Since the treatment plan made by the physicist is ultimately approved by the physician, the responsibility of accurately determining the treatment site based on the patient's health report, the final treatment plan, preserving healthy organs, informing the patient and obtaining his consent in cases where it is not possible to preserve a healthy organ due to proximity to the tumor, monitoring the patient's clinical condition to decide whether to continue or temporarily stop treatment, and in some cases prescribing medications to reduce the adverse effects of radiationو etc. are some of the responsibilities of the oncologist.
I think the legal liability should be like any other therapies that a physician might initiate. If the therapy such as treatment brings bad effects, the patient would consider the physician who suggested it that they are responsible. I think the same should apply for radiation therapy.