Not applicable, Dosimetric comparison, Radiation safety, Dosimetry, Diagnostic procedure, PET-CT, CT, Paediatric, Nuclear medicine, Hybrid Imaging, Multimodality Imaging
C. Cox, M. Segbers, M. van Straten; Rotterdam/NL
PET/CT plays an important role in the teenager population for oncologic and inflammatory indications. Both PET and CT use ionizing radiation for imaging and are complementary to each other. PET provides functional information and the CT-scan is used for attenuation correction and anatomical correlation. For this, a ldCT protocol with sufficient image quality for anatomical correlation is enough. As teenagers are more radiosensitive than adults and have a long post exposure life expectancy in which the adverse radiation effects could exhibit, it is important to keep the exposure of a PET/CT scan as low as reasonably achievable .
The PET/CT scanner provides dedicated child and adult CT protocols, which use different bowtie filters. To optimize dose and image quality of child and adult protocols, parameters like tube voltage (kV), quality reference mAs and the strengths of the automatic exposure control (AEC) are often adjusted by the user. Since teenagers of a specific age or body mass still have a wide range in body composition, some will need a child protocol and others an adult protocol for the optimal scan.
Without guidelines, the technologists will decide subjectively which protocol (adult or child) fits to a teenager of a certain body habitus. This might result in under- or overexposure and suboptimal image quality. This implies the importance of a decision rule to determine which ldCT protocol fits for a specific patient. Due to the wide range in body compositions for a given age or body mass, a decision rule based on these parameters may not be appropriate. Patient age for example does not correlate well with individual patient size .
Studies of Reid et al.  and Dong et al.  showed that abdominal circumference is the most accurate parameter to use for decision rules concerning abdominal CT protocols in pediatrics with respect to the balance between image quality and dose. Based on these results, we aim at a practical decision rule based on waist circumference for switching from a child to an adult protocol in ldCT of teenagers such that dose is minimized and the required image quality obtained.