Study	Reason for exclusion
McDonald 2013	We could not extract numeric data for outcomes per group. Study tables did not give any information that could be stratified per group. There were results for overall survival, overall local control, and toxicities, without subgroup analyses by protons and photons.
Nowakowski 1992	Out of 52 participants with tumours, 24 participants were treated for paraspinal chordoma or chondrosarcoma. Data for treatment with charged particles therapy and photon therapy were unavailable for participants with chordoma or chondrosarcoma,
Van Gompel 2015	The study is mainly an overview of presenting characteristics, imaging, pathology, and overview of different treatment modalities for chordoma, rather than comparing efficacy between protons and photons.
Weber 2005	The study mainly assesses the local control and progression‐free survival of proton therapy. Only two cases of photon therapy and no available data for those two cases.