Brain
metastases most
commonly arise from lung and breast cancers. Others common causes of brain
metastases are renal cell carcinoma and malignant melanoma. The impact of brain
metastases cannot be overstated, in view of the risk of losing functional
independence, mental abilities as well as a patient’s sense of self.
With
improvement in imaging methods, especially magnetic resonance imaging ( MRI)
scanning of the brain, the chances of identifying brain metastases in
asymptomatic patients has increased, at the same time resulting in improvement
of results of treatment due to the detection of smaller metastases.
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| MRI Image demonstarting 2 brain metastases. |
Identification
of certain molecular subtypes of lung cancer, and the development for drugs
targeting abnormal pathways such as Her
2 neu gene in breast cancer and EGFR or Alk pathway in non small cell lung cancer has also resulted
in an improvement of outcome for patients suffering from tumours carrying these
pathways.
Radiotherapy is the treatment of tumours using
high energy X rays or charged particles. It is an essential component of the
treatment of brain metastases. Traditionally, the treatment of brain metastases
has been giving radiotherapy to the whole brain.
A
sophisticated, high precision form of radiotherapy called stereotactic
radiosurgery (SRS) is the administration of a very high dose of
radiotherapy in a single session, the dose ranging from 15 Gy to 24 Gy versus
the usual conventional daily dose of radiotherapy, 1.8 – 2 Gy. When added to
whole brain radiotherapy, this method of treatment improves the survival of
patients and also decreases the chances of the treated brain lesion regrowing.
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| Stereotactic Radiosurgery plan of a patient with 2 brain metastases. |
One of the
concerns of whole brain radiotherapy is its impact on the mental abilities of
the patient receiving this form of treatment. In view of this, there is a
school of thought that advocates treating patients with SRS alone, omitting
whole brain radiotherapy. Patients who receive SRS alone have a better chance
of preserving their cognition; though with the caveat they also have a higher
chance of requiring treatment for brain metastases in other parts of the brain.
This treatment can be in the form of repeat SRS or also whole brain
radiotherapy.
Another way
of preserving cognition is administering radiation to the whole brain while
avoiding high doses to the hippocampus, a structure in the brain, responsible
for creating new memories. Though it is quite possible that the hippocampus is
not the only structure responsible for cognition, studies have proven that
patients treated with techniques that avoid dose to the hippocampus can reduce
the chance of deterioration in memory due to radiotherapy.
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| Hippocampal avoidance whole brain radiotherapy to prevent cognitive decline. |
While this
is still under investigation, in certain situations, hippocampal avoidance
radiotherapy may be combined with a simultaneous high dose to the metastatic lesions
in the brain.
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| Whole brain radiotherapy with hippocampal avoidance & simultaneous boost to brain metastases. |
These
sophisticated technqiues, SRS and hippocampal avoidance radiotherapy add
quality to life of cancer patients suffering from brain metastases. This is due to better control of metastases as well as reduction in side effects of radiotherapy.
