What method is used to spread the pencil electron beam in a clinical accelerator?

The correct method used to spread the pencil electron beam in a clinical accelerator is through electromagnetic scanning. This technique utilizes magnetic fields to manipulate the path of the electrons generated by the accelerator, allowing for precise control over the beam's spread. By adjusting the electromagnetic fields, clinicians can direct the electron beam to cover a specific area effectively, ensuring that the targeted tissue receives the appropriate dose of radiation while minimizing exposure to surrounding healthy tissues.

Electromagnetic scanning is critical in clinical settings because it provides the flexibility needed for various treatment plans, accommodating different tumor sizes and locations. This precision is crucial for achieving optimal therapeutic outcomes in radiation therapy.