When I pull up the info on these modifiers for my local MAC, it states:
"Appropriate Use: When services are related to F-18 flouro-D-glucose (FDG) PET imaging study."
"PI: Positron Emission Tomography (PET) or PET/Computed Tomography (CT) to inform the initial treatment strategy of tumors that are biopsy proven or strongly suspected of being cancerous based on other diagnostic testing."
"Append PI PET or PET/CT CPT codes when billing to inform the initial treatment strategy for solid tumors: 78608, 78811, 78812, 78813, 78814, 78815, or 78816."
"PS: Positron Emission Tomography (PET) or PET/Computed Tomography (CT) to inform the subsequent treatment strategy of cancerous tumors when the beneficiary's treating physician determines that the PET study is needed to inform subsequent antitumor strategy."
"Append Modifier PS to all procedure codes listed and billed with a cancer
diagnosis code. 78608, 78811, 78812, 78813, 78814, 78815, or 78816."
If you go off these descriptions, it appears the DX is the key factor. If the patient does not have a cancer DX, then it would be inappropriate to bill with a PS. However, if this new tumor is a reoccurrence of the previous tumor (and cancer), then it'd fall under PS and would need a cancer DX. The question is whether or not it's a reoccurrence. I tried finding guidelines regarding the length of time that has to pass before a patient is considered "cured" versus "in remission" but only came up with the "5 year rule" which appears to be frequently disputed.
http://www.mayoclinic.org/diseases-conditions/cancer/in-depth/cancer/art-20044517 https://www.cancertutor.com/war_cure_rates/
On face value, I'd be inclined to say PI, but after considering the fact that only 3ish years have passed since the previous treatment, that pushes me to PS instead. You should take a quick read through of those links and see if that sways your inclination.
