Comparison of the standards for absorbed dose to water of the NRC and the BIPM for accelerator photon beams

Abstract

A comparison of the dosimetry for high-energy accelerator photon beams was carried out between the National Research Council of Canada (NRC) and the Bureau International des Poids et Mesures (BIPM) in June 2009. The comparison was based on the determination of absorbed dose to water for three radiation qualities. The comparison result, reported as a ratio of the NRC and the BIPM evaluations, is 0.997 at 6 MV, 1.001 at 10 MV and 0.994 at 25 MV, each with a relative standard uncertainty of 6 × 10−3. This result is the first of the ongoing BIPM.RI(I)-K6 comparison.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCRI Section I, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Electron beam water calorimetry measurements to obtain beam quality conversion factors

“…Measurements with the externally mounted NE2571 chamber are performed before calorimetry measurements begin for the day, between sets of calorimetry runs and at the end of a day of measurements and before/after in‐water ionization chamber measurements. This approach was prototyped during water calorimeter measurements in linac photon beams and is current practice in the protocol of the BIPM key comparison BIPM.RI(I)‐K6 “Measurement of absorbed dose to water for high‐energy photon beams” …”

“…This approach was prototyped during water calorimeter measurements in linac photon beams and is current practice in the protocol of the BIPM key comparison BIPM.RI(I)-K6 "Measurement of absorbed dose to water for high-energy photon beams". 25…”

Direct measurement of electron beam quality conversion factors using water calorimetry

“…In radiotherapy, clinical reference dosimetry of high-energy photon and electron beams is based on absorbed dose to water standards. Generally based on calibrating ionization chambers in a standard 60 Co field, protocols such as AAPM TG-51 and IAEA TRS-398 detail recommended practices in regard to reference dosimetry. [1][2][3] For more than forty years, the development and maintenance of absorbed dose standards based on 60 Co teletherapy sources has been carried out by the primary standards dosimetry laboratories (PSDLs) of the world.…”

“…Generally based on calibrating ionization chambers in a standard 60 Co field, protocols such as AAPM TG-51 and IAEA TRS-398 detail recommended practices in regard to reference dosimetry. [1][2][3] For more than forty years, the development and maintenance of absorbed dose standards based on 60 Co teletherapy sources has been carried out by the primary standards dosimetry laboratories (PSDLs) of the world. 4 The three major classes of techniques used at PSDLs to determine absorbed dose to water are the following: (1) ionization chamber-based absorbed dose standards, (2) total absorption (i.e., Fricke)-based absorbed dose standards, and (3) calorimeter-based absorbed dose standards.…”

“…In 2007, Ross et al described a direct comparison of this vessel to alternate NRC designs and the associated correction factors in a 6 MV photon beam. 17 Traditionally, water calorimetry has been implemented as a standard of absorbed dose to water for 60 Co, [18][19][20][21][22] although its use has been extended to include absorbed dose standards for higher-energy photon beams, 10,[21][22][23][24]31 as well as the dosimetry of medium-energy x-rays, [25][26][27][28][29] protons, 21,[30][31][32][33][34] heavy-ions, 21 and high dose rate (HDR) brachytherapy sources. [35][36][37] There has also been extensive work done with using water calorimetry to measure the absorbed dose beam quality conversion factors, k Q , for ionization chambers in high-energy photon beams.…”