Methodology for comparing absorbed dose rate calculation algorithms in molecular radiotherapy dosimetry.

Area of Science:

• Medical Physics
• Radiological Sciences
• Nuclear Medicine

Background:

• Comparison of dosimetry algorithms is essential for accurate radionuclide therapy.
• Local Energy Deposition (LED), Convolution of Voxel S Values (CONV), and Monte Carlo (MC) modeling are common dosimetry algorithms.
• Open-source software facilitates reproducible research in clinical dosimetry.

Purpose of the Study:

• To compare the accuracy of LED, CONV, and MC algorithms for absorbed dose rate (ADR) calculations.
• To evaluate the impact of medium heterogeneity on dosimetry algorithm performance.
• To assess the effectiveness of density correction in heterogeneous media.

Main Methods:

• Utilized OpenDose3D software for dosimetry calculations.
• Processed 52 patient datasets treated with ⁹⁰Y, ¹⁷⁷Lu, or ¹³¹I.
• Computed voxel-based ADR maps in homogeneous (water) and heterogeneous (CT-derived) media, with density correction applied at the voxel level in heterogeneous scenarios.

Main Results:

• In homogeneous media, CONV agreed well with MC (rd ≤ 1%), while LED underestimated ADR by up to 10%.
• In heterogeneous media, LED significantly underestimated ADR (up to 50% in lungs/bone marrow for ¹³¹I).
• CONV showed excellent agreement with MC in soft tissues (rd ~ 1%) and good agreement in self-irradiation dominant tissues; density correction was less effective for cross-irradiation dominant tissues.

Conclusions:

• A procedure for evaluating ADR algorithms was proposed.
• Medium heterogeneity and cross-irradiation significantly impact dosimetry calculations.
• CONV demonstrates superior accuracy compared to LED, especially in heterogeneous environments.