Session Item

As a result of the rapid development of dynamic radiotherapy over the last decade it is today possible to create advanced treatment plans, sparing organs at risk while providing conform dose coverage of the target volume. However, one major factor limiting the reduction of the treatment volume is margins needed to account for inter- and intra-fractional anatomical variations. The purpose of this project is to describe the first clinical implementation of a commercial solution for CBCT-guided online adaptive radiotherapy (oART), driven by artificial intelligence (AI), enabling elimination of margins otherwise necessary to account for inter-fractional variations.

As the first clinic in the world we have implemented a new commercial solution for AI-driven CBCT-based daily oART. The system applies structure-guided deformation of targets and organs at risk, from original definition on a reference CT to the high quality CBCT, based on initial AI driven auto-segmentation of so-called influencer organs. Automated treatment planning and calculation-based QA then enables the choice of a re-optimized plan on the anatomy of the day. Simulated online adaptive sessions were conducted by extensive use of an emulator, which laid a foundation for commissioning and clinical implementation, enabling the first treatments in the world on this new system. The system was systematically evaluated in terms of speed, plan quality, structure propagation accuracy, and treatment delivery.

Emulator work during commissioning rendered in >600 automatic treatment plans and >100 systematically simulated online adaptive sessions, with the majority of the online sessions resulting in none or only minor editing of automatically generated structures and the choice of plan being the adapted in >90% of the treatment sessions. Limitations in auto-segmentation is currently correlated to cases where the system is not yet trained, e.g. urinary catheter, and where segmentation is also challenging for the human eye, e.g. seminal vesicles. The online adaptive process was for all the five first treated patients completed within 15-20 minutes, with influencer segmentation within 3-5 minutes and target definition within an additional 1-3 minutes. Bladder patients treated had a 40% average reduction in treatment volume, e.g. resulting in up to 30% reduction in V_45Gy and V_30Gy to the bowel bag, compared to the standard non-adaptive treatments.

A novel commercial solution for CBCT-based oART has been demonstrated to deliver accurate and fast adaptation to the anatomy of the day and was clinically implemented for the first time in the world. Initial experience demonstrates online adaptive sessions to be achievable within our standard time slots and furthermore indicate a potential in reducing the treated volume and thus also toxicity related dose parameters. The work to prove the latter by clinical studies is ongoing.