Research

Reproducibility of patient setup by surface image registration system in conformal radiotherapy of prostate cancer

Marco Krengli^1,2 , Simone Gaiano¹ , Eleonora Mones³ , Andrea Ballarè¹ , Debora Beldì¹ , Cesare Bolchini¹ and Gianfranco Loi³

¹  Department of Radiotherapy, University Hospital Maggiore della Carità, Novara, Italy

²  Department of Clinical and Experimental Medicine and Biotechnology Centre for Applied Medical Research, University of Piemonte Orientale, Novara, Italy

³  Department of Medical Physics, University Hospital Maggiore della Carità, Novara, Italy

author email corresponding author email

Radiation Oncology 2009, 4:9doi:10.1186/1748-717X-4-9

Published:	22 February 2009

Abstract

Background

The reproducibility of patient setup for radiotherapy is based on various methods including external markers, X-rays with planar or computerized image acquisition, and, more recently, surface matching imaging. We analyzed the setup reproducibility of 16 patients affected by prostate cancer who underwent conformal radiotherapy with curative intent by using a surface image registration system.

Methods

We analyzed the setup reproducibility of 16 patients affected by prostate cancer candidates for conformal radiotherapy by using a surface image registration system. At the initial setup, EPID images were compared with DRRs and a reference 3D surface image was obtained by the AlignRT system (Vision RT, London, UK). Surface images were acquired prior to every subsequent setup procedure. EPID acquisition was repeated when errors > 5 mm were reported.

Results

The mean random and systematic errors were 1.2 ± 2.3 mm and 0.3 ± 3.0 mm along the X axis, 0.0 ± 1.4 mm and 0.5 ± 2.0 mm along the Y axis, and 2.0 ± 1.8 mm and -0.7 ± 2.4 mm along the Z axis respectively. The positioning error detected by AlignRT along the 3 axes X, Y, and Z exceeded the value of 5 mm in 14.1%, 2.0%, and 5.1% measurements and the value of 3 mm in 36.9%, 13.6% and 27.8% measurements, respectively. Correlation factors calculated by linear regression between the errors measured by AlignRT and EPID ranged from 0.77 to 0.92 with a mean of 0.85 and SD of 0.13. The setup measurements by surface imaging are highly reproducible and correlate with the setup errors detected by EPID.

Conclusion

Surface image registration system appears to be a simple, fast, non-invasive, and reproducible method to analyze the set-up alignment in 3DCRT of prostate cancer patients.