Image-Guided Cobalt unit introduced in the NKI

1961 Cobalt IGRT.jpg 

In December 1960 the installation of the large cobalt unit is finished just before Christmas. The cobalt source, strength 2500 Ci (92.5 TBq), is loaded in January 1961. 

The machine is designed for image-guided treatments [43, 44]. It is a Dutch design, based on ideas of Dr. Lokkerbol. The manufacturer is Smit Röntgen in Leiden, a firm that later will merge with Philips Medical Systems. The machine attracts great attention. Hundreds of foreign visitors come to the Netherlands Cancer Institute.

This design is based on a rotating steel ring of nearly 5 meters in diameter, in which the cobalt source, X-ray tube and X-ray image intensifier are combined in an orthogonal, isocentric set up. For the X-ray image intensifier chain a recently introduced 5" X-ray image intensifier with TV system from Philips is used. The imaging system is used for setting up the patient and allows for real time imaging during irradiation.  Opposite the radiation head the counterweight contains ionisation chambers for in vivo dose measurement. The ring rotates around the horizontal axis, the isocenter lies about 1 meter above the floor.  Parts of the floor open automatically to enable a 360 degree rotation so the radiation beam can reach the patient from all angles. During the irradiation, the movements of the ring, the radiation head and the treatment table are operated from the control room.Various movements can be controlled and coordinated by an automatic steering programme. The isocentric positioning of the patient is checked on the image intensifier monitor in the control room.

1961 Cobalt Gerarda vant Riet.jpg 

Control room for the image guided cobalt unit.     The radiation therapist can see the patient through a liquid filled lead glass window and she has the monitor of the image intensifier X-ray imaging system in front of her. Radiation therapist: Gerarda van 't Riet. 

The annual report of 1960-1961 describes that, already shortly after the installation, experiments were done with the special planar localisation and setting up methods of which the radiation machine was capable. The image intensifier-television channel was used for the localisation of pituitary and lung tumours before and during the treatment. 

1961: Summary of the explanation by Dr Lokkerbol of the image-guided cobalt unit in the TV series "Being ill, getting better", presented bij Dr van Zwol.  (Dutch language) 


The large cobalt machine is the crown on 10 years of research and development in the Radiotherapy Department. From about 1950 Dr. Lokkerbol develops ideas about image-guided dynamic therapy. In 1953 he introduces a rotating X-ray machine with portal film cassette system, the Philips TU1.  For the next step towards more penetrating radiation, he does not choose the experimental linear accelerator, but instead the technically more simple cobalt unit. This enables the development of the entire system to take place in The Netherlands. Based on the image intensifier-TV system of Philips, Dr. Lokkerbol achieves the realisation of a megavolt, image-guided, treatment unit, which at that time is unique in the world.  

Krantenartikel SmitCobalt klein.jpg 

The start of this major project takes place in 1955, when the KWF (Queen Wilhelmina Fund, Dutch Cancer Fund) agrees to financial support of NLG 780,000. Converted to current values this is worth 3 to 4 million Euros. 



The Netherlands Cancer Institute remained the only client. The two other large radiation centres in The Netherlands, Rotterdam and Utrecht, buy simpler cobalt machines. The basis of the extensive image guidance project is therefore too small. In practice it is not possible to exploit all the possibilities of the machine with the small staff of the NKI. 

In 1968 the cobalt machine is replaced by a linear accelerator and it will be 25 years before new developments enable a comparable level of image-guided therapy. In the NKI physicists Harm Meertens and Marcel van Herk lay the foundations for this with the Electronic Portal Imaging Device (EPID) and advanced software for automatic analysis of X-ray images. 

SmitCobalt en team Lokkerbol klein.jpg 

December 1960. The installation of the large cobalt machine is completed.  From left to right:  Willem Smit, director of Smit Röntgen, Mattieu de Vogel, designer Smit Röntgen, a radiation therapist, Henri Lokkerbol.


Cobaltbom schets vanSlooten klein.jpg



Surgeon Emiel van Slooten often drew amusing sketches of memorable events in the medical staff. When Dr. Lokkerbol demonstrated his rotating cobalt machine to visitors in 1961, this was his reaction. This drawing hung above the desk of the head radiation therapist for a long time. 

Bronnen & Publicaties

  • [43] LOKKERBOL, H. Het telekobaltapparaat van het Antoni van Leeuwenhoekhuis. KWF-Nieuws(1961) no 16, p. 2-3. ,
  • [44] LOKKERBOL, H., J. W. SMIT , A new apparatus for telecobalttherapy. Transactions IXth International Congress of Radiology, vol. 1l. Stuttgart, 1961, p. 1498. ,