Dr. K.C.A. Valken. Note: this photo is not taken in the NKI. The radiotherapy machine is a Siemens X-ray unit of up to 250 kV. Known as the "Holfelderkanone" after the German radiation physician who was involved in its development.
Dr. G.F. (Frans) Gaarenstroom leaves the Netherlands Cancer institute in 1921. He opens a private practice in radiotherapy and treats patients in the Jewish hospitals in Amsterdam. In his place, Dr. K.C.A. Valken is engaged as first radiologist. He remains in this position until 1925.
In 1921 a powerful X-ray machine was installed by the company Siemens and Halske. This so-called deep therapy inductor machine is equipped with a Coolidge type X-ray tube which operates with 200 kV and a tube current of 3 to 4 mA. Dr. Valken introduces an improved measurement of the high voltage and implements X-ray irradiation with a high voltage of 200.000 Volts. In order to protect the personnel, a shielded control room is constructed next to the X-ray machines. The actual radiotherapy treatment room is also improved.
In 1924-1925, Valken, together with his predecessor Gaarenstroom and Louis Koopman, local representative of German manufacturers of X-ray equipment, sets up a full training course for assisting personnel in radiology. Gaarenstroom teaches X-ray treatments, Valken the diagnostic praxis and Koopman gives technical lectures and is in charge of laboratory work. This is the first documented full training of X-ray assistants in The Netherlands.