• G Baroni, A Troia, R Orecchia, and A Pedotti.
• Dipartimento di Bioingegneria, Centro di Bioingegneria Fondazione Don Carlo Gnocchi IRCCS ONLUS, Politecnico di Milano, Milan, Italy. baroni@biomed.polimi.it
• Radiol Med. 2001 Sep 1; 102 (3): 168-77.

PurposeIn radiotherapy clinical practice, the currently existing gap between the high degree of accuracy in treatment planning and, the possibility of conforming the high-energy radiation beams on the one hand, and the uncertain set-up of each irradiation session on the other is a decisive factor for optimizing radiation treatment. Indeed there is wide experimental evidence that the current methods used for patient alignment and immobilization do not guarantee the necessary precision in delivering therapy with respect to the specifications of the treatment plan. The main reason for this is the lack of control systems that may be applied systematically to provide quantitative real-time feedback on the quality of patient repositioning and immobility during radiation emission.Material And MethodsOpto-electronic techniques and body surface registration methods were sygergisically used for the automatic three-dimensional verification and correction of patient position at the therapy unit. The method is based on radiotherapy applications of real-time opto-electronic human motion analysis using passive markers to control patient repositioning and to acquire and describe body surfaces in three dimensions. The quantitative detection of the localization error relies on the real-time detection of the position of an hybrid set of control points, namely physical passive markers and laser light markers, and their immediate comparison with a reference data set. The data set consists of the reference positions of the passive markers and a three-dimensional model of the body surface. The method was experimentally tested at the Radiotherapy Division of the European Institute of Oncology to control the repositioning of a phantom and of a volunteer, with reference to the clinical realignment procedure applied for breast cancer radiotherapy.ResultsThe results confirm that the technique represents a valuable method to detect and automatically correct localization errors in the irradiation set-up. The use of the information provided by the laser markers allows one to reduce the potential inaccuracies in the manual relocation of the passive markers on the subject's skin and guarantees that position control is based on a redundant set of data describing the three-dimensional localization and configuration of the irradiated body surface portion. The experimental results show that the initial displacements of the controlled body area were systematically reduced to median values below 1 millimeter and 1.2 millimeters for the phantom and the volunteer, respectively.ConclusionsThe synergistic use of opto-electronic technologies and stereophotogrammetric techniques associated to surface registration methods proved to provide an accurate description of the spatial transformation between the reference position and the actual position of the controlled body area. This allowed us to define an effective procedure to correct the patients position and recover the quality of the irradiation set-up, in agreement with the clinical requirements. The reported results confirm that the dynamic sensing of the body surface by opto-electronic technologies is a particularly promising technique that allows to systematically achieve swift and accurate patient alignment, thus ensuring that the treatment plan specifications are reproduced in the reality of each irradiation session.

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