A clear plastic mask made specially for each patient's head, holds the patient's head still during the brief treatment. The targeting marks are lined up against the cross-beams of a laser set into the walls of the Radiotherapy room. The radiotherapy treatment is delivered to the target area from three directions.
INDICATIONS FOR RADIOTHERAPY (RT) USE IN PITUITARY ADENOMA:
Following surgical resection
If tumour persists outside pituitary fossa on post-op scan.
For functioning adenoma: if hormone levels do not fall to normal post-op and/or medical therapy is not subsequently controlling hormone secretion.
Consider for patients with recurrent disease (+/- following second operation - especially if chiasm is compressed).
Patients with small volume functioning adenoma away from the optic chiasm or recurrence following conventional radiotherapy can be considered for single fraction radiotherapy (also called radio surgery).
For inoperable disease
Radiotherapy was once regarded as a routine treatment for pituitary adenomas, especially those at higher risk of relapse (tumour >1cm in size). Many factors have led to a reduction in the routine use of radiotherapy following surgery over the past 20 years:
Patients with functioning adenomas can frequently be treated with medical therapy if hormone levels remain elevated post op, and some centres now reserve RT for those failing medical therapy e.g., in Acromegaly Somatostatin analogue therapy may be used first line and RT reserved for cases where Growth hormone fails to reach safe levels on treatment.
Changes in tumour size can now be monitored with sequential MR imaging.
Half of patients with normal pituitary function pre RT will develop hypopituitarism within 20 years of radiotherapy, necessitating regular endocrine follow up.
BENEFITS OF RADIOTHERAPY
Controls disease in 94% of cases at 10 years and 88% at 20 years.
Reduces local recurrence from 60% with surgery alone to 5% (surgery + RT).
Reduces hormone secretion in 90% cases of acromegaly, median 4 ½ years to normalisation of hormone levels.
55% of patients with impaired visual fields or acuity notice improvement following surgery and RT.
Note: because of the possibility of loss of normal pituitary function several years after RT, it is essential that all patients have regular follow-ups with an Endocrinologist.
RADIOTHERAPY DELIVERY PLANNING
In order to reduce the amount of normal brain irradiated, the patient’s head should be firmly immobilised on to the radiotherapy treatment couch, thus reducing movement. This allows the radiotherapist to minimise the margins for movement added to the tumour target volume. Three techniques can be employed to immobilise the patient:
A mask can be made in one session using a thermoplastic mesh drawn down over the patient’s face, which is then attached to a firm baseboard.
Or a perspex mask is moulded from a plaster of Paris cast of the patient’s face. This requires two hospital visits. A hole in the Perspex mask is made for mouth and nostrils. Patients with a beard will be asked to shave to give a firm fit of the mask. Accuracy for both mask systems is 5-10mm.
A stereotactic ring frame can be fitted using skull vault screws (for a single fraction treatment-radiosurgery) or using patient specific dental and occipital impressions to allow repeat usage for multiple treatments. This ring is then fixed to the treatment couch with 1-3mm accuracy.
A CT scan is performed with the patient in the immobilisation device and the radiotherapist and physicist define a treatment volume and patient specific customised plan in order to treat this volume. Usually three or four treatment fields are used on a daily basis. Patient specific shielding blocks or blocking leaflets in the machine treatment head are used to reduce the volume of normal tissue irradiated. The planning process can take 1 - 3 weeks.
Radiotherapy is usually given in small doses, every working day, for 5-6 weeks giving a typical total dose of typical almost everyone gives 45Gy in 25 fractions dose of 45 - 50 Gy. Each treatment, which is painless, lasts for 10 - 15 minutes - the actual radiotherapy about 2 minutes. Treatments are delivered using a Linear Accelerator (LINAC) machine. Lining up markers on the mask with laser beams embedded in the walls of the treatment room confirms the absolute position of the patient relative to the treatment machine, and thus safe delivery of treatment. Using the stereotactic immobilisation ring ensures slightly higher precision than the mask systems. But is more time consuming to deliver and requires specific equipment and expertise, which is not available in all departments and its benefit is still being evaluated.
Single fraction radiotherapy (radiosurgery) is occasionally used for pituitary adenomas in the specific indications outlined above. This is delivered using either a LINAC or Gamma Knife (an array of cobalt sources around the patient’s head). A dose of 50 Gy to the tumour centre is delivered in a single treatment. A steep dose gradient beyond the tumour edge aims to reduce the dose to surrounding critical structures. This treatment is sometimes prescribed by a neurosurgeon.
ADVERSE EFFECTS OF RADIOTHERAPY
Transient side effects:
Skin erythema, irritation and transient hair loss occurs at the sites of beam entry and exit. The hair almost always re-grows within a few months.
Headache - treat symptomatically, avoid steroids if possible.
Tiredness, which can last for a few months.
Long term, permanent side effects:
Hypopituitarism. In those patients with normal function before RT, 30% of patients by 10 years, 50% by 19 years develop hypopituitarism. They will need endocrine follow up with annual pituitary function tests.
Optic nerve damage. <1% of cases show some visual deterioration.
2nd tumour. 1.9% at 20 years. However, techniques for RT have improved in the last 20yrs.
CVA. Relative risk of 4 compared with normal population.
Evidence on side effects of single fraction stereotactic radiotherapy (radio-surgery) has only been available in recent years. Initial enthusiastic use resulted in a high rate of optic chiasm damage and now this treatment is reserved for cases where the doses to the optic chiasm and temporal lobe are well within the tolerance dose for these structures.
QUESTIONS PATIENTS MAY ASK
How long will it take?
The treatment itself only takes about 10-15 minutes, but radiotherapy has to be given in small doses over a long period (usually 5 weeks), so you will need to attend the radiotherapy clinic each working day during the treatment period.
Will I lose my hair?
Generally, no. A small amount of hair is lost at the sites of radiation entry and exit (i.e., the temples, above the forehead and the nape of the neck typically in front of each ear), but this almost always re-grows within a few months.
Will it hurt?
Treatment is much the same as having an X-ray - it is quite painless.
What are the possible side effects?
Tiredness starts during or after the end of the treatment schedule and can last for several weeks. Some patients occasionally experience nausea, mild headache or some reddening of the skin, but this is unusual. Rarer longer-term side effects will be discussed in more detail by the radiotherapist, however impaired pituitary function is seen in half of patients with functioning pituitaries before RT. This can occur after years. It is important the patient attends regular endocrine follow up for many years.
RESOURCES FOR PATIENTS
available from The Pituitary Foundation HelpLine or our website www.pituitary.org.uk or our Endocrine Nurse HelpLine
Patient Information Booklet: Pituitary Radiotherapy
Other information and resource links available at www.pituitary.org.uk
MORE SPECIALIST RESOURCES
Management of Pituitary Tumors: The Clinician’s Practical Guide (2003) (Second Edition), Editors and authors Michael P. Powell, Stafford L. Lightman and Edward R. Laws. Humana Press, Totowa, New Jersey
Pituitary Tumours. Recommendations for service provision and guidelines for management of patients. Consensus statement of a working party (1997) RN Clayton & JAH Wass (Eds) London: Royal College of Physicians
The Diagnosis and Treatment of Pituitary Insufficiency (1997) Lamberts SWJ (Ed) Bristol, UK: BioScientifica
Endocrinology (1997) Levy A & Lightman SL New York: Oxford University Press
The Epidemiology, Pathogenesis and Management of Pituitary Tumours (1998) Webb SM (Ed) Bristol, UK: BioScientifica
©2011 Version 3 (To be reviewed by 2013)