Quality control with the EPID is made easy with the Robot arm

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Development team  of the NKI EPID robot arm for Philips/Elekta accelerators (see also "Development EPID" in 1986). Standing left to right: Henk van der Gugten (Radiotherapy Dept. NKI, project leader), Leo de Mooy (Head Instrument Workshop, Radiotherapy Dept. NKI), Taco Richards and Michael Limburg (Polytechnical College graduates working through Engineering Office HATEC).Seated: Jaap Keijzer and Micha Paalman (instrument makers, Radiotherapy Dept. NKI). 

After the takeover of Asea Brown Boveri (ABB) Radiotherapy by Varian in the 1990's, the development of the NKI EPID by the Swiss imaging group is continued.  A robot arm is designed with which the cassette with the image detector can be placed in the radiation beam and can be folded out of the way.  The construction is designed for fitting to a Varian accelerator. The set-up range of the robot arm is too small to apply this to the larger accelerators of Philips/Elekta and BBC/ABB in the Netherlands Cancer Institute (NKI).  Also, the Varian arm with the necessary adaptation to the Philips accelerator weighs 300 kg while a maximum of 90 kg is allowed by Philips.

An increase in quality control with EPID images creates the urgent need in the NKI for an easy and accurate placement of the EPID during the irradiation. There is no system available on the market so it is decided to develop an adapted robot arm within the NKI. By courtesy of Varian the design of the original arm is available for analyses and forms a starting point for the adapted design. The support from Varian was an important contribution to the success of this project.

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The NKI robot arm with EPID camera mounted on the BBC Dynaray CH 4 (4MV X) linear accelerator in treatment room 8.  

The use of an active medical device such as the robot arm, requires by law an officially certified design in which the protection of patients and staff against mechanical and electrical dangers is safeguarded. During the 90's there are already strict European guidelines on this. Traditionally a robot mechanism during operation will be made inaccessible for humans. A new philosophy for safe use of a robot construction, unshielded in close proximity of humans is under development at this time and new guidelines are drawn up by, among others, the Fraunhofer Institute. The product liability of the NKI as manufacturer demands much care. In order to solve these bottlenecks in a responsible fashion, a collaboration with the Polytechnical College of Amsterdam (Hoge School van Amsterdam, HvA) and with the engineering office HATEC is initiated, offering young engineers from the HvA work experience. For diploma projects and HATEC work experience, the formal conditions are laid down and a detailed technical design is made. 

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Cross section of the NKI robot arm.

The arm is developed for an isocentre height of 1250 mm above the floor and a free distance between the isocentre and the front of the accelerator of 1200 mm.  The positioning range of the EPID cassette is radially from the isocentre up to 1000 mm out, and longitudinally and laterally over a distance of 540 mm.


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Set up in which the stability and accuracy of the robot arm is tested. 

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"Exploded view" of the mechanical parts

The parts are made by the instrument makers of the Radiotherapy Department.  For this purpose an investment was made in an upgrade of the equipment of the joint workshops of the NKI.  Large numerically controlled milling machines were taken into use, whereby instrument maker Leo de Mooy played an important role. Henk van der Gugten was project leader.  Four robot arms were produced.  The first one was mounted on the BBC accelerator. Thereafter robot arms were mounted on the Philips accelerators in the NKI.

A few years later, the NKI EPID was replaced by an industrially produced construction with the amorphous silicon flat panel, with which the image quality was improved.  The sale of these rose quickly and the industry introduced its own motorised panel holders.  After a while, there was no more need for the NKI robot arm.