Appendix 1. CENTRAL search strategy

#1 MeSH descriptor: [Head and Neck Neoplasms] explode all trees
#2 MeSH descriptor: [Otorhinolaryngologic Neoplasms] explode all trees
#3 MeSH descriptor: [Neoplasms] explode all trees
#4 (cancer* or carcinoma* or neoplasm* or tumor* or tumour* or metastas* or SCC*):ti,ab,kw
#5 #3 or #4
#6 (head next neck):ti,ab,kw
#7 (face or facial or thyroid or salivary or paranasal or "aero digestive" or aerodigestive or aero‐digestive or UADT or "middle ear cleft" or "nasal cavit*" or larynx or laryngeal or glottis or glottic or "oral cavity" or nasopharynx or nasopharyngeal or hypopharynx or hypopharyngeal or pharynx or pharyngeal or parapharyngeal or mouth or nose or tongue or tonsil* or velopharynx or velopharyngeal or oral or oropharyngeal or oropharynx or supraglott*):ti,ab,kw
#8 MeSH descriptor: [Larynx] explode all trees
#9 MeSH descriptor: [Pharynx] explode all trees
#10 MeSH descriptor: [Mouth] explode all trees
#11 MeSH descriptor: [Nose] explode all trees
#12 #6 or #7 or #8 or #9 or #10 or #11
#13 #5 and #12
#14 ("HNSCC" or "SCCHN" or "LACHN" or opscc or npscc or lpscc or npc):ti,ab,kw
#15 #1 or #2 or #13 or #14
#16 MeSH descriptor: [Radiotherapy] explode all trees
#17 (chemoradiotherap* or chemo‐radiotherap* or "chemo radiotherap*" or Radiochemotherap* or CCRT or CRT or "CT/RT" or chemoradiat* or radiotherap* or radio‐therap* or radiation or 3drt or 3dcrt or 3dcrt or 3‐D or irradiat* or conformal or ((three or 3) next (D or dimensional))):ti,ab,kw
#18 #16 or #17
#19 #15 and #18
#20 MeSH descriptor: [Head and Neck Neoplasms] explode all trees and with qualifier(s): [Radiotherapy ‐ RT]
#21 #19 or #20
#22 (IMRT or ARC or VMAT or ART or PBT or IMPT):ti,ab,kw
#23 ((intensity or volumetric) next modulat*):ti,ab,kw
#24 (proton near (beam or therap*)):ti,ab,kw
#25 (rapidarc or tomotherap* or replan*):ti,ab,kw
#26 (high near precision):ti,ab,kw
#27 ((novel or modern or adaptive) near (plan or planning or plans or radiotherap* or radio‐therap* or radiation or irradiat*)):ti,ab,kw
#28 #22 or #23 or #24 or #25 or #26 or #27
#29 #21 and #28
#30 MeSH descriptor: [Radiotherapy, Intensity‐Modulated] explode all trees
#31 MeSH descriptor: [Proton Therapy] explode all trees
#32 (#30 or #31) and #15
#33 #29 or #32

Appendix 2. Data extraction and management: key characteristics

We will extract the following key characteristics of each study:

Source

• Study ID (created by review author)

• Report ID (created by review author)

• Review author ID (created by review author)

• Citation and contact details

Eligibility

• Confirm eligibility for review

• Reason for exclusion

Methods

• Study design

• Total study duration

• Sequence generation

• Allocation sequence concealment

• Blinding

• Other concerns about bias

Participants

• Total number

• Setting

• Diagnostic criteria

• Age

• Sex

• Tumour stage (TNM)

• Country

• Co‐morbidity (cardiac, pulmonary, other cancers)

• Associated risk factors (nicotine, ethyl, HPV, EBV)

• Socio‐demographics

• Ethnicity

• Date of study

Interventions

• Total number of intervention groups

• Total dose (Gy) delivered per intervention groups

• Surgery

• Systemic therapy

• Overall treatment time

Outcomes

• Outcomes and time points (i) collected; (ii) reported

For each outcome of interest:

• Outcome definition (with diagnostic criteria if relevant)

• Unit of measurement (if relevant)

• For scales: upper and lower limits, and whether a high or low score is good

Results

• Number of participants allocated to each intervention group

For each outcome of interest:

• Sample size

• Missing participants

• Summary data for each intervention group (e.g. frequencies and percentages for categorical data; means and standard deviations (SDs) for continuous data)

• Estimate of effect with confidence interval; P value

• Subgroup analyses

Miscellaneous

• Funding source

• Key conclusions of the study authors

• Miscellaneous comments from the study authors

• References to other relevant studies

• Correspondence required

• Miscellaneous comments by the review authors