4-Dimensional computed tomography analysis of clinical target volume displacement in adjuvant radiation of patients with gastric cancer and its implication on radiotherapy

The present study aimed to accurately measure the displacement magnitude of the radiotherapy subsite target due to respiration, and to evaluate its implication on 4-dimensional computed tomography (4D-CT) in adjuvant radiation of gastric cancer. To investigate this, 10 patients with gastric cancer receiving adjuvant radiotherapy were enrolled. 4D-CT scans were performed on all patients and respiratory signals were recorded simultaneously. The clinical target volume (CTV) and 7 regions of interest (ROIs) were delineated in all phases of the CT imaging. The displacements of all ROIs in the cephalic-caudal, anterior-posterior and left-right directions were measured and analyzed. Two sets of plans based on planning target volume 3D (PTV(3D)) and PTV(4D), were generated for each patient and PTV(3Dcal) was calculated by expanding the non-uniform margin on CTV(3D) according to the displacement analysis data. The dosimetric parameters and target volumes of the 3 radiotherapy treatment plans were compared. The displacement of the various ROIs varied widely. The mean PTV(4D) was smaller than the PTV(3D) and PTV(3Dcal). Compared with Plan(3D), Plan(4D) reduced the mean dose of radiation to the liver and left kidney by 23.2 and 43.5%, respectively. The liver volume receiving ≥30 Gy and the left kidney volume receiving ≥20 Gy were decreased by 10.8 and 29.7%, respectively. No differences were observed in the PTV coverage and protection of organs at risk (OARs) between Plan(3Dcal) and Plan(4D). In conclusion, the breathing-induced displacement patterns of the subsite targets in patients with gastric cancer vary. The individualized CTV margins of expansion based on 4D-CT lead to a decrease PTV and radiation dose to OARs. The non-uniform margins in various directions should be considered as areas for further investigation.