Performance validation of in-house developed four-dimensional dynamic phantom

Objective: The objective of this study was to validate the performance characteristics of in-house developed four-dimensional (4D) dynamic phantom (FDDP). Materials and Methods: There are three target inserts of 1.0, 1.5 and 2.0 cm diameter. The targets were driven in sinusoidal pattern in the longitudinal direction, using the combinations of amplitudes of 0.5, 1.0, and 1.5 cm with frequencies of 0.2 and 0.25 Hz. The amplitude and frequency of motion were measured manually, and by using Real-Time Position Management (RPM) system also. The static, free-breathing, and 4D computed tomography (CT) scans of the phantom were acquired with 1.0 mm slice thickness. The 4DCT scans were sorted into 0%–90% phase, and the maximum intensity projection (MIP) images were also generated. The static, free-breathing, and 4DCT data sets and MIP images were contoured to get VStatic, VFB, V00......V90, and internal target volume ITVMIP, respectively. The individual phase volumes were summed to obtain V4D. The length of the target in the motion was measured using MIP image and compared with theoretical length (TL). The variation of 3D displacement vector of individual phase volume with respect to V00with the phase of motion was studied at amplitude and frequency of 1.0 cm and 0.25 Hz, respectively. The degree of similarity between VFBand V4Dand VFBand ITVMIPwas also studied for all the target sizes at amplitude and frequency of 1.0 cm and 0.2 Hz and 1.0 cm and 0.25 Hz, respectively. Results: The amplitude and frequency of motion agreed within the limits of uncertainty with the manually and RPM measured values. The length of target in the motion matched within 1.0 mm with TL. The 3D displacement of individual phase volume showed no target size dependence, and the degree of similarity between VFBand V4Dand VFBand ITVMIPdecreases with increase in the displacement between the two volumes. Conclusions: The mechanical and imaging performances of FDDP were found within the acceptable limits. Therefore, this phantom can be used for quality assurance of 4D imaging process in radiotherapy.