Along with coverage changes, youll have two new modifiers related to oncologic PET scans soon. These become effective July 1, and SNM warns you should not use these modifiers until the effective date. The two new modifiers indicate either an initial or subsequent scan: " Initial: 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, one per cancer diagnosis " Subsequent: PS -- Positron emission tomography (PET) or PET/computed tomography (CT) to inform the subsequent treatment strategy of cancerous tumors when the beneficiarys treating physician determines that the PET study is needed to inform subsequent anti-tumor strategy.