Graphite calorimeter in water phantom and calibration of ionization chambers in dose to water for <sup>60</sup>Co gamma radiation

Rao, I. Srinivasa; Naik, Sachindra

doi:10.1118/1.594685

Cited by 14 publications

(7 citation statements)

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“…PCT/CA2013/000523). Originally constructed at McGill University by Renaud et al 24 the calorimeter, referred to herein as the Aerrow, shares design aspects with graphite calorimeters developed at the Bhabha Atomic Research Centre during the late 1970s, 25 and more recently at the National Physical Laboratory (NPL) 17 and the Laboratoire National Henri Bequerel (LNE-LNHB). 18 Despite these similarities, the Aerrow has not been developed or ever used in a primary standards dosimetry laboratory.…”

Section: Introductionmentioning

confidence: 99%

“…In contrast to all other graphite calorimeters, the Aerrow design incorporates aerogel-based material as opposed to a vacuum to achieve thermal isolation from the surrounding environment. 10,11,[17][18][19][25][26][27][28][29][30] Air gaps have also been successfully used to provide thermal insulation in graphite calorimeter designs (e.g., NPL's portable photon/electron calorimeter), however this design feature necessitates the inclusion of mechanical supports such as expanded polystyrene beads. 23 In this work, aerogel was opted to simplify the assembly process, to maximize the compactness, and to improve the structural robustness of the device.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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Purpose: In this work, the design, operation, initial experimental evaluation, and characterization of a small-scale graphite calorimeter probe -herein referred to as the Aerrow -developed for routine use in the clinical environment, are described. Similar in size and shape to a Farmer type cylindrical ionization chamber, the Aerrow represents the first translation of calorimetry intended for direct use by clinical physicists in the radiotherapy clinic. Methods: Based on a numerically optimized design obtained in previous work, a functioning Aerrow prototype capable of two independent modes of operation (quasi-adiabatic and isothermal) was constructed in-house. Reference dose measurements were performed using both Aerrow operation modes in a 6 MV photon beam and were directly compared to results obtained with a calibrated reference-class ionization chamber. The Aerrow was then used to quantify the absolute output of five clinical linac-based photon beams (6 MV, 6 MV FFF, 10 MV, 10 MV FFF, and 15 MV; 63.2% < %dd(10)9 < 76.3%). Linearity, dose rate, and orientation dependences were also investigated. Results: Compared to an ion chamber-derived dose to water of 76.3 AE 0.7 cGy, the average doses measured using the Aerrow were 75.6 AE 0.7 and 74.7 AE 0.7 cGy/MU for the quasi-adiabatic and isothermal modes, respectively. All photon beam output measurements using the Aerrow in waterequivalent phantom agreed with chamber-based clinical reference dosimetry data within combined standard uncertainties. The linearity of the Aerrow's response was characterized by an adjusted R 2 value of 0.9998 in the dose range of 80 cGy to 470 cGy. For the dose-rate dependence, no statistically significant effects were observed in the range of 0.5 Gy/min to 5.4 Gy/min. A relative photon beam quality dependence of 1.7% was calculated in the range of 60 Co to 24 MV (58.4% < %dd(10)9 < 86.8%) using Monte Carlo. Finally, the angular dependence (gantry stationary and detector rotated) of the Aerrow's response was found to be insignificant to within AE0.5%. Conclusions: This work demonstrates the feasibility of using an ion chamber-sized calorimeter as a practical means of measuring absolute dose to water in the radiotherapy clinic. The potential introduction of calorimetry as a mainstream device into the clinical setting is powerful, as this fundamental technique has formed the basis of absorbed dose standards in many countries for decades and could one day form the basis of a new local absorbed dose standard for clinics.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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“…In either case, the aim in this work is to determine a volume-averaged absorbed dose, in which the volume is that of the calorimeter core. Graphite calorimeters of such a size have been developed before, but not with the purpose of measurement in composite fields; rather to be used in a water tank for reference dosimetry in conventional photon and electron beams [7,8].…”

Section: Introductionmentioning

confidence: 99%

An absorbed dose calorimeter for IMRT dosimetry

Duane¹,

Aldehaybes²,

Bailey³

et al. 2012

Metrologia

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A new calorimeter for dosimetry in small and complex fields has been built. The device is intended for the direct determination of absorbed dose to water in moderately small fields and in composite fields such as IMRT treatments, and as a transfer instrument calibrated against existing absorbed dose standards in conventional reference conditions. The geometry, materials and mode of operation have been chosen to minimize detector perturbations when used in a water phantom, to give a reasonably isotropic response and to minimize the effects of heat transfer when the calorimeter is used in non-reference conditions in a water phantom. The size of the core is meant to meet the needs of measurement in IMRT treatments and is comparable to the size of the air cavity in a type NE2611 ionization chamber. The calorimeter may also be used for small field dosimetry. Initial measurements in reference conditions and in an IMRT head and neck plan, collapsed to gantry angle zero, have been made to estimate the thermal characteristics of the device, and to assess its performance in use. The standard deviation (estimated repeatability) of the reference absorbed dose measurements was 0.02 Gy (0.6%).

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“…The new D w standard has been designed as a miniature three bodies (core, jacket, and shield) graphite calorimeter (Domen and Lamperti 1974), embedded in a Polymethylmethacrylate (PMMA) waterproof evacuated envelope, allowing for D w measurements in a water phantom at 2 g cm −2 depth (Sundara Rao andNaik 1980, Witzani et al 1985). The three-bodies graphite calorimeter is designed for horizontally directed radiation beams and is positioned in a cubic water phantom, having an edge length of 200 mm and realized with 1 cm thick (PMMA) plates (figure 1(a)).…”

Section: Calorimeter Design and Constructionmentioning

confidence: 99%

A graphite calorimeter for absolute measurements of absorbed dose to water: application in medium-energy x-ray filtered beams

et al. 2016

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The Italian National Institute of Ionizing Radiation Metrology (ENEA-INMRI) has designed and built a graphite calorimeter that, in a water phantom, has allowed the determination of the absorbed dose to water in medium-energy x-rays with generating voltages from 180 to 250 kV. The new standard is a miniaturized three-bodies calorimeter, with a disc-shaped core of 21 mm diameter and 2 mm thickness weighing 1.134 g, sealed in a PMMA waterproof envelope with air-evacuated gaps. The measured absorbed dose to graphite is converted into absorbed dose to water by means of an energy-dependent conversion factor obtained from Monte Carlo simulations. Heat-transfer correction factors were determined by FEM calculations. At a source-to-detector distance of 100 cm, a depth in water of 2 g cm(-2), and at a dose rate of about 0.15 Gy min(-1), results of calorimetric measurements of absorbed dose to water, D(w), were compared to experimental determinations, D wK, obtained via an ionization chamber calibrated in terms of air kerma, according to established dosimetry protocols. The combined standard uncertainty of D(w) and D(wK) were estimated as 1.9% and 1.7%, respectively. The two absorbed dose to water determinations were in agreement within 1%, well below the stated measurement uncertainties. Advancements are in progress to extend the measurement capability of the new in-water-phantom graphite calorimeter to other filtered medium-energy x-ray qualities and to reduce the D(w) uncertainty to around 1%. The new calorimeter represents the first implementation of in-water-phantom graphite calorimetry in the kilovoltage range and, allowing independent determinations of D(w), it will contribute to establish a robust system of absorbed dose to water primary standards for medium-energy x-ray beams.

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Graphite calorimeter in water phantom and calibration of ionization chambers in dose to water for ⁶⁰Co gamma radiation

Cited by 14 publications

References 0 publications

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

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

An absorbed dose calorimeter for IMRT dosimetry

A graphite calorimeter for absolute measurements of absorbed dose to water: application in medium-energy x-ray filtered beams

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Graphite calorimeter in water phantom and calibration of ionization chambers in dose to water for 60Co gamma radiation

Cited by 14 publications

References 0 publications

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

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

An absorbed dose calorimeter for IMRT dosimetry

A graphite calorimeter for absolute measurements of absorbed dose to water: application in medium-energy x-ray filtered beams

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Product

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Graphite calorimeter in water phantom and calibration of ionization chambers in dose to water for ⁶⁰Co gamma radiation