IEC 60601-2-11:1987

Specifies requirements for the safety, design and construction of
gamma beam equipments when used for radiotherapy in human medical
practice.

Applies to equipment which is intended to deliver a gamma radiation
beam(s) at normal treatment distances greater than 5 cm using a
sealed radioactive source(s).

It is the purpose of the requirements contained in this standard to
ensure that the proposed irradiation conditions are met and the
actual settings retained during irradiation and that unintentional
exposure to irradiation of the patient, operating personnel and the
environment is kept as low as reasonably achievable.