♦ Acoustic Neuromas
♦ Preoperative
- Review images and audiogram
♦ Intraoperative
Frame Placement
- Shift the frame toward the size of the lesion while remaining neutral in the anteroposterior plane (for Gamma Knife technique, y coordinate of 95 to 105 when using ear bars with the Leksell G frame)
Recommended Magnetic Resonance Imaging Sequences
- One- to 1.5-mm thick contrast-enhanced spoiled-gradient recalled acquisition in steady state (SPGR) images focused on the lesion
- One-mm thick T2-weighted imaging (to help define the intracanalicular portion and inner ear anatomy) focused on the lesion
Dose Planning
- With the Gamma Knife, use 4-mm isocenters for the intracanalicular portion, and 14-, 8-, or 4-mm isocenters for the extracanalicular portion depending on its size.
- Conformality at the anteroinferior margin is critical (the usual location of the facial and cochlear nerves).
- Recommended radiation dose:
- Eleven to 12.5 Gy margin dose (for hearing preservation)
- Twelve to 13 Gy margin dose (if no serviceable hearing is left)
- Aim to keep the brain stem dose below 13 Gy
- Recommended radiation dose:
♦ Postoperative
- Obtain follow-up imaging every 6 months for a year, then increase imaging interval if the tumor is controlled.
- An audiogram is desired at the time of imaging if the patient retains good hearing.
♦ Meningiomas
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