Background
Compelling evidence shows the association between the relative biological effectiveness (RBE) of carbon‐ion radiotherapy (CIRT) and the dose averaged linear energy transfer (
LETd
). However, the ability to calculate the
LETd
in commercially available treatment planning systems (TPS) is lacking.
Purpose
This study aims to develop a method of calculating the
LETd
of CIRT plans that could be robustly carried out in RayStation (V10B, Raysearch, Sweden).
Methods
The calculation used the fragment spectra in RayStation for the CIRT treatment planning. The dose‐weighted averaging procedure was supported by the microdosimetric kinetic model (MKM). The MKM‐based pencil beam dose engine (PBA, v4.2) for calculating RBE‐weighted doses was reformulated to become a
LET
‐weighted calculating engine. A separate module was then configured to inversely calculate the
LETd
from the absorbed dose of a plan and the associated fragment spectra. In this study, the ion and energy‐specific
LET
table in the
LETd
module was further matched with the values decoded from the baseline data of the Syngo TPS (V13C, Siemens, Germany). The
LETd
distributions of several monoenergetic and modulated beams were calculated and validated against the values derived from the Syngo TPS and the published data.
Results
The differences in
LETds
of the monoenergetic beams between the new method and the traditional method were within 3% in the entrance and Bragg‐peak regions. However, a larger difference was observed in the distal region. The results of the modulated beams were in good agreement with the works from the published literature.
Conclusions
The method presented herein reformulates the MKM dose engine in the RayStation TPS to inversely calculate
LETds
. The robustness and accuracy were demonstrated.