Sunday, December 27, 2009

Radiotherapy / Medical Applications

c) Radiotherapy

This technique is used to cure cancers or at least to alleviate the most distressing symptoms, by killing the cancerous cells. A beam of high energy X rays, gamma rays or electrons is directed towards the diseased tissue so as to give it a high dose while sparing the surrounding healthy tissue. If a tumour is deep in the body, the beam is pointed at it from several directions so as to reduce the incidental damage. Another form of treatment, in which a radiation source is placed in or on the body for a short period, is used for some cancers: it is called brachytherapy. As radiotherapy doses are strong, such treatment is only used when the outlook for a cure or relief is good and when other methods of treatment would be less effective.


Although radiotherapy can cure the original cancer, it may possibly cause cancer in other tissues or adverse hereditary effects in subsequent generations. Most people who receive radiotherapy are, however, past the age to have children and too old for delayed cancers to occur. So the aim of radiotherapy is to maximize the effectiveness of treatment while minimizing the adverse side-effects.

Tumours require absorbed doses of tens of gray to kill the cancer cells effectively. Prescribed doses to tissues are typically in the range 20-60 Gy. Considerable care is required to deliver accurate doses: too low or too high doses may lead to incom­plete treatment or unacceptable side-effects. Rigorous quality assurance procedures are needed to make sure that equipment is properly set up and maintained. If this is not done, the consequences can be grave: a miscalibrated radiotherapy beam in

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