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Medical Physics
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Medical Physics
Article . 2017 . Peer-reviewed
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Medical Physics
Article . 2017
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aerrow a probe format graphite calorimeter for absolute dosimetry of high energy photon beams in the clinical environment

Authors: Arman Sarfehnia; Arman Sarfehnia; J Renaud; Julien Bancheri; Jan Seuntjens;

aerrow a probe format graphite calorimeter for absolute dosimetry of high energy photon beams in the clinical environment

Abstract

PurposeIn 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.MethodsBased 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)× < 76.3%). Linearity, dose rate, and orientation dependences were also investigated.ResultsCompared to an ion chamber‐derived dose to water of 76.3 ± 0.7 cGy, the average doses measured using the Aerrow were 75.6 ± 0.7 and 74.7 ± 0.7 cGy/MU for the quasi‐adiabatic and isothermal modes, respectively. All photon beam output measurements using the Aerrow in water‐equivalent 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 R2 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 60Co to 24 MV (58.4% < %dd(10)× < 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 ±0.5%.ConclusionsThis 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.

Related Organizations
Keywords

Photons, Radiotherapy, Phantoms, Imaging, Uncertainty, Radiotherapy Dosage, Equipment Design, Calorimetry, Feasibility Studies, Graphite, Radiometry

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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).
    24
    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).
    Top 10%
    impulse
    This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
    Top 10%
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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!
24
Top 10%
Top 10%
Top 10%
bronze