Linear Accelerator (LINAC)

A medical linear accelerator is a large machine housed in a shielded treatment room. Inside it, microwaves push electrons along a straight tube, called a waveguide, to almost the speed of light. The electrons either leave the machine directly as an electron beam, used for tumours on or close to the skin, or strike a metal target to produce high-energy X-rays that reach deep inside the body. The treatment head sits on a rotating arm, the gantry, which turns around the couch so the beam can enter from many directions. Modern machines carry a multileaf collimator, a set of thin moving metal leaves that shape the beam to the outline of the tumour, and an imaging system that checks your position before treatment. TrueBeam STx, Varian TrueBeam, Varian Edge, Varian VitalBeam, Elekta Versa HD Signature, Ethos Adaptive Radiotherapy and TomoTherapy are examples of systems in this family.

Treatment starts with planning. You have a planning CT scan, sometimes combined with MRI or PET, lying in the exact position you will use for every session, often supported by a moulded headrest, a thermoplastic mask or small skin marks. A radiation oncologist outlines the tumour and the organs to protect, and a medical physics team calculates how the beams should be arranged. With intensity-modulated radiotherapy (IMRT) the strength of each beam varies across its width; with volumetric modulated arc therapy (VMAT) the beam is reshaped continuously while the gantry rotates, which shortens each session. Image-guided radiotherapy (IGRT) uses X-ray or cone-beam CT images taken on the couch to correct your position by millimetres. Stereotactic body radiotherapy (SBRT) uses the same tools to give a few very precise, high-dose sessions to small targets, and some systems adapt the plan each day to changes in the tumour or nearby organs.

Linear accelerators treat a wide range of cancers, including breast, prostate, lung, head and neck, brain, rectal, cervical and oesophageal tumours, lymphomas and skin cancers. Radiotherapy may be the main treatment, it may be combined with chemotherapy, or it may be given before or after surgery to shrink a tumour or lower the chance of it returning. Short palliative courses relieve pain from cancer that has spread to bone, and ease bleeding or pressure symptoms. The same machines treat small lung, liver, spine or brain lesions with stereotactic techniques, and occasionally benign conditions. Whether radiotherapy suits you, and which technique and schedule, is decided by a radiation oncologist after reviewing your pathology, imaging and other treatments, often within a multidisciplinary tumour board.

The main benefit is that a high dose can be shaped closely to the tumour while sparing surrounding organs, which lowers the risk of some side effects compared with older, less precise techniques. Treatment is given as an outpatient, you are not radioactive afterwards, and most people keep up light daily activities. Side effects depend on the area treated: tiredness and a sunburn-like skin reaction are common, while a sore throat, bowel or bladder irritation or hair loss appear only when those regions are in the beam. Most settle within weeks of finishing, although some late effects can appear months or years later. A conventional course of several weeks means a long stay away from home, so many international patients ask whether a shorter hypofractionated or stereotactic schedule is clinically appropriate, and agree in advance who will follow them up at home.