Absorbed dose to water determination with ionization chamber dosimetry and calorimetry in restricted neutron, photon, proton and heavy-ion radiation fields

Abstract

Absolute dose measurements with a transportable water calorimeter and ionization chambers were performed at a water depth of 20 mm in four different types of radiation fields, for a collimated (60)Co photon beam, for a collimated neutron beam with a fluence-averaged mean energy of 5.25 MeV, for collimated proton beams with mean energies of 36 MeV and 182 MeV at the measuring position, and for a (12)C ion beam in a scanned mode with an energy per atomic mass of 430 MeV u(-1). The ionization chambers actually used were calibrated in units of air kerma in the photon reference field of the PTB and in units of absorbed dose to water for a Farmer-type chamber at GSI. The absorbed dose to water inferred from calorimetry was compared with the dose derived from ionometry by applying the radiation-field-dependent parameters. For neutrons, the quantities of the ICRU Report 45, for protons the quantities of the ICRU Report 59 and for the (12)C ion beam, the recommended values of the International Atomic Energy Agency (IAEA) protocol (TRS 398) were applied. The mean values of the absolute absorbed dose to water obtained with these two independent methods agreed within the standard uncertainty (k = 1) of 1.8% for calorimetry and of 3.0% for ionometry for all types and energies of the radiation beams used in this comparison.

Dosimetric commissioning and quality assurance of scanned ion beams at the Italian National Center for Oncological Hadrontherapy

“…First of all, as reported in Karger et al, 14 many different W -values have been reported in the literature. Two independent studies published by Brede et al 35 and Sakama et al 36 showed an underestimation of approximately 3%-3.5% in the determination of D w for carbon ion beams when ion chambers are used. In the first case, a significant deviation between ionization chamber dosimetry and calorimetry was only found for carbon ions (not in case of protons, neutrons, or photons); in the second case, a W -value in air for carbon ion beams equal to 35.72% ± 1.5% J C −1 was found, which is 3.5% higher than the value suggested by IAEA (34.50 J C −1 ) and used for k Q determination.…”

Clinical commissioning of intensity‐modulated proton therapy systems: Report of AAPM Task Group 185

“…Accredited Dosimetry Calibration Laboratory (ADCL). Optionally, it is possible to further reduce the dose calibration uncertainty by using calorimetry [140][141][142][143][144] .…”

“…Optionally, it is possible to further reduce the dose calibration uncertainty by using calorimetry. [140][141][142][143][144] 9.C. Reference field and point of measurement Critical user choices in the calibration process are the determination of the type and size of the reference field to be used and the selection of the measurement point within the reference field.…”

Direct measurement of electron beam quality conversion factors using water calorimetry

“…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.…”