OBJECTIVETo compare the position, displacement, degree of inclusion (DI) and matching index (MI) of the gross tumor volume (GTV) for peripheral lung cancer based on 4-dimensional CT (4D CT) and 3-dimensional CT (3D CT) assisted with active breathing control (ABC).

METHODSEighteen patients with peripheral lung cancer underwent 4D CT simulation scan during free breathing and 3D CT simulation scans in end-inspiratory hold (CTEIH) and end-expiratory hold (CTEEH) in turn. The 4D CT images from each respiratory cycle were sorted into 10 phases. phase 0 was defined as end-inspiratory phase (CT0), and phase 50 was defined as end-expiratory phase (CT50). The GTVs were delineated separately on CT0, CT50, CTEIH and CTEEH images, and then GTV0, GTV50, GTVEIH and GTVEEH were constructed, respectively.

RESULTSThe median distances between the centroids of GTV0 and GTVEIH, GTV50 and GTVEEH were 3.9 mm and 3.4 mm in all patients, 3.2 mm and 3.1 mm in the upper lobe group, and 5.0 mm and 4.7 mm in the lower lobe group, respectively. In the upper lobe group, the GTV0 and GTVEIH were 65.9% and 63.1%, and the median mutual DIs of GTV50 and GTVEEH were 67.5%, 63.1%, respectively. In the lower lobe group, the GTV0 and GTVEIH were 35.3% and 21.4%, and the median mutual DIs of GTV50 and GTVEEH were 27.8% and 24.8%, respectively. In the upper lobe group, the median MI of GTV0 and GTVEIH was 0.5, and the median MI of GTV50 and GTVEEH was 0.6. In the lower lobe group, the median MI of GTV0 and GTVEIH was 0.2, and the median MI of GTV50 and GTVEEH was 0.3. Whether in the upper or lower lobe groups, all the differences between displacements of centroid positions of GTVEIH and GTVEEH (ABC displacement) and GTV0 and GTV50 (4D displacement ) were <1 mm in three dimensional directions (all P>0.05).

CONCLUSIONSThe target displacement of tumors based on 3D CT scanning in end-inspiratory hold and end-expiration hold can be used to construct internal target volume instead of that based on 4D CT scanning in extreme phase for peripheral lung cancers, but spatital mismatches of GTVs are obvious between extreme phases in 4D CT and corresponding phases in 3D CT assisted with ABC, especially for tumors of smaller volume and with larger motion amplitude.