A system for EPID‐based real‐time treatment delivery verification during dynamic IMRT treatment

Fuangrod, Todsaporn; Woodruff, Henry C.; Uytven, Eric Van; McCurdy, Boyd; Kuncic, Zdenka; O’Connor, D.J.; Greer, Peter B.

doi:10.1118/1.4817484

Cited by 38 publications

(35 citation statements)

References 28 publications

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“…[7][8][9] Moreover, linear accelerator (linac) rotation can affect gantry-mounted accessories such as the electronic portal imaging device (EPID), since the EPIDsupporting arm is not mechanically perfect and rigidly attached. With the growing application of EPIDs in preand post-treatment dosimetry verification, [10][11][12][13][14][15] realtime dosimetry verification 16,17 and real-time tumour tracking for intrafraction motion management in modern radiotherapy, [18][19][20] it is essential to characterize and account for the mechanical system imperfections of linacs.…”

Section: Conclusion and Advances In Knowledgementioning

confidence: 99%

A comprehensive study of the mechanical performance of gantry, EPID and the MLC assembly in Elekta linacs during gantry rotation

Rowshanfarzad

Riis

Zimmermann

et al. 2015

BJR

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Objective: In radiotherapy treatments, it is crucial to monitor the performance of linear accelerator (linac) components, including gantry, collimation system and electronic portal imaging device (EPID) during arc deliveries. In this study, a simple EPID-based measurement method is suggested in conjunction with an algorithm to investigate the stability of these systems at various gantry angles with the aim of evaluating machinerelated errors in treatments. Methods: The EPID sag, gantry sag, changes in source-todetector distance (SDD), EPID and collimator skewness, EPID tilt and the sag in leaf bank assembly owing to linac rotation were separately investigated by acquisition of 37 EPID images of a simple phantom with 5 ball bearings at various gantry angles. A fast and robust software package was developed for automated analysis of the image data. Nine Elekta AB (Stockholm, Sweden) linacs of different models and number of years in service were investigated. Results: The average EPID sag was within 2 mm for all tested linacs. Some machines showed .1-mm gantry sag. Changes in the SDD values were within 1.3 cm. EPID skewness and tilt values were ,1°in all machines. The maximum sag in multileaf collimator leaf bank assemblies was around 1 mm. A meaningful correlation was found between the age of the linacs and their mechanical performance. Conclusions and Advances in knowledge:The method and software developed in this study provide a simple tool for effective investigation of the behaviour of Elekta linac components with gantry rotation. Such a comprehensive study has been performed for the first time on Elekta machines.

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Section: Conclusion and Advances In Knowledgementioning

confidence: 99%

A comprehensive study of the mechanical performance of gantry, EPID and the MLC assembly in Elekta linacs during gantry rotation

Rowshanfarzad

Riis

Zimmermann

et al. 2015

BJR

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“…[3][4][5][6][7][8] To provide more direct and immediate information, many groups have investigated the use of 2D, 3D, and even 4D electronic portal imaging device (EPID) reconstructions of dose fluence. [9][10][11][12][13][14][15][16][17] Major strides have been made with this technology, but routine use in everyday fractionated delivery has not yet occurred due to some unresolved issues. 18 In addition to quality assurance, 19 Cherenkov imaging is being examined for in vivo surface dosimetry and beam tracking for real-time treatment verification.…”

Section: Introductionmentioning

confidence: 99%

Camera selection for real‐time in vivo radiation treatment verification systems using Cherenkov imaging

et al. 2015

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Purpose: To identify achievable camera performance and hardware needs in a clinical Cherenkov imaging system for real-time, in vivo monitoring of the surface beam profile on patients, as novel visual information, documentation, and possible treatment verification for clinicians. Methods: Complementary metal-oxide-semiconductor (CMOS), charge-coupled device (CCD), intensified charge-coupled device (ICCD), and electron multiplying-intensified charge coupled device (EM-ICCD) cameras were investigated to determine Cherenkov imaging performance in a clinical radiotherapy setting, with one emphasis on the maximum supportable frame rate. Where possible, the image intensifier was synchronized using a pulse signal from the Linac in order to image with room lighting conditions comparable to patient treatment scenarios. A solid water phantom irradiated with a 6 MV photon beam was imaged by the cameras to evaluate the maximum frame rate for adequate Cherenkov detection. Adequate detection was defined as an average electron count in the background-subtracted Cherenkov image region of interest in excess of 0.5% (327 counts) of the 16-bit maximum electron count value. Additionally, an ICCD and an EM-ICCD were each used clinically to image two patients undergoing whole-breast radiotherapy to compare clinical advantages and limitations of each system. Results: Intensifier-coupled cameras were required for imaging Cherenkov emission on the phantom surface with ambient room lighting; standalone CMOS and CCD cameras were not viable. The EM-ICCD was able to collect images from a single Linac pulse delivering less than 0.05 cGy of dose at 30 frames/s (fps) and pixel resolution of 512 × 512, compared to an ICCD which was limited to 4.7 fps at 1024 × 1024 resolution. An intensifier with higher quantum efficiency at the entrance photocathode in the red wavelengths [30% quantum efficiency (QE) vs previous 19%] promises at least 8.6 fps at a resolution of 1024 × 1024 and lower monetary cost than the EM-ICCD. Conclusions: The ICCD with an intensifier better optimized for red wavelengths was found to provide the best potential for real-time display (at least 8.6 fps) of radiation dose on the skin during treatment at a resolution

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“…Individual EPID image frames were acquired at 8.5 frames‐per‐second using an external PC equipped with a frame grabber. The position of each MLC leaf was extracted from each frame by means of the methodology described by Fuangrod et al, 22 , 23 , 24 which was further developed by Zwan et al (25) For each image frame acquired, the horizontal beam profile through the central axis of each leaf pair was first extracted. For each in‐field MLC the location of the 50% radiation field edge was found to subpixel accuracy using cubic‐spline interpolation.…”

Section: Methodsmentioning

confidence: 99%

The dosimetric impact of control point spacing for sliding gap MLC fields

Zwan

Hindmarsh

Seymour

et al. 2016

J Applied Clin Med Phys

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Dynamic sliding gap multileaf collimator (MLC) fields are used to model MLC properties within the treatment planning system (TPS) for dynamic treatments. One of the key MLC properties in the Eclipse TPS is the dosimetric leaf gap (DLG) and precise determination of this parameter is paramount to ensuring accurate dose delivery. In this investigation, we report on how the spacing between control points (CPs) for sliding gap fields impacts the dose delivery, MLC positioning accuracy, and measurement of the DLG. The central axis dose was measured for sliding gap MLC fields with gap widths ranging from 2 to 40 mm. It was found that for deliveries containing two CPs, the central axis dose was underestimated by the TPS for all gap widths, with the maximum difference being 8% for a 2 mm gap field. For the same sliding gap fields containing 50 CPs, the measured dose was always within ±2% of the TPS dose. By directly measuring the MLC trajectories we show that this dose difference is due to a systematic MLC gap error for fields containing two CPs, and that the cause of this error is due to the leaf position offset table which is incorrectly applied when the spacing between CPs is too large. This MLC gap error resulted in an increase in the measured DLG of 0.5 mm for both 6 MV and 10 MV, when using fields with 2 CPs compared to 50 CPs. Furthermore, this change in DLG was shown to decrease the mean TPS‐calculated dose to the target volume by 2.6% for a clinical IMRT test plan. This work has shown that systematic MLC positioning errors occur for sliding gap MLC fields containing two CPs and that using these fields to model critical TPS parameters, such as the DLG, may result in clinically significant systematic dose calculation errors during subsequent dynamic MLC treatments.PACS number(s): 87.56.nk

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A system for EPID‐based real‐time treatment delivery verification during dynamic IMRT treatment

Abstract: A real-time radiation delivery verification system for dynamic IMRT has been demonstrated that is designed to prevent major mistreatments in modern radiation therapy.

Cited by 38 publications

References 28 publications

A comprehensive study of the mechanical performance of gantry, EPID and the MLC assembly in Elekta linacs during gantry rotation

A comprehensive study of the mechanical performance of gantry, EPID and the MLC assembly in Elekta linacs during gantry rotation

Camera selection for real‐time in vivo radiation treatment verification systems using Cherenkov imaging

The dosimetric impact of control point spacing for sliding gap MLC fields

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