Follow-up/Toxicity

Question 1

The dose falloff to which structures needs to be carefully evaluated with GK SRS for ANs?

Answer 1

Cochlea and brainstem doses need to be carefully evaluated with GK SRS.

Question 2

What IDL is prescribed in GK? Why? How about for LINAC-based SRS?

Answer 2

GK: 50% (sharpest drop-off in dose is at 50% IDL)

LINAC: 80%

Question 3

What is the difference in the onset of side effects after Sg vs. RT for ANs?

Answer 3

Side effects present upfront/immediately after Sg vs. in a delayed/gradual (mos to yrs) fashion after RT.

Question 4

What is the dose threshold above which hearing preservation rates decrease with RT?

Answer 4

Preservation rates decrease at doses >13 Gy. (Japanese data: Hasegawa T et al., J Neurosurg 2005)

Question 5

What mean cochlea dose is the threshold for hearing preservation with SRS?

Answer 5

Mean cochlea 3 Gy. 2-yr hearing preservation 91% if mean cochlea <3 Gy vs. 59% if >3 Gy (Baschnagel J et al., Neurosurg 2013)

Question 6

What are some toxicities and rates of toxicities after SRS for ANs?

Answer 6

Trigeminal neuropathy/hyperesthesia: 0%–5%

Facial nerve neuropathy/palsy: 0%–5%

Hearing deficit: useful hearing preserved in 40%–60%

Question 7

What are the main toxicity differences b/t RT and Sg?

Answer 7

RT carries a lower risk of facial nerve/trigeminal nerve injury.