Comparative evaluation of volume and helical four-dimensional computed tomography using canon system.

BACKGROUND: Four-dimensional computed tomography (4DCT) is an advanced imaging technique designed to capture anatomical motion over time, enabling more accurate evaluation of tumor and organ motion owing to respiration, while minimizing motion-related artifacts. 4DCT employs two primary scanning modes-volume (cine) mode and helical mode-each with distinct clinical implications. A comprehensive evaluation of both approaches is therefore essential prior to clinical implementation.

PURPOSE: This study aimed to compare volume and helical 4DCT scan modes in terms of image quality, dimensional accuracy, and positional accuracy for respiratory-gated radiotherapy.

METHODS: 4DCT imaging was conducted using a Canon Aquilion ONE Prism CT scanner integrated with an Anzai respiratory gating system. The two scan modes were assessed under identical imaging parameters, with differences arising only from their respective acquisition protocols. Phantom experiments were conducted using a motion phantom to simulate normal, rapid, and irregular respiratory patterns. Image quality, dimensional accuracy, and positional accuracy were quantitatively evaluated. Additionally, a retrospective analysis was conducted on clinical 4DCT datasets (n = 10), including lung, liver, and pancreatic cancers.

RESULTS: Volume mode demonstrated superior dose efficiency and dimensional consistency, preserving stable object volumes across respiratory phases, particularly under rapid motion conditions. Helical mode achieved higher positional accuracy and improved temporal resolution for motion tracking, but with a greater imaging dose. These findings were consistent with the clinical datasets, wherein volume mode reduced dimensional errors and helical mode provided more accurate motion representation.

CONCLUSIONS: Both volume and helical 4DCT modes offer distinct advantages depending on clinical objectives. Volume mode is better suited for applications requiring high spatial accuracy and reduced radiation exposure, while helical mode is preferable for precise tracking of respiratory motion owing to its superior temporal resolution. Careful selection of the scan mode and system settings is essential for optimizing respiratory-gated radiotherapy planning.