Technical note: Errors introduced when using Dose Voxel Kernels for estimating absorbed dose from radiopharmaceutical...

Area of Science:

• Medical Physics
• Radiopharmaceutical Therapy
• Radiation Dosimetry

Background:

• Radiopharmaceutical therapies (RPT) often use dose voxel kernels (DVK) for absorbed dose (Dabs) calculations, offering speed and ease over Monte Carlo (MC) simulations.
• DVK assumes non-stochastic particle distribution, valid for beta emitters due to high particle counts per cell kill.
• Alpha particles' high linear energy transfer (LET) means a single traversal can kill a cell, necessitating lower activity and potentially causing DVK errors in Dabs calculations.

Purpose of the Study:

• To compare Dabs calculations using DVK and MC methods for beta and alpha emitters in small tumors.
• To illustrate the impact of DVK on Dabs estimations for alpha RPT at the microscale.

Main Methods:

• A tumor cluster model was used to compare DVK and MC methods for beta (177Lu) and alpha (211At, 225Ac, 227Th) irradiations.
• Simulations used 10^3 beta particles and 20 alpha particles per cell, reflecting clinically relevant scenarios.
• Results were analyzed using Dabs histograms, dose volume histograms, and Dabs error maps.

Main Results:

• For beta emitters (177Lu), DVK and MC methods yielded similar Dabs results.
• For all alpha emitters studied, DVK methods significantly overestimated Dabs compared to MC simulations.
• Error maps highlighted discrepancies in Dabs distribution between DVK and MC for alpha emitters.

Conclusions:

• DVK methods can lead to substantial overestimation of Dabs for alpha emitters in RPT.
• The mean Dabs metric alone may be insufficient when using DVK for alpha emitter dosimetry.
• MC simulations are recommended for accurate Dabs calculations in alpha RPT, especially at the microscale.