A water calorimeter for on-site absorbed dose to water calibrations in⁶⁰Co and MV-photon beams including MRI incorporated treatment equipment

Abstract

In reference dosimetry the aim is to establish the absorbed dose to water, D w, under reference conditions. However, existing dosimetry protocols are not always applicable for rapidly emerging new treatment modalities. For primary standard dosimetry laboratories it is generally not feasible to acquire such modalities. Therefore it is strongly desired that D w measurements with primary standards can be performed on-site in clinical beams for the new treatment modalities in order to characterize and calibrate detectors. To serve this need, VSL has developed a new transportable water calorimeter serving as a primary D w standard for (60)Co and MV-photons including MRI incorporated treatment equipment. Special attention was paid to its operation in different beam geometries and beam modalities including the application in magnetic fields. The new calorimeter was validated in the VSL (60)Co beam and on-site in clinical MV-photon beams. Excellent agreement of 0.1% was achieved with previous (60)Co field calibrations, i.e. well within the uncertainty of the previous calorimeter, and with measurements performed in horizontal and vertical MV-photon beams. k Q factors, determined for two PTW 30013 ionization chambers, agreed very well with available literature data. The relative combined standard uncertainty (k = 1) for D w measurements in (60)Co and MV-photons is 0.37%. Calibrations are carried out with a standard uncertainty of 0.42% and k Q -factors are determined with a relative standard uncertainty of 0.40%.

Aerrow: A probe‐format graphite calorimeter for absolute dosimetry of high‐energy photon beams in the clinical environment

“…As a more direct alternative method to realize absorbed dose in nonstandard fields, new graphite and water calorimeters specifically designed to measure dose based on first principles are being developed . Oftentimes, these calorimetry systems are also made to be transportable to permit operation at the user's facility . Thus, calorimetry‐based dose measurements can form the basis of a direct dose calibration of an ionization chamber in the clinically relevant field, or a derivation of their correction factors for those beams.…”

“…[17][18][19] Oftentimes, these calorimetry systems are also made to be transportable to permit operation at the user's facility. [20][21][22][23] Thus, calorimetry-based dose measurements can form the basis of a direct dose calibration of an ionization chamber in the clinically relevant field, or a derivation of their correction factors for those beams. The minimal beam quality and field size dependence of calorimeters also make them useful transfer instruments.…”

First international comparison of primary absorbed dose to water standards in the medium-energy X-ray range

“…The VSL water calorimeter for medium energy X-rays (100 -250 kVp) has been described by de Prez and de Pooter [1] in 2008. In the meantime a new water calorimeter was designed and built [4]. The new water calorimeter has the same measurement depth as the previous one, i.e.…”

Absolute dosimetry of a 1.5 T MR‐guided accelerator‐based high‐energy photon beam in water and solid phantoms using Aerrow

“…As a more direct alternative method to realize absorbed dose in MRgRT, and more generally, in nonstandard fields, new transportable graphite and water calorimeters specifically designed to measure absorbed dose based on first principles at the user’s facilities have been developed . Even among primary standards, absorbed dose calorimetry is considered the most direct and absolute method of determining absorbed dose to water since device calibration can be achieved in terms of quantities with traceable standards (i.e.…”

“…As a more direct alternative method to realize absorbed dose in MRgRT, and more generally, in nonstandard fields, new transportable graphite and water calorimeters specifically designed to measure absorbed dose based on first principles at the user's facilities have been developed. [20][21][22][23][24][25][26][27][28] Even among primary standards, absorbed dose calorimetry is considered the most direct and absolute method of determining absorbed dose to water since device calibration can be achieved in terms of quantities with traceable standards (i.e., electrical and temperature), entirely independent of radiation. [29][30][31][32] Thus, calorimetry-based measurements can form the basis of a direct absorbed dose calibration of an IC in the clinically relevant field, or a derivation of their correction factors (e.g., k B ) for those beams.…”