Application of AIP and MIP CT on Individual GTV Delineation for Tumor Moving with Respiration

Objective: To investigate the feasibility of delineating individual gross target volume (GTV) for tumors moving with respiration by using AIP/MIP CT instead of 4D-CT. Methods: CT data of three patients were acquired in Cine mode. The Cine duration time for each couch position is 4~6s, which equals to one breathing cycle plus 1s. The acquired CT data were input to a 4D-CT reconstruction system made in house to reconstruct AIP/MIP and 4D-CT. Then, the characteristics of motion tumor in AIP/MIP and 4D-CT were analyzed. The influences of window width/level on the appearance of periodical motion target in AIP/MIP CT were investigated by using a periodical motion phantom. Results: The GTV in AIP (GTVAIP) and MIP CT (GTVMIP) was bigger than that in extra-inhale phase 4D-CT (GTV4D-in) or extra-exhale phase 4D-CT (GTV4D-ex). The ratios of GTVAIP to GTV4D-in for two patients were 1.30 and 1.07, and the ratios of GTVMIP to GTV4D-ex were 1.57 and 1.21, respectively. AIP/MIP CT with appropriate window width/level can be used to derive the individual target motion envelope. Conclusions: AIP/MIP CT could be used to quickly delineate individual GTV for moving tumor, which may significantly reduce the target delineation laboring. It can be used to replace 4D-CT to derive the individual GTVs for tumors moving with respiratory.