Electron radiation therapy: Back to the future?

Electron radiotherapy has long been preferred to photons for the treatment of superficial lesions because of its physical characteristics (high dose at the surface, rapid decrease in depth). Other characteristics (penumbra, heterogeneity on an oblique or irregular surface) make them difficult to use. In most indications (skin cancers, head and neck, medulloblastoma), with technical progress, in some cases they have been replaced by intensity-modulated conformal radiotherapy, brachytherapy and contact therapy. Other indications (drainage of mesotheliomas or irradiation of benign lesions) have disappeared. The low frequency of use leads to problems of safety and cost-effectiveness. However, modern photon radiotherapy techniques are still less effective than electrons in specific indications such as total skin irradiation (mycosis fungoides) or certain thin chest wall irradiations after total mastectomy, reirradiation or paediatric treatments without protons. Flash therapy, initiated by electrons, has been developed over the last 10 years, providing high-dose irradiation in an extremely short time. Initial results show good efficacy, with fewer side effects than with conventional radiotherapy. These results are leading to clinical technological developments on a larger scale. Although it has been replaced in most indications by more modern techniques, electron radiotherapy remains essential for targeted indications in specialised centres. The emergence of flash therapy will lead to new indications, on machines equipped with this new technology, which have yet to be defined and are currently the responsibility of specialised teams.