Prospectively Registered Protocol Amendment (Version 4.0) for an Updated Scoping Review of Radiotherapy and Multimodality Management Across the Hypopharyngeal–Cervical Esophageal Junction

This registration prospectively governs the update phase (protocol v4.0) of a scoping review on hypopharyngeal–cervical esophageal junction (HPCEJ) squamous cell carcinoma and related contiguous extension lesions. The original review (protocol v3.0) included 47 independent studies (~2,796 patients) and identified severe gaps in reproducible radiotherapy target-volume reporting despite high radiotherapy use. Version 4.0 expands eligibility via tiered evidence directness (Tier 1: direct junction/contiguous-extension evidence; Tier 2: adjacent cervical esophageal radiotherapy decision evidence), introduces Search A/B/C architecture, cohort-family overlap adjudication, and elevates clinical radiotherapy outcomes in synthesis. The original review was not prospectively registered; this amendment governs the update phase only and should not be interpreted as preregistration of the original review. At registration (frozen 2026-07-31), eligibility rules, search strategies, extraction forms, overlap adjudication procedures, and synthesis framework are finalized. Limited pre-registration operational checks (PubMed strategy trials, pilot extraction/overlap testing) were completed for instrument validation only. Formal updated database searching, deduplication, screening, data charting, and evidence synthesis have not begun and will commence only after registration submission. Expected outcomes: a PRISMA-ScR evidence map stratified by evidence tier and clinical domain; tier-separated denominators; identification of reporting gaps in radiotherapy target delineation, nodal management, failure patterns, and functional outcomes; and a standardization framework for future primary studies.