Assessment of proton versus photon therapy in the reduction of lymphopaenia in thoracic cancers: A scoping review.

Background: Lymphopaenia is characterised by a substantial decrease in lymphocytes, and is experienced by patients receiving radiation therapy for lung and oesophageal cancers. Tumour control and overall survival may be negatively impacted by lymphopaenia. Because of dosimetric benefits which reduce healthy tissue exposure, proton therapy may potentially reduce the prevalence of lymphopaenia, compared to photon therapy.The purpose of this scoping review was to evaluate the difference in lymphopenia experienced by patients treated with photon or proton therapy for lung and oesophageal cancers. It assessed the incidence and severity of radiation-induced lymphopenia for each treatment modality and dose to lymphoid organs. Methodology: A systematic search of PubMed, EMBASE, and Web of Science was conducted. The review included both patients who developed lymphopaenia and those who did not, allowing for comparative analysis. Results: Proton therapy was associated with reduces rates of severe lymphopaenia (Grade ≥ 3), compared with photon therapy. Evidence linking reduced lymphopaenia and overall survival varied, with some studies indicating benefits, while others found no difference. Conclusion: Proton therapy demonstrated an advantage in minimising lymphopaenia compared to photon therapy. There is a need to establish dose volume constraints for lymphoid organs and determine the impact of lymphopaenia on survival.