By carefully selecting the energy of a pencil beam of proton particles, most of its energy can be released at the desired depth within the tissues of a patient suffering from cancer, specifically at the depth of their target tumour volume (see how it works). Accurate positioning of the patient before the delivery of each treatment fraction is consequently crucial to ensuring the sterilization of cancer cells while minimizing toxicity to surrounding healthy organs. This preparation may require adapting the treatment plan to account for any changes in the patient’s anatomy.

As early as 2014, Ion Beam Applications SA (IBA) was first to integrate its proton therapy systems with the Cone-beam Computed Tomography (CBCT) technology, an X-ray on-board system used to acquire volumetric scans of the patient’s anatomy (see how it works at William Beaumont Hospital). Beyond its use for patient positioning, the CBCT emerges as the cornerstone of the online adaptive proton therapy workflow, whose technological completion is pursued by Work Package #3 of the RAPTORplus project. Its image quality is benefiting from a continuous upgrade program at IBA to reach the highest standard of guidance, with both hardware and software improvements, and ultimately support the computation of adapted plans.

The CBCT reconstructs a single 3D image from hundreds of 2D projections acquired at all angles over a period of more than 1 minute. Unfortunately, even the finest algorithms won’t prevent this reconstruction from exhibiting artefacts in the case of any respiratory motion within the captured field of view.