A quantitative 3D intramodality ultrasound (US) imaging system was verified for daily in-room prostate localization, and compared to prostate localization based on implanted fiducial markers (FMs).
Thirteen prostate patients underwent multiple US scans during treatment. A total of 376 US-scans and 817 matches were used to determine the intra- and interoperator variability. Additionally, eight other patients underwent daily prostate localization using both US and electronic portal imaging (EPI) with FMs resulting in 244 combined US-EPI scans. Scanning was performed with minimal probe pressure and a correction for the speed of sound aberration was performed. Uncertainties of both US and FM methods were assessed. User variability of the US method was assessed.
The overall US user variability is 2.6 mm. The mean differences between US and FM are: 2.5 ± 4.0 mm (LR), 0.6 ± 4.9 mm (SI), and −2.3 ± 3.6 mm (AP). The intramodality character of this US system mitigates potential errors due to transducer pressure and speed of sound aberrations.
The overall accuracy of US (3.0 mm) is comparable to our FM workflow (2.2 mm). Since neither US nor FM can be considered a gold standard no conclusions can be drawn on the superiority of either method. Because US imaging captures the prostate itself instead of surrogates no invasive procedure is required. It requires more effort to standardize US imaging than FM detection. Since US imaging does not involve a radiation burden, US prostate imaging offers an alternative for FM EPI positioning.
The authors like to thank the patients who agreed to participate in the study and the therapy staff at the treatment units. The authors gratefully acknowledge Elekta for their technical support of this work. Comments by Dr M. Lachaine from Elekta on the work are gratefully acknowledged. The authors also would like to thank Dr. L. Beaulieu for his exchange of views on FM-based prostate localization and Dr. Enrica Seravalli and Dr. L. Murrer for their help with the planning of part of the study. The authors would like to thank R. Houben for his help with the statistics. S.v.d.M. is in part supported by GROW (School for Oncology and Developmental Biology, Maastricht University). The authors report no conflicts of interest in conducting the research.
II. MATERIALS AND METHODS
II.A. 3D ultrasoundIGRT system
II.B. User variability
II.C. Comparison of prostate localization
II.D. Data analysis and statistics
II.E. Speed of sound corrections in USimaging
III.A. User variability
III.B. Comparison of prostate localization from US and MV EPI FM imaging
III.C. Speed of sound corrections in USimaging
IV.A. Accuracy issues
IV.B. Comparison of the two IGRT techniques
- Medical imaging
- Speed of sound
- Computed tomography
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