Comparison of physical dose and dose-averaged linear energy transfer between treatment planning system and Monte Carlo simulation in carbon-ion radiotherapy

Ishikawa, Akihisa*; Koba, Yusuke*; Furuta, Takuya   ; Chang, W.*; Hashimoto, Shintaro  ; Yonai, Shunsuke*; Matsumoto, Shinnosuke*; Sato, Tatsuhiko   

There found to be a relationship between the dose-averaged linear energy transfer LETd and local tumor control in carbon-ion radiotherapy (CIRT). However, only physical dose and biological dose are registered in the past treatment records of CIRT in QST hospital and LETd can not be deduced directly. There is a method to estimate LETd based on RBE-LETd-fitted function but some problems such as non-singularity at the end point of carbon ions are known. On the other hand, we propose a method to reproduce the CIRT by reconstructing the beam transport geometry based on the treatment planning data and conduct Monte Carlo simulation. The LETd can be also computed directly. We therefore compared LETd obtained by Monte Carlo simulation with estimated LETd using the treatment planning data. We found that underestimation around the end point of carbon ions but the influence was local and thus the LETd estimates are valid for the purpose computing in organ scale.