[Experience with a double dose-monitoring system in the 18 MeV betatron therapy (author's transl)]

Correct setting of the patient dose within a range of about +/- 3% is only achieved if a second exposure monitoring system controls the output variations of a betatron beam. A sealed thimble chamber attached in the centre of the field on the patient, which switches off the betatron when a given exposure has exceeded proved as a safe device.