# A phantom study of internal target volume and mid-position accuracy in adaptive and conventional four-dimensional computed tomography across regular and irregular motion

## TL;DR

This study compares adaptive and conventional 4DCT techniques for tracking tumor motion during irregular breathing, finding that adaptive 4DCT improves accuracy in defining tumor targets for radiotherapy.

## Contribution

The study introduces evidence that adaptive 4DCT reduces ITV deviations and improves motion fidelity under irregular breathing conditions.

## Key findings

- Adaptive 4DCT reduces internal target volume (ITV) deviations during irregular breathing.
- Mid-position accuracy is consistent across adaptive and conventional 4DCT methods.
- Adaptive 4DCT provides better motion fidelity and less variability in volume and amplitude metrics.

## Abstract

•Adaptive 4DCT reduces ITV deviations under irregular breathing conditions.•Mid-position accuracy remains robust across adaptive and conventional acquisition techniques.•Adaptive 4DCT shows superior motion fidelity compared to conventional 4DCT.•Conventional 4DCT exhibits greater variability in volume and amplitude metrics.

Adaptive 4DCT reduces ITV deviations under irregular breathing conditions.

Mid-position accuracy remains robust across adaptive and conventional acquisition techniques.

Adaptive 4DCT shows superior motion fidelity compared to conventional 4DCT.

Conventional 4DCT exhibits greater variability in volume and amplitude metrics.

This technical note evaluates the performance of an adaptive four-dimensional computed tomography (4DCT) acquisition method compared to conventional 4DCT using a motion phantom. Metrics assessed include deviations in volume, CT number, diameter, peak-to-peak amplitude and determination of the internal target volume (ITV) and mid-position. Under regular breathing, most measurements fall within predefined clinical tolerances for all systems. Under irregular motion, the adaptive method showed reduced deviations in ITV and minimal impact on mid-position determination. These findings support the clinical value of adaptive 4DCT in improving motion management and target definition accuracy in radiotherapy planning.