Comparison of PET/CT and CT-based tumor delineation and its effects on the radiation treatment planning for non-small cell lung cancer

Tumor volume delineation is the most important step in the radiation treatment planning. In this study the impact of PET/CT data on the tumor delineation precision of non-small cell lung cancer (NSCLC) was investigated.
PET/CT images of 20 patients with primary NSCLC were obtained and imported to the treatment planning system for image fusion, contouring and radiation treatment planning. For each patient two separate gross tumor volumes were delineated based on CT and PET/CT images as GTVCT and GTVPET/CT, respectively. In addition, three different indices including conformity index (CI), geographic miss index (GMI) and geographic include index (GII) were calculated to quantify the match and mismatches degree between derived volumes. Then, for each patient an appropriate 3D conformal treatment plan was made based on the PTVCT and then these plans were applied on the PTVPET/CT. Afterwards, the dose coverage of PTVPET/CT was estimated through several dosimetric parameters.
The GTVPET/CT was larger than GTVCT for majority of cases. The 25% exceeded volumetric alterations were observed in 8 of all cases (40%). Mean values of CI, GMI and GII were 0.43, 0.42 and 0.34, respectively. Also, dosimetric parameters indicated inadequate dose coverage of PTVPET/CT in CT-based RT plans for most of the patients.
Incorporating PET data into tumor delineation process had a great potential to improve the quality of radiation treatment planning for NSCLC.