Evaluation of effective field size characteristics for small megavoltage photon beam dosimetry

Keivan, H.; ,; Maskani, R.; ,; Shahbazi-Gahrouei, D.; ,; Shanei, A.; ,; Pandesh, S.; ,; Tarighati Sereshke, E.; ,

doi:10.52547/ijrr.20.1.25

Cited by 3 publications

(3 citation statements)

References 21 publications

(33 reference statements)

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“…This shows the possibility of replacing diodes as semiconductor dosimeters. PDD trends in TlBr and thimble chambers were not significantly different, including the need for correction factors for sensitive volume and energy dependence of the dosimeter [18].…”

Section: Discussionmentioning

confidence: 90%

Evaluation of polycrystalline thallium (I) bromide dosimeter for radiotherapy quality assurance

et al. 2020

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In radiotherapy, dose assessment is performed as part of quality assurance (QA) to verify the dose accuracy of the treatment administered to patients. Various dosimeters are used depending on the part of the body and the desired purpose, and tools such as the thermoluminescent dosimeter (TLD) and semiconductor dosimeter are used as in vivo dosimeters. However, TLDs have demonstrated measurement errors of approximately 11.8%, and the diodes used in semiconductor dosimeters fluctuate in performance owing to radiation damage. Consequently, various photoconductor materials are being researched to replace diodes. In particular, Thallium (I) bromide (TlBr) is being used as a substitute material for semiconductors because of its low cost and high performance. Therefore, this study determined the optimised performance of TlBr, which is a potential photoconductor material to replace other materials commercially, using the particle-in-binder deposition method. Upon evaluating the reproducibility and linearity, all sensors demonstrated remarkable performance at 6 MV and 15 MV as the results demonstrated a relative standard deviation (RSD) less than 1.5% and R2 value above 0.9998, which were the evaluation criteria. A 3:1 material ratio was chosen, as the performance demonstrated in this case was superior to that of other material ratios. The results of the monitor unit rate dependence and percent depth dose (PDD) were compared with those of silicon diode and thimble chambers, which are widely used for dose measurement. According to the monitor unit rate dependence results, the RSD was 0.66% at 6 MV and 0.27% at 15 MV with the standard set at 100 MU, indicating that the diode was outperformed by less than 1%. Similar results were obtained for the PDD with the ion chamber, and the surface dose required for in vivo dose measurement indicated an error within 8.67%. Therefore, this study provides basic data for polycrystalline TlBr dosimeters, which can replace the existing semiconductor dosimeters for QA.

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Section: Discussionmentioning

confidence: 90%

Evaluation of polycrystalline thallium (I) bromide dosimeter for radiotherapy quality assurance

et al. 2020

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“…There was no significant difference in the PDD results compared with the thimble chamber, although PDD was relatively high after a depth of 5 cm. This reflects the need for a correction factor for the sensitive volume and energy dependence of the dosimeter [16]. In the case of surface dose, the difference from the thimble chamber at 0.1 cm was approximately 1.62% at 6 MV and 8.67% at 15 MV.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

Evaluation of two-dimensional dosimeter based on thallium (I) bromide for measurement of surface dose in radiotherapy

Han¹,

Yang²,

Lee³

et al. 2021

J. Inst.

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In radiotherapy, side effects can occur on the skin because each patient's skin has a different level of sensitivity to radiation. Therefore, in clinical practice, point dose is measured to verify skin doses, although there is a problem, in that it is difficult to analyse the dose distribution for the body surface area. In this study, we constructed a film dosimeter based on polycrystalline thallium (I) bromide, evaluated its performance, and analysed the electrical properties according to the number of bending cycles to evaluate the mechanical flexibility. Further, an array dosimeter was constructed, and the dose distribution was analysed to evaluate the clinical effectiveness. As a result of the performance evaluation, reproducibility, linearity, and dose-rate dependence all satisfied the evaluation criteria. Percent depth dose showed similar results, and a difference of 0.027 when the slope of the depth in the range of 20–10 cm was compared with that of the thimble chamber. With regard to mechanical flexibility, as the number of bending cycles increased, the sensitivity tended to decrease. The clinical efficacy evaluation showed that the difference in dose distribution between the boundary field and non-field was approximately ≥ 40%, which decreased exponentially as the distance from the boundary field increased. The gap dose distribution showed an average difference of approximately ≥ 47% compared with the beam profile central axis. This suggests the possibility of application as a radiotherapy digital dosimeter, as well as the possibility of analysing the dose distribution on the body surface.

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“…One of the important tasks in small field dosimetry is the determination of ROFs. It has been shown that detector-specific output correction factors , , depend on many factors such as the perturbation of particle fluence and volume averaging effects, in particular, on the field size, detector type, and the design, size, and non-water equivalency of most of the detectors [16]- [18].…”

Section: Introductionmentioning

confidence: 99%

A multi-detector comparison to determine convergence of measured relative output factors for small field dosimetry

Chi,

Toan,

Hill

2023

Phys Eng Sci Med

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Purpose: Good clinical practice in small field dosimetry relies on using multiple detectors for the determination of relative output factors (ROFs). The TRS-483 Code of Practice (CoP) provides recommended output correction factors, k, for a range of detectors and beam energies as used in small field dosimetry. In this work, the convergence of the ROFs for 6MV x-ray beams with and without flattening-filters were investigated under a different combinations of beam collimation and published detector correction factors.Method: Three IBA detectors SFD, PFD and CC04 were used to measure ROFs on a TrueBeam STx linear accelerator with small fields collimated by the high definition MLC which has 2.5 mm and 5.0 mm wide leaves. Two configurations were used for the collimators being 1) fixed-jaws at 10 × 10 cm 2 and 2) with a 2 mm offset from the MLC edge, in line with the recommended geometry from IROC-H as part of their auditing program and published dataset. The k factors for the three detectors were taken from the TRS483 CoP and other published works. Results:The standard deviation in measured ROFs between detectors under 6MV-WFF beam are 1.4% and 1.9% while these under 6MV-FFF beam are 2.3% and 2.4% in MLC field with fixed-jaw and with 2 mm jaws-offset, respectively. The relative difference in averaged ROFs of three reference detectors from corresponding IROC-H dataset are 2.0% and 3.1% under 6MV-WFF beam while they are 2.4% and 3.2% under 6MV-FFF beam at the smallest available field size 2 × 2 cm 2 . For smaller field sizes, the uncertainty in averaged ROFs of three reference detectors from corresponding results of from 2 mm jaws-offset setting by Akino and Dufreneix showed the largest difference are 6.6% and 6.2% under 6MV-WFF beam while they are 3.4% and 3.6% under 6MV-WFF beam at smallest field size 0.5 × 0.5 cm 2 . Conclusion:The corresponding datasets provided by TRS-483 and IROC-H are generic and may not statistically large enough with 6MV-FFF and also MLC field with 2 mm jaws-offset setting, so that clinical users should use at least three different types of small field detector in measurements. The IROC-H dataset is not available for field size smaller than 2 × 2 cm 2 so that user should carefully check with other publications with the same setting.

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Evaluation of effective field size characteristics for small megavoltage photon beam dosimetry

Cited by 3 publications

References 21 publications

Evaluation of polycrystalline thallium (I) bromide dosimeter for radiotherapy quality assurance

Evaluation of polycrystalline thallium (I) bromide dosimeter for radiotherapy quality assurance

Evaluation of two-dimensional dosimeter based on thallium (I) bromide for measurement of surface dose in radiotherapy

A multi-detector comparison to determine convergence of measured relative output factors for small field dosimetry

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