Technical Note: A simple algorithm to convert EPID gray values into absorbed dose to water without prior knowledge

Boutry, C.; Sors, A.; Fontaine, J.; Delaby, N.; Delpon, G.

doi:10.1002/mp.12587

Cited by 7 publications

(6 citation statements)

References 23 publications

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“…The calibration of greyscale pixel values to absorbed doses to water relies on empirical modeling of the relative differences in EPID response in a highly non-water equivalent setup to that of an unperturbed dose distribution in water in the absence of a detector. [29][30][31][32][33][34][35][36] The main difficulty is that EPIDs are almost always calibrated against clinical point dosimeters and occasionally 2D film or ionization chamber array measurements under reference conditions that differ vastly in terms of scatter and attenuation from the EPID setup itself (i.e., in water or water-equivalent solid phantoms), imposing the need for several corrections. 28,[37][38][39][40] For instance, if a smaller phantom is used to calibrate the EPID, corrections are required to account for lateral scatter within the EPID and backscatter originated from the arm assembly, quantities that depend on every beam parameter.…”

Section: Discussionmentioning

confidence: 99%

Assessing the accuracy of electronic portal imaging device (EPID)‐based dosimetry: II. Evaluation of a dosimetric uncertainty budget and development of a new film‐in‐EPID absorbed dose calibration methodology

Renaud

Muir

2022

Medical Physics

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The aim of this study is to reduce the uncertainty associated with determining dose-to-water using an amorphous silicon electronic portal imaging detector (EPID) under reference conditions by developing a direct calibration formalism based on radiochromic film measurements made within the EPID panel and detailed Monte Carlo simulations. To our knowledge, this is the first EPID-based dosimetry study reporting an uncertain budget Methods: Pixel sensitivity and relative off -axis response were mapped by simultaneously irradiating film contained within the imager panel and acquiring an EPID image set. The detector panel was disassembled for the purpose of modeling the EPID in detail using the EGSnrc DOSXYZnrc usercode, which was in turn used to calculate dose-to-film in the EPID and dose-to-water in water conversion factors Results: A direct comparison of the two correction methodologies investigated in this work, the previously established empirical method and the proposed simultaneous measurement approach involving in-EPID film dosimetry, produced an agreement with an RMS deviation of 1.4% overall. A combined standard relative uncertainty of 3.3% (k = 1) was estimated for the determination of absorbed dose to water at the position of the EPID using the proposed calibration methodology Conclusions: This work describes a direct method of calibrating EPID response in terms of absorbed dose to water requiring fewer measurements than other empirical approaches, and without 2D spatial interpolation of correction factors.

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Section: Discussionmentioning

confidence: 99%

Assessing the accuracy of electronic portal imaging device (EPID)‐based dosimetry: II. Evaluation of a dosimetric uncertainty budget and development of a new film‐in‐EPID absorbed dose calibration methodology

Renaud

Muir

2022

Medical Physics

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“…In the second approach, EPID images were calculated to the absorbed dose at the water. Then the dose estimation at the water was compared to TPS's dose calculation [27,28]. The advantage of the second approach is the potential to directly verify the TPS algorithm's accuracy [29].…”

Section: Discussionmentioning

confidence: 99%

Planar EPID-Based Dosimetry for SRS and SRT Patient-Specific QA

Thongsawad

Chanton

Saiyo

et al. 2021

Life

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The study’s purpose was to develop and validate Electronic Portal Imaging Device (EPID)-based dosimetry for Stereotactic Radiosurgery (SRS) and Stereotactic Radiation Therapy (SRT) patient-specific Quality Assurance (QA). The co-operation between extended Source-to-Imager Distance (SID) to reduce the saturation effect and simplify the EPID-based dosimetry model was used to perform patient-specific QA in SRS and SRT plans. The four parameters were included for converting the image to dose at depth 10 cm; dose-response linearity with MU, beam profile correction, collimator scatter and water kernel. The model accuracy was validated with 10 SRS/SRT plans. The traditional diode arrays with MapCHECK were also used to perform patient-specific QA for assuring model accuracy. The 150 cm-SID was found a possibility to reduce the saturation effect. The result of model accuracy was found good agreement between our EPID-based dosimetry and TPS calculation with GPR more than 98% for gamma criteria of 3%/3 mm, more than 95% for gamma criteria of 2%/2 mm, and the results related to the measurement with MapCHECK. This study demonstrated the method to perform SRT and SRT patient-specific QA using EPID-based dosimetry in the FFF beam by co-operating between the extended SID that can reduce the saturation effect and estimate the planar dose distribution with the in-house model.

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“…EPID has been introduced to LINAC systems since the early 1980s 4 . It was initially developed for verifying the patient position and was later applied to LINAC QA 5‐12 . Compared with films and other QA devices, EPID has two major advantages 13‐15 : first, since EPID is integrated with the LINAC gantry, the QA procedure can be setup more quickly; second, the EPID data are in a digital form, which greatly facilitates the postprocessing, transfer, analysis, and storage of the data.…”

Section: Introductionmentioning

confidence: 99%

An electronic portal image device (EPID)‐based multiplatform rapid daily LINAC QA tool

Wang²,

Mai

et al. 2021

J Applied Clin Med Phys

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PurposeTo develop an efficient and economic daily quality research tool (DQRT) for daily check of multiplatform linear accelerators (LINACs) with flattening filter (FF) and flattening filter‐free (FFF) photon beams by using an Electronic Portal Image Device (EPID).Materials and MethodsAfter EPID calibration, the monitored parameters were analyzed from a 10 cm × 10 cm open and 60° wedge portal images measured by the EPID with 100 MU exposure. Next, the repeatability of the EPID position accuracy, long‐term stability, and linearity between image gray value and exposure were verified. Output and beam quality stability of the 6‐MV FF and FFF beams measured by DQRT with the introduced setup errors of EPID were also surveyed. Besides, some test results obtained by DQRT were compared with those measured by FC65‐G and Matrixx. At last, the tool was evaluated on three LINACs (Synergy, VersaHD, TrueBeam) for 2 months with two popular commercial QA tools as references.ResultsThere are no differences between repeatability tests for all monitored parameters. Image grayscale values obtained by EPID and exposure show good linearity. Either 6 MV FF or FFF photon beam shows minimal impact to the results. The differences between FC65‐G, Matrixx and DQRT results are negligible. Monitor results of the two commercial tools are consistent with the DQRT results collected during the 2‐month period.ConclusionWith a shorter time and procedure, the DQRT is useful to daily QA works of LINACs, producing a QA result quality similarly to or more better than the traditional tools and giving richer contents to the QA results. For hospitals with limited QA time window available or lack of funding to purchase commercial QA tools, the proposed DQRT can provide an alternative and economic approach to accomplish the task of daily QA for LINACs.

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Technical Note: A simple algorithm to convert EPID gray values into absorbed dose to water without prior knowledge

Abstract: Without a prior irradiation settings knowledge except the incident energy beam, we use EPID as a reliable dose to water detector for both homogeneous and modulated beams.

Cited by 7 publications

References 23 publications

Assessing the accuracy of electronic portal imaging device (EPID)‐based dosimetry: II. Evaluation of a dosimetric uncertainty budget and development of a new film‐in‐EPID absorbed dose calibration methodology

Assessing the accuracy of electronic portal imaging device (EPID)‐based dosimetry: II. Evaluation of a dosimetric uncertainty budget and development of a new film‐in‐EPID absorbed dose calibration methodology

Planar EPID-Based Dosimetry for SRS and SRT Patient-Specific QA

An electronic portal image device (EPID)‐based multiplatform rapid daily LINAC QA tool

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