PURPOSE: PET and PET-CT are being successfully used in pediatric oncology in children with Hodgkin and non-Hodgkin lymphomas and seem promising for monitoring treatment response in children with osteosarcomas and rhabdomyosarcomas, Ewing's sarcoma, neuroblastoma. The goal OF this study is to determine whether low dose CT attenuation correction images are OF sufficient quality to allow follow-up studies.
METHOD AND MATERIALS: Using a variety OF phantoms, CT images were acquired on both a PET-CT (Discovery LS, 4-slice system) and a dedicated CT unit (GE Lightspeed 8-slice systems) using two different protocols: (1) a diagnostic acquisition CTDIvol OF 9 to 14 mGy for a weight range OF 5 to 15 kg, and (2) attenuation correction CT images using a CTDIvol OF 3 to 6 mGy. The image quality was assessed by means OF a mathematical model (i.e. non-prewhitening matched filter) confirmed by images OF a CT contrast-detail phantom (AFC study). RESULTS: When reducing the CTDIvol from 14 mGy to 3 mGy, image noise increased from 6 to 19 HU. The large CTDI used in a diagnostic acquisition allowed detecting target sizes as small as 2 mm whereas the CTDI used in attenuation correction images only allowed detection OF size OF 3 to 6 mm (contrast OF the target: 10 HU).
CONCLUSION: In patients where the detection OF small low contrast structure is not required, follow-up can be performed using CTDI VALUEs comparable to the one used for attenuation correction and image fusion in PET/CT. Using optimal CT technique in children allows to significantly reduce radiation exposure by adjusting CT parameters to the CLINICAL question. The dose reduction can be performed without decreasing image quality when high-contrast organs are considered.
CLINICAL RELEVANCE/APPLICATION: Avoiding unnecessary CT examinations on children.