New cancer scan could guide brain surgery

A type of ultrasound scan can detect cancer tissue left behind after a brain tumour is removed more sensitively than surgeons, and could improve the outcome from operations, a new study suggests.

The new ultrasound technique, called shear wave elastography, could be used during brain surgery to detect residual cancerous tissue, allowing surgeons to remove as much as possible.

Researchers believe that the new type of scan, which is much faster to carry out and more affordable than ‘gold standard’ MRI scans, has the potential to reduce a patient’s risk of relapse by cutting the chances that a tumour will grow back.

A multi-institutional team led by The Institute of Cancer Research, London, and the National Hospital for Neurology and Neurosurgery, London, compared three different techniques to detect tumour tissue during surgery – shear wave scans, a standard 2D ultrasound, and a surgeon’s opinion – in 26 patients.

The research was conducted in collaboration with clinicians from The Royal London Hospital and University Hospital Southampton.

Researchers performed shear wave scans and 2D ultrasounds during the operation – before, during and after tumour removal. The researchers also asked surgeons to identify potentially cancerous tissue before providing them with scan findings. The team then compared all techniques with gold-standard MRI scans after surgery.

The study is published in the journal Frontiers in Oncology and was funded by the Royal Free Charity and the Engineering and Physical Sciences Research Council, part of UKRI. It found that shear wave elastography was more sensitive in detecting residual tumour tissue than a standard ultrasound or the surgeon alone.

More sensitive at detecting residual tumour:
Shear wave scans detected tumour tissue with 94 per cent sensitivity – compared with 73 per cent for standard ultrasound and 36 per cent for the surgeon. This means that when there was residual tumour, shear wave scans were 2.5 times better than the surgeon at detecting it.

However, shear wave scans detected tumour tissue with only 77 per cent specificity – better than the 63 per cent for standard ultrasound but less good than the 100 per cent for surgeons.

That means that the new technique could yield more ‘false positives’ than surgeons – and for that reason the researchers believe it would be best used in combination with a surgeon’s opinion.

Shear wave elastography measures tissues’ stiffness and stretchiness. Vibrations or ‘shear waves’ are created and detected as they move through tissue – moving faster through stiffer tissue.

Creating a map of stiffness:
Brain tumours tend, on average, to be stiffer than normal brain tissue and the technique works by mapping suspicious areas of particular stiffness, which can then be examined and removed during surgery.

Patient outcomes from brain tumour surgery are known to be better when as much of the tumour as possible is removed. In order to make sure that none of the resectable tumour is left behind, neurosurgeons use tools to guide them during surgery.

But although MRI scans are the most accurate, their use during surgery is not normally an option – as they are costly, not normally available in operating theatres and would increase the duration of surgery by almost two hours.

Shear wave scans were shown to be as good as post-surgery MRIs at detecting tumour tissue that had been left behind – making them a cheaper, faster and more feasible alternative. The study is the first to demonstrate the potential of shear wave elastography as a neurosurgical tool to confirm during surgery the completeness of tumour removal – although the benefits of the technique will now need to be confirmed in larger studies before it can be recommended as standard practice.