How would you treat very locally aggressive rectal cancer extending into muscle and causing internal iliac tumor thrombus, in a patient who is not a surgical candidate?

I would treat with chemoradiation, 50.4 Gy/28 fx using a 3D conformal technique and standard rectal cancer volumes. The lumbosacral plexus prevents doses higher than 60 Gy, and in general there not much evidence of dose response between 50Gy and 60Gy.