Image-guided radiation therapy (IGRT) allows radiation dose deposition with a high degree of geometric accuracy. Previous studies have demonstrated that such therapies may benefit from the employment of deformable image registration (DIR) algorithms, which allow both automatic tracking of a continuously deforming anatomy and accumulation of the therapeutic dose over time in a spatially consistent manner. Since future adaptive therapy strategies might include this data in the decision-making process, the estimated deformations must be subjected to stringent quality assurance (QA) measures in order to ensure patient care and safety. In the present study we propose to extend the state-of-the-art methodology for QA of DIR algorithms by a set of novel biomechanical criteria. The proposed biomechanical criteria imply the calculation of the normal and shear mechanical stress, which would occur within the observed tissues as a result of the estimated deformations. The calculated stress is then compared to plausible physiological limits, providing thus the anatomical plausibility of the estimated deformations. The criteria were employed for the QA of three DIR algorithms in the context of abdominal conebeam computed tomography and magnetic resonance radiotherapy guidance. An initial evaluation of the dice similarity coefficient indicated that all three algorithms have similar contour alignment capabilities. However, an analysis of the deformations with respect to the proposed QA criteria revealed different degrees of anatomical plausibility within soft tissue boundaries, with respect to the mechanical properties of the individual tissues. Regarding dose accumulation, it was also demonstrated that each of the proposed QA criteria corresponds to a particular range of errors within the deformed dose map. The proposed QA criteria provide a tissue-dependent assessment of the anatomical plausibility of the deformations estimated by online DIR algorithms, showcasing potential in ensuring patient safety for future adaptive IGRT treatments.< Leer menos