Traditional medical linear accelerators that produce high-energy X-rays, kilovoltage treatment X-ray units, or devices that looked like linear accelerators but employed a sealed radioactive source like the one in the image above were used to administer two-dimensional beams of Radiotherapy.

 A single radiation beam is primarily used in conventional external beam Radiotherapy, and it is frequently supplied to the patient from the front, back, and both sides. The terms "conventional" and "radiation beam arrangements" refer to the usual well-established arrangements of the radiation beams to achieve a desired plan. Conventional also refers to the way the treatment is planned or simulated on a specially calibrated diagnostic X-ray machine known as a simulator because it replicates the linear accelerator actions (or occasionally by eye).

The goal of simulation is to precisely target or localise the treated volume. This method is tried-and-true, generally efficient, and dependable. It's a concern that some high-dose therapies might be constrained by the radiation toxicity capacity of healthy tissues that are adjacent to the target tumour volume.

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