Dr. P.N. Plowman
St Bartholomews Hospital

Pituitary tumours are almost invariably benign, which means they are not cancerous as they do not have the malignant potential to spread to other sites in the body.

They do, however, have a tendency to grow and after surgery, even if a few cells or groups of cells are left behind, they can be the seed of a recurrence in the same area. Whilst there is no doubt that surgery is the first treatment for most pituitary tumours (except prolactinomas), a wide 'margin of surgical safety' may not be possible, especially for larger tumours, without risking damage to neighbouring structures such as the optic nerves or major blood vessels. Thus recurrences may occur after surgery - albeit often many years later. That is why serial MRI scans are performed during follow-up in the outpatient clinic.

Surgery is rarely needed first for prolactinomas, which usually respond very well to Bromocriptine or similar drugs and need no other therapy. Even large tumours shrink well after treatment. If treatment is stopped too early, however, these tumours can recur.

The question therefore arises as to whether anything else can be done to increase cure rate in pituitary disease.

Radiotherapy is normally associated with the treatment of malignant tumours, but it has been known for several decades that it also has the potential to cure benign pituitary tumours. Interestingly, the dose needed to control these pituitary tumours seems to be only approximately two thirds of that needed for the common malignant brain tumours.

There are overwhelming data now available to show that post-operative radiotherapy substantially reduces the recurrence rate of pituitary tumours. In some centres it is also used in prolactinomas to allow earlier termination of treatment with bromocriptine or similar drugs.

The actual radiation is delivered in small daily doses (called fractions) over approximately five weeks and the radiation beams are shone from three directions, effecting a cross-fire of the pituitary. This enables us to concentrate the dose on the pituitary without damaging the tissues the radiation goes through on its way to the pituitary.

A linear accelerator, an instrument which generates modern high voltage x-ray beams, is used. The patient lies on the treatment couch, immobilised in an individually constructed head cast, for approximately fifteen minutes daily for the positioning and delivery of the therapy. The patient does not feel this treatment and leaves the treatment room having sensed nothing of the x-ray beam therapy. At the end of the course of treatment, there is a little hair loss in the temples and high forehead which later regrows. Some patients get a little tiredness at the end of the treatment course.

The effects of radiotherapy are gradual and cumulative over a period of several years. There is an increased chance of requiring pituitary hormone replacement as time goes on after radiotherapy, particularly for patients whose pituitary function has been harmed by the tumour. Later complications to the visual pathways (which pass so close above the pituitary) used to be considered an occasional risk, but with modern treatment techniques which are used in all centres in the UK, this risk has virtually disappeared.

Recently, the technique of radiosurgery has been applied to the treatment of pituitary tumours. By one of several methods, a more highly 'focused' beam of radiation is used to treat the tumour in a single very large dose. The two methods available to do this and in routine use in the UK are the gamma-knife and the x-knife methods. The perceived advantage of this method is the higher degree of 'focusing', but the perceived disadvantage is that the visual pathways can be overdosed if the tumour is close to the optic nerves. My own view is that this is a useful new method of primary treatment that is applicable for pituitary tumours lying low down in the pituitary fossa or extending sideways into the surgically risky area called the cavernous sinus, and also when the tumours needs retreating.

In conclusion, radiotherapy has curative potential for pituitary tumours, but is best employed in conjunction with surgery or dopamine agonist (usually bromocriptine) therapy and usually as the second therapy. With modern methodologies, complications of radiation therapy should be rare.