Yes, it seems to be standard procedure here in the US. I had a spot ( nodule) on my lung last October. It was discovered on a regular chest x-ray. The radiologist wrote on his report that it seemed to be non cancerous. They can tell by the density etc.. Still, the pulmonary doctor urged me to get a CT scan. The CT evaluation also that it was considered less than 5 % cancer. In spite of this i was told that I had to have CT scans every 6 months. As you probably know, CT scans give you quite a bit of radiation and the radiation dose is accumulative
I refused to have any further done. An x-ray in May showed that the "spot" is no more. When I researched the topic at the time, I found out that over 50 % of the elderly have lung spots. Sometimes they are just shadows, like a nipple shadow!
So I would ask the doctor exactly what the chances are that it is something bad. The most important question is -is it growing? If not, and the chance of malignancy is very small, I would not object myself to large doses of radiation. The protocol was mostly established because of liability issues, in other words doctors don't want to get law suits. Ct s can are pretty accurate and should give your doctor all this information.-The fact that your father's spot comes and goes, makes me think that is not a serious problem. A cancer would be getting larger, not disappear and come back.
This is just my opinion and not to be taking as medical advice.

I agree with Heike.
I have had 3 nodules on my lungs for years. They do not disappear, but they do not move or grow either, which is good !!

My pulmy doctor , during my last physical with him, did not see the need for a cat scan because the last x rays, showed they had not moved in over 2 years,
but the last time I was so sick and went to the hospital here, and thy did not know what was wrong, to rule out lung cancer, they gave me a cat scan,(Even tho Dr. Sanchez said I did not need one, different hosp...) and I did not have cancer, but still had the nodules !!
My pulmy said, on finding out I was in hosp, and had that done, said the results were as he suspected, non cancerous and with a 1% chance of it turning in to lung cancer.
I do not see the reason for so many scans on your dad, if it was non cancerous, and then went away.... It could be "trying" to form a cancer, it could be scar tissue, it could be shadows,it could be non cancerous nodules formig (like mine) if he was a smoker,or worked around chemicals.
But I can not give you advice, however if it were me, and I knew an oncologist that I could talk to that was covered by my insurance and would just look at the test results, I would ask the oncologist about it.
Or even a scan once a year or every two years, if it is non cancerous, but I would certainly question it.
I was to sick when I was in this little country hospital in Gatesville, Or I would have protested that cat scan and told them Sanchez has already ruled on that.....
Anyway, ask the doctor why, if there is no evidence of cancer, would he need to get so many scans.
(I guess they could eventually give us cancer that way !!),
and ask what is the percentage of folks with spots like his that do not appear to be cancerous, and come and go, what are the percentages that actually turn into cancer....
Blessings to you and Blessings to your dad, but these doctors need to stop treating us older folks like "Well, she i dying,anyway, can't hurt" attiude. Get some answers
Hugs
BJ