aSi-EPID transit signal calibration for dynamic beams: a needful step for the IMRT in vivo dosimetry

Greco, Francesca; Piermattei, Angelo; Azario, L.; Placidi, L.; Cilla, Savino; Caivano, Rocchina; Fusco, Vincenzo; Fidanzio, A.

doi:10.1007/s11517-013-1094-x

Cited by 8 publications

(11 citation statements)

References 26 publications

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“…The gamma analysis supplies a transit dosimetry to verify the treatment reproducibility, which can be affected by the patient setup, linac output factor variations, beam interruptions, dose calculations, and the presence of patient morphological changes. The ratio

R

between the reconstructed and planned isocenter doses is considered in tolerance when 0.95 ≤ R ≤ 1.05 considering the difficulty in chest wall dosimetry and the statistical propagation of the errors for

R

(uncertainties of D iso estimated in 4% in inhomogeneous tissues, uncertainties in D tps within 3%) . The global

γ

‐analysis adopted two gamma criteria: (a) the EPID percentage signal agreement, Δ S %, and (b) the distance to agreement, Δ d (mm).…”

Section: Methodsmentioning

confidence: 99%

Evaluation of interfraction setup variations for postmastectomy radiation therapy using EPID‐based in vivo dosimetry

Kang

et al. 2019

J Applied Clin Med Phys

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Postmastectomy radiation therapy is technically difficult and can be considered one of the most complex techniques concerning patient setup reproducibility. Slight patient setup variationsparticularly when high-conformal treatment techniques are usedcan adversely affect the accuracy of the delivered dose and the patient outcome. This research aims to investigate the inter-fraction setup variations occurring in two different scenarios of clinical practice: at the reference and at the current patient setups, when an image-guided system is used or not used, respectively.The results were used with the secondary aim of assessing the robustness of the patient setup procedure in use. Forty eight patients treated with volumetric modulated arc and intensity modulated therapies were included in this study. EPID-based in vivo dosimetry (IVD) was performed at the reference setup concomitantly with the weekly cone beam computed tomography acquisition and during the daily current setup. Three indices were analyzed: the ratio R between the reconstructed and planned isocenter doses, γ% and the mean value of γ from a transit dosimetry based on a two-dimensional γ-analysis of the electronic portal images using 5% and 5 mm as dose difference and distance to agreement gamma criteria; they were considered in tolerance if R was within 5%, γ% > 90% and γ mean < 0.4. One thousand and sixteen EPID-based IVD were analyzed and 6.3% resulted out of the tolerance level.Setup errors represented the main cause of this off tolerance with an occurrence rate of 72.2%. The percentage of results out of tolerance obtained at the current setup was three times greater (9.5% vs 3.1%) than the one obtained at the reference setup, indicating weaknesses in the setup procedure. This study highlights an EPID-based IVD system's utility in the radiotherapy routine as part of the patient's treatment quality controls and to optimize (or confirm) the performed setup procedures' accuracy. K E Y W O R D Sbreast radiotherapy, in vivo dosimetry, volumetric modulated arc therapy ---

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R

R

(uncertainties of D iso estimated in 4% in inhomogeneous tissues, uncertainties in D tps within 3%) . The global

γ

‐analysis adopted two gamma criteria: (a) the EPID percentage signal agreement, Δ S %, and (b) the distance to agreement, Δ d (mm).…”

Section: Methodsmentioning

confidence: 99%

Evaluation of interfraction setup variations for postmastectomy radiation therapy using EPID‐based in vivo dosimetry

Kang

et al. 2019

J Applied Clin Med Phys

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“…The integral EPID image, referred to each single static or dynamic beam of the treatment fraction, is elaborated to determine: the R ratio between the reconstructed isocenter dose (D iso, EPID ) by EPID image and that planned by TPS, D iso, TPS . In particular, D iso, EPID was determined as the average reconstructed dose values obtained from the points in ▵r side square area (around the beam central axis).The dose reconstruction algorithms for the 3 techniques used are reported in the literature, 27 - 35 where the global accuracy for the R ratio is determined considering both the D iso, EPID accuracy (in inhomogeneous tissues estimated in 4%) 13 , 28 – 34 and the D iso, TPS accuracy (generally estimated well within 3%). The statistical propagation of the uncertainties supplies for R ratio index the tolerance level 0.95 ≤ R ≤ 1.05; γ-Like analysis which is the comparison between the EPID signal, S, of the reference image (after the optimized patient setup) and that of the EPID image measured with current patient setup.…”

Section: Methodsmentioning

confidence: 99%

“… 2 – 6 The in vivo dosimetry (IVD) is strongly recommended by various organizations 7 - 10 so that in some countries, IVD tests are required as a routine check to detect the causes of dosimetric errors. 11 , 12 Several researchers 13 - 35 have implemented IVD systems to reconstruct the delivered dose to the patients using the amorphous silicon electronic portal imaging device (aSi-EPID) associated with the linear accelerator (LINAC). The results showed that aSi-EPIDs can be used to reconstruct the dose in single points, 2 dimensional (2D), and entire 3-dimensional (3-D) dose distribution.…”

Section: Introductionmentioning

confidence: 99%

A Feasibility Study for in vivo Dosimetry Procedure in Routine Clinical Practice

Falco¹,

Giancaterino²,

Nicola³

et al. 2018

Technol Cancer Res Treat

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Purpose:The aim of the in vivo dosimetry, during the fractionated radiation therapy, is the verification of the correct dose delivery to patient. Nowadays, in vivo dosimetry procedures for photon beams are based on the use of the electronic portal imaging device and dedicated software to elaborate electronic portal imaging device images.Methods:In total, 8474 in vivo dosimetry tests were carried out for 386 patients treated with 3-dimensional conformal radiotherapy, intensity-modulated radiotherapy, and volumetric modulated arc therapy techniques, using the SOFTDISO. SOFTDISO is a dedicated software that uses electronic portal imaging device images in order to (1) calculate the R index, that is, the ratio between daily reconstructed dose and the planned one at isocenter and (2) perform a γ-like analysis between the signals, S, of a reference electronic portal imaging device image and that obtained in a daily fraction. It supplies 2 indexes, the percentage γ% of points with γ < 1 and the mean γ value, γmean. In γ-like analysis, the pass criteria for the signals agreement ΔS% and distance to agreement Δd have been selected based on the clinical experience and technology used. The adopted tolerance levels for the 3 indexes were fixed in 0.95 ≤ R ≤ 1.05, γ% ≥ 90%, and γmean ≤ 0.5.Results:The results of R ratio, γ-like, and a visual inspection of these data reported on a monitor screen permitted to individuate 2 classes of errors (1) class 1 that included errors due to inadequate standard quality controls and (2) class 2, due to patient morphological changes. Depending on the technique and anatomical site, a maximum of 18% of tests had at least 1 index out of tolerance; once removed the causes of class-1 errors, almost all patients (except patients with 4 lung and 2 breast cancer treated with 3-dimensional conformal radiotherapy) presented mean indexes values (trueR¯, trueγ¯%, and γ¯mean ) within tolerance at the end of treatment course. Class-2 errors were found in some patients.Conclusions:The in vivo dosimetry procedure with SOFTDISO resulted easily implementable, able to individuate errors with a limited workload.

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“…Figure 3a-c provides lateral dose profiles measured with a detector array (black line) and EPID (red dotted line) normalized to the dose at the center of the radiation field. The green dashed line in Figure 3 presents the EPID profile corrected by the correction factor k profile from Equation (5).…”

Section: Correction Factor For Inhomogeneities In the Beam Profile K ...mentioning

confidence: 99%

The fast calibration model for dosimetry with an electronic portal imaging device

Schade

Engenhart‐Cabillic

Zink

et al. 2022

J Applied Clin Med Phys

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The aim of this study was to develop an algorithm that corrects the image of an electronic portal imaging device (EPID) of a linear accelerator so that it can be used for dosimetric purposes, such as in vivo dosimetry or quality assurance for photon radiotherapy. For that purpose, the impact of the field size, phantom thickness, and the varying spectral photon distribution within the irradiation field on the EPID image was investigated. Methods: The EPID measurements were verified using reference measurements with ionization chambers. Therefore, absolute dose measurements with an ionization chamber and relative dose measurements with a detector array were performed. An EPID calibration and correction algorithm was developed to convert the EPID image to a dose distribution. The algorithm was validated by irradiating inhomogeneous phantoms using square fields as well as irregular IMRT fields. Results: It was possible to correct the influence of the field size, phantom thickness on the EPID signal as well as the homogenization of the image profile by several correction factors within 0.6%. A gamma index analysis (3%, 3 mm) of IMRT fields showed a pass rate of above 99%, when comparing to the planning system. Conclusion:The developed algorithm enables an online dose measurement with the EPID during the radiation treatment. The algorithm is characterized by a robust, non-iterative, and thus real-time capable procedure with little measuring effort and does not depend on system-specific parameters. The EPID image is corrected by multiplying three independent correction factors. Therefore, it can easily be extent by further correction factors for other influencing variables, so it can be transferred to other linear accelerators and EPID configurations.

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aSi-EPID transit signal calibration for dynamic beams: a needful step for the IMRT in vivo dosimetry

Cited by 8 publications

References 26 publications

Evaluation of interfraction setup variations for postmastectomy radiation therapy using EPID‐based in vivo dosimetry

Evaluation of interfraction setup variations for postmastectomy radiation therapy using EPID‐based in vivo dosimetry

A Feasibility Study for in vivo Dosimetry Procedure in Routine Clinical Practice

The fast calibration model for dosimetry with an electronic portal imaging device

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