ESTRO 2024 - Abstract Book

S5 ESTRO 2024 accumulated dose can be increased compared to intrafraction dose accumulation, for example due to different imaging modalities (e.g. CT to CBCT or CT to MRI). Also mass changes of the patient and/or tumor can lead to an increased uncertainty of the DIR or of the dose mapping/interpolation method [7]. Additionally, the mapped dose to the filling of hollow organs such as bladder or bowel is not meaningful, since the filling was exchanged from one day to the other. Especially during adaptive radiotherapy with substantial changes in the target or relevant organs at risk (OARs) the accumulated doses between adaptive treatments are hard to interpret, since the treatment goal might have changed for some voxels. Combined treatments between different treatment modalities do require dose accumulation. The corresponding dose accumulation uncertainties varies. For example, if proton, photon and electron doses are optimized on the same image, the dose accumulation uncertainty is small. It can however be large if different patient anatomies are enforced, as in the combined radiotherapy and brachytherapy. This can extent the common regularization parameters implemented in most DIRs [8]. Different BEDs between different modalities can further increase the dose accumulation uncertainty. This can be even more extreme in the case of reirradiations. With months or even years between the treatments, anatomical changes can be large, for example due to surgical resection or fibrosis [9,10]. A dose mapping to the new anatomy can be important to account for previously irradiated dose in individualized prescriptions and reduced dose tolerances to OARs and normal tissue [11]. Recovery patterns of normal tissues after irradiation are rarely investigated, but will gain importance with increasing numbers of reirradiations [9,12]. The mapped dose from the primary treatment can also be correlated to places of local failure and side effects visible in follow up images to the previous delivered dose [13]. Outcome modeling employs inter-patient DIR to map the planned (or delivered) dose to a reference anatomy. Side effects are correlated to specific voxel groups [14]. This method does contain large DIR uncertainties, due to large inter-patient differences but has the advantage that it allows for substructure analysis. In summary, dose accumulation did arrive in clinical practice. Its uncertainties are however not well quantified, depending on the application accumulated doses should be interpreted with care [15]. Invited Speaker

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https://doi.org/10.1016/j.phro.2023.100465.