Kubben 2014.

Study characteristics
Methods	Randomised controlled trial. Randomisation: Participants were randomised and allocated to either conventional neurosurgery or iMRI. Randomisation was performed by the first author using specific software for randomisation in clinical trials. No randomisation blocks were used. Sample size: "To reduce the chance for type I errors (false positive) we used an alpha value of 0.05. To reduce the chance for type II errors (false negative) we used a beta value of 0.2 leading to a power of 0.8. We considered a 10% additional resection of the preoperative tumor volume as the minimal clinically relevant difference, with an estimated standard deviation of approximately 12%. This led to 23 patients in each treatment group. To compensate for loss to follow‐up we intended to include a total of 54 patients for the complete study." Blinding: "The neurosurgeon could not be blinded for the procedure. We did not intend to blind the physicians on the ward, nor the patients. Volumetric assessment of pre‐ and postoperative tumor volume was performed by a single blinded researcher."
Participants	Inclusion criteria: Supratentorial brain tumour suspected to be glioblastoma on contrast‐enhanced diagnostic MRI, indication for gross total resection of the tumour, age 18 years or older, WHO Performance Scale 2 or better, ASA class 3 or better, adequate knowledge of the Dutch or French language, and informed consent. Exclusion criteria: Recurrent brain tumour, multiple brain tumour localisations, earlier skull radiotherapy, earlier chemotherapy for glioblastoma, chronic kidney disease or other renal function disorder, and a known magnetic resonance‐contrast allergy.
Interventions	Intervention: Low field intraoperative MRI (Medtronic PoleStar N20 0.15 Tesla moveable magnet and the StarShield tent). Control: Neuronavigation guided tumour resection.
Outcomes	Residual tumour volume; complications; quality of life (EORTC QLQ‐C30); overall survival
Notes	Sponsored by Medtronic: "This study is part of the PhD thesis of the first author, and has been financially supported by Medtronic Navigation. Medtronic Navigation was not involved in writing the protocol, had no access to the data, was not involved in writing the manuscript, and had no veto right for submission." Definitions: Residual tumour volume (RTV) percentage is used as the primary endpoint to assess extent of tumour resection. Pre‐ and postoperative tumour volume was calculated by segmenting the hyperintense area on contrast‐enhanced T1 MRI (including enclosed central necrosis) and subtracting the hyperintense area on native T1 MRI to compensate for blood in the resection cavity. Measurements were performed using OsiriX software (Pixmeo SARL, Bernex, Switzerland) on Mac OS X using a Wacom Bamboo pen mouse for contour drawing. Postoperative tumour volume was divided by preoperative tumour volume to calculate the fraction of RTV. Multiplying the fraction with 100% provided the RTV. In formula: RTV = (postoperative contrast enhancement/preoperative contrast enhancement) × 100%
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomisation was performed by the first author using TEN‐ALEA software for randomisation in clinical trials.
Allocation concealment (selection bias)	Unclear risk	Not stated
Blinding of participants and personnel (performance bias) All outcomes	High risk	"The neurosurgeon could not be blinded for the procedure. We did not intend to blind the physicians on the ward, nor the patients. Volumetric assessment of pre‐ and postoperative tumor volume was performed by a single blinded researcher."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	"The neurosurgeon could not be blinded for the procedure. We did not intend to blind the physicians on the ward, nor the patients. Volumetric assessment of pre‐ and postoperative tumor volume was performed by a single blinded researcher."
Incomplete outcome data (attrition bias) All outcomes	Low risk	All participants are accounted for and included in the analysis.
Selective reporting (reporting bias)	High risk	Quality of life data not reported: "After consultation of a health‐technology assessment expert we decided to refrain from any further statistical analyses due to the small sample size."
Other bias	High risk	1. Interim analysis/abbreviated study. Stopped on the basis of the interim analysis, although this was not specified a priori. Reasons for stopping included slow recruitment, technical issues with the equipment, prolonged duration of surgery, and concerns over effect size ("the main reason was that we estimated that our minimally required difference of 10% would not be consistent with the actual results"). 2. Industry sponsorship: "This study is part of the PhD thesis of the first author, and has been financially supported by Medtronic Navigation. Medtronic Navigation was not involved in writing the protocol, had no access to the data, was not involved in writing the manuscript, and had no veto right for submission."