Significant dose reduction is feasible in FDG PET/CT protocols without compromising diagnostic quality

To reduce the radiation dose to patients by optimizing oncological FDG PET/CT protocols.

The baseline PET/CT protocol in our institution for oncological PET/CT examinations consisted of the administration of 5.18 MBq/kg of FDG and a CT acquisition with a reference current-time product of 120 mAs. In 2016, FDG activity was reduced to 4.44 and 3.70 MBq/kg and reference CT current-time-product was reduced to 100 and 80 mAs. 322 patients scanned with different protocols were retrospectively evaluated. For each patient, effective dose was calculated. The overall image quality was subjectively rated by the referring physician on a 4-point scale (IQ score: 1 excellent, 2 good, 3 poor but interpretable, 4 poor not interpretable). Image quality was quantitatively evaluated measuring noise in the liver.

CT Results: Effective dose was progressively reduced from 9.5 ± 2.8 to 8.0 ± 2.3 and 6.2 ± 1.5 mSv (p < 0.001). A mean dose reduction of 34.9% was achieved. There was a significant degradation of IQ score (p < 0.05) and noise (p < 0.001). Nevertheless, the number of poor quality studies (IQ score >2) did not increase. PET Results: Effective dose was gradually reduced from 6.5 ± 1.4 to 5.7 ± 1.3 and 5.0 ± 1.0 mSv (p < 0.001). Average dose reduction was 23.4%. IQ score (p < 0.05) and noise (p < 0.001) significantly degraded for lower activity protocols. However, all images with reduced activity were scored as interpretable (IQ score ≤ 3).

A significant radiation dose reduction of 28.7% was reached. Despite a slight reduction in image quality, the new regime was successfully implemented with readers reporting unchanged clinical confidence.