Radiotherapy and nuclear Medicine: Is it time to find a common language? The importance of accumulating doses across various modalities.

The rising application of therapeutic nuclear medicine (NM) procedures alongside external beam radiotherapy (EBRT) is increasing the number of patients exposed to multimodal irradiation. In this scenario, a shared dosimetric framework that enables cumulative assessment across modalities is needed. As more patients undergo combined treatments, comprehending cumulative absorbed dose distributions becomes crucial for predicting toxicity and enhancing patient safety. However, EBRT and NM rely on different dosimetric paradigms (fractionated high dose-rate irradiation vs protracted, time-dependent absorbed dose-rate delivery driven by radiopharmaceutical biokinetics), making direct accumulation non-trivial. In this work, we aim to summarize the primary challenges and suggest some strategies to to support clinically meaningful cross-modality cumulative evaluations.