Technical note: TERMA scaling as an effective heterogeneity correction model for convolution-based external-beam photon dose calculations.

Background: In highly heterogeneous medium, such as one with lung tissue or air cavities, the dose in the low-density region or after it, as calculated by the conventional methods based on convolution with an energy-spreading kernel, is usually overestimated in comparison with measurements or more accurate predictions.

Purpose: To correct the overestimation, we propose a method of scaling the total energy released per mass (TERMA).

Methods: The scaling depends on both the density distribution and the effective beam size in the lateral direction.

Monte Carlo modeling of Halcyon and Ethos radiotherapy beam using CAD geometry: validation and IAEA-compliant phase space.

A Monte Carlo (MC) model of a Halcyon and Ethos (Varian Medical Systems, a Siemens Healthineers Company) radiotherapy beam was validated and field-independent phase space (PHSP) files were recorded above the dual-layer multileaf collimators (MLC).The treatment head geometry was modeled according to engineering drawings and the dual-layer MLC was imported from CAD (computer-aided design) files. The information for the incident electron beam was achieved from an iterative electromagnetic solver.