Assessment of cross-dose contributions from tumors within computational phantoms using a Geant4 radiation dosimetry tool exploiting hybrid analytical/voxelised geometries.

Background: Dosimetry software tools developed for Radiopharmaceutical Therapy, such as OLINDA/EXM or IDAC-Dose, account only for radiation dose to organs from radiopharmaceutical taken up in other organs.

Purpose: The aim of this study is to present a methodology, that can be applied to any voxelised computational model, able to account for cross-dose to organs from tumors of any shape and number enclosed within an organ.

Methods: A Geant4 application using hybrid analytical/voxelised geometries has been developed as an extension to the ICRP110_HumanPhantom Geant4 advanced example and validated against ICRP publication 133. In this new Geant4 application, tumors are defined using the Geant4 Parallel Geometry functionality, which allows the co-existence of two independent geometries in the same Monte Carlo simulation. The methodology was validated by estimating total dose to healthy tissue from Y and from Lu distributed within tumors of various sizes localized within the liver of the ICRP110 adult male phantom.

Results: Agreement of the Geant4 application with ICRP133 was within 5% when masses were adjusted for blood content. Total dose to healthy liver and to tumors was found to agree within 1% when compared to the ground truth.

Conclusions: The methodology presented in this work can be extended to investigate total dose to healthy tissue from systemic uptake of radiopharmaceuticals in tumors of different sizes using any voxelised computational dosimetric model.