Radiotherapy Physics
Medical Physicists in Radiotherapy
Radiotherapy is a form of cancer treatment which delivers x-rays to cancer cells with the aim of killing them . Radiotherapy is most usually delivered by a linear accelerator – a large, rotating machine which sends out invisible x-rays. The expertise of many different staff groups is needed in a radiotherapy department, including radiographers, doctors, nurses, engineers and medical physicists. Medical physicists are scientists with a strong background in the behaviour of x-rays, human anatomy and computer systems. This page gives an overview of the main roles of medical physicists in providing cancer care.
Treatment Planning – making treatments uniquely suited to each patient
Medical physicists are involved in creating and checking the treatment plan for each patient. Creating a plan means programming how the linear accelerator should rotate in order to send out the correct amount of x-rays to the tumour. At the same time, we try to prevent the x-rays from hitting the healthy tissue around the tumour. This minimises the side effects of treatment. Each planning decision needs to be carefully balanced to achieve the best possible results for each patient. No two treatment plans are exactly the same, because no two patients’ tumours and anatomy are exactly the same. When a plan is ready, it is thoroughly checked by an independent physicist. This helps to make sure no mistakes have been made.
Quality Assurance – checking that the treatment machines are working accurately
Physicists perform thorough testing of the linear accelerators regularly. We want to make sure that the machines behave exactly as expected at all times. This is important for treatments to be delivered as intended, because treatment plans are made assuming that everything is working normally. All the tests we perform are collectively called quality assurance, and their aim is to ensure that no errors occur during treatments; that each treatment is delivered with great accuracy; and that patients get the same, high-quality treatment day in and day out.
Brachytherapy – a special type of radiotherapy
Brachytherapy is a special type of radiotherapy which is helpful in treating certain cancers, particularly some cervix cancers. The cervix is the lower part of the womb opening into the vagina. Brachytherapy delivers radiation from inside the body to cancer cells by placing a radioactive material – a “source” – in positions inside or near the tumour for specified lengths of time. Physicists carefully decide these source positions and durations so that it kills as much of the tumour and as little of the nearby healthy organs as possible. The source is no larger than a grain of rice.
Physicists also regularly perform quality assurance tests of the machine which houses the radioactive source and moves it into the various positions during treatment. The source needs replacing every three months. As physicists, we test the new source to find out its exact strength, which is crucial to know when planning the treatments.
Media
Radiotherapy Physicists: Their role in the radiotherapy treatment journey - YouTube
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