@oldgreenpaint I had in mind a comment made by Mack Roach in a video. Dr. Roach is recognized as a world authority on RT. He was discussing the history of radiation treatment for prostate cancer.

He said he had been the first to publish, several decades ago, about how the method of putting tattoos on patients to aid machine operators in lining up the patient so their external beam would hit their target, could completely fail if patients were too obese.

The tattoos could not be relied upon to indicate accurately where the prostate was because the thick layer of fat these patients had allowed the skin the tattoos were on to shift too much. He said in some cases the external beam treatment would miss the prostate entirely! !!

Todays RT is light years ahead of this type of thing. However, when RT gets even better in coming years, todays less catastrophic sources of error will become more commonly discussed....