Thoracic cord

[deleted4401]

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Everything says 50 Gy for tolerance, right? RTOG protocols, etc...
But, my physics/dosi peeps have 45 Gy stuck in their head and 47 Gy on a lung plan is "too cordy" for them. They always give me a hard time when I tell them to improve coverage and go up to 50 Gy.
What are you all using?
S

 

[Gfunk6]

I'm using 50 Gy maximum dose to spinal cord + 3 mm. This of course assumes daily IGRT. Per QUANTEC the probability of cord myelopathy after 50 Gy at 2 Gy per fraction is 0.2%. This assumes that the full thickness of the cord is irradiated, if not then the risk of myelopathy will be even less. If you assume alpha/beta of 2 for spinal cord, the BED is 100 for 50/2 and 85.5 for 45/1.8.

 

[medgator]

I'm using 50 Gy maximum dose to spinal cord + 3 mm. This of course assumes daily IGRT.

Yeah that's my max dose as well. C-cord may have a slightly higher tolerance compared to T-cord

 

[deleted4401]

Okay cool.

Since I'm going to 60 Gy in 30 fractions, the cord dose is 50 Gy in 30 Fx, or 1.66 Gy/fx. So, the BED is closer to 91 and risk is even lower then.
S

 

[seper]

No, I still use 45 Gy for cord Dmax and 50 Gy for cord+5mm.

 

[radiaterMike]

SimulD is right- much of the data suggesting a tolerance of 45 Gy comes from the pre-3D era. So the cord was likely in the field, getting full dose (if not greater, due to a hot spot) after which you would go off cord. With 3D planning to 60-70 Gy, the fractional dose to the cord is going to be much less than 1.8-2 Gy, allowing for a bit more wiggle room in cord dose.

 

[thesauce]

50 Gy to cord + 3mm with RT alone. 45 Gy with chemo.