Problems of a correct approach to radiation therapy of lung cancer are reported. The identification of factors related to the site and function (respiratory motion, critical organs etc) allows systematization of a Quality Assurance procedure in treatment planning and implementation. Already in the diagnostic phase modern technology (CT, MRI) can supply useful information for a more correct staging and consequently for a more suitable treatment, while in the therapeutic phase it helps in the identification of irradiation volumes (simulation), in the use of treatment plans on CT imaging (multislide, 3D), in the use of conformal therapy able to increase the target dose while sparing the critical organs, and in checking correct patient set-up.