Evaluation of 4D CT acquisition methods designed to reduce artifacts

Our plain-English summary of Evaluation of 4D CT acquisition methods designed to reduce artifacts, by S.J. Castillo, R. Castillo, E. Castillo, et al (Journal of Applied Clinical Medical Physics, 2015).

The study

• Authors: S.J. Castillo, R. Castillo, E. Castillo, T. Pan, G. Ibbott, P. Balter, B. Hobbs, T. Guerrero
• Journal: Journal of Applied Clinical Medical Physics
• Published: 2015;16(2):4949
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Four-dimensional computed tomography (4D CT) is used to account for respiratory motion in radiation treatment planning, but artifacts resulting from the acquisition and postprocessing limit its accuracy. We investigated the efficacy of three experimental 4D CT acquisition methods to reduce artifacts in a prospective institutional review board approved study. Eighteen thoracic patients scheduled to undergo radiation therapy received standard clinical 4D CT scans followed by each of the alternative 4D CT acquisitions: 1) data oversampling, 2) beam gating with breathing irregularities, and 3) rescanning the clinical acquisition acquired during irregular breathing. Relative values of a validated correlation-based artifact metric (CM) determined the best acquisition method per patient. Each 4D CT was processed by an extended phase sorting approach that optimizes the quantitative artifact metric (CM sorting). The clinical acquisitions were also postprocessed by phase sorting for artifact comparison of our current clinical implementation with the experimental methods. The oversampling acquisition achieved the lowest artifact presence among all acquisitions, achieving a 27% reduction from the current clinical 4D CT implementation (95% confidence interval = 34-20). The rescan method presented a significantly higher artifact presence from the clinical acquisition (37%; p < 0.002), the gating acquisition (26%; p < 0.005), and the oversampling acquisition (31%; p < 0.001), while the data lacked evidence of a significant difference between the clinical, gating, and oversampling methods. The oversampling acquisition reduced artifact presence from the current clinical 4D CT implementation to the largest degree and provided the simplest and most reproducible implementation. The rescan acquisition increased artifact presence significantly, compared to all acquisitions, and suffered from combination of data from independent scans over which large internal anatomic shifts occurred.

In plain English

This study was not about asbestos exposure. It was a prospective study at M.D. Anderson Cancer Center of CT scans for planning chest radiation therapy. The 18 patients (8 women, 10 men) had non-small cell lung cancer (12), esophageal cancer (4) or mesothelioma (2). Each had a standard clinical 4D CT scan, which tracks breathing motion, then three experimental scans: oversampling (more images), gating (beam stopped during irregular breathing) and rescanning (repeating irregular-breathing sections). Oversampling reduced image flaws (artifacts) by 27% compared with the current clinical method, the clinical scan with phase sorting (95% confidence interval 34 to 20). Rescanning produced significantly more artifacts than the other three scans. With the same artifact-score sorting applied to all three, the data lacked evidence of a significant difference among the clinical, gating and oversampling scans. Under clinically comparable settings, all experimental methods were estimated to give higher radiation doses; oversampling averaged 64.8 mSv, against 32.2 mSv for the clinical scan. The authors considered oversampling the best combination tested, and noted patients spent at least 20 extra minutes on the table.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Prospective, institutional review board approved study in which every patient received the standard clinical 4D CT scan and all three experimental 4D CT acquisition methods. The scans were compared using a correlation-based artifact metric (CM).
• Who was studied: 18 patients scheduled to receive thoracic radiation therapy (8 women, 10 men; mean age 66.3 years, standard deviation 10.1), enrolled under an M.D. Anderson Cancer Center review board protocol. Diagnoses were non-small cell lung cancer (12), esophageal cancer (4) and mesothelioma (2). Study dates are not given.
• Exposure: No asbestos exposure was studied. The study compared four 4D CT acquisition methods: the clinical scan, oversampling (at least 2 breathing cycles captured per couch position), manual X-ray beam gating during breathing irregularities, and rescanning couch positions where breathing was irregular. The clinical scans used 100 mA and the experimental scans a dose-sparing 50 mA. Effective doses were estimated with experimental settings adjusted to match the clinical scan.
• Main results:
  • Oversampling: 27% reduction in artifact presence compared with the clinical acquisition processed by phase sorting (95% confidence interval 34 to 20).
  • Rescan method: higher artifact presence than the clinical acquisition (37%; p less than 0.002), the gating method (26%; p less than 0.0052) and the oversampling method (31%; p less than 0.001).
  • When the clinical, gating and oversampling acquisitions were all processed with CM sorting, no significant difference among them was shown. Oversampling had the lowest mean and median artifact metric values.
  • Mean estimated effective dose per patient, calculated with the clinical tube current and scan extent: clinical 32.2 mSv (plus or minus 5.4), gating 37.0 mSv (plus or minus 8.4), rescan 43.5 mSv (plus or minus 7.4), oversampling 64.8 mSv (plus or minus 11.8). These are clinically comparable estimates, not the doses actually delivered in the study.
  • The gating method increased acquisition time by 66.7% (plus or minus 39.2%) compared with the clinical scan.
  • Across all 72 scans, a mean of 28.0% of breathing phases were irregular. The estimated probability of breathing irregularities did not differ significantly among the four methods.
• The authors' conclusion: The authors concluded that oversampling gave the highest statistically significant artifact reduction from the current clinical method and was the simplest and most reproducible to implement. They also concluded that the rescan method had the highest artifact presence of all methods.
• Limitations the authors state:
  • Patients stayed on the CT table at least 20 minutes longer than for routine scans and often became tired or uncomfortable. The experimental scans were therefore performed during the patient's worst state.
  • The artifact metric does not correlate exactly with visual assessment.
  • The gating method relied on visual detection of breathing irregularities and had no automatic X-ray beam control.
  • Only cine 4D CT was studied.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma, Throat and laryngeal cancer.

Medical terms in this study, explained in our Lexicon: CT Scan, confidence interval.

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