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A special meeting, run as a 1-day Workshop, of the Brachytherapy Standards Working Group (BSWG) of the section I “dosimetry” of the Consultative Committee for Ionizing Radiation - CCRI(I), was held at Minamisoma city, Fukushima prefecture, Japan, 15 September 2025 with the support of F-REI and NMIJ. 46 participants, 7 of them connected remotely, discussed the status and future developments in metrology for brachytherapy dosimetry.

This “workshop” started with 3 presentations providing an overview of brachytherapy in clinical practice and was followed by 3 technical reviews of the physical standards in brachytherapy dosimetry (High Dose Rate, Low Dose Rate, Electronic Brachytherapy). 13 NMIs and DIs then presented their current activities to provide a global picture of brachytherapy standards and dissemination. The final session of the workshop was a discussion on the needs for new comparisons, options for maintaining the current BIPM.RI(I)-K8 comparison for HDR Ir-192 air kerma, and how CCRI(I) and BIPM should address future developments and emerging needs.

A clear outcome from the discussions was that the BIPM.RI(I)-K8 based on bi-lateral comparisons between NMIs/DIs and the BIPM should continue in its current form with the strong recommendation of the addition of a second BIPM well chamber to provide improved robustness, and a third one as a preferred option.

The workshop attendees also supported the relaunch of the BSWG(I) with a new term of reference, a new chair appointment and the support from BIPM IR staff. To reflect all the expressed needs during the meeting, the terms of reference should include the expansion of brachytherapy comparisons to LDR I-125, the exploration of the value of adopting a D _w formalism in brachytherapy dosimetry protocols (to be consistent with external beam dosimetry), a survey of electronic brachytherapy, the definition of CCRI recommendations on source model correction factors and the development of international guidelines (CCRI/IAEA) on the values to be entered into HDR brachytherapy treatment units (afterloaders). In regard to this final point, it was clearly stated that measured, rather than manufacturer-provided, values should be used.

This “workshop” was followed by a meeting of the CCRI(I), where these recommendations were discussed and approved.