The Toshiba simulator and the transversal tomograph (left on the picture).
When choosing the beam directions, the radiation oncologist in the 70's is guided by X-ray images and what was palpable under the skin of a patient. Directing small well focussed megavoltage photon beams at larger depth in the patient requires better geometric and topographic insight. With the introduction of linear accelerators, the simulator becomes an important tool in the preparation of a radiotherapy treatment.
A simulator examination is performed before the time consuming treatment planning process is performed on the digital computer.
The department of radiotherapy now has 3 megavoltage treatment machines, and there is a need for a second simulator to treat the growing number of patients. In addition to the Rotterdam simulator, a simulator from Toshiba is installed.
This Japanese brand was chosen because a transversal tomograph was bought from the same manufacturer. Both devices are placed in the same room and share the treatment table.
During the simulator examination the treatment couch can be turned to the position in which a cross sectional image of the patient can be made. The resulting X-ray images are used for the planning of the treatment to determine the position of the organs at risk and the target volume. The tomograph rotates around the patient, and stays directed at a fixed point on the vertically hanging X-ray film. In this way part of the anatomy, around the centre of rotation, is imaged sharper than areas further away.
These images are of poorer quality than those obtained with the modern computer tomography - the CT scanner.
The first CT scanner has been constructed in 1969 as a head scanner by Godfrey Hounsfield in England. At the end of the '70s the new CT scanners are able to image cross sections of the whole body. In 1979 the Netherlands Cancer Institute acquires its first CT scanner from Siemens after strong pressure from the head of the department of radiotherapy, Professor Klaas Breur.
The simulator that was built in Rotterdam has been moved from the Sarphatistraat to Slotervaart.
Data obtained during a simulator session concern the shape of the body contour and the dimensions of the cross section. In addition to X-ray images, a flexible lead strip or lead wire was used. It was bent according to the curvature of the body after which that contour could be redrawn on a piece of paper.
The contour measuring device, which is called the "porcupine" because of its appearance with many protruding pins, is a great improvement is. In this device dozens of sliding pins are mounted in one plane in a square frame that encloses the patient. The pins are pushed up to the skin thus creating the shape of the desired contour. The contour measuring device is then split into several pieces, taken away from the patient, recombined on the drawing table and used to redraw the contour.