<> "The repository administrator has not yet configured an RDF license."^^ . <> . . "Daily adaptive magnetic resonance-guided radiotherapy – analysis of patient benefit"^^ . "Magnetic resonance (MR)-guided radiotherapy enables daily adaptation of a patient’s treatment plan to the current patient anatomy. Previous reports have already shown the resulting advantages, especially good sparing of organs at risk while simultaneously achieving optimal target volume coverage. However, patient geometry can change during the adaptation process, which takes significantly longer than conventional radiotherapy treatments. So far, there is limited research on the effects of these intrafractional changes. In particular, gastrointestinal organs at risk might exhibit large shifts and deformations, which could also have a negative impact on the benefits gained by adaptive radiotherapy. In order to evaluate the impact of intrafractional organ movement and allow for patient-specific compensation, it is necessary to determine the extent of organ movement before the first adaptive treatment. Simulation MR-images acquired for treatment planning could offer this possibility, as they do not require additional dose to the patient and therefore a large number can be acquired to determine organ movement. However, adaptation currently takes a very long time with reported adaptation times of one hour or more. This raises the question of whether a more robust result could be achieved with shorter adaptation times. As a result, the following hypotheses will be investigated:\r\n1)\t“In some cases, adaptation has no benefit\"\r\n2)\t“More robust adaptive treatments can be obtained by predicting the extent of intrafractional organ movement before the first treatment”\r\n3)\t“Shorter adaptation times do not necessarily lead to more robust results” \r\nPatients who received adaptive MR-guided radiotherapy for the treatment of abdominal lesions were retrospectively analyzed. The main focus of this study was on lesions located in close proximity to organs at risk. Dose differences in organs at risk caused by adaptation as well as by intrafractional changes were determined. Furthermore, the range of organ movement during simulation and adaptation was determined for each patient and agreement between both values was examined. In addition, the duration of adaptation and simulation sessions was determined in order to establish a possible correlation between the extent of organ movements and the magnitude of dose differences.\r\nThe evaluation of dose differences shows that the number of violations of organ at risk tolerance dose could be significantly reduced by adaptation. However, an increase in organ dose was also observed in the majority of patients as a result of adaptation, while respective tolerance dose was still met. Possible causes for this increase are either a lack of optimization objective for organs at risk with some distance to the PTV or the possibility to increase organ dose in order to optimize target volume coverage while still not violating tolerance doses. Additionally, the number of tolerance dose violations increased again as a result of intrafractional changes, and it was even higher than it would have been without plan adaptation. Using simulation MR-images, the extent of risk organ movement can already be determined before the first treatment, though, which opens up the possibility of compensating for intrafractional changes. With the method presented in this study, there was an agreement between the range of organ at risk movement during adaptation and simulation in over 75% of analyzed cases. Acquisition of multiple simulation images and a longer simulation duration led to better overall agreement. In addition, there was no correlation between adaptation time and the magnitude of dose change for the adaptation times examined in this study. This signifies that a longer duration does not lead to a greater dose difference. Furthermore, evaluation of simulation images showed large organ at risk movement in a short time span of only five minutes and no correlation between the extent of organ movement and the duration of simulation sessions could be found.\r\nOverall, these results demonstrate that adaptation has no benefit in some cases, at least when considering the dosimetric advantage for organs at risk. In particular, intrafractional organ movement leads to violations of organ at risk tolerance dose. However, the extent of these organ movements can be determined in advance with the help of the simulation images. As a result, a special focus can be put on those organs at risk with a high mobility and it opens up the possibility to compensate for them. Major changes in the position of gastrointestinal organs at risk can occur within a very short time span. Therefore, it does not appear to be sufficient to simply shorten the adaptation time in order to achieve a more robust adaptation result."^^ . "2025" . . . . . . . "Carolin"^^ . "Buchele"^^ . "Carolin Buchele"^^ . . . . . . "Daily adaptive magnetic resonance-guided radiotherapy – analysis of patient benefit (PDF)"^^ . . . "Buchele_Carolin_10_08_1992_Dissertation.pdf"^^ . . . "Daily adaptive magnetic resonance-guided radiotherapy – analysis of patient benefit (Other)"^^ . . . . . . "lightbox.jpg"^^ . . . "Daily adaptive magnetic resonance-guided radiotherapy – analysis of patient benefit (Other)"^^ . . . . . . "preview.jpg"^^ . . . "Daily adaptive magnetic resonance-guided radiotherapy – analysis of patient benefit (Other)"^^ . . . . . . "medium.jpg"^^ . . . "Daily adaptive magnetic resonance-guided radiotherapy – analysis of patient benefit (Other)"^^ . . . . . . "small.jpg"^^ . . . "Daily adaptive magnetic resonance-guided radiotherapy – analysis of patient benefit (Other)"^^ . . . . . . "indexcodes.txt"^^ . . "HTML Summary of #35983 \n\nDaily adaptive magnetic resonance-guided radiotherapy – analysis of patient benefit\n\n" . "text/html" . . . "600 Technik, Medizin, angewandte Wissenschaften"@de . "600 Technology (Applied sciences)"@en . . . "610 Medizin"@de . "610 Medical sciences Medicine"@en . .