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

Abstract

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_S-ADJ), and for size and scan length (DLP_SL-ADJ). DLP_S-ADJ variation was assessed by body region and facility. To ascertain whether sites use AC/AL or diagnostic doses, we compared each facility's DLP_S-ADJ in CTs from PET-CT vs diagnostic CT exams of analogous body regions (not associated with PET), controlling for scan length using DLP_SL-ADJ. 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_S-ADJ = 1004 vs 341 mGy-cm, respectively). For body exams, DLP_S-ADJ was higher in older children than adults, and there was wide inter-facility variation (median DLP_S-ADJ 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.