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

Renaud, James; Sarfehnia, Arman; Bancheri, Julien; Seuntjens, J

doi:10.1002/mp.12669

Cited by 26 publications

(52 citation statements)

References 43 publications

(117 reference statements)

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“…This raises critical issues surrounding traceability to primary absorbed dose‐to‐water standards that must be carefully considered when proposing how such a device might be deployed clinically. Previous work has elaborated on this point …”

Section: Discussionmentioning

confidence: 93%

“…All ICs were used with absorbed dose calibration coefficients,

N_{D, w}^{60_{italicCo}}

, traceable to the National Research Council of Canada (NRC) primary standard water calorimeter. The Exradin A19 was chosen based on the history of stability and widespread use of Farmer‐type ICs . On the other hand, the Exradin A1SL was included based on its k B values in the literature, which are generally much closer to unity than those associated with Farmer‐type ICs .…”

Section: Methodsmentioning

confidence: 99%

“…The Exradin A19 was chosen based on the history of stability and widespread use of Farmer-type ICs. 34,63 On the other hand, the Exradin A1SL was included based on its k B values in the literature, which are generally much closer to unity than those associated with Farmer-type ICs. 12,13 For both ICs, the uncertainty FIG.…”

Section: D Reference Dosimetrymentioning

confidence: 99%

“…Aerrow is a probe‐format graphite calorimeter that has been developed for the purpose of accurately measuring absorbed dose to water in the clinic with a minimum disruption to the existing clinical workflow . Several design and operational aspects of Aerrow set it aside from other standards‐level graphite calorimeters.…”

Section: Introductionmentioning

confidence: 99%

“…Aerrow is a probe-format graphite calorimeter that has been developed for the purpose of accurately measuring absorbed dose to water in the clinic with a minimum disruption to the existing clinical workflow. [33][34][35] Several design and operational aspects of Aerrow set it aside from other standards-level graphite calorimeters. For instance, its relatively small, cylindrical form factor was purposely chosen to resemble a Baldwin-Farmer IC, to ensure a certain degree of familiarity with its usage for clinicians.…”

Section: Introductionmentioning

confidence: 99%

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Absolute dosimetry of a 1.5 T MR‐guided accelerator‐based high‐energy photon beam in water and solid phantoms using Aerrow

et al. 2020

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Purpose In this work, the fabrication, operation, and evaluation of a probe‐format graphite calorimeter — herein referred to as Aerrow — as an absolute clinical dosimeter of high‐energy photon beams while in the presence of a B = 1.5 T magnetic field is described. Comparable to a cylindrical ionization chamber (IC) in terms of utility and usability, Aerrow has been developed for the purpose of accurately measuring absorbed dose to water in the clinic with a minimum disruption to the existing clinical workflow. To our knowledge, this is the first reported application of graphite calorimetry to magnetic resonance imaging (MRI)‐guided radiotherapy. Methods Based on a previously numerically optimized and experimentally validated design, an Aerrow prototype capable of isothermal operation was constructed in‐house. Graphite‐to‐water dose conversions as well as magnetic field perturbation factors were calculated using Monte Carlo, while heat transfer and mass impurity corrections and uncertainties were assessed analytically. Reference dose measurements were performed in the absence and presence of a B = 1.5 T magnetic field using Aerrow in the 7 MV FFF photon beam of an Elekta MRI‐linac and were directly compared to the results obtained using two calibrated reference‐class IC types. The feasibility of performing solid phantom‐based dosimetry with Aerrow and the possible influence of clearance gaps is also investigated by performing reference‐type dosimetry measurements for multiple rotational positions of the detector and comparing the results to those obtained in water. Results In the absence of the B‐field, as well as in the parallel orientation while in the presence of the B‐field, the absorbed dose to water measured using Aerrow was found to agree within combined uncertainties with those derived from TG‐51 using calibrated reference‐class ICs. Statistically significant differences on the order of (2–4)%, however, were observed when measuring absorbed dose to water using the ICs in the perpendicular orientation in the presence of the B‐field. Aerrow had a peak‐to‐peak response of about 0.5% when rotated within the solid phantom regardless of whether the B‐field was present or not. Conclusions This work describes the successful use of Aerrow as a straightforward means of measuring absolute dose to water for large high‐energy photon fields in the presence of a 1.5 T B‐field to a greater accuracy than currently achievable with ICs. The detector‐phantom air gap does not appear to significantly influence the response of Aerrow in absolute terms, nor does it contribute to its rotational dependence. This work suggests that the accurate use of solid phantoms for absolute point dose measurement is possible with Aerrow.

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Section: Discussionmentioning

confidence: 93%

“…All ICs were used with absorbed dose calibration coefficients,

N_{D, w}^{60_{italicCo}}

Section: Methodsmentioning

confidence: 99%

Section: D Reference Dosimetrymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Absolute dosimetry of a 1.5 T MR‐guided accelerator‐based high‐energy photon beam in water and solid phantoms using Aerrow

et al. 2020

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Density effects of silica aerogel insulation on the performance of a graphite probe calorimeter

et al. 2019

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Purpose: With the introduction of a novel graphite probe calorimeter, called the Aerrow, various thermal insulating materials are being explored to further improve the device. Silica-based aerogels are proving to be an optimal material due to their low densities, small thermal conductivities, rigidity, and machinability. The aim of this work is to determine how various silica aerogel densities affect the Aerrow's performance. Methods: Performance concerns three areas: heat transfer from the core, the Aerrow's beam quality dependence, and the effects of an applied magnetic field on its measurement of absorbed dose to water. A numerical heat transfer study was done to determine heat transfer time constants. The EGSnrc radiation transport toolkit was used to determine absorbed dose conversion factors which are used to quantify the Aerrow's beam quality dependence. Dose conversion factors for Cobalt-60 and two clinical photon beams (6 and 10 MV) were determined. Magnetic field perturbation factors are used to characterize the Aerrow's performance under an applied magnetic field. EGSnrc with the magnetic field transport algorithm was used to determine these perturbations for a 1.5 T MR-linac. Several aerogel densities (0.01-0.55 g cm À3 ) were examined for each performance area. Results: Heat transfer time constants were found to vary from 52 AE 2 to 117.4 AE 0.4 s. The time constants decreased with increasing aerogel density. The Aerrow's beam quality dependence varied between 0.5% and 1%, decreasing with increasing aerogel density. Beam quality dependence was determined in the range of 60 Co to 10 MV (58.4% ≤ %ddð10Þ x ≤ 73.5%). Under an applied magnetic field, perturbations were smallest when the Aerrow was parallel to the field. Perturbations varied more so when the Aerrow was perpendicular to the magnetic field and increased with increasing aerogel density. In all cases, perturbations were less than 0.6% from unity with a relative uncertainty of 0.1%. Conclusion: Silica-based aerogels demonstrate an improved performance over thermal insulation used in previous iterations of the Aerrow. With it, the Aerrow has shown to be robust in several areas. If heat transfer can be properly corrected for in the dose determination and the parallel orientation is used under a magnetic field, then the high density aerogel is possibly more preferable.

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

et al. 2021

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To 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 acceleratorbased photon beams. Methods: This 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 (%dd(10) x = 63.5%) and 10 MV (%dd(10) x = 71.1%) flattening filter-free (FFF) photon beams for two field sizes,characterized by S clin 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 d max in water. Results:The field output correction factors for this dosimeter design were computed for field sizes ranging from S clin = 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, S clin = 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. Conclusion:The 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 7476

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

Cited by 26 publications

References 43 publications

Absolute dosimetry of a 1.5 T MR‐guided accelerator‐based high‐energy photon beam in water and solid phantoms using Aerrow

Absolute dosimetry of a 1.5 T MR‐guided accelerator‐based high‐energy photon beam in water and solid phantoms using Aerrow

Density effects of silica aerogel insulation on the performance of a graphite probe calorimeter

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

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