Scan choices: Is there a radiologist in the house?

[Rich66]

So..mom has mets to liver and lung. She had a PET/CT early June which showed mostly inactive liver mets but significant uptake in one of the lung nodules. Been following stubborn lung module with CT late June and early September and it's time for another scan. I have found articles about benefits of tracking chemo efficacy with PET/CT. The doc thinks CT would be more apples to apples with last scan but I know it wouldn't tell much about the liver activity or whether uptake is less in lung nodule. My sense so far is that dedicated CT is better than the non-contrast, low dose cT included in a PET/CT. To complicate things, they want mom to skip contrast in the next CT due to perceived reactions to the contrast.
So...
I'm leaning towards PET/CT giving more overall information than non-contrast traditional chest and ab CTs. But if CT w/o contrast is still measurably superior in terms of tracking the lung nodule absolute size, that might sway things...though that would not say anything about activity in liver or change in uptake which can precede size changes.

One option might be to have insurance pay for the more expensive (eye to thigh) PET/CT and if lung nodule is equivocal, pay for a less expensive chest CT for clarification.
Thoughts?

They are also wanting a mammo..which surprised me given the state of things.