To ensure that the cancer is being treated we need first to map it out. This mapping out is called simulation. Once we have correctly identified the tumour (which obviously needs to be treated) and normal tissues that need to be avoided, the treatment can be planned then commenced.

For most patients, CT-simulation is the best method of simulation, as CT scans are an excellent way to visualize tumours and normal tissues. Certainly conventional simulators (which just use plain x-rays) are inferior in almost all situations.

For certain patients CT is not good enough and MRIs are required. This is true for patients with prostate, brain and head and neck cancers. A good example is shown below.

MRI-CT Planning

The image on the left is a CT. It is impossible to tell what is prostate and what is muscle, so radiation doctors have to guess about where the prostate is when they mark it out. On the right is an MRI, and the prostate is seen easily (arrowed). Patients should request MRI-CT simulation if they are having prostate, brain anr head and neck cancer treatment. MRI-CT simulation should be used in conjunction with 3D-conformal radiotherapy or IMRT. Sometimes (e.g. for lung cancer) PET-planning is better.

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