Is a clinical target volume (CTV) necessary for locally advanced non-small cell lung cancer treated with intensity-modulated radiotherapy? -a dosimetric evaluation of three different treatment plans.

Abstract

The aim of this study was to determine the feasibility of omitting the clinical target volume (CTV) in patients with locally advanced non-small cell lung cancer (NSCLC) treated with intensity-modulated radiotherapy (IMRT) by comparing dosimetric characteristics of three different IMRT plans with or without CTV implementation. Thirteen patients with stage III NSCLC were reviewed. Target volumes were contoured such that the planning target volume (PTV) derived from the gross tumor volume (GTV) directly was named PTV_g and that from GTV plus CTV margin was named PTV_c. The PTV margin to generate PTV_g or PTV_c was the same within each case. Three IMRT plans were retrospectively generated to deliver: (I) 60 Gy to PTV_g in plan_routine; (II) 60 Gy to PTV_c in plan_CTV, and (III) 50 Gy to PTV_c while the dose was simultaneously escalated to 60 Gy to PTV_g in plan_SIB, achieved using the simultaneous integrated boost (SIB) technique. Optimization was performed to minimize the dose volumes of the irradiated normal lung, heart, esophagus, and spinal cord. Dose distributions and dosimetric indexes for the target volumes and critical structures in the three plans were computed and compared. In plan_routine, the 50-Gy isodose line covered at least 95% of the GTV plus CTV margins in all 13 patients. The statistics showed better sparing of the organs at risk (OAR) in plan_routine than in plan_CTV, and the best OAR sparing in plan_SIB. In patients with locally advanced lung cancer, IMRT planning without CTV implementation provides sufficient dose coverage of subclinical disease while reducing the dose to normal tissues. The omission of CTV was feasible in our cohort of patients. However, when CTV was implemented, IMRT planning that included the SIB technique had further dosimetric benefits to the patients. This strategy thus merits further evaluation in clinical trials.