Has SBRT shown to improve OS or PFS in patients with localized pancreatic cancer who are not a eligible for surgery due to other comorbidities?

No. 33Gy / 5 fx, "Low-dose palliative SBRT" may not help at all. In spite of what you will hear many radiation oncologists tell you, it is a palliative therapy with similar overall survival to 50.4Gy in 28 fractions in every study of usually highly selected patients. It's only more convenient and less toxic. There is a very good likelihood that it does not improve survival at all over chemotherapy alone. That is because it is a 40% reduction from an ablative dose.

Ablative doses of radiation, ho...

I have been giving definitive doses for LAPc for the past 10 years using CT-on-rails at MDACC and now CBCT since moving to Memorial Sloan-Kettering 1.5 years ago. I have probably only been giving the ablative doses listed above for the past 6 years. The initial criteria essentially were that I looked for tumors that were 1 cm from the nearest duodenum, stomach or jejunum. However, since that time with experience my personal selection criteria are very liberal and I treat anyone that does not hav...