Optimizing ¹³¹I-mIBG Dosimetry: Validation of Simplified Time-Point and Segmentation Approaches.

Area of Science:

• Nuclear Medicine
• Medical Physics
• Radiopharmaceutical Therapy

Background:

• Accurate dosimetry for ¹³¹I-mIBG therapy is crucial for effective treatment and minimizing toxicity.
• Current reference dosimetry methods can be complex and time-consuming, posing challenges in clinical workflow, particularly for pediatric applications.

Purpose of the Study:

• To evaluate simplified dosimetry protocols for ¹³¹I-mIBG therapy.
• To assess methods that maintain agreement with reference dosimetry while reducing clinical workflow burdens.

Main Methods:

• A hybrid protocol combining planar whole-body scans and SPECT/CT was implemented in 24 patients.
• Three liver segmentation methods (whole-organ, 4 mL homogeneous sphere, 4 mL peak sphere) were compared.
• Time-integrated activity coefficients (TIACs) were estimated using various data reduction strategies, including the Hänscheid single-time-point method.

Main Results:

• Dual 24h/48h imaging showed minimal bias for both liver and whole-body absorbed doses compared to the reference method.
• The Hänscheid method at 48h demonstrated superior performance among single-time-point methods.
• Peak sphere segmentation overestimated absorbed doses, while homogeneous spheres showed a slight underestimation.

Conclusions:

• Clinically feasible ¹³¹I-mIBG dosimetry can be achieved using dual 24h/48h imaging (less than 6% mean bias).
• The single 48h Hänscheid method is also a viable option with less than 6% mean bias.
• Homogeneous sphere liver segmentation offers a simplified approach with less than 8% mean difference from the reference.