Abstract: ObjectiveTo investigate the effect of radiotherapy target area delineation on efficacy and toxicity in locally advanced small cell lung cancer. 
MethodsFrom October 2012 to October 2014， 128 patients with locally advanced small cell lung cancer were randomly divided into control group（n=64） and observation group（n=64）. The target areas were identified by enhanced CT localization and scanning. The two groups of PTVT were all expanded after chemotherapy. In the control group， PTVN was defined as a positive lymph node drainage area extending outward. The PTVN in the observation group was the lateral spread error of GTVN. PTVT and PTVN prescription dose was 60 Gy／30 fraction， 2 Gy／f， 5 fractions per week. The mean lung dose （MLD）， double lung V20 and curative effect were compared between the two groups， and the recurrence and toxic reaction of the patients in 3 years were followed up. 
ResultsThe observation group MLD and V20 of double lung were （955±228） Gy and （2165±376）％， lower than the control group （1275±243） Gy and （2532±423）％， the difference was statistically significant （P＜005）. The remission rate（RR） in the observation group was 672％ （43／64）， while that in the control group was 719 （46／64）. There was no significant difference between the two groups （P＞005）. The 3year recurrence rate of the two groups was 100％. In the control group， 45 cases recurred in the radiation field， and 19 cases recurred out of the radiation field. In the observation group， 48 cases recurred in the radiation field， and 16 cases recurred out of the radiation field. There was no significant difference between the two groups （P＞005）. The observation group of more than 3 hematological toxicity， acute radiationinduced pneumonia， weight loss rate was 47％， 266％ and 234％， were lower than the control group 188％， 547％ and 516％， the differences were statistically significant （P＜005）. 
ConclusionTarget delineation （PTVN） can effectively reduce MLD and V20 of double lung of locally advanced small cell lung cancer patients after chemotherapy， had no effect on the clinical efficacy and recurrence of the tumor， and can significantly reduce the adverse reaction.

Key words: Small cell lung cancer, Radiotherapy, Target area delineation