Validation of Monte Carlo Iodine-131 radiopharmaceutical dosimetry workflow using a 3D printed anthropomorphic head and neck phantom

Abstract: Purpose: In this study, we present the creation of an anthropomorphic, head and neck, nuclear medicine phantom and its characterization for the validation of a Monte Carlo, SPECT image based, Iodine-131 RPT dosimetry workflow. Methods: 3D printing techniques were used to create the anthropomorphic phantom from a patient CT dataset. Three Iodine-131 SPECT/CT imaging studies were performed using a homogeneous, Jaszczak, and an anthropomorphic phantom to quantify the SPECT images. The impact of collimator detector response (CDR) modeling and volume-based partial volume corrections (PVC) upon the absorbed dose was calculated using an image based, Geant4 Monte Carlo RPT dosimetry workflow and compared against a ground truth scenario. Finally, uncertainties were quantified in accordance with recent EANM guidelines. Results: The 3D printed anthropomorphic phantom was an accurate re-creation of patient anatomy including bone. The extrapolated Jaszczak recovery coefficients were greater than that of the 3D printed insert (~22.8 ml) for both the CDR and non-CDR cases. Utilizing Jaszczak phantom PVCs, the absorbed dose was underpredicted by 0.7% and 4.9% without and with CDR, respectively. Utilizing anthropomorphic phantom RCs overpredicted the absorbed dose by 3% both with and without CDR. All dosimetry scenarios that incorporated PVC were within the calculated uncertainty of the activity. The uncertainties in the cumulative activity ranged from 25.6% to 113% for Jaszczak spheres ranging in volume from 0.5 ml to 16 ml. Conclusion: The accuracy of Monte Carlo-based dosimetry for Iodine-131 RPT in head and neck cancer was validated with an anthropomorphic phantom. Future applications of the phantom could involve 3D printing and characterizing patient specific volumes for more personalized RPT dosimetry estimates.