Motivation - This research deals with the identification of collective production of a safe radiotherapy treatment and its potential assistance through computer-supported environments. It takes place at the beginning of a four years design project involving software companies and and scientific and clinical institutions. Research approach - This work presents an exploratory analysis of cooperation between the four professionals involved in the production of radiotherapy treatment. Our general research objective is to investigate how to support managed safety in the design of a computer-supported cooperative environment. Uses and functions of cooperative tools have been outlined through observations and the "think aloud" technique. Findings/Design - We identify three types of cooperation tools (computer-based tools, including an existing workflow, unformal verbal exchanges, and the patient body) involved in the production of a safe treatment. Their main functions are : to produce shareable data between professionals, to share the progress in the construction of a treatment and to share procedures and work practices. Research limitations/Implications - This paper aims at contributing to the articulation of two research approaches: CSCW and safety in healthcare. Originality/Value - Our study reveals informal strategies that participate to a "managed" healthcare safety performed by professionals. Take away message - Our work may contribute to transform the initial technocentric approach of the design project into a more anthropocentric design project and flexible CSCW tool.