Gantry angle-dependent correction of dose detection error due to panel position displacement in IMRT dose verification using EPIDs

Jin, Guo Fan; Zhu, Jinhan; Chen, Li Xin; Deng, Xiao Wu; Huang, Bo; Yuan, Kun; Liu, Xiao wei

doi:10.1016/j.ejmp.2013.05.042

Cited by 10 publications

(6 citation statements)

References 30 publications

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“…These values were comparable with the previous reports on Elekta linacs. 12,25 The EPID sag pattern in the cross-plane showed a leap at around zero gantry angle similar to the one previously observed in Varian linacs. 21,26 This was attributed to the complexity of the mechanical structure of the system that has many junctions and several sliding or bolted mechanical parts.…”

Section: Discussionsupporting

confidence: 61%

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: Discussionsupporting

confidence: 61%

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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“…As reported by Mijnheer et al , 10 one of the reasons for the limited routine application of IVD is the workload involved in this procedure, and another reason is the confidence of the physicist in quality control methods as the pretreatment tests. 34 –36 Nowadays pretreatment tests can identify many potential errors in dose calculation and data transfer, but it is the opinion of the present and other authors 2 that all treatments with curative intent should be verified through IVD measurements, replacing the pretreatment verification with the in vivo EPID dosimetry.…”

Section: Discussionmentioning

confidence: 99%

“…As reported in the literature, [33][34] the comparison between EPID integral images, obtained for each beam, can be used to verify the presence of changes in patient setup, machine output, and leaf behavior during each treatment. 35,36 In this work. for each IMRT beam, the reference 2D-EPID images obtained in the first therapy fraction (In vivo dosimetry section) were used as a surrogate of signals that the EPID should supply if the plan was carried out with high reproducibility.…”

Section: Reconstruction Of D Iso and G-analysismentioning

confidence: 96%

Step-and-Shoot IMRT by Siemens Beams

Russo

Piermattei

Greco

et al. 2016

Technol Cancer Res Treat

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Three radiotherapy centers applied the in vivo dose procedure at 30 clinical intensity-modulated radiotherapy treatments, each one obtained with 5 or 7 beams, and planned for patients undergoing radiotherapy for prostatic tumors. Each treatment beam was checked 5 times, obtaining 900 tests of the ratios R = Diso/Diso,TPS. The average R value was equal to 1.002 ± 0.056 (2 standard deviation), while the mean R value for each patient was well within 5%, once the causes of errors were removed. The γ-analysis of the electronic portal imaging device images, with 3% 3 mm acceptance criteria, showed 90% of the tests with Pγ < 1 ≥ 95% and γmean ≤ 0.5. The off-tolerance tests were found due to incorrect setup or presence of morphological changes. This preliminary experience shows the great utility of obtaining the in vivo dose results in quasi real time and close to the linac, where the radiotherapy staff may immediately spot possible causes of errors. The in vivo dose procedure presented here is one of the objectives of a project, for the development of practical in vivo dose procedures, financially supported by the Istituto Nazionale di Fisica Nucleare.

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“…The backscatter correction kernel was modeled as a radially symmetric Gaussian and applied to the raw EPID data [ 24 ]. To ensure positioning accuracy during image acquisition, a gantry-angle-dependent correction associated with the panel position displacement was applied [ 25 ]. The EPID displacement was measured by comparing the image acquired at each gantry angle to the 0° image in the 10 cm × 10 cm field.…”

Section: Methodsmentioning

confidence: 99%

Fast 3D dosimetric verifications based on an electronic portal imaging device using a GPU calculation engine

Zhu

Chen

et al. 2015

Radiat Oncol

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PurposeTo use a graphic processing unit (GPU) calculation engine to implement a fast 3D pre-treatment dosimetric verification procedure based on an electronic portal imaging device (EPID).MethodsThe GPU algorithm includes the deconvolution and convolution method for the fluence-map calculations, the collapsed-cone convolution/superposition (CCCS) algorithm for the 3D dose calculations and the 3D gamma evaluation calculations. The results of the GPU-based CCCS algorithm were compared to those of Monte Carlo simulations. The planned and EPID-based reconstructed dose distributions in overridden-to-water phantoms and the original patients were compared for 6 MV and 10 MV photon beams in intensity-modulated radiation therapy (IMRT) treatment plans based on dose differences and gamma analysis.ResultsThe total single-field dose computation time was less than 8 s, and the gamma evaluation for a 0.1-cm grid resolution was completed in approximately 1 s. The results of the GPU-based CCCS algorithm exhibited good agreement with those of the Monte Carlo simulations. The gamma analysis indicated good agreement between the planned and reconstructed dose distributions for the treatment plans. For the target volume, the differences in the mean dose were less than 1.8%, and the differences in the maximum dose were less than 2.5%. For the critical organs, minor differences were observed between the reconstructed and planned doses.ConclusionsThe GPU calculation engine was used to boost the speed of 3D dose and gamma evaluation calculations, thus offering the possibility of true real-time 3D dosimetric verification.

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Gantry angle-dependent correction of dose detection error due to panel position displacement in IMRT dose verification using EPIDs

Cited by 10 publications

References 30 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

Step-and-Shoot IMRT by Siemens Beams

Fast 3D dosimetric verifications based on an electronic portal imaging device using a GPU calculation engine

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