RESUMO
PURPOSE: To investigate the use of weight-based protocols during full- and half-body fluorodeoxyglucose F 18 (FDG) positron emission tomography-computed tomography (PET-CT) and their effect on image quality, radiation dose, and lifetime attributable risks. METHODS: A total of 1817 patients were referred for FDG PET-CT studies. Each scanning group (4 total: full-body groups A and C and half-body groups B and D) was randomly allotted into conventional or weight-based CT. Groups A and B followed a conventional protocol of 120 kVp, 120 mA, 0.5 second rotation time, and pitch 0.8 mm/rotation for all body weights. Groups C and D were scanned using 1 of 4 weight-based CT protocols. All 4 weight-based protocols used 140 kVp, 0.75 seconds rotation time, and pitch 0.8 mm/rotation. Milliamperage varied by body weight as follows: protocol I (≤ 60kg [132.3 lb]), 35 mA; protocol II (61-80 kg [134.5-176.4 lb]), 50 mA; protocol III (81-100 kg [178.6-220.5 lb]), 65 mA; and protocol IV (> 100kg [222.7 lb]), 100 mA. All protocols (weight based and conventional) employed tube current modulation. CT quantitative image quality measurements were evaluated for each protocol, and lifetime attributable risks were calculated for each age group and sex. RESULTS: Patient demographics demonstrated no significant differences between groups. Mean effective dose was significantly lower for group C (full body, weight based) compared with A (full body, conventional) (P < .001), as were lifetime attributable risks (P < .001). Mean effective dose and lifetime attributable risks also were significantly lower (P < .001) for group D (half body, weight based) compared with B (half body, conventional). Contrast-to-noise ratios showed no difference between groups (P = .12), supporting a preference for the weigh-based protocols used for groups C and D. For half-body, weight-based protocols (group D), the lifetime attributable risks decreased for men by 91.9% and for women by 38.9%. For full-body, weight-based protocols (group C), the lifetime attributable risks decreased by 72.5% and 66.3% for men and women, respectively. DISCUSSION: Radiologists and radiologic technologists face the challenge of balancing the potential risks of radiation-induced cancer against providing diagnostic-quality images and uncompromised disease detection. Weight-based protocols address this challenge without compromising image quality or pathology detection. CONCLUSION: Significant reductions in radiation dose and lifetime attributable risks can be achieved using CT weight-based protocols during half- and whole-body FDG PET-CT without compromising CT image quality.
