Electron beam water calorimetry measurements to obtain beam quality conversion factors

Muir, B; Cojocaru, C. D.; McEwen, M; Ross, C. K.

doi:10.1002/mp.12463

Cited by 15 publications

(26 citation statements)

References 27 publications

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“…They also compared their results to several other measured and calculated results that were available at the time of that publication and observed very good agreement. Since then other publications have also provided data, also in good agreement with that of Muir and Rogers …”

Section: Introductionsupporting

confidence: 81%

“…

D_{normalw} = M N_{D, w}^{normalQ},

where

N_{normalD, normalw}^{Q}

is the calibration coefficient for the chamber in the beam of interest. NRC primary standards for absorbed dose are described elsewhere and are in good agreement with other primary standards dosimetry laboratories . Three of the chambers used in this investigation (the NACP‐02, the PTW Roos and the NE2571) have been calibrated directly against NRC primary standards.…”

Section: Methodsmentioning

confidence: 65%

“…The parameter

k_{R_{50}}

is further factored into

k_{R_{50}}^{'} k_{ecal}

because the chamber‐to‐chamber variation of

k_{R_{50}}^{'}

is much less than that for

k_{R_{50}}

and

k_{ecal}

is required for cross‐calibrating parallel‐plate chambers against cylindrical chambers. The TG‐51 protocol also states that

k_{ecal}

is directly measurable by primary standards labs and, since the publication of TG‐51, at least three standards labs have developed this capability . It is fixed for a given chamber model (although measurements of

k_{ecal}

might be subject to chamber‐to‐chamber variations for chambers of the same type) and is equal to

k_{R_{50}}

for an electron beam of quality

Q_{ecal}

.…”

Section: Introductionmentioning

confidence: 99%

“…Equation () then becomes.

D_{normalw} = M k_{Q}^{'} k_{Q, ecal} N_{D, w}^{Co}

where

k_{Q}

is still factored, allowing for the use of a modified cross calibration procedure for parallel‐plate chambers. This is useful because of stability issues noted previously for parallel‐plate chambers, which are avoided if cross‐calibration against a stable cylindrical chamber is performed at the time reference dosimetry measurements are made. Equation () then becomes

{(k_{Q, ecal} N_{D, w}^{Co})}^{pp} = \frac{{false(M k_{Q}^{'} k_{normalQ, ecal} N_{normalD, normalw}^{Co} false)}^{cyl}}{{false(M k_{Q}^{'} false)}^{pp}} .

…”

Section: Introductionmentioning

confidence: 99%

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A modified formalism for electron beam reference dosimetry to improve the accuracy of linac output calibration

Muir

2020

Medical Physics

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Purpose To present and demonstrate the accuracy of a modified formalism for electron beam reference dosimetry using updated Monte Carlo calculated beam quality conversion factors. Methods The proposed, simplified formalism allows the use of cylindrical ionization chambers in all electron beams (even those with low beam energies) and does not require a measured gradient correction factor. Data from a previous publication are used for beam quality conversion factors. The formalism is tested and compared to the present formalism in the AAPM TG‐51 protocol with measurements made in Elekta Precise electron beams with energies between 4 MeV and 22 MeV and with fields shaped with a 10 × 10 cm2 clinical applicator as well as a 20 × 20 cm2 clinical applicator for the 18 MeV and 22 MeV beams. A set of six ionization chambers are used for measurements (two cylindical reference‐class chambers, two scanning‐type chambers and two parallel‐plate chambers). Dose per monitor unit is derived using the data and formalism provided in the TG‐51 protocol and with the proposed formalism and data and compared to that obtained using ionization chambers calibrated directly against primary standards for absorbed dose in electron beams. Results The standard deviation of results using different chambers when TG‐51 is followed strictly is on the order of 0.4% when parallel‐plate chambers are cross‐calibrated against cylindrical chambers. However, if parallel‐plate chambers are directly calibrated in a cobalt‐60 beam, the difference between results for these chambers is up to 2.2%. Using the proposed formalism and either directly calibrated or cross‐calibrated parallel‐plate chambers gives a standard deviation using different chambers of 0.4%. The difference between results that use TG‐51 and the primary standard measurements are on the order of 0.6% with a maximum difference in the 4 MeV beam of 2.8%. Comparing the results obtained with the proposed formalism and the primary standard measurements are on the order of 0.4% with a maximum difference of 1.0% in the 4 MeV beam. Conclusions The proposed formalism and the use of updated data for beam quality conversion factors improves the consistency of results obtained with different chamber types and improves the accuracy of reference dosimetry measurements. Moreover, it is simpler than the present formalism and will be straightforward to implement clinically.

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Section: Introductionsupporting

confidence: 81%

“…

D_{normalw} = M N_{D, w}^{normalQ},

where

N_{normalD, normalw}^{Q}

Section: Methodsmentioning

confidence: 65%

“…The parameter

k_{R_{50}}

is further factored into

k_{R_{50}}^{'} k_{ecal}

because the chamber‐to‐chamber variation of

k_{R_{50}}^{'}

is much less than that for

k_{R_{50}}

and

k_{ecal}

is required for cross‐calibrating parallel‐plate chambers against cylindrical chambers. The TG‐51 protocol also states that

k_{ecal}

k_{ecal}

might be subject to chamber‐to‐chamber variations for chambers of the same type) and is equal to

k_{R_{50}}

for an electron beam of quality

Q_{ecal}

.…”

Section: Introductionmentioning

confidence: 99%

“…Equation () then becomes.

D_{normalw} = M k_{Q}^{'} k_{Q, ecal} N_{D, w}^{Co}

where

k_{Q}

{(k_{Q, ecal} N_{D, w}^{Co})}^{pp} = \frac{{false(M k_{Q}^{'} k_{normalQ, ecal} N_{normalD, normalw}^{Co} false)}^{cyl}}{{false(M k_{Q}^{'} false)}^{pp}} .

…”

Section: Introductionmentioning

confidence: 99%

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A modified formalism for electron beam reference dosimetry to improve the accuracy of linac output calibration

Muir

2020

Medical Physics

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“…To date, calorimetry has been used widely in conventional high energy photon beams, [6][7][8][9][10][11] and to a somewhat lesser extent in medium/high LET particle beams, 6,[11][12][13][14] high-energy electron beams, 11,[15][16][17][18] and brachytherapy. 11,[19][20][21] Calorimetry efforts in the area of MR-integrated linacs have been limited.…”

Section: Introductionmentioning

confidence: 99%

First‐stage validation of a portable imageable MR‐compatible water calorimeter

et al. 2020

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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. Methods: 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 6 MV 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. Results: 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). Conclusions: An MR-compatible water calorimeter was successfully built and absolute absorbed dose to water under a conventional 6 MV FFF beam was determined successfully as a first-stage validation of the system.

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A multicenter study of modified electron beam output calibration

Mahfirotin,

Ferliano,

Handika

et al. 2023

J Applied Clin Med Phys

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PurposeThis study aims to assess the accuracy of a modified electron beam calibration based on the IAEA TRS‐398 and AAPM‐TG‐51 in multicenter radiotherapy.MethodsThis study was performed using the Elekta and Varian Linear Accelerator electron beams with energies of 4–22 MeV under reference conditions using cylindrical (PTW 30013, IBA FC65‐G, and IBA FC65‐P) and parallel‐plate (PTW 34045, PTW 34001, and IBA PPC‐40) chambers. The modified calibration used a cylindrical chamber and an updated based on Monte Carlo calculations, whereas TRS‐398 and TG‐51 used cylindrical and parallel‐plate chambers for reference dosimetry. The dose ratio of the modified calibration procedure, TRS‐398 and TG‐51 were obtained by comparing the dose at the maximum depth of the modified calibration to TRS‐398 and TG‐51.ResultsThe study found that all cylindrical chambers’ beam quality conversion factors determined with the modified calibration to the TRS‐398 and TG‐51 vary from 0.994 to 1.003 and 1.000 to 1.010, respectively. The dose ratio of modified/TRS‐398cyl and modified/TRS‐398parallel‐plate, the variation ranges were 0.980–1.014 and 0.981–1.019, while for the counterpart modified/TG‐51cyl was found varying between 0.991 and 1.017 and the ratio of modified/TG‐51parallel‐plate varied in the range of 0.981–1.019.ConclusionThis multi‐institutional study analyzed a modified calibration procedure utilizing new data for electron beam calibrations at multiple institutions and evaluated existing calibration protocols. Based on observed variations, the current calibration protocols should be updated with detailed metrics on the stability of linac components.

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Electron beam water calorimetry measurements to obtain beam quality conversion factors

Cited by 15 publications

References 27 publications

A modified formalism for electron beam reference dosimetry to improve the accuracy of linac output calibration

A modified formalism for electron beam reference dosimetry to improve the accuracy of linac output calibration

First‐stage validation of a portable imageable MR‐compatible water calorimeter

A multicenter study of modified electron beam output calibration

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