History

For many decades, radiotherapy was developed without computers. Isodose planning and linear accelerators both pre-date the use of computers. In the 1960s, the first investigations were made into using computers for radiotherapy. Such use required access to one of the small number of large ‘mainframe’ computers, probably at a university, since personal computers were not invented until the 1970s. The first widespread use of computers was for calculating isodose distributions, replacing laborious manual calculations. In the late 1970s, the first use was made of computed tomography (CT) data for radiotherapy planning. This required a magnetic tape reader connected to the planning system to read the CT scanner tapes.

As networking technology became available, it was possible to connect computers directly together. However, CT scanners still used different file formats. In 1985, the American College of Radiology and the National Electrical Manufacturers Association created a standard for medical images called ACR-NEMA. In the third version, in 1991, the standard was developed to specify how systems should communicate directly. To mark this change a new name for the standard was used: ‘Digital Imaging and Communication in Medicine’, or DICOM 3.0.

In the 1980s, the first record and verify systems appeared. Later, it became possible to transmit plans from the planning computer to the record and verify system, driven by the use of multileaf collimators in the 1990s. It was also in the 1990s that electronic portal imaging devices were developed. Accompanying them was a need to obtain reference images in electronic form, whether digital simulator images or digitally reconstructed radiographs.

At the turn of the millennium, radiotherapy centres were filled with computer systems transferring data. Managing these could be difficult and expectations frequently exceeded the realities of what could be achieved. These frustrations led to the recent development of radiotherapy, or oncology, information systems. These act as a central hub of the network: receiving and organizing data from various sources. This coordination of data is going to be vital for the era of image guided radiotherapy.

Benefits and hazards of computerization

The more advanced techniques that we practise would not be possible at all without the assistance of computers. Intensity modulated radiotherapy would be totally unfeasible without computers or data communication. Even simple techniques are enhanced by the use of computers. If data are transferred directly between computers there is less chance of human error. The use of record and verify systems has certainly reduced the number of random human errors at the point of treatment delivery [4].

Ultimately, the hazards of computerization relate to our increased dependence on computer systems and the faulty assumption that they are reliable. Computers and networks do fail. A radiotherapy department that is reliant on a system can be crippled if that system is the victim of component failure, a virus, or even theft.

As systems become more complicated, they are harder to check for errors. It should never be assumed that the computer is correct. Furthermore, computers do not remove the risk of human error altogether. Proper use of a system relies on operators performing tasks correctly. If they do not then incorrect information can be passed down the line and used at a later stage. Where errors do occur in computerized systems they may affect a series of patients or a single patient for every fraction of their treatment [5].

In order to reduce these risks, we need to reverse the assumption that the computer is reliable. Key checks should be made, during system testing and for individual treatments. Is the isocentre correct? Is the patient reference position correct? Where there are multiple data sets, has the correct one been used for the treatment? When every plan had to be calculated and delivered manually, each person involved had to understand fully the technique and the treatment. Now that the treatment can be delivered at the touch of a button, that level of understanding is critical to detect errors.

Link layer: physical infrastructure

Two computers can be connected by a single cable. But what if four computers need to be connected? It is possible to connect them via a network loop so that a packet of data sent by A is visible to B, C and D, but will only be picked up by the computer it is intended for. The problem with this is that it would be impossible for A and B to communicate at exactly the same time as C and D. The solution is to have each computer connected to a central network switch or hub. The switch only makes connections that are in use and prevents network traffic on one part of a network affecting another part (Figure 12.1).

Figure 12.1 Network loop (A) versus network switch (B).

In a very large network, such as a hospital, there will be a large number of such switches, controlling and routing the flow of data in the hospital. In such a large network, the computers may be organized into subnetworks, or subnets. Access between subnets is controlled by ‘gateways’ which can prevent unauthorized access between areas (Figure 12.2).

Figure 12.2 Two subnets separated by a gateway.

Network layer: addressing

When you type ‘www.estro.be’ into a web browser, how does your computer connect to the computer that contains the homepage of the European Society for Therapeutic Radiotherapy and Oncology? Each domain name is registered to a computer address called an IP address which consists of four numbers. Your computer initially sends a request to a directory to find out the correct IP address. Then it sends a request to that IP address to retrieve the correct web page.

Inside a private network, such as a hospital, computers are still referenced using an IP address. Special ranges of numbers are reserved for use in private networks to avoid confusion with Internet traffic. On many windows computers, it is possible to see the network configuration by typing the command ‘ipconfig’ at a command prompt¹. If you do this, and your computer is attached to a network, you will see something like that shown in Figure 12.3.

Figure 12.3 Sample output of ipconfig.

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