Through a combination of circumstances and the military occupation of the Netherlands in May 1940, the department of radiology at the Netherlands Cancer Institute (NKI) falls into a period of decline and stagnation that will last until 1946.
The Rotterdam Radiotherapy Institute (Het Rotterdams Radiotherapeutisch Instituut, RRTI) announces in February 1940 that they would appoint Daniel den Hoed as director of the Institute. On 1 July, he leaves the NKI together with his future wife, the resident S. Sytsema. This is a huge loss to the already small clinical staff of the NKI. For the time being, Dr. Betty Levie carries out the radiotherapy treatments. However, at the end of 1940, she is forbidden, as a Jewish physician, to treat any patients in the NKI. As a result, within a few months, the NKI loses two of its most experienced radiologists.
In 1941, Dr. Wassink has found a new job for Betty Levie and, in that way, he is able to bypass the ban on the treatment of Jewish patients in the NKI. Betty obtains appointments in Jewish hospitals in Amsterdam, in particular in the Central Israeli Hospital (Centrale Israëlietische Ziekenverpleging,CIZ) and in the Netherlands Israeli Hospital (Nederlands Israëlitische Ziekenhuis, NIZ). There, she is able to treat the Jewish NKI patients. This ceases in 1943 when large scale raids result in the Jewish population being deported from Amsterdam. The hospitals were cleared and Betty Levie, with the help of Daniel den Hoed, is able to go into hiding. More on this subject can be found in the item "1941 German occupation forces removal of Jewish employees"
The radiotherapy treatments in the NKI at the beginning of 1941 are temporarily taken over by varying residents and less experienced radiologists, under the supervision of the head of the clinic, surgeon Willem Wassink.
On 1 August 1942, radiologist Dr. van Griethuysen, who since 1 January 1941 had a temporary position, leaves for Arnhem. He is succeeded by Dr. E. Schoenmaeckers, resident radiologist, after a three month training period with Den Hoed in Rotterdam.
As of September 1944, there is a large decrease in the number of patients treated. Due to the war, communications in The Netherlands are disrupted. Patients suddenly stop reporting for treatment and out-patient clinics are often cancelled. Those patients that did come, often had an advanced stage tumour. In the last phase of the war, the threat of military action also reaches Amsterdam. Power is cut off, and it is decided to protect the vulnerable components of the inactive Millionair by protecting it under a bed of sand against possible bombardments.
After the liberation on 5 May 1945, Dr. Schoenmaeckers resigns and becomes the radiologist at the Hospital on the Prinsengracht (Vereniging voor Ziekenverpleging) in Amsterdam. Wassink is left with a depleted radiology department and with poorly trained personnel.
It is Professor Ebbenhorst Tengbergen who offers his assistance from the University of Amsterdam by convincing the recently trained radiologist Dr. Henri Lokkerbol to start working at the Netherlands Cancer Institute.