OncoGap is a bilingual, web-based clinical decision-support tool that helps radiation oncologists compensate for interruptions in a patient's radiotherapy course — whether caused by machine downtime, illness, or holidays — by recalculating the remaining treatment plan using biologically effective dose (BED) and EQD2 modeling grounded in the linear-quadratic radiobiology model. Clinicians can choose between adding extra treatment fractions, escalating the dose per fraction, or switching to twice-daily (BID) dosing, while the tool automatically accounts for tumor repopulation and incomplete tissue repair and checks that nearby organs-at-risk stay within safe dose limits. The application is accessible without login for quick, guest calculations and printable reports, while registered users can save cases to patient records for future reference, with every saved result preserved as an immutable snapshot so historical reports remain accurate even as presets or the calculation engine evolve. Administrators can manage treatment-site and organ-tolerance presets, reference lookups, and user accounts, and the entire interface — including calendars, number formatting, and clinical terminology — is fully localized for both English and Persian-speaking users.