Helical 4D CT pitch management for the Brilliance CT Big Bore in clinical practice.

Guido Hilgers,André Minken,Tonnis Nuver

doi:10.1120/jacmp.v16i3.5111

Guido Hilgers, André Minken + Show 1 more

Open Access

https://doi.org/10.1120/jacmp.v16i3.5111

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Abstract

In external beam radiotherapy treatment planning for patients with thoracic malignancies, respiratory‐correlated CT (4D CT) is used to obtain high quality studies in the presence of respiratory motion. When helical 4D CT scans are acquired with a Brilliance CT Big Bore, the pitch must meet two conditions. It must be low enough to avoid motion artifacts, and high enough to cover the entire scan length within 120 s to prevent overheating of the X‐ray tube. We developed a nomogram that can be used to obtain a suitable pitch satisfying both requirements. We also assessed the effects on the image quality of a pitch that exceeds the maximum pitch, and of a field of view (FOV) reduction. It was shown that, for AV G and MIP reconstructions, the manufacturer's maximum pitch equation yields an underestimation due to its FOV term.PACS number: 87.57.Q‐, 87.57.cp

Highlights

In external beam radiotherapy treatment planning for patients with thoracic malignancies, respiratory-correlated CT (4D CT) is used to obtain high quality studies in the presence of respiratory motion.(1) When 4D CT scans are acquired in helical mode, the pitch — defined as the table travel per gantry rotation divided by the detector collimation — must be low enough to illuminate each voxel of patient anatomy for an entire respiratory cycle.(2) This requirement can be translated into a maximum pitch that depends on the patient’s respiratory frequency
The nomogram can be used to obtain a suitable pitch. This pitch is both low enough to illuminate each voxel of patient anatomy for an entire respiratory cycle and high enough to complete the scan within 120 s
We presented a nomogram that can be used to select a suitable helical 4D CT pitch for patients with thoracic malignancies whose planning study is made with a Brilliance CT Big Bore

Summary

Introduction

In external beam radiotherapy treatment planning for patients with thoracic malignancies, respiratory-correlated CT (4D CT) is used to obtain high quality studies in the presence of respiratory motion.(1) When 4D CT scans are acquired in helical mode, the pitch — defined as the table travel per gantry rotation divided by the detector collimation — must be low enough to illuminate each voxel of patient anatomy for an entire respiratory cycle.(2) This requirement can be translated into a maximum pitch that depends on the patient’s respiratory frequency. Since the manufacturer has limited the maximum scan time to 120 s, to prevent overheating of the X-ray tube,(3) the pitch must be high enough to make sure that the entire scan length can be covered during this timeframe. This requirement can be translated into a minimum pitch that depends on the scan length and, on the patient’s anatomy and tumor location(s). If the actual pitch is lower than the minimum pitch, the planning study is shorter than desired and might not be suited for treatment planning

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