The role of radiotherapy

What is radiotherapy?

Radiotherapy is the use of ionising radiation in the treatment of disease. As radiation passes through tissue it collides with atoms along its path. Energy is deposited and utilised by molecules to inflict damage to the DNA of a cell.  If this damage is not repaired death of the cell may occur.

Normal tissues usually have better repair mechanisms than tumour cells which allow them a better degree of protection.

How is radiotherapy delivered?

This can be done in two ways.

External beam radiotherapy accounts for the majority of treatments given and is where radiation is produced from a machine and delivered to the target area from the outside, for example x-rays produced by a linear accelerator.

Before treatment can be given a process of planning has to be undertaken. This is in order to arrange the beams of radiation so that the area to be treated receives the prescribed dose whilst the dose to surrounding normal tissue is minimised. The number of treatments making up a course of
radiotherapy will vary from a single treatment to 6 weeks of daily visits. It will depend on many factors including the site and size of the target area, whether surgery has been performed and if the treatment is aimed at achieving a cure or at controlling symptoms.

Is radiotherapy of any use in ovarian cancer?

Over the past two decades platinum-based chemotherapy (cisplatin or carboplatin) has become the mainstay of treatment, with clear benefits in control of the cancer and survival.  Although there continues to be much effort in looking for new drug combinations which will improve the outlook further, radiotherapy does have a role to play in both cure and symptom control in patients with ovarian cancer.

Radiotherapy as curative treatment

In early-stage disease, trials have shown radiotherapy to the whole abdomen followingsurgery to be a very effective treatment, with results comparable to the use of chemotherapy.

Although there are no completed randomised controlled trials which have compared this treatment with platinum chemotherapy, its use in this situation has largely been superseded by chemotherapy. There remain some centres, particularly in Canada, where suitable patients with early disease are treated primarily with radiotherapy rather than chemotherapy.

For patients with early disease but in whom there are features that might mean they are at a slightly higher risk of recurrence (e.g. poorly differentiated tumour, disease spread outside the ovaries) there may be a role for radiotherapy following surgery and chemotherapy. Trials which have looked at this method of treatment have not shown a benefit with the addition of radiation; however, a new study in the United States and Canada is under way re-addressing this question.

Brachytherapy using radioactive phosphorous or gold which is instilled into the abdomen has been used in early disease. But because of the difficulty in ensuring an even distribution of the material, and hence dose of radiation, it is not widely used.

Targeted treatment based on this technique is now being studied, whereby antibodies to the cancer are attached to a radioactive substance.  The antibodies are injected into the abdomen and are drawn to the cancer cells, allowing the radiation to be delivered to the tumour only. This type of treatment is in the experimental stage and only available as part of a study.

For patients who have cancer which persists despite chemotherapy there may well be a role for whole abdominal radiotherapy. It is most likely to be successful if only small amounts of disease remain.

Radiotherapy to control symptoms

Even a single radiotherapy can be very effective at improving symptoms. The commonest problems in ovarian cancer that need treating are bleeding and pain. Radiation is directed in the region that is causing the problem (which may not necessarily be in the pelvis) and works partly by causing the tumour to shrink. It is often possible to re-treat an area if a symptom recurs.

Where next?

Although chemotherapy is currently the treatment of choice for ovarian cancer there is still scope for improvement. With better techniques and equipment available in radiotherapy departments, now may be the time to revist the use of radiation in ovarian cancer.

Melanie Powell
St Bartholomew’s Hospital, London