What is the optimal dose fractionation for treating liver metastases in the central liver causing obstruction of biliary flow?

This question is somewhat controversial, which is surprising to me. The standard ablative dose for ablation of liver mets is 100 Gy BED10. This results in local tumor control of 90% at 2 years for CRC liver mets, but drops off to 70% at 5 years. Other histologies may be more sensitive. The biliary tree is a relatively resistant structure. Strictures are uncommon, but they do happen. Most people think that 50 Gy in 5 fractions is safe, but I have seen patients treated outside who have had strictures from this regimen. I don't know if there is any literature that defines the risk in 5 fractions. The consequences can be either atrophy of the segment or lobe or stent placement and lifelong management. I have never caused a stricture. If I did, ...