Methods and evidence in economic evaluations of modern radiotherapy: a systematic mapping review protocol.

introductionModern radiotherapy modalities have increased treatment precision and clinical effectiveness. However, the economic evidence that underpins their adoption is highly heterogeneous, with substantial variation in costing methods, data sources, analytic designs (trial-based, real-world/observational and decision-analytic modelling), perspectives and the treatment of uncertainty. We propose a systematic mapping review to characterise the peer-reviewed evidence base and identify methodological gaps relevant to health technology assessment and policy-making. This systematic mapping review aims to: (1) systematically catalogue the published, peer-reviewed evidence and the methodological approaches used in economic evaluations of modern radiotherapy; (2) identify methodological trends, including the uptake and implementation of value of information analysis and (3) highlight evidence gaps by tumour type, geographical region and methodological approach. METHODS AND ANALYSIS: Following the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guidelines, we searched PubMed (MEDLINE), Embase, Scopus, Web of Science Core Collection and EconLit for economic evaluations of radiotherapy published from 2005 onwards, with an initial search on 24 February 2026 and a planned search update before synthesis. Study selection is ongoing; extraction and quality appraisal in duplicate have not been undertaken and no results are reported. Reporting completeness, methodological limitations and uncertainty will be appraised as three separate dimensions using the Consolidated Health Economic Evaluation Reporting Standards (CHEERS) 2022 checklist, the Bias in Economic Evaluation (ECOBIAS) checklist and the TRansparent Uncertainty ASsessmenT (TRUST) framework, applied descriptively and not combined into a single quality score. Methodological information will be extracted, including model structure (eg, Markov model), analytical perspective (eg, healthcare payer), time horizon, costing approach (eg, diagnosis-related group (DRG)-based) and utility measurement (eg, EQ-5D). The methods used to assess uncertainty will be mapped for all studies, with the ECOBIAS checklist and the TRUST framework only applied to decision-analytic model-based evaluations. Findings will be synthesised descriptively as an evidence gap map and visualised as heat maps and bubble plots. A conceptual co-occurrence network, analysed in R with visualisation in VOSviewer, will map how modalities, tumour sites and economic characteristics cluster across studies. No meta-analysis is planned, given the expected heterogeneity of our findings. ETHICS AND DISSEMINATION: This review does not require ethical approval, as it will use data from previously published studies. The results will be disseminated through peer-reviewed publications, conference presentations and open-access releases of data extraction files and visual maps in the Open Science Framework (OSF). REGISTRATION: This review protocol was prospectively registered (9 February 2026) in the OSF Registries (DOI: 10.17605/OSF.IO/6W2TJ).