Effectiveness of 4-dimensional maximum intensity projection (4D-MIP) for respiratory motion management with uncertain interobserver delineation.

This study was conducted to evaluate the use of 4-dimensional (4D) maximum intensity projection (4D-MIP) to compensate for the disadvantages of average intensity projection (AIP), which is used to determine the internal target volume (ITV) in lung tumors. A respiratory motion phantom with a simulated tumor was imaged using 4D computed tomography (4D-CT). AIP and 4D-MIP were generated based on 10 phases of 4D-CT, followed by contouring of the ITVAIP and ITVMIP; these were compared with the ITV contoured in 10 phases of 4D-CT (ITV10). Additionally, the profile curves of the ITVAIP and ITVMIP were obtained, and the full width at half maximum (FWHM) was measured. There was no significant difference between the ITV10 and ITVMIP; however, the ITVAIP demonstrated a lower value. The FWHM values of the ITVAIP were smaller than those of ITVMIP owing to decreased CT values in the superior-inferior margin. 4D-MIP may contribute to improving the consistency of the ITV delineation.