Park 2006.

Study characteristics
Methods	Study design: an observational study, participants with primary (N = 16), and recurrent (N = 11) chordoma were treated by proton/photon radiation therapy, either alone (6 participants), or combined with surgery (21 participants) For participants who could not return to be seen, data were collected from reports from the physicians and nurses, and by questionnaires or telephone interviews of the participants or their families Study date: November 1982 to November 2002 Duration of participation (follow‐up): mean follow up (SD): 91.11(62.23) months
Participants	Total number: 27 ( 22 protons and 5 photons) Age: median age was 56 years (range 35 to 81 years) in 14 primary, and 55 years (range 52 to 60 years) in 7 participants with recurrent chordoma Gender: 10 females/17 males, female/male ratio 0.588 Tumour location: primary and recurrent sacral chordoma Type of surgery and extent of resection were unclear
Interventions	Proton therapy: 18 participants were treated by surgery combined with protons, photons, or both; 4 participants received only proton combined with photon 73.0 Gy to 77.4 Gy Proton therapy dose: dose was 73.0 Gy to 77.4 Gy in proton combined with photon; mean doses were 71 Gy (E) in 36 fractions for primary, and 77 Gy (E) in 41 fractions for recurrent chordomas Photon therapy: 2 participants received photons only (60 Gy and 62 Gy) Mean duration of treatment was 80 days (range 30 to 172 days) for primary, and 73 days (range 38 to 112 days) for recurrent chordomas
Outcomes	Local control (LC) rate was 71.7%, continuous disease‐free survival rate was 60.5%, and overall survival (OS) rate was 82.5% at 5 years; local control rate was 57.5%, continuous disease‐free survival rate was 48.6%, and overall survival rate was 62.5% at 10 years We re‐analysed data from study tables 1, 2, and 3 to assess LC, OS, and recurrence per group OS: estimated OS log HR, SE (log HR): ‐0.698, 0.736 Local control: estimated log HR, SE (log HR): 1.676, 1.069 Recurrence: estimated log HR, SE (log HR): ‐0.215, 0.725
Notes	Study author e‐mail: lilypark@hotmail.com
Risk of bias
Bias	Authors' judgement	Support for judgement
Bias due to confounding	High risk	Study authors mentioned potential confounders (location, dose and extent of resection) but did not use appropriate analysis method that adjusted for them in context of association between type of intervention and outcomes.
Bias in selection of participants into the study	High risk	Selection of participants for both arms based on participant characteristics observed after surgery.
Bias in classification of interventions	High risk	No information used to define intervention groups was recorded at the start of the intervention.
Bias due to deviations from intended interventions	Unclear risk	Not specified
Bias due to missing data	Low risk	Complete outcomes reported for both arms.
Bias in measurement of outcomes	Low risk	Most outcome measures were objective; would not be influenced by knowledge of the intervention received.
Bias in selection of the reported result	Low risk	Complete outcomes reported for both arms.