In Radiation Dosimetry, we are interested in visualising the particle tracks and geometries in our Monte Carlo simulations. In the past this has required special-purpose software, preferably running on expensive workstations. The graphics performance of standard PCs has improved so much that much cheaper solutions are now possible. We have therefore developed software utilities to convert the standard graphical (IWATCH) output of particle tracks in the EGS system into VRML, a standard language in which to represent 3-D graphics.

What is VRML?

The Virtual Reality Modelling Language (VRML, or 'vermal') is an ISO standard language for representing a virtual world of 3 dimensional objects on the world wide web. Such virtual worlds can be navigated using freely-available VRML browsers, which run either standalone or as plug-ins to the usual web browsers. VRML provides many features to make worlds look realistic, including perspective, lighting, transparency effects, etc. Links to VRML resources (including browsers) are given below. You will need a VRML browser (such as Cortona VRML client) to view the following examples.

Visualisation examples using EGS4

Electrons are shown in green, photons in yellow and positrons in red.

Note for experts:
In all cases, our selection of data to show is rather biased: we show only the histories 'of interest'.

Two world files are provided in each case. The first has many histories and is linked to the thumbnail image, but may take a long time to download: you may prefer to view the single history version, at least to start with. Once your browser has loaded the world files, the quality and responsiveness of the display is independent of the speed of your link to the internet.

You should be faced with four large coloured spheres and a number of small white spheres. The spheres are touch sensitive, so if you click on them they toggle the visibility of the following items blue-geometry, green-electrons, yellow-photons and red-positrons. The white spheres toggle the visibility of the shower from each initial particle.

1.	A 16 MeV electron beam incident on a Fricke dosimeter at 2 cm depth in a 30 cm cube water phantom (the large box).
		Only histories which interact with the dosimeter (a totally absorbing region) are shown. [233 kB] or single history version [28 kB]
2.	A 6 MV X-ray beam from a Varian 2100C clinical accelerator incident on a stemless ion chamber at 5 cm depth in a water phantom.
		Only histories which interact with the ion chamber are shown. Particles that reach the surface of the chamber (a totally absorbing region) are stored. [221 kB] or single history version [26 kB]
		Ion chamber simulation using the particles stored in the previous example. [374 kB] or single history version [108 kB]
3.	Simulations of the NPL linear accelerator. A schematic representation of the geometry is shown, including the target, collimators, beam flattening and additional filters. Further shielding around the collimators and target is not shown. Only those histories that result in photons reaching the scoring plane (at 90 cm from the target) are displayed.
		First set up to produce 4 MV X-rays with our normal beam filtration. [376 kB] or single history version [79 kB]
		As above but with a bremmstrahlung splitting factor of 10 to increase the photon yield. [561 kB] or single history version [131 kB]
		16 MV X-rays with our normal beam filtration. [514 kB] or single history version [90 kB]

VRML resources

Useful links to VRML resources:

1. VRML Browsers and Plug-ins.
2. VRML archives (including the VRML97 ISO specification).
3. The Web3D consortium.

If you would like further information please contact David Shipley or Simon Duane