Performance evaluation of an LED flatbed scanner for triple channel film dosimetry with EBT3 and EBT-XD film

Walt, Marchant Van der; Marsh, Linda; Baines, John; Gibson, S. M.; Shoobridge, Ariadne; Vine, Glenn de

doi:10.1007/s13246-022-01161-z

Cited by 5 publications

(7 citation statements)

References 26 publications

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“…4, Table 1, Table 2, and Table 3. Film dosimetry used in this investigation followed a protocol that yielded a dose uncertainty below 3.0 % [39].…”

Section: Resultsmentioning

confidence: 99%

“…Irradiating lms parallel to the beam, in the coronal plane, within solid water blocks of dimensions 20´30 ´n cm 3 would minimise this issue; however, these were not available during this investigation. Film data, while noisy compared to Geant4 and Monaco TPS PDD curves, demonstrate that lm can be useful to experimentally generate a continuous depth dose pro le, whereas the MOSkin™ is point dose speci c. The lm data demonstrates the sensitivity of air gaps on lm dosimetry in the MR-linac despite following a protocol that yields an uncertainty below 3.0 % [39].…”

Section: Discussionmentioning

confidence: 98%

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High-resolution entry and exit surface dosimetry in a 1.5 T MR-linac

Patterson

Stokes

Cutajar

et al. 2022

Preprint

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The magnetic field of a transverse MR-linac alters electron trajectories as the photon beam transits through materials, causing lower doses at flat entry surfaces and increased doses at flat beam-exiting surfaces. This study investigated the response of a MOSFET detector, known as the MOSkin™, for high-resolution surface and near-surface percentage depth dose measurements on an Elekta Unity. Simulations with Geant4 and the Monaco treatment planning system (TPS), and EBT-3 film measurements, were also performed for comparison. Measured MOSkin™ entry surface doses, relative to dmax, were (9.9 ± 0.2) %, (10.1 ± 0.3) %, (11.3 ± 0.6) %, (12.9 ± 1.0) %, and (13.4 ± 1.0) % for 1 × 1 cm2, 3 × 3 cm2, 5 × 5 cm2, 10 × 10 cm2, and 22 × 22 cm2 fields, respectively. Similarly at the beam exit MOSkin™ doses were (37.2 ± 4.9) %, (50.0 ± 2.9) %, (54.9 ± 2.0) %, (63.9 ± 1.6) %, and (62.4 ± 3.0) %. For the investigated fields, the maximum absolute dose differences for Geant4, TPS, and film at the beam entry, relative to MOSkin™ surface doses, were 1.0%, 16.4%, and 24.3%, respectively and at the beam exit, 5.0%, 3.1%, and 5.7%, respectively. The largest increase in exit dose, due to the electron return effect, was 18.0% for the 22 × 22 cm2 field size, using Geant4 calculations. The results presented in the study validate the suitability of the MOSkin™ detector for transverse MR-linac surface dosimetry.

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“…4, Table 1, Table 2, and Table 3. Film dosimetry used in this investigation followed a protocol that yielded a dose uncertainty below 3.0 % [39].…”

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 98%

High-resolution entry and exit surface dosimetry in a 1.5 T MR-linac

Patterson

Stokes

Cutajar

et al. 2022

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

“…Irradiating films parallel to the beam, in the coronal plane, within solid water blocks of dimensions 20 × 30 × n cm 3 would minimise this issue; however, these were not available during this investigation. The continuous depth dose film data demonstrates the sensitivity of air gaps on film dosimetry in the MR-linac despite following a protocol that yields an uncertainty below 3.0% [ 47 ]. Perpendicular film irradiation has the potential to address the overestimation of surface dose obtained by irradiating the film in a parallel orientation.…”

Section: Discussionmentioning

confidence: 99%

“…Due to scan resolution, film entry and exit measurement points begin at a depth of 0.34 mm within the solid water phantom. Film dosimetry used in this investigation followed a protocol that yielded a dose uncertainty below 3.0% [ 47 ].…”

Section: Methodsmentioning

confidence: 99%

High-resolution entry and exit surface dosimetry in a 1.5 T MR-linac

et al. 2023

View full text Add to dashboard Cite

The magnetic field of a transverse MR-linac alters electron trajectories as the photon beam transits through materials, causing lower doses at flat entry surfaces and increased doses at flat beam-exiting surfaces. This study investigated the response of a MOSFET detector, known as the MOSkin™, for high-resolution surface and near-surface percentage depth dose measurements on an Elekta Unity. Simulations with Geant4 and the Monaco treatment planning system (TPS), and EBT-3 film measurements, were also performed for comparison. Measured MOSkin™ entry surface doses, relative to Dmax, were (9.9 ± 0.2)%, (10.1 ± 0.3)%, (11.3 ± 0.6)%, (12.9 ± 1.0)%, and (13.4 ± 1.0)% for 1 × 1 cm2, 3 × 3 cm2, 5 × 5 cm2, 10 × 10 cm2, and 22 × 22 cm2 fields, respectively. For the investigated fields, the maximum percent differences of Geant4, TPS, and film doses extrapolated and interpolated to a depth suitable for skin dose assessment at the beam entry, relative to MOSkin™ measurements at an equivalent depth were 1.0%, 2.8%, and 14.3%, respectively, and at a WED of 199.67 mm at the beam exit, 3.2%, 3.7% and 5.7%, respectively. The largest measured increase in exit dose, due to the electron return effect, was 15.4% for the 10 × 10 cm2 field size using the MOSkin™ and 17.9% for the 22 × 22 cm2 field size, using Geant4 calculations. The results presented in the study validate the suitability of the MOSkin™ detector for transverse MR-linac surface dosimetry.

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“…Films were scanned as previously for calibration, and lateral scanner variations were corrected using a MAT-LAB script. 42 Profiles across the ESE distribution in the x-direction were created in FilmQA™ Pro using a 25.0 × 0.3 cm 2 ROI. Along each profile, the dose corresponding to the position of the point-dose dosimeter measurements was recorded.…”

Section: Measurementsmentioning

confidence: 99%

Electron streaming dose measurements and calculations on a 1.5 T MR‐Linac

Patterson,

Powers,

Metcalfe

et al. 2024

J Applied Clin Med Phys

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PurposeTo evaluate the accuracy of different dosimeters and the treatment planning system (TPS) for assessing the skin dose due to the electron streaming effect (ESE) on a 1.5 T magnetic resonance (MR)‐linac.MethodSkin dose due to the ESE on an MR‐linac (Unity, Elekta) was investigated using a solid water phantom rotated 45° in the x‐y plane (IEC61217) and centered at the isocenter. The phantom was irradiated with 1 × 1, 3 × 3, 5 × 5, 10 × 10, and 22 × 22 cm2 fields, gantry at 90°. Out‐of‐field doses (OFDs) deposited by electron streams generated at the entry and exit surface of the angled phantom were measured on the surface of solid water slabs placed ±20.0 cm from the isocenter along the x‐direction. A high‐resolution MOSkin™ detector served as a benchmark due to its shallower depth of measurement that matches the International Commission on Radiological Protection (ICRP) recommended depth for skin dose assessment (0.07 mm). MOSkin™ doses were compared to EBT3 film, OSLDs, a diamond detector, and the TPS where the experimental setup was modeled using two separate calculation parameters settings: a 0.1 cm dose grid with 0.2% statistical uncertainty (0.1 cm, 0.2%) and a 0.2 cm dose grid with 3.0% statistical uncertainty (0.2 cm, 3.0%).ResultsOSLD, film, the 0.1 cm, 0.2%, and 0.2 cm, 3.0% TPS ESE doses, underestimated skin doses measured by the MOSkin™ by as much as –75.3%, –7.0%, –24.7%, and –41.9%, respectively. Film results were most similar to MOSkin™ skin dose measurements.ConclusionsThese results show that electron streams can deposit significant doses outside the primary field and that dosimeter choice and TPS calculation settings greatly influence the reported readings. Due to the steep dose gradient of the ESE, EBT3 film remains the choice for accurate skin dose assessment in this challenging environment.

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Performance evaluation of an LED flatbed scanner for triple channel film dosimetry with EBT3 and EBT-XD film

Cited by 5 publications

References 26 publications

High-resolution entry and exit surface dosimetry in a 1.5 T MR-linac

High-resolution entry and exit surface dosimetry in a 1.5 T MR-linac

High-resolution entry and exit surface dosimetry in a 1.5 T MR-linac

Electron streaming dose measurements and calculations on a 1.5 T MR‐Linac

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