Room: AAPM ePoster Library
Purpose: Recently, deviceless four-dimensional (DL-4D) computed tomography (CT), which can create internal respiratory signals from six extracted features via cine CT image processing, was developed to enable lung cancer radiotherapy planning. Validation of DL-4D CT in comparison with standard 4D (ST-4D) CT systems, which requires an external respiratory signal device for target definition and dose calculation, is therefore necessary. This study aimed to validate whether DL-4D CT is consistent with ST-4D CT by comparing its target volume (TV), position, and Hounsfield unit (HU) values with those of ST-4D CT.
Methods: Cine CT images of a thorax 4D phantom, which reproduces the target and body surface movement, were collected and sorted into 10 phases using both ST-4D and DL-4D CT. TVs were contoured using a threshold method and the centroid positions of TVs were measured on the 10-phase CT images of both 4D methods. We also retrospectively measured the images of 9 patients who underwent radiotherapy for lung cancer using the same method as in the phantom study. In addition, the HU values of the TV, lung, and heart contours were measured on the expiration phase CT images obtained using both 4D methods.
Results: For the phantom study, the ST-4D and DL-4D CT results for the TV and position differed by 0.82 cm3 and 1.5 mm on average, respectively, i.e., the difference was insignificant (P = .190 and P = .971). For the studies conducted with patients, the average differences between ST-4D and DL-4D in terms of the TV and position were insignificant (P > .05), and ranged from 0.01–2.25 cm3 and 0.6–4.0 mm, respectively. The average difference in HU values within 20 HU for all contours.
Conclusion: The results for the TV, position, and HU values obtained with DL-4D CT were consistent with those of ST-4D CT.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Number JP17K16459. The authors declare that they have no competing interests.