Monte Carlo dose mapping on deforming anatomy

Area of Science:

• Medical Physics
• Radiotherapy
• Computational Imaging

Background:

• Accurate dose calculation in radiotherapy is crucial, especially for moving targets.
• Deformable image registration (DIR) is used to track anatomical changes.
• Existing dose mapping methods can introduce significant errors.

Purpose of the Study:

• To introduce a novel Monte Carlo-based method, energy and mass congruent mapping (EMCM), for calculating radiation dose on deforming anatomy.
• To compare the accuracy and efficiency of EMCM against traditional dose interpolation methods.

Main Methods:

• Developed EMCM to separately map energy and mass using displacement vector fields from DIR.
• Implemented EMCM, energy-based dose interpolation (EBDI), and trilinear dose interpolation (TDI) in EGSnrc/DOSXYZnrc.
• Validated methods using a numerical deformable phantom and clinical lung cancer IMRT data.

Main Results:

• EMCM achieved exact dose mapping on a numerical phantom, unlike EBDI (2.5% error) and TDI (6.0% error).
• Clinical data showed EBDI and TDI differed from EMCM by 1.96% and 7.3% in lung IMRT plans.
• EMCM demonstrated accuracy comparable to 3D Monte Carlo simulations.

Conclusions:

• EMCM provides accurate dose calculation for deforming anatomy.
• The method is suitable for 4D dosimetry quality assurance and dose accumulation.
• EMCM represents a significant advancement for precise radiotherapy delivery.