Clinical implementation of voxel-based dosimetry using image-based RT-PHITS Monte Carlo simulations for...

Area of Science:

• Nuclear Medicine
• Medical Physics
• Radiotherapy

Background:

• 177Lu-DOTATATE peptide receptor radionuclide therapy (PRRT) is a key treatment for neuroendocrine tumors.
• Accurate dosimetry is essential for optimizing PRRT efficacy and minimizing toxicity.
• Monte Carlo (MC) simulations offer advanced capabilities for patient-specific dose calculations.

Purpose of the Study:

• To evaluate the RadioTherapy extension of the Particle and Heavy Ion Transport code System (RT-PHITS) MC simulation for absorbed dose estimation in 177Lu-DOTATATE therapy.
• To compare RT-PHITS dosimetry with a conventional organ-based method (IDAC-Dose 2.1).
• To assess the impact of patient-specific dosimetry on dose calculations.

Main Methods:

• Quantitative SPECT/CT imaging from 17 patients treated with 177Lu-DOTATATE.
• Automated organ segmentation (TotalSegmentator) and manual tumor delineation.
• Image registration and voxel-level time-integrated activity (TIA) map generation.
• Absorbed dose calculation using RT-PHITS and IDAC-Dose 2.1 for comparison.

Main Results:

• RT-PHITS consistently yielded higher mean absorbed doses per unit of administered activity compared to IDAC-Dose 2.1.
• Relative dose differences ranged up to 15.35%, with the right kidney showing the largest discrepancy.
• When using identical time-integrated activity data, relative differences between methods remained below 10.40%.

Conclusions:

• RT-PHITS is a capable tool for patient-specific absorbed dose calculation in 177Lu-DOTATATE therapy.
• The MC simulation provides higher dose estimates than organ-based methods, highlighting the importance of advanced dosimetry.
• Patient-specific dosimetry using RT-PHITS is particularly beneficial for organs near or containing tumors.