Investigation of ¹⁸F and ⁸⁹Zr Isotopes Self-Absorption and Dose Rate Parameters for PET Imaging

This work concerns study of self-absorption factor (SAF) and dose rate constants of zirconium-89 (⁸⁹Zr) for the purpose of radiation protection in positron emission tomography (PET) and to compare them with those of ¹⁸F-deoxyglucose (¹⁸F-FDG). We analyzed the emitted energy spectra by ¹⁸F and ⁸⁹Zr through anthropomorphic phantom and calculated the absorbed energy using Monte Carlo method. The dose rate constants for both radionuclides were estimated with 2 different fluence-to-effective dose conversion coefficients. Our estimated SAF value of 0.65 for ¹⁸F agreed with the recommendation of the American Association of Physicists in Medicine (AAPM). The SAF for ⁸⁹Zr was in the range of 0.61-0.66 depending on the biodistribution. Using the fluence-to-effective dose conversion coefficients recommended jointly by the American National Standards Institute and the American Nuclear Society (ANSI/ANS), the dose rate at 1 m from the patient for ¹⁸F was 0.143 μSv·MBq^-1·hr^-1, which is consistent with the AAPM recommendation, while that for ⁸⁹Zr was 0.154 μSv·MBq^-1·hr^-1. With the conversion coefficients currently recommended by the International Committee on Radiological Protection (ICRP), the dose rate estimates were lowered by 2.8% and 2.6% for ⁸⁹Zr and ¹⁸F, respectively. Also, we observed that the AAPM derived dose is an overestimation near the patient, compared to our simulations, which can be explained by the biodistribution nature and the assumption of the point source. Thus, we proposed new radiation protection factors for ⁸⁹Zr radionuclide.