Proton Beam Project
Proton therapy is the use of beams of protons to deliver radiation to tumours. A type of particle therapy, this cancer treatment uses protons from a hydrogen atom, accelerating them to 70% of the speed of light, and targeting them at tumours. The beam is targeted by a specialised nozzle, which can be rotated into position anywhere on the patient's body, thanks to a gantry with a 360-degree rotation. Hitachi has further improved accuracy thanks to techniques called spot scanning and image gating.
Spot-scanning proton beams aren't cancer treatments of the future – they're used clinically now, and have been for a decade. Spot-scanning technology arrived in 2008 – Hitachi was the first health-care company to obtain approval from the FDA in the US, while its image-gating system received clearance last year. Although the technology is cutting edge, it can be delivered to clinics in a plug-and-play setup, making it easy for hospitals to install it quickly.
In proton-beam therapy, the beam is controlled by a gantry that can move around the patient in all directions, helping to focus on the tumour from the best angle. The thin beam emitted was previously a generic shape, but cut-out templates, spot scanning and image gating have further improved accuracy.
Once targeted, the beam is fired for a short time at the tumour. When proton beam reaches the tumour, it releases the protons' energy for radiation treatment, which kills the diseased cells. The more accurately the beam is targeted, the less damage there is to surrounding healthy tissue. The beam then stops, so there's no exit dose, helping to avoid further damage to healthy tissue. That means there's fewer side effects compared to traditional radiotherapy.
Proton therapy focuses the radiation, so less damage is done to healthy tissue than with other treatments. But there's always room for improvement, and researchers have found ways to limit the impact of the beam on healthy tissue. Early versions of proton therapy used a broad beam nozzle with collimator which cutouts the beam to the shape of the tumour.
New technology called spot scanning which Hitachi developed first in industry in 2008 aims for further minimizing of side effects. That's done first by thinning the beam – for this reason, spot scanning is also known as pencil-beam scanning, as its spot size is just a few millimeters wide. Second, the beam is turned on and off more quickly, delivering the dose point by point, layer by layer, and beam accuracy is controlled by computers programmed with a treatment plan. With this narrower beam, there's less radiation spilling out on to healthy surrounding tissue, and with smaller doses, it's easier to layer the treatment into the tumour more precisely.
Spot scanning improved the accuracy of proton beam treatments, but there was another challenge: keeping that pencil-thin beam focused in the right spot if the patient moves – even tiny movements such as inhaling and exhaling can impact treatment accuracy, meaning the beam misses its target, and risks damaging healthy tissue. Hitachi and Hokkaido University worked together for a solution, developing a target-tracking system called Real-Time Image Gating Motion Management. This gives physicians a way to match the beam to the spot – even if it moves.
The tumour's location is pinpointed using a 1mm gold marker, which the proton-beam system can track using fluoroscopy, which is an X-ray image that's continuously updated. When the marker moves into the correct position, the beam fires, delivering the dose of radiation to the correct spot, regardless of how much motion there is in the patient's body. This helps to treat tumours that are attached to critical organs, without dangerous side effects.
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