Whole Brain After H&N RT

[Haybrant]

Got a patient that has comprehensive neck definitive chemo RT in 2015 now has 8 or 9 brain mets from small cell lung that developed over a short time period, all above the tentorium not symptomatic ranging between .5 and 1.8cm. Anyone w experience in this situation giving whole brain, how do you plan this and manage constraints. Thank you

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[CaesarRO]

SRS

 

[Palex80]

If you do not want wish to perform SRS (which I can understand given the number of mets and histology), I would plan with IMRT/VMAT.
Just contour brain and then transfer the isodoses from the H&N treatment plan to your current planning CT.

Prescribing depends on several factors:
- life expectancy
- functional status
- where the mets currently are (within/outside prior H&N treated volumes)

I wouln't be all to concerned about causing toxicity. Brain tissue that has seen a dose of 40-50 Gy in 2015 can still well manage 10 x 3 Gy WBRT which is given 7 years later. We know that from GBM retreatment, where we often given hypofractionated 25-35 Gy after 30 x 2 Gy within a shorter time frame. You could however also do something like "WBRT with 10 x 3 Gy to areas outside the previously irradiated brain volume and 10 x 2.5 Gy to areas within that volume". If you go for IMRT, you can easily focally boost (SIB) those macroscopic brain mets (although we have no hard data to support dose escalation here).

 

[Neuronix]

Depends on dose received at base of skull. If base of skull structures got full dose then I do IMRT 20/10 at optic pathway and brainstem, 30/10 to rest of brain. If base of skull structures got say 30 Gy max before they can take a full 30/10 now IMO. I don't worry about brain dose for something that long ago.

 

[TheWallnerus]

The worry with re-irradiation of CNS is the cumulative late effects... euphemistically known as the total BED Gy-2 (or BED Gy-3 depending on your particular radiobiological proclivities) of all the plans/courses... assuming there's no forgiveness from previous RT courses (this is a wrong but very safe/conservative assumption). One way to lower total BED Gy-2/Gy-3 in reirradiation situations is to give the reirradiation at the same planned total dose in smaller fractions but over the same total elapsed time period; ie, BID RT. The brain handles BID RT just fine to 40 Gy at 2 Gy fractions. Thus 30 Gy in 1.5 Gy fractions is a WBRT chip shot, but it's a chip shot that will still exterminate a lot of SCLC cells. I would give 30 Gy/20 fx's WBRT (there are definitely lesions up there you CAN'T see) BID over 2 weeks... all the lesions (if they're smallish) will disappear, so definitely get a pre-RT "planning MRI." You could do "involved site" post-WBRT stereo boosts to the pre-RT met volumes with 2 or 3 fractions of 5 Gy each. SCLC seems like a disease for us to always be looking to find an excuse to think twice-a-day in my book.

 

[seper]

Agree. Just do normal WBRT 30/10. May consider field reduction after 24 Gy if feeling particularly skittish

 

[evilbooyaa]

My only scenario I'd be concerned would be if it was like a bad nasopharynx/nasal cavity tumor with concern of significant dose (agree with 30Gy as a cut-off) really to optics alone, or previous high dose (say 54-60Gy) to say brainstem.

For a run of the mill nasopharynx or pretty much any primary lower (even if treating high level IIs) I wouldn't really worry.

That being said, given overlap you would have justification for IMRT if you wanted