Artifacts in conventional computed tomography (CT) and free breathing four-dimensional CT induce uncertainty in gross tumor volume determination

Purpose: Artifacts impacting the imaged tumor volume can be seen in conventional three-dimensional CT (3DCT) scans for planning of lung cancer radiotherapy but can be reduced with the use of respiration-correlated imaging, i.e., 4DCT or breathhold CT (BHCT) scans. The aim of this study was to compare delineated gross tumor volume (GTV) sizes in 3DCT, 4DCT, and BHCT scans of patients with lung tumors. Methods and Materials: A total of 36 patients with 46 tumors referred for stereotactic radiotherapy of lung tumors were included. All patients underwent positron emission tomography (PET)/CT, 4DCT, and BHCT scans. GTVs in all CT scans of individual patients were delineated during one session by a single physician to minimize systematic delineation uncertainty. The GTV size from the BHCT was considered the closest to true tumor volume and was chosen as the reference. The reference GTV size was compared to GTV sizes in 3DCT, at midventilation (MidV), at end-inspiration (Insp), and at end-expiration (Exp) bins from the 4DCT scan. Results: The median BHCT GTV size was 4.9 cm ³ (0.1-53.3 cm ³). Median deviation between 3DCT and BHCT GTV size was 0.3 cm ³ (-3.3 to 30.0 cm ³), between MidV and BHCT size was 0.2 cm ³ (-5.7 to 19.7 cm ³), between Insp and BHCT size was 0.3 cm ³ (-4.7 to 24.8 cm ³), and between Exp and BHCT size was 0.3 cm ³ (-4.8 to 25.5 cm ³). The 3DCT, MidV, Insp, and Exp median GTV sizes were all significantly larger than the BHCT median GTV size. Conclusions: In the present study, the choice of CT method significantly influenced the delineated GTV size, on average, leading to an increase in GTV size compared to the reference BHCT. The uncertainty caused by artifacts is estimated to be in the same magnitude as delineation uncertainty and should be considered in the design of margins for radiotherapy.