14 August 2021
CyberKnife accurate to the millimetre
Advances in medical technology have helped make 2021 “the most exciting time” in radiotherapy, according to Perth-based oncologist Professor David Joseph.
Speaking at the Medical Oncology Group of Australia (MOGA) 2021 scientific meeting session on innovation, Professor Joseph said treatment innovations such as intensity modulation radiotherapy (IMRT), CyberKnife and FLASH radiotherapy all offer a glimpse into the future of the field.
Where conventional external beam radiation therapy uses a uniform field of beams, IMRT utilises non-uniform beams, sparing the normal tissue around a cancer as opposed to simply shielding it.
“[IMRT] beams vary across the field, and we utilise a system called ‘inverse planning’ where we specify where we don’t want to treat, so we can avoid critical structures,” Professor Joseph said.
“The aim is to get a higher degree of conformality with normal tissue sparing, and you can actually shape the beam – the next steps were to alter the beam even more with multi-leaf collimators, so you can vary it during actual treatment.”
One application for IMRT has been prostate cancer, as it is able to reach concave regions such as the prostate while avoiding the rectum.
The problem with IMRT, however, is that if the target malignancy can move around, radiologists run the risk, in Professor Joseph’s words, of delivering “a very accurate treatment to the wrong place”.
In these instances, he said, it is essential to use image-guided therapy in conjunction with IMRT, which entails implanting a substance such as gold into the target structure, organ or tumour.
Professor Joseph also spoke to the benefits of CyberKnife, a fully robotic radiation therapy system.
There are only two CyberKnife systems in Australia, both in Perth – Professor Joseph is among the few Australian doctors familiar with the machine.
“The thing that is different with the CyberKnife is that you can adapt it to treat anywhere in the body, as long as you can track the lesion,” Professor Joseph said.
“It may require image guidance [for some malignancies], but anywhere in the brain or spine can be tracked by the CyberKnife, and you can adjust the beam using a multi-leaf collimation.”
The CyberKnife is accurate down to less than a millimetre, and can treat spinal lesions but miss the spinal cord, and target moving lung lesions without damaging healthy tissue.
“The robot can track a lesion in the lung, and it will go up and down as the patient breathes, so you don’t have to treat a really big bit of the lung,” he said.
Treatment with the CyberKnife is generally finished within five sessions, and Professor Joseph said this had ensured minimum disruption over the course of the pandemic.
In terms of what is yet to come, Professor Joseph said he believed FLASH radiotherapy – the ultra-fast delivery of high doses of radiation – would be the next technique to take off.
“Very, very high doses of radiation, not like we could do even with hypofractionation, are seeming to have a significant impact on tumours,” he said.
“I think this is something to watch for the future.”