Is there a field size in which you would consider single fraction palliative radiation unsafe?

There is nothing to suggest a larger field size when treating multiple body levels increases the risk of complications with 8 Gy single fraction. Radiobiologically it is less dose to cord than 30 Gy in 10 fractions. We routinely use it. Only if a large GI volume gets treated small bowel or stomach) would I consider using a fractionated (5 fraction) course to reduce the likelihood and severity of acute GI symptoms.