Proton Cancer Therapy: Synchrotron-Based Clinical Experiences 2020 Update

Proton therapy is an efficient high-precision radiotherapy technique. The number of installed proton units and the available medical evidence has grown exponentially over the last 10 years. As a technology driven cancer treatment modality, specific sub-analysis based on proton beam characteristics and proton beam generators is feasible and of academic interest. International synchrotron technology-based institutions have been particularly active in evidence generating actions including the design of prospective trials, data registration projects and retrospective analysis of early clinical results. Reported evidence after 2010 of proton therapy from synchrotron based clinical results are reviewed. Physics, molecular, cellular, animal investigation and other non-clinical topics were excluded from the present analysis. The actual literature search (up to January 2020) found 192 publications, including description of results in over 29.000 patients (10 cancer sites and histological subtypes), together with some editorials, reviews or expert updated recommendations. Institutions with synchrotron-based proton therapy technology have shown consistent and reproducible results along the past decade. Bibliometrics of reported clinical experiences from 2008 to early 2020 includes 58% of publications in first quartile (1q) scientific journals classification and 13% in 2q (7% 3q, 5% 4q and 17% not specified). The distribution of reports by cancer sites and histological subtypes shown as dominant areas of clinical research and publication: lung cancer (23%), pediatric (18%), head and neck (17%), central nervous system (7%), gastrointestinal (9%), prostate (8%) and a miscellanea of neplasms including hepatocarcinoma, sarcomas and breast cancer. Over 50% of lung, pediatric, head and neck and gastrointestinal publications were 1q.