In the era of digital PET/CT, does switching from weight-based to BMI-based FDG dosing result in reduced radiation exposure to and from patients? A technologist perspective

Objectives: In patients undergoing FDG PET/CT scanning, switching from TOF analog to TOF digital PET/CT system have resulted in reduced radiation exposure to both patients and technologists. This was particularly true for obese patients when the maximum injected dose dropped from 15 mCi for analog to 10 mCi for digital scanner. We set out to investigate if switching from a weight-based to BMI-based injected FDG dose would result in further radiation reduction to patients and PET technologists, without compromising image quality. Methods/Materials: A total of 40 patients undergoing a standard of care F-18 FDG PET/CT exam on a digital TOF scanner received an FDG dose based on BMI as follows: 6 mCi for BMI < 25, 8 mCi for BMI 26-34 and 10 mCi for BMI > 35. These same 40 patients had a prior exam on the same digital TOF scanner after a weight-adjusted dose of 0.14 mCi/kg. A log was created to compare the F-18 FDG doses to patients. To assess the radiation exposure to technologists, dosimetry reports for 2 months with identical volume (89 patients) were compared before and after the switch to BMI-based dosing. The 3 components to the dosimetry report are the Whole Body Deep Dose Equivalent (DDE), Lens of Eye Dose Equivalent (LDE) and Whole Body Shallow Dose Equivalent (SDE).

Results: When comparing doses of the 40 patients scanned using both the weight-based dose and BMI-based dose, our preliminary data (Table 1) has shown an average F-18 FDG dose reduction of 34.86% in patients with a BMI of 25 or less, 17.61% in patients with a BMI between 26-34, and -0.58% in patients with a BMI of 35 or higher. Given that the max FDG dose was kept the same (10 mCi) for patients with BMI ≥35, switching from weight-based to BMI based resulted in greater reduction of radiation doses to patients with BMI < 35. However, based on the dosimeter readings for the 2 months (Table 2), the switch from weight-based to BMI-based did not significantly change radiation exposure to technologists. Conclusion: Ongoing data collection comparing weight-based to BMI-based dosing for the digital TOF PET/CT scanner continues to be acquired. However, our initial assessment has shown reduction of dose to patients, without compromising image quality. In our experience, the radiation exposure to technologists was not significantly reduced when switching to BMI-based dosing instead of weight-based dosing. Table 1: Comparison of weight-based dosing to BMI-based dosing on Digital TOF PET (0.14mCi/kg) vs. Digital TOF PET (BMI kg/m2 ) Dosing Systems

Table 2: Technologist Exposure (0.14mCi/kg) vs (BMI kg/m2 )