Document Type

Article

Publication Date

4-1-2026

Comments

This article is the author’s final published version in Journal of Applied Clinical Medical Physics, Volume 27, Issue 4, 2026, Article number e70550.

The published version is available at https://doi.org/10.1002/acm2.70550. Copyright © 2026 The Author(s).

 

Abstract

PURPOSE: Four-dimensional computed tomography (4DCT) is susceptible to a geometrical error when respiration changes upon patient shift. 4DCT using 16-cm detector arrays, not needing the shift, has been shown to improve geometrical accuracy, compared with a conventional 4DCT (4-cm array), albeit with some Hounsfield unit discrepancies. The 4DCTs were validated for 4D planning.

MATERIALS AND METHODS: A lung-mimicking phantom containing a spherical target with ten respiratory traces and three tumor-shaped targets with their traces was respectively imaged when, to each of the ten-positions/phases, the lung was moved (1) step-wisely by helical scan at each movement (ground truth; 4DCTGT), (2) continuously by 4D scan with 16 cm detectors (4DCT16), and (3) similarly with 4 cm detectors (4DCT4). Respiratory irregularities affected 4DCT4 only due to shifts. Treatment plans included volumetric modulated arc therapy (VMAT) and intensity-modulated proton therapy (IMPT) on averaged CT images from 4DCT16 and 4DCT4. IMPT was targeted to internal gross target volumes (iGTVs) with density overrides (1.0 g/cm3), while VMAT to iGTVs+3 mm, with the objective Vprescribed dose(PD) ≥ 95%. The plans were recalculated on each phase image of 4DCTGT and those of 4DCT16 were additionally calculated on its phase images. The calculated doses were registered to the maximum-exhale image, and summed.

RESULTS:  (1) 4DCT16: IMPT plans met the objective, despite under-coverages in certain phase images, achieving 98.95 ± 1.09% and 98.27% in averaged VPD for the spherical and tumor targets, respectively. VMAT plans showed 97.26 ± 1.60% and 94.41% for the respective targets. (2) 4DCT4: IMPT plans did not meet the objective with 93.83 ± 9.29% and 97.38% for them. VMAT plans yielded 93.20 ± 5.81% and 91.17% for them. (3) 4DCT16 versus 4DCTGT: 4D doses based on 4DCT16 matched those on 4DCTGT with 62.76 Gy versus 62.76 ± 0.19 Gy for IMPT plans and 63.79 Gy versus 63.90 ± 0.28 Gy for VMAT plans.

CONCLUSIONS: The 4DCT16 demonstrated accurate and reliable imaging of a lung tumor in 4D dose by IMPT plans. However, it could be affected by phase-sorting uncertainty.

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Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

PubMed ID

41917747

Language

English

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