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We are writing to provide information to supplement Usman Chaudry's1 reference to the option of “stereotactic gamma-knife radiosurgery” for follow-up of residual tumour in a patient with a nonfunctioning pituitary macroadenoma.
The term “radiosurgery” implies delivery of a single large fraction of stereotactic radiation. Gamma-knife therapy does typically involve single-fraction treatment, because the patient must be positioned in a stereotactic head frame, and patient discomfort becomes a factor if more than one dose is required. However, for tumours such as pituitary adenomas, with proximity to the optic chiasm or tracts, medial temporal lobe or other important functional brain structures, it may be advantageous to use a fractionated technique (multiple treatments), with a smaller dose per fraction, to minimize injury to the adjacent normal tissues. Such treatment is properly referred to as “stereotactic radiotherapy.”
The geometric advantage of the multiple beams or arc radiation used in stereotactic treatments declines with increasing tumour volume. Therefore, this treatment is generally considered only if the tumour is less than 3 to 4 cm in maximum dimension.
As opposed to the gamma-knife, linear accelerator (LINAC) radiation delivery systems have the versatility to be used for both radiosurgery and fractionated stereotactic radiotherapy. In addition, LINAC systems have a micro-multileaf collimator, which can produce complex beam shapes, and therefore can be used to deliver treatment with a single complex isocentre. This feature can achieve superior conformity and homogeneity of the radiation dose over the multiple-isocentre approach of the gamma-knife.
The Stereotactic Radiotherapy Program at Dalhousie University is the referral centre for Atlantic Canadian patients requiring such treatment. We usually treat residual or recurrent pituitary adenomas with a fractionated LINAC-based technique, as do all other Canadian centres offering this treatment modality. Others have identified the advantage of this fractionated approach.2
Liam Mulroy Dorianne E. Rheaume Department of Radiation Oncology Ian Fleetwood Division of Neurosurgery Jason Schella James Robar Department of Radiation Oncology — Medical Physics Dalhousie University Queen Elizabeth II Health Sciences Centre Halifax, NS
Footnotes
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Competing interests: None declared.