How do you choose between Grenz ray in a short course (e.g., ~5–7 fractions) versus longer-course superficial/megavoltage external beam regimens for large, ill-defined lentigo maligna on the cheek when surgery is not feasible?  

My understanding of Grenz ray therapy is that it was a historic treatment popularized in the 1920s for benign skin diseases that has largely now been replaced by systemic, biologic therapies. It had been used at doses of 200 cGy per week to reduce dendritic Langerhans cells, thereby treating psorias...