ISO 28057:2019

Overview

ISO 28057:2019 - Clinical dosimetry: Dosimetry with solid thermoluminescence detectors (TLD) specifies procedures, system requirements and quality rules for using solid thermoluminescence detectors in clinical radiotherapy dosimetry. The standard covers the probe method (single TL detectors or TL probes in thin-walled PMMA casings) used in water or tissue‑equivalent phantoms and on/in patients. It applies to solid LiF detectors (LiF:Mg,Ti and LiF:Mg,Cu,P) in rod, chip or microcube form for photon (20 keV–50 MeV) and electron (4 MeV–25 MeV) beams and to photon‑emitting brachytherapy sources. LiF powders and beta‑brachytherapy are excluded.

Key technical topics and requirements

• Measurement procedure and cycle: rules for handling, pre‑irradiation annealing, irradiation, post‑irradiation annealing and reading to ensure consistent TL response.
• Measured quantity and absorbed dose to water: basic formulae, background subtraction, indicated value (M), individual calibration coefficients (N) and required correction factors (k).
• Uncertainty and repeatability: guidance to achieve repeatability within a fraction of a percent and a total measurement uncertainty of a few percent (including traceability to primary standards) for doses > 1 mGy; practical upper minimum measuring ranges are in the order of 10–100 Gy.
• TLD system requirements: technical, hardware and software components; documentation and access to a calibration irradiation device; acceptance testing and stability checks.
• Detector and reader requirements: characteristics and reusability of TL materials, calibration and individual variation management, TL‑indicating instrument performance (mechanical, electrical, thermal and data backup).
• Special factors: treatment of neutron contributions in megavoltage photon beams, batch‑dependent variations, intrinsic effects in TL material response, and energy dependence (noting electron k values are energy independent in clinical ranges).

Practical applications and users

ISO 28057 is designed for practical clinical use and quality assurance:

• Patient in vivo dosimetry and point dose verification
• Phantom and end‑to‑end commissioning for teletherapy and brachytherapy
• Small‑field and stereotactic dose mapping where high spatial resolution is required
• Complementary measurements to ionization chamber dosimetry in radiotherapy QA

Primary users:

• Medical physicists and clinical dosimetrists
• Radiotherapy QA engineers and service providers
• Manufacturers of TLD systems and TL readers
• Regulatory and accreditation bodies setting dosimetry procedures

Related standards and context

• Complements ionization‑chamber based clinical dosimetry practices and national traceability systems.
• Fits within radiological protection and radiotherapy QA frameworks to ensure traceable, repeatable TLD measurements in clinical settings.

Keywords: ISO 28057:2019, thermoluminescence dosimetry, TLD, LiF:Mg,Ti, LiF:Mg,Cu,P, probe method, clinical dosimetry, radiotherapy, brachytherapy, absorbed dose to water, TLD system requirements.