Uncertainties in high precision radiation therapy: Impact of deformable image registration methods and of delineation variations on the accumulating dose distribution

• Applicants: Dr. Kristina Giske; Dr. Eva Maria Stoiber
• Subject Area: Medical Physics, Biomedical Technology ; Nuclear Medicine, Radiotherapy, Radiobiology
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 252959556

In recent years, technical developments in radiation therapy have resulted in ever more precise dose application techniques; hence, modern techniques are also referred to as high-precision radiotherapy. The physical dose can be applied precisely to the tumor in the defined target volumes while sparing the adjacent organs at risk from irradiation.Many developments were necessary to achieve this improved precision. Improved dose calculation and optimization methods allowed for the computer-assisted planning of complex irradiation plans that can also cover convex and irregular shaped target volumes. The fusion of imaging devices with irradiation devices allowed for a reduction in positioning uncertainties and made it possible to visualize anatomical changes during radiation therapy. Today, image processing methods help to relocate target volumes and organs at risk at every point during the treatment course; this allows adapting the irradiation plan precisely to temporal changes. However, using these methods, the radiation therapy chain has also become more complex. Even though the respective steps in the treatment course carry only small uncertainties, the uncertainties add up during the iterative use of the methods in the therapy course.To assess the quality of the entire treatment course, or to be able to intervene in the treatment course e.g. by employing various correction strategies, it is required to take the accumulated uncertainties into consideration. Therefore, it is important to simulate the entire treatment course and to include the occurring uncertainties.It is still a challenge to perform such a simulation. Especially the determination of temporal variable deformations through deformable image registration methods is hard to validate. Different methods result in different results for the same input images; in addition, the quality of the methods depends on the context in which they are used. These uncertainties will have to be reflected in the uncertainties of the accumulated dose distribution.The goal of this research project is to integrate common image registration methods with a treatment planning system. We plan to investigate image registration methods regarding their uncertainties in dose distribution by developing a new virtual patient and employing widely used evaluation methods. This will enable us to determine the image registration methods most suited for usage in radiation therapy and to evaluate the propagation of uncertainties in the accumulated dose distribution. With this we can e.g. compare competing adaptive correction strategies, or determine the potentially remaining dose tolerance in case of planning a re-irradiation of previously treated patients.

• DFG Programme: Research Grants