Water Calorimeter Research Articles

Suitability of novel 3D-printed and coated vessels for water calorimetry.

In water calorimetry, absolute dose to water is determined by measuring radiation-induced temperature rises. In conventional water calorimeters, temperature detectors are housed in handmade glass vessels that are filled with high-purity water, thus mitigating radiation-induced exo/endothermic chemical reactions of impurities that would otherwise introduce additional heat gain/loss, known as heat defect. Being hand-crafted, these glass vessels may suffer from imperfections, have shape and design constraints, are often backordered, and can be prohibitively expensive. The purpose of this work is to determine suitability of 3D-printed plastic vessels that are further coated for use in water calorimetry applications, and to study their stability and characterize their associated heat defect correction factor ( . This novel vessel production technique would allow for cost-effective rapid construction of vessels that can be produced with high accuracy and designs that are simply not practical with current glass vessel construction techniques. This in turn enables water calorimetry applications in many novel radiation delivery modalities, which may include spherical vessels in GammaKnife ICON water calorimetry as an example. Eight vessels were 3D-printed using Accura ClearVue in an SLA 3D-printer. Two vessels were coated with Parylene C and four were coated with Parylene N. The water calorimetry preparation procedures followed for these vessels was identical to that of our traditional glass-vessels (i.e., same cleaning procedures, same high purity water, and same saturation procedures with high purity hydrogen gas). The performance of each vessel was characterized using our in-house built water calorimeter in an Elekta Versa using both 6MV flattening filter-free (FFF) and 18MV beams. The stability of the coating as function of time and accumulated dose was evaluated through repeated measurements. of each vessel was determined through cross-comparisons against an Exradin A1SL ionization chamber with direction calibration link to Canada's primary standard laboratory. of the two uncoated vessels differed by 2.8% under a 6MV FFF beam. Vessels coated with Parylenes resulted in a stable and reproducible heat defect for both energies. An overall of 1.001±0.010 and 1.005±0.010 were obtained for Parylene N and Parylene C coated vessels respectively. All Parylene coated vessels showed agreement, within the established uncertainties, to the zero-heat defect observed in a hydrogen-saturated glass vessel system. An additional long-term study (17 days) of a Parylene N vessel showed no change in response with accumulated dose and time. Electron microscopy images of a Parylene N coated vessel showed a uniform intact coating after repeated irradiations. An uncoated 3D-printed vessel is not viable for water calorimetry because it exhibits an unstable vessel-dependent heat defect. However, applying a Parylene coating stabilizes the heat defect, suggesting that coated 3D-printed vessels may be suitable for use in water calorimetry. This method facilitates the creation of intricate vessel shapes, which can be efficiently manufactured using 3D printing.

Surface Heat Flux Measurements Based on the Non-Integer System Identification Method Using Surface Temperature Data

This paper presents an experimental approach to inversely determine surface heat flux from surface temperature data for an arbitrary body. The relation between heat flux and temperature is calibrated using the non-integer system identification method. The surface temperature is measured using an infrared camera. The approach is applied using a well-established plasma wind tunnel condition so that the results are comparable to a reference measurement with a water calorimeter. The maximum deviation between the reference and the novel heat flux measurement was 6.3% and 14.3% for two separately generated impulse responses, respectively. In conclusion, this new method allows in future applications an additional heat flux determination based on surface temperature data. Since surface temperature data is a standard measurement, only an additional calibration step is needed to standardize this heat flux measurement method.

The PTB water calorimeter for determining the absolute absorbed dose to water in ultra-high pulse dose rate electron beams

Objective. The purpose of this investigation is to establish the water calorimeter as the primary standard in PTB’s ultra-high pulse dose rate (UHPDR) 20 MeV reference electron beams. Approach. The calorimetric measurements were performed at the PTB research linac facility using the UHPDR reference electron beam setups that enable a dose per pulse between about 0.1 Gy and 6 Gy. The beam is monitored by an in-flange integrating current transformer. The correction factors required to determine the absorbed dose to water were evaluated using thermal and Monte Carlo simulations. Measurements were performed with different total doses delivered per pulse by modifying the instantaneous dose rate within a pulse and by changing the pulse length. The obtained temperature–time traces were compared to the simulated ones to validate the thermal simulations. In addition, absorbed-dose-to-water measurements obtained using the secondary standard alanine dosimeter system were compared to measurements performed with the primary standard. Main results. The simulated and measured temperature–time traces were shown to be consistent, within combined uncertainties, with one another. Measurements with alanine dosimeters proved to be consistent within k = 1 of the total combined uncertainty with the absorbed dose to water determined using the primary standard. Significance. The total relative standard uncertainty of absorbed dose to water determined using the PTB water calorimeter primary standard in UHPDR electron beams was estimated to be less than 0.5%, and the combined correction factors were found to deviate from 1 by less than 1% for both PTB UHPDR 20 MeV reference electron beams. The water calorimeter is therefore considered to be an established primary standard for the higher energy UHPDR reference electron beams.

Development and application of absorbed dose primary standard for 60Co and high-energy photon beams using water calorimetry

Several new glass vessels, thermistor probes, and water phantoms have been designed and built at the National Institute of Metrology (China) to upgrade and develop the existing water calorimeter. The increased plane-parallel vessels have shorter thermal stability times and shallower positioning depths (∼1.3 cm) than the previous cylindrical vessels, which makes them suitable for electron beams. The sensitivity of the new probes is 10% greater than the previous ones. In this study, detailed experimental and theoretical investigations of various factors affecting the new water calorimeter are performed. The system uncertainty of the water calorimeter is reduced and the robustness of the determination of the absorbed-dose-to-water D w is improved using a variety of geometric detector vessels and two kinds of high-purity water systems saturated with high-purity gases. This new calorimeter is employed as a primary standard for determining the D w, has achieved a combined standard uncertainty of 0.24% for a 60Co beam, 0.27% for 6 MV and 10 MV photon beams and 0.30% for a 25 MV photon beam. The beam quality conversion factors kQ of ten cylindrical and three plane-parallel ionization chambers are measured using the new calorimeter to improve the reference dosimetry accuracy of high-energy clinical photon beams.

The PTB water calorimeter for determining the absolute absorbed dose to water in ultra-high pulse dose rate electron beams

The PTB water calorimeter for determining the absolute absorbed dose to water in ultra-high pulse dose rate electron beams

Direct determination of k Q for Farmer-type ionization chambers in a clinical scanned carbon-ion beam using water calorimetry

Within two studies, k Q factors for two Farmer-type ionization chambers have been experimentally determined by means of water calorimetry in the entrance channel (EC) of a monoenergetic carbon-ion beam (Osinga-Blättermann et al 2017 Phys. Med. Biol. 62 2033–54) and for a passively modulated spread-out Bragg peak (SOBP) (Holm et al 2021 Phys. Med. Biol. 66 145012). Both studies were performed at the Heidelberg Ion Beam Therapy Center (HIT) using the PTB portable water calorimeter but applying different initial beam energies of 429 MeV u−1 for the EC and 278 MeV u−1 for the SOBP as well as different scanning patterns of the irradiated field. Comparing their results revealed differences between the experimental k Q factors of up to 1.9% between the EC and the SOBP. To further investigate this unexpected difference, we performed additional k Q determinations for the EC of an 278 MeV u−1 monoenergetic carbon-ion beam and reevaluated the original data of Osinga-Blättermann et al (2017 Phys. Med. Biol. 62 2033–54). This new experimental data indicated no difference between the k Q factors for the EC and the SOBP and the reevaluation led to a substantial reduction of the originally published k Q factors for the EC of the 429 MeV u−1 beam (Osinga-Blättermann et al 2017 Phys. Med. Biol. 62 2033–54). Finally, no significant difference between the data for the EC and the data for the SOBP can be found within the standard measurement uncertainty of experimental k Q factors of 0.8%. The results presented here are intended to correct and replace the k Q data published by Osinga-Blättermann et al (2017 Phys. Med. Biol. 62 2033–54) and in Osinga-Blättermann and Krauss (2018 Phys. Med. Biol. 64 015009).

Evaluation of VHIT values compared to other diagnostic tests that can be performed in a patient with dizziness and balance disorders.

<b>Introduction:</b> Dizziness and imbalance occur in 20-30% of adults, which is a significant health problem.</br></br> <b>Aim:</b> The aim of the study was to assess the value of the VHIT test against the background of other diagnostic tests, including videonystagmographic (VNG) examination, Dix-Hallpike maneuver, VHIT test, posturographic examination, which are possible to perform in a patient with dizziness. </br></br> <b>Material and methods:</b> The study was performed in 200 patients aged 18-78 years, who were divided into two groups: I study - 100 patients with mixed dizziness, aged 18-78 years, II (reference group) - 100 healthy patients (students of the Faculty of Mili-tary and Medical University of Lodz and patients of the Clinic, without anamnesis of body imbalances (preventive examination), aged 20-60 years. After performing an otorynolaryngological subjective and physical examination, each patient was subjected to a caloric test according to Fitzgerald-Hallpike in the VNG test using a water calorimeter. Then the Dix-Hallpike maneuver was performed, while the activity of semicircular canals in the VHIT test was determined on the basis of the GAIN value. In randomly selected patients, posturographic examinations were additionally carried out.</br></br> <b>Results:</b> Based on the positive Dix-Hallpike maneuver, damage in the posterior semicircular canal in group I was found in 9 women (9.0%) and 4 men (4.0%), while a negative maneuver was noted in all people in group II. In group I in the VHIT study, damage to the semicircular canals most often concerned the following parts: anterior in 29 women (44.60%) and in 15 men (42.85%); posterior, in 19 (29.23%) and 8 (22.85%), respectively; lateral, in 3 (4.61%) and 3 (8.57%), respectively. </br></br> <b>Conclusions:</b> The VHIT study in detail assesses the labyrinth canal deficit in all cases of peripheral and mixed dizziness, inc-luding otolithic origin, but does not allow for evident differentiation of BPPV with mixed dizziness of other origin. The VHIT test is a recommended diagnostic tool in BPPV in combination with other positional tests that allow to determine otolithiasis, such as: Hallpike test for the posterior semicircular canal. The VHIT test should be analyzed against the background of other diagnostic tests that can be performed in a patient with dizziness and balance disorders.

Water calorimetry-based k Q factors for Farmer-type ionization chambers in the SOBP of a carbon-ion beam

The dosimetry of carbon-ion beams based on calibrated ionization chambers (ICs) still shows a significantly higher uncertainty compared to high-energy photon beams, a fact influenced mainly by the uncertainty of the correction factor for the beam quality k Q . Due to a lack of experimental data, k Q factors in carbon-ion beams used today are based on theoretical calculations whose standard uncertainty is three times higher than that of photon beams. To reduce their uncertainty, in this work, k Q factors for two ICs were determined experimentally by means of water calorimetry for the spread-out Bragg peak of a carbon-ion beam, these factors are presented here for the first time. To this end, the absorbed dose to water in the 12C-SOBP is measured using the water calorimeter developed at Physikalisch-Technische Bundesanstalt, allowing a direct calibration of the ICs used (PTW 30013 and IBA FC65G) and thereby an experimental determination of the chamber-specific k Q factors. Based on a detailed characterization of the irradiation field, correction factors for several effects that influence calorimetric and ionometric measurements were determined. Their contribution to an overall uncertainty budget of the final k Q factors was determined, leading to a standard uncertainty for k Q of 0.69%, which means a reduction by a factor of three compared to the theoretically calculated values. The experimentally determined values were expressed in accordance with TRS-398 and DIN 6801-1 and compared to the values given there. A maximum deviation of 2.3% was found between the experiment and the literature.

Direct determination of for cylindrical ionization chambers in a 6 MV 0.35 T MR-linac

To ensure accurate reference dosimetry with ionization chambers in magnetic resonance linear accelerators (MR-linacs), the influence of the magnetic field on the response of the ionization chambers must be considered. The most direct method considering the influence of magnetic fields in dosimetry is to apply an appropriate absorbed-dose-to-water primary standard. At PTB, a new water calorimeter has been designed which is capable to determine Dw,Q in an MR-linac. The new device allows the direct calibration of ionization chambers in terms of absorbed dose to water for MR-linac irradiation conditions. Hence, the correction factors can be determined which replace the current radiation-quality dependent correction factors for dosimetry in the presence of magnetic fields. In cooperation with Heidelberg University Hospital, factors were measured at the 6 MV 0.35 T Viewray MR-linac for different cylindrical ionization chambers with sensitive volumes ranging from 0.015 cm3 to 0.65 cm3. The chambers were placed both perpendicular and parallel in respect to the magnetic field. Standard uncertainties of about 0.5% were achieved.

Water calorimetry in MR-linac: Direct measurement of absorbed dose and determination of chamber .

To use a portable 4°C cooled MR-compatible water calorimeter to measure absorbed dose in a magnetic resonance-guided radiation therapy (MRgRT) system. Furthermore, to use the calorimetric dose results and direct cross-calibration to experimentally measure the combined beam quality and magnetic field correction factor ( ) of a clinically used reference-class ionization chamber placed under the same radiation field. An Elekta Unity MR-linac (7MV FFF, B=1.5T) was used in this study. Measurements were taken using the in-house designed and built water calorimeter. Following preparation and cooling of the system, the MR-compatible calorimeter was positioned using a combination of MR and EPID imaging and the dose to water was measured by monitoring the radiation-induced temperature change. Immediately after the calorimetric measurements, an A1SL ionization chamber was placed inside the calorimeter for direct cross-calibration. The results allowed for a direct and absolute experimental measurement of for this chamber and comparison against existing Monte Carlo values. The calorimeter was successfully positioned using imaging in under an hour. The 1-hour setup time is from the time the calorimeter leaves storage to the first calorimetric measurement. Absorbed dose was successfully measured with a relative combined standard uncertainty of 0.71 % (k=1). Through a cross-calibration, the for an Exradin A1SL ionization chamber, set up perpendicular to the incident photon beam and opposite to the direction of the Lorentz force, was directly determined in water in absolute terms to be 0.977±0.010. The currently published results, obtained via Monte Carlo calculations, agree with experimental measurements in this work within combined uncertainties. A novel design of an MR-compatible water calorimeter was successfully used to measure absorbed dose in an MR-linac and determine an experimental value of for a clinically used ionization chamber.

Direct measurement of ionization chamber absorbed dose kQ factors in clinical electron beams

An electron water calorimeter is described and is used to experimentally determine beam quality dependent conversion factors, kQ, for two ionization chamber types in high-energy electron beams. The current water calorimeter was upgraded to obtain reproducible measurements in electron beams from 10 MeV to 22 MeV (corresponding beam quality index R50 ranging over 4.20–8.97 g cm−2). Measurements of radiation induced temperature rise are made using a plane-parallel glass vessel with calibrated thermistor probes in a 4 °C water phantom. Three types of plane-parallel chambers (PTW Roos, IBA PPC40 and SNC 1045) and two types of cylindrical chambers (PTW30013 and IBA FC65-G) are measured to directly derive beam quality correction factors in the same water phantom. Relative combined standard uncertainty for kQ factors of 0.56% for 10 MeV beams and above were achieved. General agreement is obtained between the relative electron energy dependencies of the kQ factors measured in this work and those derived from TRS-398 of the IAEA and recent other experimental investigations. Furthermore, the experimental kQ values obtained here will impact future updates of reference dosimetry protocols, and the current standard uncertainties in electron reference dosimetry can be reduced by the method proposed in this work.

First-stage validation of a portable imageable MR-compatible water calorimeter.

The purpose of this study is to design a water calorimeter with three goals in mind: (a) To be fully magnetic resonance (MR)-compatible; (b) To be imaged using kV cone beam computed tomography (CBCT), MV portal imaging or MRI for accurate positioning; (c) To accommodate both vertical and horizontal beam incidence, as well as volumetric deliveries or Gamma Knife®. Following this, the calorimeter performance will be measured using an accelerator-based high-energy photon beam. A portable 4°C cooled stagnant water calorimeter was built using MR-compatible materials. The walls consist of layers of acrylic plastic, aerogel-based material acting as thermal insulation, as well as tubing for coolant to flow to keep the calorimeter temperature stable at 4°C. The lid contains additional pathways for coolant to flow through as well as two hydraulically driven stirrers. The water calorimeter was positioned in an Elekta Versa using kV CBCT imaging as well as orthogonal MV image pairs. Absolute absorbed dose to water was then determined under a 6MV flattening filter-free (FFF) beam. This was compared against reference dosimetry results that were measured under identical conditions with an Exradin A1SL ionization chamber with a calibration coefficient directly traceable to the National Research Council Canada. The dose to water determined with the calorimeter (n=30) agreed with the A1SL ionization chamber reference dose measurements (n=15) to within 0.25%. The uncertainty associated with the water calorimeter absorbed dose measurement was estimated to be 0.54% (k=1). An MR-compatible water calorimeter was successfully built and absolute absorbed dose to water under a conventional 6MV FFF beam was determined successfully as a first-stage validation of the system.

Establishment of calculation methodology and thermal analysis for the development of a water calorimeter

As an early stage in the development of a water calorimeter, this study established a computer simulation methodology for analyzing the thermal behavior of a water calorimeter based on radiation transport and energy deposition. As a result, this study developed a method wherein the energy deposition distribution, which is obtained by applying Monte Carlo methods in water calorimeters, is directly used as a heat source for the thermal analysis model. Based on the proposed method, heat transfer in a water vessel and the effect of thermistor self-heating were analyzed. Through an analysis of the water velocities with and without a water vessel, it was found that a water vessel can serve as a convection barrier. Furthermore, it was confirmed that when considering thermistor self-heating, the water temperature change at the thermistor location is 0.219 mK higher compared to that when the thermistor was not considered. Therefore, thermistor self-heating must be considered to analyze the thermal behavior of a water calorimeter more accurately.

Comparing EAS registered with PRISMA-32 array and CWC NEVOD

Results of comparing events detected with two detectors of the Experimental complex NEVOD: PRISMA-32 array and Cherenkov water calorimeter (CWC) NEVOD – are presented. The PRISMA-32 is an array for simultaneous registration of the EAS electron-photon and neutron components. It consists of 32 en-detectors deployed over the area of about 500 m2, along the perimeter of the CWC NEVOD. The CWC NEVOD is a detector of a calorimetric type with a volume of 2000 cubic meters in which the registration system of 91 quasispherical modules (546 FEU-200 photomultipliers) is placed. CWC provides measurement of the intensity of Cherenkov radiation from any direction with practically the same efficiency.

Investigation of the Energy Loss of Muon Bundles in the Cherenkov Water Calorimeter

Investigations of the energy loss of muon bundles are being conducted at the Experimental complex NEVOD. Such investigations are directed to detailed study of “muon puzzle” (the excess of multi-muon events observed in several cosmic ray experiments at ultra-high energies). Results of measurements of the muon bundle energy deposit during a long period of observations in primary cosmic ray energy range 10–1000 PeV have been obtained and have been compared with simulations performed on the basis of the CORSIKA code.

Study of EAS Registered by the PRISMA-32 Array and the Cherenkov Water Calorimeter NEVOD

Two installations that allow to detect the EAS hadron component in a continuous mode, the Cherenkov water calorimeter (CWC) NEVOD and PRISMA-32 are operated in MEPhI. The comparison of the characteristics of EAS simultaneously registered by CWC NEVOD and PRISMA-32 are presented. Groups of events with different positions of the shower axis are considered.

Direct measurement of ion chamber correction factors, kQ and kB, in a 7 MV MRI-linac

The output of MRI-integrated photon therapy (MRgXT) devices is measured in terms of absorbed dose to water, Dw. Traditionally this is done with reference type ion chambers calibrated in a beam quality Q0 without magnetic field. To correct the ion chamber response for the application in the magnetic field, a factor needs to be applied that corrects for both beam quality Q and the presence of the magnetic field B, kQ,B. This can be expressed as the product of kQ, without magnetic field, and ion chamber magnetic field correction, kB. kB depends on the magnetic field strength and its direction, the direction of the beam and the orientation and type of the ion chamber. In this study, for the first time, both kQ and kB were measured directly for six waterproof ion chambers (3 × PTW 30013 and 3 × IBA FC65-G) in a pre-clinical 7 MV MRI-linac at 0 T and at 1.5 T. Measurements were done with the only available primary standard built for this purpose, a water calorimeter. Resulting kQ factors for PTW and IBA chambers were 0.985(5) and 0.990(4), respectively. kB factors were measured with the chambers in antiparallel direction to the magnetic field (|| 180°), and perpendicular direction (⊥ −90°). kB|| and kB⊥ for the PTW chambers were 0.985(6) and 0.963(4), respectively and for IBA chambers 0.995(4) and 0.956(4). Agreement with the available literature values was shown, partly caused by the relatively large standard deviation (SD) in those values. The values in this study are currently the only available measured values for kQ and kB in an MRI-linac that are directly linked to the international traceability framework for the quantity absorbed dose to water, Dw.

OC-0289 A water calorimeter as a primary standard for absorbed dose in magnetic fields

OC-0289 A water calorimeter as a primary standard for absorbed dose in magnetic fields

Thermal properties of fractions of corn stover

Abstract The properties of agriculture by-products make them applicable for insulating materials production. One of the potential source of natural insulating material is corn stover, especially the stalks. In the present study the density, specific heat and volumetric specific heat capacity of individual fractions of corn stover were determined. The separation of the corn fractions allowed to identify the most suitable fractions for insulating panels production. Four separated fractions, i.e. stalks, leaves, husks and cobs, were in focus of the study. The specific heat measurements of selected corn factions were carried out with a water calorimeter. The measurements were made for the oven dry materials which were placed in a heat shrinkable membrane to prepare samples of a cylindrical shape. The obtained values of specific heat and volumetric specific heat capacity confirmed that the thermal properties of corn stover fractions should be determined separately. Only leaves and stalks were characterized by similar values of specific heat and volumetric specific heat capacity. The highest value of specific heat equal to 1723 J/(kg·K) was determined for husks. The observed high values of volumetric specific heat capacity determined for all corn stover fractions confirmed their ability of heat accumulation.

Commissioning of a water calorimeter as a primary standard for absorbed dose to water in magnetic fields

MRI guided radiotherapy devices are currently in clinical use. Detector responses are affected by the magnetic field and need to be characterized in terms of absorbed dose to water, Dw, against primary standards under these conditions. The aim of this study was to commission a water calorimeter, accepted as the Dutch national standard for Dw in MV photons and to validate its claimed standard uncertainty of 0.37% in the 7 MV photon beam of a pre-clinical MRI-linac in a 1.5 T magnetic field.To evaluate the primary standard on a fundamental basis, realisation of Dw at 1.5 T was evaluated parameter by parameter. A thermodynamic description was given to demonstrate potential temperature effects due to the magneto-caloric effect (MCE). Methods were developed for measurement of depth, variation in detector distance and beam output in the bore of the MRI-linac. This resulted in Dw measurements with a magnetic field of 1.5 T and, after ramp-down, without magnetic field.It was shown that the measurement of ΔTw and calorimeter corrections are either independent of or can be determined in a magnetic field. The chemical heat defect, h, was considered zero within its stated uncertainty, as for 0 T. Evaluation of the MCE and measurements done during magnet ramp-down, indicated no changes in the specific heat capacity of water. However, variations of the applied monitor system increased the uncertainty on beam output normalization.This study confirmed that the uncertainty for measurement of Dw with a water calorimeter in a 1.5 T magnetic field is estimated to be the same as under conventional reference conditions. The VSL water calorimeter can be applied as a primary standard for Dw in magnetic fields and is currently the only primary standard operable in a magnetic field that provides direct access to the international traceability framework.