Dosimetric analysis of normal tissue toxicity in 3D conformal radiotherapy planning with fused PET-CT imaging in non-small cell lung carcinoma

Introduction: The prime modality for inoperable NSCLC is radiation therapy and or chemo-radiation and better results can be achieved by a higher dose of radiation. However dose escalation is difficult due to presence of critical and dose limiting sensitive structures in the vicinity of lung. Therefore success of radiotherapy in such tumors solely depends on the selective delivery of adequate dose to target with minimal irradiation of surrounding structures. The precision in target and normal tissue delineation needs to be achieved. So the aim of this study is to explore the possibility of using fused PET-CT images for accurate target and normal tissue delineation in 3D-conformal radiotherapy planning in patients of carcinoma lung (NSCLC) who are referred to us for radical radiotherapy. Materials and Methods: It's a hospital based prospective study in which 14(n) cancer patients who had biopsy proven NSCLC and were referred to us for radical radiotherapy. After CT simulation and FDG-hybrid PET data sets were transferred to CMS planning system. The co-registration was done in Focal Pro using an auto fusion, 3D rotation and translation rigid body program, and the fiducial markers. The gross tumor volume (GTV), planning target volume (PTV) and normal tissue parameters were defined using the CT data and PET-CT data. 3D-CRT plans were generated for both CT data and PET-CT data sets and dosimetric analysis was done for same. Results: The mean age was 65 yrs, 78.5% (11) patients are male and 21.5 % (3) are female. The registration of fused images of PET with planning CT scan decreased the gross tumor volume (GTV) in 10 patients (71.42%), decreased volume in 4 patients (28.58%). The 3D-CRT planes were modified in 5patients (35%). CT-PET planning did not reduce the radiation fields in all patients. When all constraints of the lung, esophagus, and spinal cord were taken into account, normal tissue exposure was reduced with use of CT-PET. V20 decreased from 31.86% ± 4.17% to 28.66% ± 4.23% (p = 0.2676) and MLD was 17.08 ±1.94 Gy to 15.53 ± 2.02 Gy (p