37.5 Gy in 15 fractions for Optic Nerve tolerance

[XRT_doc]

What do you guys think of 37.5 Gy in 15 fractions for optic nerve tolerance?

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[thaddeus]

Should be fine. This was the dose/fractionation for WBRT in RTOG 9508, and I don't think any optic nerve issues were reported. Also, basic BED calculation with alpha/beta = 3 gives a tolerance BED of ~90 Gy for optic nerve (assuming tolerance of 54 Gy at standard fx); BED of 37.5/15 is ~70.

 

[seper]

That's my standard WBRT dose.

 

[Burt Radnolds]

Others already beat me to the punch, but should be totally fine.

Say you took a conservative constraint like 54Gy point dose @ 2gy/fx, and assumed a low end a/b ratio of 1.5. BED(a/b 1.5) for 5400 would be 126Gy. A dose of 37.5Gy @ 2.5Gy would have a BED (a/b 1.5) of 100Gy making it well below what is already a conservative tolerance IMO.

If you are doing some sort of IMRT with inhomogeneity, and want to know the max that equates to a dose of 5400 @ 2Gy, this would be 46.87Gy.

 

[Gfunk6]

I concur with above. Per RTOG, this is the standard WBRT dose for non-radio sensitive brain mets.

 

[Palex80]

That's fine. I've done 42/3 several times and not seen toxicity either.

 

[Areion]

I think it depends on what you're trying to treat. Is this a WBRT question? if so multitudes of patients have been treated with this for years. if you're targeting around the optic nerve, I favor smaller fraction sizes (as in 180 cGy to 5220 for an optic nerve sheath meningioma)