Treatment of lung cancer in radiotherapy was evaluated by considering damages to normal tissues. Small and large tumors were examined for two portals, rotational and conformation irradiation. The considered damages were irreversible late effects in lung and injury to spinal cord. For the small tumor of 3.5 cm in diameter, rotational irradiation showed the smallest damage. For the large tumor of 12 cm X 10 cm in cross section, conformation irradiation resulted in the smallest damage.