What RT dose/fractionation would you use to treat an unresectable grade 3 solitary fibrous tumor abutting the optic nerve and chiasm?

Generally, I would consider treating an unresectable grade 3 solitary fibrous tumor to up to 59.4/60 Gy, or possibly higher. The location of this tumor makes it difficult to treat entirely using this dose while respecting the optic nerve/chiasm constraints. How is the patient's vision? If intact, options to consider would be to "cold spot" the optic nerve/chiasm to a max dose of 55 Gy. If impaired, you may go higher and have a discussion about optic neuropathy with the patient.

From a non-CNS sarcoma standpoint, there is published European experience with definitive-intent RT for unresected SFT, and a clear dose-response relationship, with ~80% local control at 60+ Gy vs ~30% at lower palliative doses. Thus, trying to get as much of the tumor to a definitive dose, while respecting optic constraints as outlined by my esteemed CNS colleagues, seems reasonable. There are no good α/β estimates for SFT specifically, but a typical benchmark for soft-tissue sarcomas is around 4, so there is likely still some radiobiological advantage to fractionation with respect to effects on the likely lower α/β optic apparatus. Speaking tentatively as a sarcoma specialist, I wonder if my CNS colleagues might accept a higher optic Dmax...

There isn't a perfect answer for this case, but we would consider 59.4 Gy-60 Gy in 1.8 Gy/2 Gy and maintain optic constraint of ~54 Gy abutting it and use ExacTrac/IGRT to be able to treat within 1 mm (i.e., let the constraint drive coverage). Interestingly, I also polled our sarcoma group, and a couple of considerations came up - they have considered hypofrac (mostly outside the brain) of 45 Gy in 15 fx for unresectable disease that is published. Another consideration from a senior member was that for unresectable disease, RT alone would not likely be a curative modality, and thus an approach that minimized optic toxicity with a fractionated, durable, safe dose may be ideal (over escalation above 60 Gy).

Before launching into XRT for this CNS patient, I would review with Sarcoma Med Onc regarding initial treatment with an antiangiogenic agent. SFTs have a relatively high rate of PR with those agents, which might provide some extra room for working around the visual apparatus. If embarking on that approach, I would continue to see the patient frequently to participate in clinical surveillance for progression that might warrant moving on to XRT.

The standard recommendation would be 60 Gy conventionally fractionated, with constraints on the chiasm and optic nerves held to 54 Gy. For this tumor, I would be willing to push OARs to 55.8 Gy without much hesitation. If the patient has a lateralized tumor, then pushing the dose higher to the ipsilat...