Use of diagnostic vs low-dose computed tomography in positron emission tomography-CT examinations.

Objectives: To examine CT radiation dose variation in PET-CT and understand how often providers use diagnostic vs lower doses for attenuation correction and anatomic localization (AC/AL).

Methods: Retrospective, multi-centered study of PET-CT exams from 2010 to 2021. Exams were categorized as body or brain. Radiation dose was quantified using dose length product (DLP), adjusted for patient size (DLP), and for size and scan length (DLP). DLP variation was assessed by body region and facility. To ascertain whether sites use AC/AL or diagnostic doses, we compared each facility's DLP in CTs from PET-CT vs diagnostic CT exams of analogous body regions (not associated with PET), controlling for scan length using DLP. Lastly, we categorized exams as likely diagnostic if they used multiple phases and/or contrast to compare dose and frequency with likely non-diagnostic exams.

Results: Sixty-four thousand two hundred ten exams included 93% body, 7% brain. Doses were higher and more variable in the body than brain exams (adult mean DLP = 1004 vs 341 mGy-cm, respectively). For body exams, DLP was higher in older children than adults, and there was wide inter-facility variation (median DLP range = 245-2391 mGy-cm). Most facilities used higher CT doses in body PET-CT than in diagnostic CT exams even controlling for scan length. Fifty-three percent of adult and 76% of child body exams were likely diagnostic based on the use of diagnostic techniques.

Conclusion: While diagnostic CT is sometimes indicated for PET-CT, body exams generally do not use AC/AL protocols. Doses were higher than previously reported, higher than analogous diagnostic CT exams, and higher in older children than adults when size adjusted.

Key Points: Question How does CT radiation dose vary in PET-CT and how often do providers use diagnostic vs lower doses for AC/AL? Findings Most facilities did not use AC/AL protocols for body PET-CT, and CT effective doses were higher than previously reported. Clinical relevance The considerable inter-facility variation observed suggests ample opportunity to reduce ionizing radiation doses for CT in body PET-CT by adopting low-dose (AC/AL) protocols and other dose reduction techniques.