Lack of dose dependency for radiation pneumonitis after chemoradiotherapy with the use of tomotherapy for lung cancer.

A 71-year-old man with stage IIB (Union for International Cancer Control, 8 edition) non-small cell lung cancer underwent intensity-modulated radiation therapy with a dose of 66 Gy administered in 33 fractions concomitant with carboplatin and paclitaxel therapy. On computed tomography after completion of radiation therapy, ground-glass opacity, which was larger on the contralateral side, was observed, but it was not observed in the high-dose area on the ipsilateral side. Although the adverse event theoretically shows dose dependency, it was finally diagnosed as radiation pneumonitis. The presence of an atypical distribution of radiation pneumonitis should be recognized to improve the diagnosis, and it is suggested that the relative volume of the normal contralateral lung receiving a dose of ≥5 Gy is a possible risk factor for radiation pneumonitis.