Biological effects of human lung cells MRC-5 in CBCT positioning for image-guided radiotherapy

Image-guided radiotherapy (IGRT) provides precise positioning for the tumor target, but it may bring extra irradiation dose in the target positioning with a cone beam CT (CBCT) which has been increasingly used in IGRT. In this work, we focused on biological effects of the low-dose irradiation in IGRT, which have not been considered so far. Primary human fibroblasts cells from the lung and MRC-5 were irradiated by a CBCT. DNA doublestrand breaks (γ-H2AX foci) and micronucleus frequency of the irradiated samples were analyzed. Compared to the control, the γ-H2AX foci yields of the samples irradiated to 16 mGy increased significantly, and the micronuclei rate of the samples irradiated for 3 days increased notably. The dose by imaging guidance device can be genotoxic to normal tissue cells, suggesting a potential risk of a secondary cancer. The effects, if confirmed by clinical studies, should be considered prudentially in designing IGRT treatment plans for the radiosensitive population, especially for children. (authors)