitive effects in long-term survivors and cranial neuropathy when nerves are included in the target, minimized with fractionation and conformal planning.
Simulation process
The patient is positioned supine in a thermoplastic mask matched to the treatment site, with CT simulation and contrast-enhanced thin-slice MRI fused to define the tumor and dural tail. The optic apparatus, brainstem, cochlea, hypothalamus, and any cranial nerves in proximity are contoured as organs at risk with dose constraints. For skull-base lesions, IMRT or fractionated stereotactic planning with daily image guidance is standard.
Treatment process
Typical regimens are 52.8–54 Gy in 28–30 daily fractions over about six weeks, or stereotactic radiosurgery to 12–14 Gy at the margin in a single session for small lesions away from critical structures. Fractionated stereotactic RT (21–25 Gy in 5 fractions) is an intermediate option for small- to medium-sized skull-base tumors near the optic nerve. Local control for benign meningiomas exceeds 90% at ten years; follow-up is annual MRI for life.
Key takeaways for students
- 54 Gy in 30 fractions is the classic benign regimen; 12–14 Gy SRS for small peripheral tumors.
- Subtotal resection plus radiation equals the control rates of complete resection.
- Optic nerve and brainstem constraints shape every plan.