A generalized calibration procedure for in vivo transit dosimetry using siemens electronic portal imaging devices

Fidanzio, A.; Greco, Francesca; Gargiulo, Laura; Cilla, Savino; Sabatino, Domenico; Cappiello, Massimo; Felice, Cinzia Di; Castro, Elisabetta Di; Azario, L.; Russo, Mariateresa; Pompei, Luciano de Melo; D'Onofrio, Guido; Piermattei, Angelo

doi:10.1007/s11517-010-0699-6

Cited by 5 publications

(3 citation statements)

References 34 publications

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“…In addition, EPID-based in vivo dosimetrics, which measure transmission images during patient delivery for intensitymodulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT), have been demonstrated to be feasible in recent years (10)(11)(12). Fuangrod et al (13) used statistical process control and other methods to compare the consistency of the calculated and actually measured dose accumulation points in real time, and the dose delivery error could be found within 2 s. Miri et al ( 14) used Varian's aS1200 DMI panel to develop a QA model for IMRT delivery verification.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of Daily CT for EPID-Based Transit In Vivo Dosimetry

Feng

et al. 2021

Front. Oncol.

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PurposeThe difference in anatomical structure and positioning between planning and treatment may lead to bias in electronic portal image device (EPID)-based in vivo dosimetry calculations. The purpose of this study was to use daily CT instead of planning CT as a reference for EPID-based in vivo dosimetry calculations and to analyze the necessity of using daily CT for EPID-based in vivo dosimetry calculations in terms of patient quality assurance.Materials and MethodsTwenty patients were enrolled in this study. The study design included eight different sites (the cervical, nasopharyngeal, and oral cavities, rectum, prostate, bladder, lung, and esophagus). All treatments were delivered with a CT-linac 506c (UIH, Shanghai) using 6 MV photon beams. This machine is equipped with diagnosis-level fan-beam CT and an amorphous silicon EPID XRD1642 (Varex Imaging Corporation, UT, USA). A Monte Carlo algorithm was developed to calculate the transmit EPID image. A pretreatment measurement was performed to assess system accuracy by delivering based on a homogeneous phantom (RW3 slab, PTW, Freiburg). During treatment, each patient underwent CT scanning before delivery either once or twice for a total of 268 fractions obtained daily CT images. Patients may have had a position correction that followed our image-guided radiation therapy (IGRT) procedure. Meanwhile, transmit EPID images were acquired for each field during delivery. After treatment, all patient CTs were reviewed to ensure that there was no large anatomical change between planning and treatment. The reference of transmit EPID images was calculated based on both planning and daily CTs, and the IGRT correction was corrected for the EPID calculation. The gamma passing rate (3 mm 3%, 2 mm 3%, and 2 mm 2%) was calculated and compared between the planning CT and daily CT. Mechanical errors [ ± 1 mm, ± 2 mm, ± 5 mm multileaf collimator (MLC) systematic shift and 3%, 5% monitor unit (MU) scaling] were also introduced in this study for comparing detectability between both types of CT.ResultThe average (standard deviation) gamma passing rate (3 mm 3%, 2 mm 3%, and 2 mm 2%) in the RW3 slab phantom was 99.6% ± 1.0%, 98.9% ± 2.1%, and 97.2% ± 3.9%. For patient measurement, the average (standard deviation) gamma passing rates were 87.8% ± 14.0%, 82.2% ± 16.9%, and 74.2% ± 18.9% for using planning CTs as reference and 93.6% ± 8.2%, 89.7% ± 11.0%, and 82.8% ± 14.7% for using daily CTs as reference. There were significant differences between the planning CT and daily CT results. All p-values (Mann–Whitney test) were less than 0.001. In terms of error simulation, nonparametric test shows that there were significant differences between practical daily results and error simulation results (p < 0.001). The receiver operating characteristic (ROC) analysis indicated that the detectability of mechanical delivery error using daily CT was better than that of planning CT. AUCDaily CT = 0.63–0.96 and AUCPlanning CT = 0.49–0.93 in MLC systematic shift and AUCDaily CT = 0.56–0.82 and AUCPlanning CT = 0.45–0.73 in MU scaling.ConclusionThis study shows the feasibility and effectiveness of using two-dimensional (2D) EPID portal image and daily CT-based in vivo dosimetry for intensity-modulated radiation therapy (IMRT) verification during treatment. The daily CT-based in vivo dosimetry has better sensitivity and specificity to identify the variation of IMRT in MLC-related and dose-related errors than planning CT-based.

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Section: Introductionmentioning

confidence: 99%

Evaluation of Daily CT for EPID-Based Transit In Vivo Dosimetry

Feng

et al. 2021

Front. Oncol.

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“…It is in principle translatable to any linear accelerator equipped with a standard flat panel EPID, provided that the acquisition mode captures the entire delivery (ie, cine or integrated) and that the same mode is used at commissioning and at measurement. For Elekta 16-bit imaging systems, 38 the 2 14 offset described in the section “Dose at isocenter” must be replaced by 2 16 .…”

Section: Discussionmentioning

confidence: 99%

A Simple Method for 2-D In Vivo Dosimetry by Portal Imaging

Peca

Brown

Smith

2017

Technol Cancer Res Treat

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Purpose:To improve patient safety and treatment quality, verification of dose delivery in radiotherapy is desirable. We present a simple, easy-to-implement, open-source method for in vivo planar dosimetry of conformal radiotherapy by electronic portal imaging device (EPID).Methods:Correlation ratios, which relate dose in the mid-depth of slab phantoms to transit EPID signal, were determined for multiple phantom thicknesses and field sizes. Off-axis dose is corrected for by means of model-based convolution. We tested efficacy of dose reconstruction through measurements with off-reference values of attenuator thickness, field size, and monitor units. We quantified the dose calculation error in the presence of thickness changes to simulate anatomical or setup variations. An example of dose calculation on patient data is provided.Results:With varying phantom thickness, field size, and monitor units, dose reconstruction was almost always within 3% of planned dose. In the presence of thickness changes from planning CT, the dose discrepancy is exaggerated by up to approximately 1.5% for 1 cm changes upstream of the isocenter plane and 4% for 1 cm changes downstream.Conclusion:Our novel electronic portal imaging device in vivo dosimetry allows clinically accurate 2-dimensional reconstruction of dose inside a phantom/patient at isocenter depth. Due to its simplicity, commissioning can be performed in a few hours per energy and may be modified to the user’s needs. It may provide useful dose delivery information to detect harmful errors, guide adaptive radiotherapy, and assure quality of treatment.

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“…Researchers from Universita Cattolica del Sacro Cuore, Rome, Italy, proposed a generic measurement-based model but the method was only for single point comparisons, which may not be suitable for IMRT verifications [36][37][38][39][40]. Although the model was later extended by Peca and Brown 41 to perform 2D verification, it was only tested for 3D conformal fields.…”

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confidence: 99%