Using a systems-theoretic approach to analyze safety in radiation therapy-first steps and lessons learned

•STPA beginners struggle the most with the graphical modeling of the analyzed process.•STPA applied in radiation therapy finds mostly the same hazards like HFMEA.•STPA is able to find also new hazards, not previously discovered by HFMEA.•The first steps in STPA do not require a full involvement of domain experts.•In early design stages of new RT processes, STPA is a better candidate than HFMEA.