Feasibility of integrating a multi-camera optical tracking system in intra-operative electron radiation therapy scenarios.

Intra-operative electron radiation therapy (IOERT) combines surgery and ionizing radiation applied directly to an exposed unresected tumour mass or to a post-resection tumour bed. The radiation is collimated and conducted by a specific applicator docked to the linear accelerator. The dose distribution in tissues to be irradiated and in organs at risk can be planned through a pre-operative computed tomography (CT) study. However, surgical retraction of structures and resection of a tumour affecting normal tissues significantly modify the patient's geometry. Therefore, the treatment parameters (applicator dimension, pose (position and orientation), bevel angle, and beam energy) may require the original IOERT treatment plan to be modified depending on the actual surgical scenario. We propose the use of a multi-camera optical tracking system to reliably record the actual pose of the IOERT applicator in relation to the patient's anatomy in an environment prone to occlusion problems. This information can be integrated in the radio-surgical treatment planning system in order to generate a real-time accurate description of the IOERT scenario. We assessed the accuracy of the applicator pose by performing a phantom-based study that resembled three real clinical IOERT scenarios. The error obtained (2 mm) was below the acceptance threshold for external radiotherapy practice, thus encouraging future implementation of this approach in real clinical IOERT scenarios.