Circular proton systems change energy slowly, with low transmission, and fire large diameter beams. This results in inhomogeneous doses to the tumour and lower conformity.
The advent of the linear proton accelerator is designed to solve these problems, treat more cancer indications and reduce toxicities.
In circular proton therapy systems, protons are accelerated to a maximum energy and have to be slowed down by mechanically moving thick pieces of carbon, called "energy degraders", into the proton beam. These degraders waste many of the protons in the process, demanding thick, expensive radiation shielding and reducing the number of protons available for the patient's treatment.
LIGHT is fundamentally different in that respect. Instead of accelerating protons in a spiral, LIGHT speeds up the protons in a straight line. This design results in a much higher transmission. LIGHT has a transmission of more than 95% for all the energies required to treat patients.
In contrast, the transmission of a conventional cyclotron with energy degraders is less than 20% (50%) for an energy of 170MeV (210MeV).
LIGHT is designed to provide volumetric rescanning with fast energy changes. Owing to the fast, electronic control of beam energy, and therefore of the depth of dose, the system will provide 3D dynamic beam patient target alignment, using active range control This will improve the accuracy of treating moving targets such as lung and liver and the oesophagus and decrease normal tissue irradiation.
LIGHT offers the potential for further development of smaller spot sizes and is thus ideally suited for the novel minibeam treatment.
This kind of therapy provides greater conformity to the target and a reduced entrance dose. It significantly reduces side effects in comparison to photons.
Recent in-vivo studies demonstrate that electrons delivered at high dose rates within 0.5 s (FLASH) to cancerous tissues provide the same level of tumour control as with conventional therapy, whilst sparing normal tissues to a much greater extent. Currently, electron linacs and proton passive scattering are used to deliver FLASH-like doses. In a study presented by Dr Kolano at PTCOG 2019, we investigated the possibility of using proton pencil beam scanning (PBS) for uniform FLASH irradiations using a pulsed proton linac and considered the beam parameters needed to achieve FLASH dose rates. The study indicates that with appropriate pulse scheme, spot weight and spacing, LIGHT is designed to deliver doses in the FLASH regime in excess of 40 Gy in less than 0.5 s.
The medical benefits of using a linear proton accelerator make the LIGHT system uniquely adapted to treatments with high dose rates. You can read more about how LIGHT could be used for hypofractionation and for FLASH Therapy in this section of our website.