Comparative post-therapeutic dosimetry between 2D planar-based and hybrid-based methods for personalized Lu-177...

Area of Science:

• Nuclear Medicine
• Medical Physics
• Radiopharmaceutical Therapy

Background:

• Personalized dosimetry is crucial for optimizing radionuclide therapies like ¹⁷⁷Lu-PSMA I&T and ¹⁷⁷Lu-DOTATATE.
• Accurate absorbed dose calculation relies on appropriate imaging protocols and dosimetry software.
• HERMES HybridViewer offers advanced dosimetry capabilities integrating various imaging modalities.

Purpose of the Study:

• To compare absorbed doses in organs and tumors using different imaging protocols and calculation methods in HERMES HybridViewer.
• To evaluate dosimetry for ¹⁷⁷Lu-PSMA I&T and ¹⁷⁷Lu-DOTATATE therapies.
• To assess the impact of imaging methodology on radiation dose calculations.

Main Methods:

• Acquired whole-body planar and SPECT/CT images from 18 patients undergoing ¹⁷⁷Lu-therapies.
• Calculated time-integrated activity (TIA) in organs and tumors.
• Determined absorbed doses using the Medical Internal Radiation Dose (MIRD) scheme via HERMES HybridViewer with OLINDA/EXM V.2.1 and NURBS digital phantoms.

Main Results:

• Planar-based dosimetry yielded higher dose per injected activity than hybrid-based dosimetry, attributed to organ overlap.
• The spleen showed the largest absorbed dose difference (up to 51.6%) between methods.
• Differences in other organs and tumors were less than 40%.

Conclusions:

• 2D planar dosimetry significantly overestimates absorbed dose compared to the hybrid method.
• The hybrid method provides superior tumor visualization and overlap-free organ delineation.
• Hybrid dosimetry is recommended for more accurate dose assessment in ¹⁷⁷Lu-therapies.