The best data supporting this is from a Randomized trial from France, published in the JCO by Sundstom in 2004.
421 patients with locally advanced stage III or stage IV NSCLC, with no curative options, with chest symptoms or centraltumor threatening the airways.
17 Gy / 2 fx
42 Gy /15 fx
50 Gy / 25 fx
There were no differences in survival or QOL measures.
The caveats - in the 2 fraction arm, treatments were separated by 7 days. They were also treated with steroids the day before, the day of, and the day after each fraction. The length of spinal cord was limited to 12cm. Also at three years there was a trend towards worse survival in the hypofractionated arm (3 yr OS 1% 2 fx, 9% 15 fx, 6% 25fx, p=0.06).
We have reserved this option for patients who's estimated survival is on the order of 3 months, and for whom transport for multiple fractions would be great hardship to them.