# Risk-based quality management of the radiotherapy process (TG-100 failure mode and effects analysis)

Source: https://onco.cc/protocols/radiotherapy-risk-analysis-fmea/  
OnCo record `radiotherapy-risk-analysis-fmea` (Protocol). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Most radiotherapy errors come not from broken machines but from steps in the process: a wrong image, a mistyped number, a missed message. Departments therefore map every step of the treatment pathway, ask what could go wrong at each, score how likely, how harmful and how hard to spot each failure would be, and put their safety checks where the risk is highest.

## Summary

AAPM Task Group 100 (2016) set out the reference method, starting from the observation that many errors are failures of workflow and process rather than of devices and software. A multidisciplinary team maps the process in detail, lists the failure modes at each step, scores occurrence (O), severity (S) and lack of detectability (D), usually from 1 to 10, and ranks them by the risk priority number (RPN = O x S x D). TG-100 looked at the top 20% to 25% by RPN and by severity, leaving each team to set its own threshold; studies commonly treat the top quartile of RPN and any severity of 8 or more as high risk. Fault tree analysis traces how failures propagate, and the quality management programme is then designed around the high-risk failure modes. MPPG 8.b (2023) asks every centre to run its own analysis, with published RPNs used only as a guide.

A 2025 systematic review found 62 prospective hazard analyses in external beam radiotherapy: FMEA in 75%, STPA in 10%; 579 high-risk failure modes, half in treatment delivery sessions and a quarter in contouring and planning; and mitigations that tended to add workload and sit low on the hierarchy of effective interventions. A 2026 Ontario multi-institution exercise by nine physicists found the automotive-industry 'action priority' table, which weights severity and occurrence over detectability, picked out the same critical failures with less scoring disagreement. Incident learning, checklists, training and staffing are the commonest other safety recommendations across seven international documents.

## Fields

- Kind: Protocol
- Last checked: 2026-11-11
- Also known as: FMEA radiotherapy; failure mode and effects analysis; TG-100; prospective hazard analysis; risk priority number; RPN; fault tree analysis; process map radiotherapy; risk-based QA; STPA

## Connected records

- protocols: [Linear accelerator quality assurance: daily, weekly, monthly and annual machine checks](https://onco.cc/protocols/linear-accelerator-quality-assurance/), [Patient identification and pre-treatment time-out in radiotherapy](https://onco.cc/protocols/radiotherapy-patient-identification-and-time-out/)
- technologies: [C-arm medical linear accelerators (TrueBeam, Versa HD and others)](https://onco.cc/technologies/c-arm-linac/), [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/)

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