QuADProBe: Quality Assurance Detector for Proton Beam Therapy
Lead Research Organisation:
University College London
Department Name: Physics and Astronomy
Abstract
Modern cancer treatment is largely a combination of 3 techniques: surgery, chemotherapy and radiotherapy. Radiotherapy uses beams of X-rays to irradiate the tumour from many different directions. The effect is to kill the cancer by depositing as much radiation dose in the tumour as possible, whilst minimising the dose to the surrounding area to spare healthy tissue.
Proton therapy is a more precise form of radiotherapy that provides significant benefits over conventional X-ray radiotherapy. Protons lose energy - and therefore deposit their dose - in a much smaller region within the body, making the treatment much more precise: this leads to a more effective cancer treatment with a smaller chance of the cancer recurring. This is particularly important in the treatment of deep-lying tumours in the head, neck and central nervous system, particularly for children whose bodies are still developing and are particularly vulnerable to long-term radiation damage. The advantages of proton therapy, coupled to the falling cost of the equipment, has led to a surge in interest in proton therapy treatment worldwide: there are now over 100 centres, with this number currently doubling every 3 years. In the UK, the NHS has funded 2 full-sized proton therapy centres - at University College Hospital in London and The Christie in Manchester - to operate alongside the eye treatment facility at the Clatterbridge Cancer Centre. These will provide treatment for a much wider range of cancers, allowing more patients to be treated closer to home.
Treating these cancers requires machinery that is significantly more complex than a conventional radiotherapy system. Protons are accelerated to the right energy for treatment by a particle accelerator: once the beam leaves the accelerator, it then has to be transported to the treatment rooms many metres away by a series of steering and focussing magnets. When the proton beam reaches the treatment room, it has to be delivered through a gantry to the correct place. Proton therapy gantries are enormous - more than 3 storeys tall and weighing more than a hundred tonnes - and have to rotate around the patient to deliver the beam from any angle with millimetre precision. In order to ensure that treatment with such complex machinery is carried out safely, a range of quality assurance (QA) procedures are carried out each day before treatment starts. This means checking that the proton beam is in the correct position, is the right shape and size, and travels the correct depth: this must be checked for a range of different beam positions and energies to ensure treatment is safe. These QA measurements take significant time to set up and adjust for different energies: the full procedure can take over an hour.
We are developing a detector that can make faster and more accurate measurements of the proton beam size, position and range than existing systems. The detector is made of two parts. The first is a profile monitor made of two arrays of scintillating optical fibres, mounted at right angles to each other, that emit light when the proton beam passes through. This light can be measured with photodiodes to determine the beam size and position. Behind this is a detector built from layers of plastic scintillator that resembles a sliced loaf of broad. Protons passing through this scintillator stack deposit energy in each layer which is converted into light: by recording the light from each layer, the amount of energy the protons deposit along their path can be measured. Such a system provides a direct measurement of the range of protons in tissue, since the absorption of the plastic is virtually identical to human tissue. As such, the full morning beam QA procedure could be carried out in a few minutes, with an accuracy well below a millimetre in size, position and range. At the two new NHS centres, this would translate into being able to treat an extra 12-18 patients every single day.
Proton therapy is a more precise form of radiotherapy that provides significant benefits over conventional X-ray radiotherapy. Protons lose energy - and therefore deposit their dose - in a much smaller region within the body, making the treatment much more precise: this leads to a more effective cancer treatment with a smaller chance of the cancer recurring. This is particularly important in the treatment of deep-lying tumours in the head, neck and central nervous system, particularly for children whose bodies are still developing and are particularly vulnerable to long-term radiation damage. The advantages of proton therapy, coupled to the falling cost of the equipment, has led to a surge in interest in proton therapy treatment worldwide: there are now over 100 centres, with this number currently doubling every 3 years. In the UK, the NHS has funded 2 full-sized proton therapy centres - at University College Hospital in London and The Christie in Manchester - to operate alongside the eye treatment facility at the Clatterbridge Cancer Centre. These will provide treatment for a much wider range of cancers, allowing more patients to be treated closer to home.
Treating these cancers requires machinery that is significantly more complex than a conventional radiotherapy system. Protons are accelerated to the right energy for treatment by a particle accelerator: once the beam leaves the accelerator, it then has to be transported to the treatment rooms many metres away by a series of steering and focussing magnets. When the proton beam reaches the treatment room, it has to be delivered through a gantry to the correct place. Proton therapy gantries are enormous - more than 3 storeys tall and weighing more than a hundred tonnes - and have to rotate around the patient to deliver the beam from any angle with millimetre precision. In order to ensure that treatment with such complex machinery is carried out safely, a range of quality assurance (QA) procedures are carried out each day before treatment starts. This means checking that the proton beam is in the correct position, is the right shape and size, and travels the correct depth: this must be checked for a range of different beam positions and energies to ensure treatment is safe. These QA measurements take significant time to set up and adjust for different energies: the full procedure can take over an hour.
We are developing a detector that can make faster and more accurate measurements of the proton beam size, position and range than existing systems. The detector is made of two parts. The first is a profile monitor made of two arrays of scintillating optical fibres, mounted at right angles to each other, that emit light when the proton beam passes through. This light can be measured with photodiodes to determine the beam size and position. Behind this is a detector built from layers of plastic scintillator that resembles a sliced loaf of broad. Protons passing through this scintillator stack deposit energy in each layer which is converted into light: by recording the light from each layer, the amount of energy the protons deposit along their path can be measured. Such a system provides a direct measurement of the range of protons in tissue, since the absorption of the plastic is virtually identical to human tissue. As such, the full morning beam QA procedure could be carried out in a few minutes, with an accuracy well below a millimetre in size, position and range. At the two new NHS centres, this would translate into being able to treat an extra 12-18 patients every single day.
