The purpose of this study was twofold: first, we wanted to understand what role social interactions play in decision making processes during radiotherapy; second, we aimed to highlight in what extent these decisions can create patient risk. Our analysis focused on the real existing activity which is performed for preparing radiotherapy treatments. We found eight situations in which decision making is needed: for half of them, interactions among professionals or between professionals and patients have a key role; for all of them, decision making implies potential risks for patients. These findings stress the importance of taking into account social informal interactions to better understand decision making and its inherent risks for patients treated with radiotherapy. To conclude, some psychosocial processes that could be involved in these situations are discussed.