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Dr Edward Yang, a Senior Consultant in Radiation Oncology at Parkway Cancer Centre, talks about how improving radiotherapy technologies are giving doctors more options in the treatment of brain cancer.
Tumours in the brain, whether originating in situ, or having metastasised from elsewhere, are difficult tumours to treat.
It is hard to surgically remove because the brain is such a delicate organ that even doing biopsies can be dangerous in certain circumstances, let alone surgery. Even if the tumour is successfully removed, surgery could affect brain function depending on the site of the lesion.
Moreover, some of these tumours may be benign and doing surgery may impose a significant risk which outweighs the benefit.
In addition, “the blood-brain barrier” which protects the brain from pathogens, can prevent many chemotherapy drugs from concentrating in the brain making them less effective. Hence, radiotherapy is now often considered as an important therapy option for brain tumours.
Radiotherapy, however, had its downsides as well. More than 20 years ago, radiotherapy for brain cancer meant irradiating large portions of the brain or the whole brain in some circumstances like metastatic cancer to the brain. This meant that even if a tumour/tumours occupied only five per cent of the volume of the brain, the other 95 per cent of the brain had to be irradiated as well, noted Dr Edward Yang, a Senior Consultant in Radiation Oncology at Parkway Cancer Centre.
Whole brain radiotherapy takes two to three weeks and has a potential to cause neurotoxicity. As a result of the treatment, patients could become cognitively impaired or develop difficulties in walking or communicating. This significantly affects the patient’s quality of life. This often occurs a year or two later.
However, thanks to developments in radiotherapy, radiation oncologists can now deliver targeted beams of radiation to the tumour, sparing the rest of the brain, which means that there is now less need to use whole brain radiation.
One of the main therapies used now is stereotactic radiosurgery. This is where many tiny beams of radiation are aimed at the cancer very precisely. As a result, a high dose of radiation can be given accurately and safely, with a single treatment or a few treatments depending on the situation.
Now, we also have intensity-modulated radiation therapy (IMRT). This delivers radiation in a way that is shaped to the tumour.
Another new technology is image-guided radiation therapy (IGRT) where scans are done before and during treatment to ensure accurate targeting. Sometimes, these different procedures are combined to increase efficiency and accuracy.
“Stereotactic radiotherapy with intensity modulated solutions allows us to shape a dose to conform to the tumour extremely accurately with IGRT to verify its accuracy daily,” said Dr Yang.
“And with image-based stereotactic surgery, we can target the tumour and avoid the normal brain tissues very effectively, safely and accurately, reducing the radiation dose to the normal brain and therefore, reducing the risk of toxicity and damage.”
These developments make radiosurgery the treatment of choice for benign tumours especially.
“With very accurate radiosurgery or stereotactic radiotherapy, a lot of benign tumours like meningiomas and acoustic neuromas are not removed because of the risks of surgery and the excellent results of radiation,” said Dr Yang.
“The results are so good with stereotactic radiotherapy/radiosurgery and the risks are so low that it is not worth putting the patient at risk by doing a major surgery unless surgery is necessary for urgent decompression, or tumours are so large that debulking them may have benefit.”
The ability to target individual tumours directly with radiation has already resulted in a change in the way people with multiple secondary brain tumours are treated. Previously subjected to whole brain radiation, these days, they receive stereotactic radiosurgery which avoids neurotoxicity.
Stereotactic radiosurgery is not the answer to all brain tumours, though.
For malignant tumours in the brain, surgery is still the first option where it is possible, said Dr Yang.
However, sometimes surgery is not possible because of the size of the tumour, its location or because the patient is too ill to undergo major surgery. This is where stereotactic radiotherapy comes in.
In addition, whole brain radiation has not gone away completely. Dr Yang still uses whole brain radiation if a patient has more than 10 secondary tumours in the brain.
However, the use of whole brain radiation has dropped drastically compared to the past.
“Fifteen years ago, about 95 per cent of cases of radiotherapy for brain metastases would be whole brain radiotherapy,” he said. “Today, we would offer fractionated stereotactic radiotherapy whenever feasible as to lower the neurotoxicity risk and time required for treatment.”
Added Dr Yang: “The increased accuracy of radiotherapy means that it can be safely used for dealing with benign and malignant tumours where the risks of surgery outweigh the benefits.
“In addition, the increasing use of stereotactic radiosurgery over whole brain radiation for people suffering from secondary brain tumours means considerably fewer side effects, and patients would thus be able to enjoy a better quality of life after treatment.”
Brain tumours are abnormal cells that grow in the brain. About two-thirds of brain tumours are secondary tumours, meaning that they originated elsewhere, usually the lung, breast or colorectal region. These cancers then metastasised to the brain. The remaining one-third are primary tumours where the tumours originate in the brain.
Most of the time, doctors do not know the cause of primary brain tumours but some can be related to rare genetic disorders, said Dr Yang. Among primary tumours, a significant proportion are benign.
People who have primary brain tumours can sometimes not have symptoms for a long time because the brain can adapt and compensate, he said.
Symptoms, when they appear, are non-specific and include headaches, nausea, vomiting, giddiness, unsteady gait and fits. If the tumour is near the area that controls speech, people can have problems verbalising or if it is in the motor area, they may develop unilateral weakness.
Patients have to undergo an MRI to see if their symptoms are a result of a tumour or a stroke. If a tumour is detected and a biopsy needs to be done, then using image guidance, the coordinates of the tumour is found, a small hole is drilled into the skull and a needle is carefully inserted to extract the tissues for the biopsy.
However, because of better imaging, there are many conditions where biopsies are not needed, said Dr Yang. “We know they are benign because of the location and if they are expanding rather than infiltrating.”
Even benign tumours need to be dealt with because of the potential damage they can cause as they expand. This is where stereotactic radiosurgery can come in.
“With radiotherapy, the risk of damaging adjacent tissue is very low because we can now concentrate the radiation to exactly where we want, with very good accuracy,” said Dr Yang.
“This treatment is outpatient, less costly and safe. You may not even have hair loss in some situations.”
With benign primary tumours, the aim of radiotherapy is curative. With malignant tumours, radiotherapy is used for tumours which are difficult to remove surgically or when patients are too ill for major surgery. Patients who undergo surgery often get post-operative radiation.
“We often require radiation to deal with microscopic or macroscopic disease left behind,” said Dr Yang.
“Unlike other tumours – like the cancer of the colon where we can remove a section of the colon with a good margin – in the brain, we dare not take large margins because we would be cutting into the normal brain.”
Stereotactic radiation treatment takes about 20 minutes each day and lasts about five to six weeks. Sometimes chemotherapy is added to enhance the effectiveness of radiation in malignant brain tumours. Most patients can walk in for the treatment and then walk home.
Written by Jimmy Yap
|POSTED IN||Cancer Treatments|
|TAGS||brain cancer, cancer quality of life, metastatic cancer, radiotherapy (radiation therapy), tumours|