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Purpose: By calibrating brachytherapy (BT) sources to the TG‐43U1 reference position at 1cm in water, named the nominal absorbed dose‐rate to water, Ḋw,1, accuracy and precision for patient treatment will be increased. Traceability must be provided to Ḋw,1 ‐primary‐standards; which soon become available. Methods and Materials: Efforts have been made in discussions with fellow scientists from many countries, by reviewing concerned literature, and similarities are drawn from documents (e.g. extending TG‐43U1). Results: From the study of primary photon interaction mechanisms, a need was recognized to classify BT‐photon radiation qualities as: high‐energy >100keV, medium energy 40keV to 100keV, and low energy <40keV. It was further recognized that Monte Carlo simulation based primary and scatter dose separation provides characterization for radionuclide BT‐sources and electronic X‐ray BT‐sources, for BT‐detectors and BT‐phantoms. A need was felt for developing reference data‐sets and calibration data of BT‐sources, ‐detectors and ‐phantoms, through which the end‐user medical‐physicist could critically evaluate the data supplied by the manufacturer by using established methods, prior to clinical application. Plastic scintillators appeared to be a choice of detector as future high precision transfer‐standard and high resolution, fast, direct reading dosemeter for detailed quality assurance of BT‐sources, ‐software, ‐planning, and ‐verification. Conclusion: There is the need for international standardization of clinical dosimetry in photon radiation brachytherapy similar to that described in ISO‐21439 (2009) for beta radiation BT‐sources. Based on AAPM TG‐43U1, this planned ISO‐standard will provide guidance for clinical BT‐dosimetry in terms of absorbed dose to water and for estimating the uncertainty of this quantity. Most standardized procedures can be given by referring to AAPM‐ and ESTRO‐reports. Recommendations will be prepared to replace the reference air‐kerma‐rate (air‐kerma strength) by the nominal absorbed dose‐rate to water as basic dosimetric quantity, to increase brachytherapy accuracy and precision and to become consistent with external beam radiotherapy.

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The results of the comparison between SSDL-ININ and SSDL-CPHR (pilot laboratory) demonstrates the competence of the SSDL-ININ for the performance of the KR in 192Ir. The RININ/CHPR ratio for the calibration coefficients is 0.989 ± 0.005. The comparison uses three SI-HDR 1000-Plus as transfer chambers, series: A02423, A941755 and A973052. CPHR used a secondary standard PTW 3304 chamber, s/n 154, calibrated at PTB and ININ employed a secondary standard SI-90008 s/n A963391, calibrated at NPL. To determine KR, the SSDL-CPHR used the IAEA TEC-DOC-1274 and the SSDL-ININ used the IPEM (UK) code of practice. The latter uses a correction factor by source's geometry, ksg. The results show that both codes are equivalent; however, for the use of well chambers in the highlands or in locations with reduced atmospheric pressure, it is needed to apply an additional factor k'P, or, to design a well chamber with air-equivalent walls for the application of the conventional kPT.

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