CT/PET is useful in early diagnosis, staging, follow-up and in radiotherapy treatment planning especially for tumors located in motion involved anatomic areas (chest and abdomen). We analysed the treatment planning for radiotherapy of two pulmonary cancer patients. A comparison was performed between GTV (Gross Tumor Volume) and PTV (Planning Target Volume) identified with CT images alone and GTV and PTV evaluated with CT/PET images. CT/PET imaging was demonstrated to significantly modify the target volume if compared with CT imaging: volumes were reduced by 32-49%.