Room: AAPM ePoster Library
Purpose: Dual-isotope peptide receptor radionuclide therapy using DOTATATE labeled with ¹77Lu and ?°Y is a promising treatment for neuroendocrine tumours. In order to not exceed dose limits to critical organs while optimizing tumour control, personalized dosimetry should be performed. If identical biodistributions of ¹77Lu- and ?°Y-DOTATATE are assumed, dose estimates for ¹77Lu and ?°Y can be done using ¹77Lu SPECT imaging. However, Bremsstrahlung photons created by ?°Y might cloud the ¹77Lu distribution, posing a challenge for activity quantification. The aim of this work is to determine if dosimetry based on quantitative imaging of ¹77Lu in the presence of ?°Y is possible.
Methods: Monte Carlo GATE simulations of spheres filled with ¹77Lu, ?°Y, or both placed in a cylindrical water phantom were created. Images were generated with a simulated Siemens SPECT camera. Eighteen concentrations of ¹77Lu and/or ?°Y placed in the spheres and two background activities for each concentration were simulated. Two different scatter window widths for triple energy window scatter correction (TEW-SC) were investigated. The quantification error and contrast to noise ratios (CNRs) were determined for every configuration.
Results: Quantification error of ¹77Lu remained within ±6% for all configurations and concentrations of ¹77Lu and ?°Y. The presence of ?°Y increased the accuracy of quantification due to the reduction of errors associated with TEW-SC. Better accuracy was achieved with a narrower scatter window width. The presence of ?°Y did not impact the CNRs in any configuration, and all CNRs were well above the threshold of 5 suggested by the Rose Criterion.
Conclusion: Our study indicates that quantitative imaging of ¹77Lu in the presence of ?°Y may provide more accurate results than imaging ¹77Lu alone. The presence of ?°Y also does not negatively impact image noise. In summary, ?°Y does not negatively affect quantitative imaging and dosimetry in dual-isotope PRRT.
Quantitative Imaging, SPECT, Dosimetry