Survey of CT dose for PET/CT localization and attenuation correction

Objectives The CT portion of a PET/CT scanner provides localization and attenuation correction of the PET data. Unlike diagnostic CT, recommended dose levels for CT localization and attenuation correction of PET are limited. This work presents a survey of CT dose estimates from PET/CT sites participating in the SNMMI Clinical Trials Network (CTN).

Methods From September 2008 to September 2014, CT acquisition parameters were collected from 269 sites participating in the CTN PET/CT accreditation program. 168 of the 269 sites provided complete datasets for estimating CT dose (scan region, kVp, mA, rotation time, pitch, and collimation) using their standard clinical imaging protocols. The CT dose index (CTDI_vol­) and effective dose were estimated using the ImPACT CT Patient Dosimetry Calculator. Histograms of CTDI_vol and effective dose were calculated for a scan length of 85cm (eye-to-thigh) for all 168 sites. An additional 66 of the 168 sites had multiple accreditation cycles over several years and were used to examine changes in dose over time.

Results The CTDI_vol ranged from 0.5 mGy to 27.6 mGy with a median CTDI_vol of 5.8 mGy (95% CI, 6.2-7.6 mGy). The effective dose ranged from 0.6 mSv to 43.0 mSv with a median effective dose of 8.3 mSv (95% CI, 9.0-11.1 mSv). The wide range of the CTDI_vol and effective dose indicates a large variation in the CT techniques across sites. There was no observable pattern of increasing or decreasing CT dose over multiple accreditation cycles.

Conclusions Some of the CTDI_vol values reported here are above the American College of Radiology reference level for abdomen (25 mGy). The wide range of CT doses suggests that recommendations and standardization of appropriate CT acquisition parameters would be beneficial for lowering CT dose in PET/CT localization and attenuation correction.