THE EFFECT OF USING PET - CT FUSION ON TARGET VOLUME DELINEATION AND DOSE TO ORGANS AT RISK IN 3D RADIOTHERAPY PLANNING OF PATIENTS WITH NSSLC

Background: three - dimensional conformal radiation therapy (3DCRT) planning remains the standard option in the management of locally advanced NSSCL, a technique that makes the radiation oncologist face the challenge of target volume delineation based on CT scan alone, which will eventually affect target volume coverage, i.e. gross tumor volume (GTV) and planning target volume (PTV), as well as dose to the surrounding normal tissues at risk. Purpose: To prospectively study the impact of fusing 18F - fluoro - deoxy - 2 - glucose hybrid positron emission tomographic (FDG - PET) images with CT images on the planning target volume (PTV) delineation, target coverage, and critical organ dose in radiation therapy planning of non ? small - cell lung carcinoma. Methods and Materials: Twenty p atients with Stages I ? III NSCLC were referred to our radiotherapy department in the period between Jan 1st 2015 and Aug 30, 2016, planned for treatment via radiotherapy alone or with concurrent chemo - radiation. Each patient underwent a planning CT with imm obilization devices. FDG - PET scan was ordered for every patient and done in the department of nuclear medicine very soon after or before the day of CT simulation. Both the CT and PET/CT image data sets were fused and used in the radiation treatment plannin g workstation for contouring. Each FDG - PET study was reviewed with the interpreting nuclear radiologist before tumor volumes were contoured. A three - dimensional conformal radiation therapy (3DCRT) plan was calculated based on contours done on the CT scan o nly. A second plan based on the fused PET/CT images was generated. The PTV was defined by a 20 mm margin around the GTV. The two 3DCRT plans for each patient were compared with respect to the GTV, PTV, mean lung dose, volume of normal lung receiving >20 Gy (V20), and mean esophageal dose