Abstract
BackgroundThe purpose of this study is to investigate intra-fraction setup variability in hypo-fractionated cranial and body radiotherapy; this is achieved by means of integrated infrared optical localization and stereoscopic kV X-ray imaging.Method and MaterialsWe analyzed data coming from 87 patients treated with hypo-fractionated radiotherapy at cranial and extra-cranial sites. Patient setup was realized through the ExacTrac X-ray 6D system (BrainLAB, Germany), consisting of 2 infrared TV cameras for external fiducial localization and X-ray imaging in double projection for image registration. Before irradiation, patients were pre-aligned relying on optical marker localization. Patient position was refined through the automatic matching of X-ray images to digitally reconstructed radiographs, providing 6 corrective parameters that were automatically applied using a robotic couch. Infrared patient localization and X-ray imaging were performed at the end of treatment, thus providing independent measures of intra-fraction motion.ResultsAccording to optical measurements, the size of intra-fraction motion was (median ± quartile) 0.3 ± 0.3 mm, 0.6 ± 0.6 mm, 0.7 ± 0.6 mm for cranial, abdominal and lung patients, respectively. X-ray image registration estimated larger intra-fraction motion, equal to 0.9 ± 0.8 mm, 1.3 ± 1.2 mm, 1.8 ± 2.2 mm, correspondingly.ConclusionOptical tracking highlighted negligible intra-fraction motion at both cranial and extra-cranial sites. The larger motion detected by X-ray image registration showed significant inter-patient variability, in contrast to infrared optical tracking measurement. Infrared localization is put forward as the optimal strategy to monitor intra-fraction motion, featuring robustness, flexibility and less invasivity with respect to X-ray based techniques.
Highlights
The purpose of this study is to investigate intra-fraction setup variability in hypo-fractionated cranial and body radiotherapy; this is achieved by means of integrated infrared optical localization and stereoscopic kV Xray imaging
Over the last few years, the development of Image Guided Radiation Therapy (IGRT) technologies has resulted in the design and realization of systems allowing precise patient setup and monitoring at each therapy fraction [1,2,3]
Along with inter-fraction variations, intra-fraction uncertainties due to physiological and/or random movements of the patient may influence the treatment quality, especially for extra-cranial sites. This requires the definition of specific procedures for the verification of intra-fractional patient motion as part of IGRT treatment protocols
Summary
The purpose of this study is to investigate intra-fraction setup variability in hypo-fractionated cranial and body radiotherapy; this is achieved by means of integrated infrared optical localization and stereoscopic kV Xray imaging. Morphological changes, tumor shrinkage and organ motion effects lead to inter-fraction variations that random movements of the patient may influence the treatment quality, especially for extra-cranial sites This requires the definition of specific procedures for the verification of intra-fractional patient motion as part of IGRT treatment protocols. Actual real-time patient monitoring is usually achieved by tracking external surrogates, like Infra-Red (IR) markers [11,12] or the entire skin surface [13,14] or by acquiring the position of implanted seeds These latter can either be radio-opaque markers, to be detected by fluoroscopy, or electromagnetic transponders, which can be localized continuously with non ionizing radiation [15,16,17,18]. Their application needs to be supported by studies aiming at understanding their reliability with respect to image-based procedures
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