How do you approach liver SBRT in patients with hepatocellular carcinoma who aren't candidates for surgery or other interventional procedures when the overall liver volume is small making it difficult to achieve liver constraints?  

These are tough situations. I have used proton and photons for HCC. In the situation you described, I would generally favor IMPT due to improved low dose distribution and keeping the parenchyma not treated to a minimum while still giving an ablative dose more comfortably. Although the mean liver dos...