SSRMP Recommendations No 9: Reference dosimetry in low and medium energy x-ray beams

Aspradakis, Maria M; Buchillier, Thierry; Kohler, Götz; Kottler, Christian; Krayenbühl, J.

doi:10.1016/j.zemedi.2022.12.003

Cited by 3 publications

(1 citation statement)

References 34 publications

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“…As in our study the absorbed dose relative to water, for a given x-ray irradiation, has been normalized to Co-60, the resulting energy response is lower for thicker films at low x-ray energies. From these results, one could propose to increase the thickness of the film to lower the energy dependence, but thicker films will disturb the radiation field and it is generally the aim to keep detectors thin enough (Aspradakis et al 2023).…”

Section: Discussionmentioning

confidence: 99%

New optically stimulated luminescence dosimetry film optimized for energy dependence guided by Monte Carlo simulations

De Saint-Hubert,

Caprioli,

de Freitas Nascimento

et al. 2024

Phys. Med. Biol.

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Optically stimulated luminescence (OSL) film dosimeters, based on BaFBr:Eu2+ phosphor material, have major advantages but as they are not made of tissue-equivalent materials they exhibit an energy-dependent over-response at low photon energies. In this work, the OSL energy-dependent response was optimized by lowering the phosphor grain size, seeking an optimal choice of phosphor concentration and film's thickness with sufficient sensitivity. This optimization process combines measurement-based assessments of energy response in narrow X-ray beams with in-silico metrics involving theoretical approaches and Monte Carlo (MC) dose simulations for for homogeneous phosphor distributions and for isolated phosphor grains of different dimensions, where the dose in the phosphor grain was calculated. In total 8 OSL films were manufactured with different BaFBr:Eu2+ median particle diameters (D50): 3.2 µm, 1.5 µm and 230 nm and different phosphor concentrations (1.6%, 5.3% and 21.3 %) and thicknesses (from 5.2 µm to 49 \µm). Films were irradiated in narrow X-ray spectra (N60, N80, N-150 and N-300) and the signal intensity relative to the nomimal dose-to-water value was normalized with respect to Co-60. Finally we experimentally tested the response of several films in Varian 6MV, 10x10 cm2 field, 0° gantry angle, 90 cm SSD, 10 cm depth.A reduced energy response was measured in X-rays for the smallest grain size with an inverse correlation between response and grain size. The N-60 irradiation showed a 43% reduction in the energy over-response when going from 3 µm to 230 nm grain size and 5% phosphor concentration. In-silico metrics calculation, using homogeneous dispersion of the phosphor, underestimated the experimental response and was not able to obtain the experimental correlation between grain size and energy response. Isolated grain size modeling allowed for a good agreement to experimental data, and enabled steering the production of optimized OSL-films to further test in clinical 6 MV beams.

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Section: Discussionmentioning

confidence: 99%

New optically stimulated luminescence dosimetry film optimized for energy dependence guided by Monte Carlo simulations

De Saint-Hubert,

Caprioli,

de Freitas Nascimento

et al. 2024

Phys. Med. Biol.

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Determination of kilovoltage x-ray therapy depth doses with open-ended applicators

Perkins,

Healy,

Coldrey

2024

Phys Eng Sci Med

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The purpose of this work was to determine percentage depth dose (PDD) curves for kilovoltage x-rays from the WOmed-T105 unit, with open-ended steel applicators and beam qualities ranging from 0.5 to 4.2 mm Al. Measurements were made with parallel plate chambers in a water phantom, with extrapolation based on a fth order polynomial used to estimate the surface dose. Measurements were also made with parallel plate chambers in a plastic water phantom, with thin plastic sheets used to obtain detailed measurements at shallow depths (less than 1 mm). Monte Carlo simulations were performed using the EGSnrc package, with two different sources as input: a SpekPy simulation of the xray beam and a full simulation of the x-ray tube, treatment head and applicators. Results showed that all four methods (two measurements and two simulations) agreed within the measurement uncertainty at depths greater than 2 mm. At shallow depths, signi cant differences were noted. At depths less than 0.1 mm, the full Monte Carlo simulation and the solid water measurements showed a sharp spike in surface dose which is attributed to electron contamination, which was not seen in the SpekPy Monte Carlo simulation or the extrapolated water measurements. At depths between 0.1 mm and 2 mm, beyond the range of contaminant electrons, the extrapolated water measurements underestimate the dose by up to 13% compared to the full Monte Carlo simulation and the solid water measurements., attributed to uorescent photons generated in the applicators. This work demonstrates that for open-ended applicators, measurement of depth doses in water with extrapolation of surface dose has the potential to signi cantly underestimate the dose at shallow depths between the surface and 2 mm, even after eliminating electron contamination from the beam.

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Determination of kilovoltage x-ray therapy depth doses with open-ended applicators

Perkins,

Healy,

Coldrey

2023

Preprint

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The purpose of this work was to determine percentage depth dose (PDD) curves for kilovoltage x-rays from the WOmed-T105 unit, with open-ended steel applicators and beam qualities ranging from 0.5 to 4.2 mm Al. Measurements were made with parallel plate chambers in a water phantom, with extrapolation based on a fifth order polynomial used to estimate the surface dose. Measurements were also made with parallel plate chambers in a plastic water phantom, with thin plastic sheets used to obtain detailed measurements at shallow depths (less than 1 mm). Monte Carlo simulations were performed using the EGSnrc package, with two different sources as input: a SpekPy simulation of the x-ray beam and a full simulation of the x-ray tube, treatment head and applicators. Results showed that all four methods (two measurements and two simulations) agreed within the measurement uncertainty at depths greater than 2 mm. At shallow depths, significant differences were noted. At depths less than 0.1 mm, the full Monte Carlo simulation and the solid water measurements showed a sharp spike in surface dose which is attributed to electron contamination, which was not seen in the SpekPy Monte Carlo simulation or the extrapolated water measurements. At depths between 0.1 mm and 2 mm, beyond the range of contaminant electrons, the extrapolated water measurements underestimate the dose by up to 13% compared to the full Monte Carlo simulation and the solid water measurements., attributed to fluorescent photons generated in the applicators. This work demonstrates that for open-ended applicators, measurement of depth doses in water with extrapolation of surface dose has the potential to significantly underestimate the dose at shallow depths between the surface and 2 mm, even after eliminating electron contamination from the beam.

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SSRMP Recommendations No 9: Reference dosimetry in low and medium energy x-ray beams

Cited by 3 publications

References 34 publications

New optically stimulated luminescence dosimetry film optimized for energy dependence guided by Monte Carlo simulations

New optically stimulated luminescence dosimetry film optimized for energy dependence guided by Monte Carlo simulations

Determination of kilovoltage x-ray therapy depth doses with open-ended applicators

Determination of kilovoltage x-ray therapy depth doses with open-ended applicators

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