Air kerma and absorbed dose standards for reference dosimetry in brachytherapy

Abstract

This article reviews recent developments in primary standards for the calibration of brachytherapy sources, with an emphasis on the currently most common photon-emitting radionuclides. The introduction discusses the need for reference dosimetry in brachytherapy in general. The following section focuses on the three main quantities, i.e. reference air kerma rate, air kerma strength and absorbed dose rate to water, which are currently used for the specification of brachytherapy photon sources and which can be realized with primary standards from first principles. An overview of different air kerma and absorbed dose standards, which have been independently developed by various national metrology institutes over the past two decades, is given in the next two sections. Other dosimetry techniques for brachytherapy will also be discussed. The review closes with an outlook on a possible transition from air kerma to absorbed dose to water-based calibrations for brachytherapy sources in the future.

A radiation quality correction factor kQ for well‐type ionization chambers for the measurement of the reference air kerma rate of 60Co HDR brachytherapy sources

“…14,[29][30][31] The numerical values of the RAKR and of the equivalent but dimensionally different quantity air kerma strength 19 S K are identical. 20,21 PTB has been offering calibrations of HDR brachytherapy sources in terms of RAKR for several years. 32 A photograph of the calibration facility at PTB is shown in Fig.…”

“…13,[18][19][20] Using a well-type chamber there is no need for accurate source-todetector distance measurement and owing to its large detection volume, the ionization current is high and thus easy to measure with high precision. For 192 Ir HDR brachytherapy sources the traceability to a national standard is provided by several national metrology institutes (NMIs), [20][21][22][23][24][25] whereas in the case of 60 Co only the German NMI-the Physikalisch-Technische Bundesanstalt (PTB)-offers a calibration service. 26 In this work, an investigation was performed to find out whether a chamber type-specific radiation quality correction factor k Q can be determined in order to enable the measurement of the reference air kerma rate (RAKR) of a 60 Co HDR brachytherapy source with acceptable uncertainty by means of a well-type ionization chamber calibrated for 192 Ir HDR sources.…”

Guidelines by the AAPM and GEC‐ESTRO on the use of innovative brachytherapy devices and applications: Report of Task Group 167

“…4 With the increased accessibility to PSDLs and SSDLs, this practice is diminishing. Calibration standards for HDR 192 Ir using similar techniques have been developed at a number of European PSDLs such as LNHB, NPL, and PTB, and at the National Research Council of Canada, 47 but not yet at NIST in the U.S. Intercomparisons of these standards have shown good agreement. [48][49][50][51][52] The preferred method for traceability in clinical source calibrations is to have the well-type chamber calibrated against the traceable standard (e.g., at an ADCL).…”

Electronic brachytherapy—current status and future directions

“…[3][4][5][6][7][8] The past decade has seen the development of a new form of treatment, termed electronic brachytherapy (EB), 9 and there are now .400 systems worldwide. These miniature X-ray sources, operating at low kilovoltage energies, have many of the advantages of established radiotherapy approaches, but with further benefits of their own ( Table 1).…”

“…The overall aim remains to have a total uncertainty in delivered dose of ,10% (k 5 2), although this may be difficult to achieve. 5 …”