Cherenkov imaging for visualizing radiotherapy: one year of clinical use PlatoBlockchain Data Intelligence. Vertical Search. Ai.

Cherenkov imaging for visualizing radiotherapy: one year of clinical use

Clinical implementation: The Cherenkov imaging system, showing a Cherenkov camera mounted to the right of the treatment couch (left panel) and the Cherenkov image display at the treatment console (right panel). (Courtesy: E Chen et al tipsRO 10.1016/j.tipsro.2022.08.011)

As radiotherapy techniques become increasingly complex, and the use of hypofractionation continues to grow, the accuracy of radiation delivery is more important than ever. Delivering high-quality treatments relies on the ability to monitor and adapt to any changes in patient position during irradiation. One emerging technique offering this ability is Cherenkov imaging, which enables real-time, on-patient treatment verification, without additional radiation exposure.

Cherenkov light is produced when a charged particle travels at a velocity exceeding that of light through a specific medium. During radiotherapy, Cherenkov light is emitted when photon or electron beams travel through tissue. This light reveals the shape and extent of the treatment field on the patient surface, with an intensity that’s proportional to the delivered dose.

Early clinical trials by researchers at Dartmouth Health and Dartmouth Engineering indicated that Cherenkov imaging during radiotherapy can identify patient misalignments and detect stray radiation, improving treatment delivery for individual patients. Following on from this initial experience, the team has now implemented the first Cherenkov imaging system for routine clinical use in a community-based hospital.

Reporting their findings in Technical Innovations & Patient Support in Radiation Oncology, the researchers describe their first year of using Cherenkov imaging to image patients undergoing routine radiotherapy.

Clinical experience

The group at Cheshire Medical Center installed the BeamSite Cherenkov imaging system in September 2020, calibrating the system, optimizing room lighting conditions and setup protocols, and performing end-to-end testing before starting clinical use in March 2021.

Over the next 12 months, they used the system to monitor over 1700 cancer treatments, including both free-breathing and deep-inspiration breath-hold (DIBH) radiotherapy and around 50 treatments with electron beams. During each irradiation, the therapists reviewed the patient body position images and Cherenkov images in real time. After treatment, the physicists analysed the recorded images.

During this year, the team detected several anomalies during treatments, modifying the treatment procedures to ensure patient safety and improve delivery accuracy. In some cases, for example, the Cherenkov images detected dose to body parts where it was not expected. The researchers report two example cases where unplanned dose was found in patients receiving a boost treatment to the left breast. In one case, exit dose from a treatment field was observed in the right breast; in the other, dose was delivered to the chin due to a head rotation. In response to such anomalies, the therapists can alter treatment fractions, or even halt treatment delivery

The Cherenkov imaging system also detected set-up inaccuracies or unexpected patient motion. The team describe an example 3D conformal treatment to the spine. Using the Cherenkov image intensity outline from the first fraction as a reference, the therapists observed intrafractional motion and paused the treatment. Elsewhere, a patient receiving DIBH radiotherapy to the left breast exhibited large variability in arm position between each fraction.

The team also describe a more unusual use of this new technology, in a treatment of a tumour located above the heart where electron DIBH was used to reduce heart dose. As linacs cannot currently provide gated electron delivery, the team employed Cherenkov image guidance to manually gate the DIBH delivery, as well as to verify treatment delivery accuracy in real time.

The researchers conclude that Cherenkov imaging proved a valuable clinical tool for improving treatment delivery safety and accuracy. They point out that after just one hour of hands-on operational training, the therapists could operate the system, monitor patients and review the Cherenkov images in real time. This enabled them to pause, adjust or even abort treatment delivery as required.

To fully exploit this technology, the team suggest several software developments. These include the system interfacing with the record and verify system, as well as automatic generation of body position outlines, markers and cumulative Cherenkov image intensity outlines. Combination with surface image setup guidance could also provide a powerful tool for future treatments.

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