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. 2024 Mar 19;16(6):1206. doi: 10.3390/cancers16061206

Table 2.

A brief comparison of the three current online ART technologies.

MRI CBCT PET
Current systems Elekta Unity 1.5 T MRI with a 7MV FFF LINAC
ViewRay MRIdian (legacy system) 6MV FFF 0.35 T MRI		 Varian Ethos 6MV FFF RefleXion X1 6MV FFF
ART workflow Unity: Adapt to position (ATP) and adapt to shape (ATS).
MRIdian: Choice between scheduled vs. adaptive plans.		 Choice between scheduled vs. adaptive plans. Offline ART feasible;
online ART under development.
Strengths

  • Superior soft-tissue contrast;

  • No radiation dose, can therefore provide continuous real-time monitoring during treatment;

  • Functional and metabolic imaging.

  • Faster imaging speed, especially with HyperSightTM;

  • High throughput;

  • Cheaper and more accessible than the other two modalities;

  • Planning directly on CBCT with HyperSightTM.

  • Metabolic and functional imaging;

  • On-board kVCT provides good imaging quality;

  • Real-time tracking;

  • Multi-target delivery.
Limitations

  • Expensive;

  • Longer imaging time and slow throughput;

  • Need electron density for planning (MRIdian: DIR; Unity: bulk electron density);

  • MR safety compatibility;

  • Technical interference with LINAC.

  • Limited soft-tissue contrast;

  • Radiation dose;

  • No functional imaging.

  • Expensive;

  • Longer imaging time;

  • Radiation dose;

  • Requires management of radiotracers;

  • Need to combine with CT for anatomy and planning;

  • Technical interference with LINAC.
Key clinical sites

  • Abdominal;

  • Pelvic.

  • Pelvic;

  • Head and neck;

  • Breast;

  • Lung.

  • Lung;

  • Bone.