A more accurate way to destroy tumours using beams of radioactive particles could help target hard-to-treat cancers that are close to sensitive organs, such as the spinal cord or optic nerve.
Most radiotherapy uses beams of X-rays to destroy cancerous cells, but for tumours deep inside the body, this can damage healthy tissue in the beam鈥檚 path.
Newer methods that use beams of particles, such as proton therapy, can instead deliver most of their radiation in an extremely small space deep inside the body. This is because as the particles travel through the person, they slow down, which means they interact with electrons in the body鈥檚 cells for longer and transfer more energy.
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However, it is difficult to precisely direct where this peak radiation dose is absorbed, which can risk damaging nearby tissue in sensitive organs.
Now, at the Technical University of Darmstadt in Germany and his colleagues have demonstrated a new kind of particle beam, using radioactive carbon ions, that can be directed much more precisely.
When these ions enter the body, they decay and produce positrons, the antimatter counterpart of electrons. These positrons then collide with nearby electrons, annihilate each other and emit gamma rays, which can be used to locate the exact point at which the beam is depositing its radiation.
鈥淚f you can see where the beam is during the radiation, then you have no problems,鈥� says Durante. 鈥淵ou can adjust the position of the beam and you can make sure that you are not shooting in the wrong position.鈥�
Durante and his team used a beam of radioactive carbon isotopes 鈥� unstable carbon atoms with 11 neutrons rather than 12 鈥� produced by a particle accelerator at the GSI Helmholtz Centre for Heavy Ion Research near Darmstadt. They pointed this beam at a cancerous tumour next to the spinal cord of 32 mice and used a PET scan, which detects gamma rays, to ensure the beam was on target.
In mice that received a low dose of the beam therapy, there was a reduction in tumour growth compared with mice that did not receive the beam therapy. In another group of mice that received a higher dose, the tumour stopped growing completely, and no damage to the mouse鈥檚 spinal cord was detected.
鈥淚t鈥檚 incredibly exciting and potentially useful,鈥� says at University College London. 鈥淭he Achilles heel of particle therapy is this range uncertainty, [not] knowing where the peak stops. It鈥檚 been the source of uncertainty, research and concern for 30 years in particle therapy.鈥�
However, showing that the technique works for cancers in humans will take many years and full clinical trials, says Amos. There is also an increased risk of dangerous radiation coming off the beam before it reaches the body, so this will have to be carefully managed, he says.
arXiv
