Optimizing positron emission tomography radiation dose using Monte Carlo N-particle simulations

Positron emission tomography (PET) is a functional imaging procedure that uses a radioactive tracer to visualize organ or tissues functions for the purposes of diagnoses, staging and therapy monitoring of cancer. However, reconstructed images produced by PET are often accompanied with noise resulting in inaccuracies in diagnoses and other treatment procedures. This has been more apparent with patients who are grossly overweight or morbidly obese. The present study was conducted to quantitatively determine the optimal amount of injected radiotracer required to attain sufficient quality of PET images based on differing physiques. A simulation process was undertaken and completed in three main phases: (i) modelling of four different sizes of phantoms typifying underweight, normal, overweight and obese patients using Monte Carlo N-particle (MCNP); (ii) reconstructing images in the range of 435-650 keV energy window using MATLAB programming platform; and (iii) determining optimal dose of activity required to induce adequate tumor signal-to-noise ratio (Snr) value for a proposed imaging system. Three different activities were tested with modelled National Electrical Manufacturers Association (Nema) International Electrotechnical Commission (IEC) PET phantom starting from 6, 8 and 10 mCi of ¹⁸F-fluorodeoxyglucose (FDG) with tumor-to-background ratio (Tbr), ranging from 2:1 to 6:1. Results showed that reducing activity of injected radiotracer in PET imaging was possible for variations in body weights while maintaining image quality. The Snr value for different dosages differed only by maximum value less than 2.0. The present study serves as a basis for further clinical PET studies using reduced radiotracer doses as compared with conventional PET protocols. (Author)