Method to detect the Water Equivalent Path Length (WEPL) in proton CT therapy

Proton therapy has the potential of being a paradigm shifting treatment modality for cancer. This is due to a physical property of heavier charged particles, which can come to a complete stop in a medium depositing the majority of their energy at the end of their track (Bragg peak). For a given energy of the particle and given medium, the range of such a particle is well known to within a few millimetres. This knowledge can be harnessed to produce dose distributions that spare normal tissue better than classical photon–based treatments.

There is an increasing number of proton therapy facilities, but anatomical and setup uncertainties are currently hampering the effectiveness of therapy. Current approaches to address this issue include using transmission and CT imaging to determine errors, prompt gamma detectors and TOF PET, and methods to directly measure residual ranges. However, this can require complex, expensive and large detector setups, which are challenging for clinical use.

Researchers at the University of Oxford have developed an alternative and less complex method of inferring the Water Equivalent Path Length (WEPL) map, by analysing the beam characteristics detected by a generalised 2D detector placed beyond the patient. Measuring WEPL in a patient can provide valuable information about how the treatment is progressing. This does not require reconstruction of each single particle path within the patient. The method involves the use of indirect data and the combination of parameters using machine learning to determine the WEPL of the proton beam inside the patient.

This method could be used to remove unnecessary complex equipment, enable targeting of a proton beam within a patient, and provide information on the accuracy and safety of the delivered treatment.

Oxford University Innovation has filed a patent application on this method and is interested in speaking to companies who would like to licence the technology.

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