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Medical Physics
Article . 2021 . Peer-reviewed
License: Wiley Online Library User Agreement
Data sources: Crossref
Medical Physics
Article . 2021
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feasibility of operating a millimeter scale graphite calorimeter for absolute dosimetry of small field photon beams in the clinic

Authors: Julien Bancheri; Jan Seuntjens; Arman Sarfehnia; Arman Sarfehnia; Benjamin Côté; J Renaud; J Renaud; +1 Authors

feasibility of operating a millimeter scale graphite calorimeter for absolute dosimetry of small field photon beams in the clinic

Abstract

AbstractPurposeTo characterize and build a cylindrically layered graphite calorimeter the size of a thimble ionization chamber for absolute dosimetry of small fields. This detector has been designed in a familiar probe format to facilitate integration into the clinical workflow. The feasibility of operating this absorbed dose calorimeter in quasi‐adiabatic mode is assessed for high‐energy accelerator‐based photon beams.MethodsThis detector, herein referred to as Aerrow MK7, is a miniaturized version of a previously validated aerogel‐insulated graphite calorimeter known as Aerrow. The new model was designed and developed using numerical methods. Medium conversion factors from graphite to water, small‐field output correction factors, and layer perturbation factors for this dosimeter were calculated using the EGSnrc Monte Carlo code system. A range of commercially available aerogel densities were studied for the insulating layers, and an optimal density was selected by minimizing the small‐field output correction factors. Heat exchange within the detector was simulated using a five‐body compartmental heat transfer model.In quasi‐adiabatic mode, the sensitive volume (a 3 mm diameter cylindrical graphite core) experiences a temperature rise during irradiation on the order of 1.3 mK·Gy−1. The absorbed dose is obtained by calculating the product of this temperature rise with the specific heat capacity of the graphite. The detector was irradiated with 6 MV ( = 63.5%) and 10 MV ( = 71.1%) flattening filter‐free (FFF) photon beams for two field sizes, characterized by dimensions of 2.16 and 11.0 cm. The dose readings were compared against a calibrated Exradin A1SL ionization chamber. All dose values are reported at in water.ResultsThe field output correction factors for this dosimeter design were computed for field sizes ranging from  = 0.54 to 11.0 cm. For all aerogel densities studied, these correction factors did not exceed 1.5%. The relative dose difference between the two dosimeters ranged between 0.3% and 0.7% for all beams and field sizes. The smallest field size experimentally investigated,  = 2.16 cm, which was irradiated with the 10 MV FFF beam, produced readings of 84.4 cGy (±1.3%) in the calorimeter and 84.5 cGy (±1.3%) in the ionization chamber.ConclusionThe median relative difference in absorbed dose values between a calibrated A1SL ionization chamber and the proposed novel graphite calorimeter was 0.6%. This preliminary experimental validation demonstrates that Aerrow MK7 is capable of accurate and reproducible absorbed dose measurements in quasi‐adiabatic mode.

Country
Canada
Keywords

Photons, Feasibility Studies, Graphite, heat transfer modeling, small-field do, Radiometry, calorimetry, Monte Carlo Method

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  • citations
    This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
    2
    popularity
    This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
    Top 10%
    influence
    This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
    Average
    impulse
    This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
    Average
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citations
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
2
Top 10%
Average
Average
bronze