A Review of Proton Radiation Therapy and the Path to Widespread Clinical Adoption

After many years of development, proton therapy is finally reaching the point of mass adoption in clinical practice. Advances in particle accelerator technology and improved dose delivery techniques have provided strong driving forces for expanded use. Pencil beam scanning (PBS) is the generic name for radiation dose delivery to a target volume using individually controlled small pencil beams of accelerated protons. The first proton beam patients were treated with PBS at the PSI facility in Switzerland in 1996, but it took many years for PBS to become available at more facilities. Today, PBS is in routine clinical use in the majority of proton therapy facilities. PBS has truly revolutionized proton therapy, offering increased flexibility in dose shaping and improved dose conformality. Large and non-contiguous targets benefit especially from pencil beam scanning proton therapy, and general utilization has now expanded to almost all sites in the body. The traditional limitations related to range uncertainty have been further reduced with PBS through robust optimization. Treatment plans are now calculated with advanced optimization strategies and dose algorithms, which account for perceived uncertainties. PBS treatment plan deliveries are now robust against changes and uncertainties throughout the entire treatment process. We can now talk about the certainties of PBS proton therapy rather than traditional uncertainties. This certainty provides physicians with vastly improved confidence in the dose delivered to the target. Pencil beam scanning is enabling another paradigm shift, i.e. that we now face the question of which targets will not benefit from proton therapy, rather than the inverse. KeywordsProton, Radiation Therapy, Pencil Beam Scanning, IMRT, Multi Field Optimization.