Novel radiotherapy technique may advance fight against cancer

Microbeam radiation therapy (MRT), a novel technology delivering small beams of radiation 50 times stronger than standard treatment safely, is a step closer  following a study led by a Monash University researcher.

Associate Professor Sasha Senthi, radiation oncologist at the Alfred Hospital, was senior author on a study determining the best use of MRT against cancer at the Australian Synchrotron. MRT delivers an array of ultra-high dose beams of radiation a few microns wide – the size of some human cells – while maintaining low doses in between.

“Standard radiotherapy is delivered in an equal, homogenous dose throughout the patient,” Associate Professor Senthi said. “With MRT it is heterogenous and you have these peaks and valleys. Within the peaks, almost no cell survives. In the valleys, the normal cells that survive repair their damage and heal damaged areas, which tumour tissues cannot do,” he said.

“This is a novel technology and we still don’t completely understand the mechanism by which it works. In animal models, it appears that destroying some of the cells within a tumour with MRT results in the entire tumour dying.”

Associate Professor Senthi said his colleagues at the Australian Synchrotron had previously shown that MRT interacts with the immune system differently to standard radiotherapy.

“We need more evidence from animal models that MRT is safe and effective before we start using it on patients,” he said. “The synchrotron was built with the vision of eventually treating people but we currently don’t have the infrastructure to accurately treat patients. At The Alfred I can currently treat patients with sub-millimetre accuracy and monitor them during treatment. I want to be able to do the same thing with MRT.”

The study, which appeared in Physica Medica, used patient CT data sets to identify optimal scenarios for its clinical testing, assessing which tumour locations in the body would be best suited to being in the first in-human trials. It was the first study to do this.

“The aim was to find the scenarios where the highest peak doses could be delivered while maintaining low enough valley doses that normal tissue could repair. We found patients with recurrent tumours in the head or neck would be most likely to benefit from MRT, while those with chest wall, breast or brain tumours near the skull wall could also benefit,” Associate Professor Senthi said.

Patients with tumours in the lung or spine appear to benefit least. “We found MRT was able to treat tumours deeper within the body than previously thought.

“This groundwork is a step towards what could be a huge advance in the fight against cancer.”

Radiation therapy is used in about 50 per cent of cancer patients and benefits the vast majority of them.

“I hope MRT will benefit those where it does not and when current treatments such as chemotherapy or immunotherapy don’t work,” Associate Professor Senthi said. “This treatment is really to provide another avenue by which we can prolong life and maintain quality of life.”

Smyth LML, Day LR, Woodford K, Rogers PAW, Crosbie JC, Senthi S. Identifying optimal clinical scenarios for synchrotron microbeam radiation therapy: A treatment planning study. Phys Med. 2019 Apr;60:111-119. doi: 10.1016/j.ejmp.2019.03.019. Epub 2019 Mar 30.