The Barrel of Monkeys Philosophy

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It doesn’t matter how you model your linear accelerator, in your Monte Catlo simulation, so long as the output of that virtual linear accelerator matches the output of your real linear accelerator. If modelling your linear accelerator as a barrel of monkeys results in data that consistently matches your experimental measurements, then you should model your linear accelerator as a barrel of monkeys.

If you subscribe to this philosophy, you need to be very careful to ensure that you don’t use your barrel of monkeys model to simulate situations in which the barrel of monkeys is invalid. For example, if you decide to modify your linear accelerator model by including extra (unrealistic) shielding, to produce a (realistic) field with minimal background radiation, then you cannot use that model to simulate smaller or (especially not!) larger fields.

You also need to understand that your barrel of monkeys model will never provide you with useful information regarding the transmission of radiation within the linear accelerator itself (unless your linear accelerator really is made out of monkeys). For example, the monitor chamber is an important component of the real linear accelerator, used for monitoring the energy and symmetry of the beam, but it is not needed in a Monte Carlo model of the linear accelerator; its absence will not affect the output of the model linac. The obvious but important point is that a model which does not include a monitor chamber cannot be used to study the deposition of dose in the monitor chamber. (In fact, a model of the Varian linear accelerator that does not include a monitor chamber cannot be used to evaluate absolute dose without the use of estimated values of collimator backscatter. See here.)

And if you subscribe to this philosophy, you will always, always, always have to face questions about whether your model really works (and you will need to be able to show that your model really works) in the situations where you are using it. But these are questions we should all be asking ourselves all the time, anyway.

Working with barrels of monkeys is challenging, requires creativity and can be a lot of fun. I recommend The Barrel of Monkeys Philosophy to you.

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