Acquiring 4D thoracic CT scans using a multislice helical method

TLDR

Respiratory motion degrades anatomic reproducibility, requiring larger margins and causing delivery errors, while synchronously acquired CT can be reconstructed into 4D scans for motion‑aware treatment planning. The study aimed to develop, test, and clinically implement a multislice helical method for acquiring 4D thoracic CT scans. The method combined a commercial respiratory‑monitoring system with a third‑generation multislice scanner, adapted 4D cardiac reconstruction algorithms, and was evaluated on a phantom under stationary, periodic, and non‑periodic motion as well as on a lung‑cancer patient using audio‑visual breathing coaching. Eight‑phase 4D CT images were successfully obtained, though respiration reproducibility and breathing period relative to scanner settings limited performance, and lung mass varied by only 2.1% across phases while lung volume changed by 20%, demonstrating the technique’s applicability to 4D radiotherapy, gating,.

Abstract

Respiratory motion degrades anatomic position reproducibility during imaging, necessitates larger margins during radiotherapy planning and causes errors during radiation delivery. Computed tomography (CT) scans acquired synchronously with the respiratory signal can be used to reconstruct 4D CT scans, which can be employed for 4D treatment planning to explicitly account for respiratory motion. The aim of this research was to develop, test and clinically implement a method to acquire 4D thoracic CT scans using a multislice helical method. A commercial position-monitoring system used for respiratory-gated radiotherapy was interfaced with a third generation multislice scanner. 4D cardiac reconstruction methods were modified to allow 4D thoracic CT acquisition. The technique was tested on a phantom under different conditions: stationary, periodic motion and non-periodic motion. 4D CT was also implemented for a lung cancer patient with audio-visual breathing coaching. For all cases, 4D CT images were successfully acquired from eight discrete breathing phases, however, some limitations of the system in terms of respiration reproducibility and breathing period relative to scanner settings were evident. Lung mass for the 4D CT patient scan was reproducible to within 2.1% over the eight phases, though the lung volume changed by 20% between end inspiration and end expiration (870 cm3). 4D CT can be used for 4D radiotherapy, respiration-gated radiotherapy, 'slow' CT acquisition and tumour motion studies.