Dose Distribution Degradation of Carbon-ion Radiotherapy Caused by Tumor Cell-specific Relative Biological Effectiveness of Osteosarcoma: A Simulation Study Using Experimental Results.

BACKGROUND/AIM: Dose distributions of carbon-ion radiotherapy (C-ion RT) have been created with the relative biological effectiveness (RBE) of human salivary gland cells (HSG). However, no dose distributions have been created using various tumor cell-specific RBE values. Hence, we conducted in vitro experiments to determine the RBE of human osteosarcoma cells (U2OS) and used this RBE value (RBE) to calculate the dose distribution for C-ion RT.

MATERIALS AND METHODS

To obtain RBE values for various linear energy transfer (LET) levels, we exposed U2OS cells to different doses of X-rays and varying doses and LET levels of C-ion beams (13, 30, 50, and 70 keV/μm). Subsequently, we converted the RBE of HSG (RBE) to RBE in the treatment planning system and reconstructed the dose distribution for a typical osteosarcoma case. We performed a dose-volume histogram (DVH) analysis, evaluating the percentage of the minimum dose that covered 98%, 50%, and 2% (D, D, and D, respectively), as well as the homogeneity index [HI; calculated as (D-D)/D].

RESULTS

The RBE values for C-ion beams with LET of 13, 30, 50, and 70 keV/μm were 1.77, 2.25, 2.72, and 4.50, respectively. When comparing DVH parameters with the planning target volume, we observed the following values: D, D, D, and HI for RBE were 64.1, 70.1, 72.4 Gy (RBE), and 0.12, respectively. For RBE, these values were 86.2, 95.0, 107.9 Gy (RBE), and 0.23, respectively.

CONCLUSION

We utilized RBE to calculate the dose distribution of carbon ion radiotherapy, revealing potential degradation in dose distribution and particularly worsening of the HI.