Abstract - Purpose – The purpose of this paper is to evaluate and improve the quality and the reliability of pre-treatment quality controls of an efficient technique of radiotherapy called IMRT (intensity-modulated radiation therapy). The aim is then to determine if the controls can be safely reduced while keeping an optimal level of quality. Design/methodology/approach – The statistical process control method (SPC) was applied to quality assurance in IMRT. In order to characterize prostate and head-and-neck treatment process variability, individual value control charts and moving-range control charts were established. Findings – Control charts showed that prostate and head-and-neck treatment processes are only subject to random causes of variability, which means they are statistically controlled. It was proved that both processes are statistically stable and capable. Originality/value – The paper shows that SPC is an efficient method to objectively determine if quality controls can be reduced.