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Accuracy frameless system: Methods

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Frameless system: Sub-millimeter accuracy

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Mean 3D vector of 0.6 mm (SD 0.9 mm)

Quality assurance of a system for improved target localization and patient

set-up that combines real-time infrared tracking

and stereoscopic X-ray imaging

Dirk Verellen * , Guy Soete, Nadine Linthout, Swana Van Acker, Patsy De Roover,

Vincent Vinh-Hung, Jan Van de Steene, Guy Storme

Department of Radiotherapy, Oncologic Center, Academic Hospital, Free University of Brussels (AZ-VUB), Laarbeeklaan 101, B-1090 Brussels, Belgium

Received 5 December 2001; received in revised form 11 October 2002; accepted 25 October 2002

Abstract

Background and purpose

: The aim of this study is to investigate the positional accuracy of a prototype X-ray imaging tool in combination

with a real-time infrared tracking device allowing automated patient set-up in three dimensions.

Material and methods

: A prototype X-ray imaging tool has been integrated with a commercially released real-time infrared tracking

device. The system, consisting of two X-ray tubes mounted to the ceiling and a centrally located amorphous silicon detector has been

developed for automated patient positioning from outside the treatment room prior to treatment. Two major functions are supported: (a)

automated fusion of the actual treatment images with digitally reconstructed radiographs (DRRs) representing the desired position; (b)

matching of implanted radio opaque markers. Measurements of known translational (up to 30.0 mm) and rotational (up to 4.0

) set-up errors

in three dimensions as well as hidden target tests have been performed on anthropomorphic phantoms.

Results

: The system’s accuracy can be represented with the mean three-dimensional displacement vector, which yielded 0.6 mm (with an

overall SD of 0.9 mm) for the fusion of DRRs and X-ray images. Average deviations between known translational errors and calculations

varied from

0.3 to 0.6 mm with a standard deviation in the range of 0.6–1.2 mm. The marker matching algorithm yielded a three-

dimensional uncertainty of 0.3 mm (overall SD: 0.4 mm), with averages ranging from 0.0 to 0.3 mm and a standard deviation in the range

between 0.3 and 0.4 mm.

Conclusions

: The stereoscopic X-ray imaging device integrated with the real-time infrared tracking device represents a positioning tool

allowing for the geometrical accuracy that is required for conformal radiation therapy of abdominal and pelvic lesions, within an acceptable

time-frame.

Keywords:

Automated patient positioning; Intra-fractional correction of three-dimensional set-up errors; Infrared markers; Stereoscopic X-ray imaging

Radiotherapy and Oncology 67 (2003) 129–141

Radiotherapy and Oncology 67 (2003) 129–141