Four-Dimensional Computed Tomography (4DCT) in Radiation Oncology: A Practical Overview

It has been 20 years since four-dimensional computed tomography (4DCT) was adopted in radiation oncology. By acquiring respiratory-correlated CT images, 4DCT allows characterization of tumour motion during radiotherapy target delineation. This technology has improved tumour delineation accuracy, in fact, it is now considered essential for highly conformal, high radiation, and precise radiotherapy treatment delivery. Nevertheless, due to the sampling of irregular patient breathing cycles, 4DCT suffers from image artefacts that can compromise tumour delineation accuracy. Addressing this challenge has been the driving motivation behind the latest advancements in 4DCT implementations. The purpose of this review is to provide a practical overview on 4DCT technology, its developments, and how it is used in radiation oncology.

The most significant hardware advancement in helical CT scanner technology has been the increase of CT-slices from 16 to 256/320-slice, allowing faster scan times. In terms of software developments, reconstruction algorithms have greatly improved, and a multitude of artefact reduction techniques has been demonstrated to be beneficial—though not all are commercially available. Nowadays, it is possible to significantly reduce artefacts to nearly non-discernible levels. This is achievable through recent innovations in 4DCT which merge advanced hardware and software tools to implement patient-specific models that account for breathing irregularities to efficiently acquire high-integrity CT data.

This article provides a practical review of how 4DCT technology has evolved in radiation oncology, from both a technical and logistical point of view.