Stereotactic Radiosurgery and Radiation Oncology
Core concepts
Understand the principles of stereotactic radiosurgery (SRS): single high-dose focused radiation, steep dose fall-off, and the importance of accurate targeting and immobilization. Know the indications: small meningiomas, vestibular schwannomas, brain metastases, arteriovenous malformations, and selected functional disorders. Learn the radiobiology (DNA damage, repair, the 4 Rs of radiobiology) and the difference between SRS and fractionated radiotherapy. Also cover complications: radiation necrosis, optic neuropathy, and cranial nerve deficits, and their timing.
Traps
- Assuming SRS is suitable for large lesions; size limits apply (often around 3 cm).
- Confusing radiation necrosis (months after treatment, ring-enhancing, mimics tumor) with tumor progression.
- Forgetting that the optic apparatus has a dose tolerance limit.
- Missing that SRS for AVMs takes years to obliterate and carries a latency-period hemorrhage risk.
Worked example / rule of thumb
A patient with a small vestibular schwannoma and serviceable hearing may be offered SRS as an alternative to surgery. Rule of thumb: radiation necrosis typically appears months after treatment and can mimic tumor recurrence; advanced imaging or serial follow-up helps distinguish them.