Investigation of the mechanical performance of Siemens linacs components during arc: gantry, MLC, and electronic portal imaging device

Rowshanfarzad, Pejman; Häring, Peter; Riis, H.L.; Zimmermann, S.J.; Ebert, Martin A.

doi:10.2147/mder.s89725

Cited by 7 publications

(8 citation statements)

References 37 publications

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“…It is well established that imperfections in linac gantry rotation caused by the strong pull of gravity lead to slight deviations to the isocentre during treatment delivery. Several studies have investigated this effect, and its angular dependence has been well quantified (5)(6)(7)(8). Although QA programs are designed at an institution level, they are informed by vendor specifications as well as recommendations from the literature and professional organisations such as the American Association of Physicists in Medicine (AAPM).…”

Section: Introductionmentioning

confidence: 99%

Dosimetric impact of mechanical movements of the Linac gantry during treatments with small fields

et al. 2022

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ObjectiveCurrent accepted linac Quality Assurance (QA) guidelines used for Volumetric Modulated Arc Therapy (VMAT) suggest a mechanical isocentre tolerance level of 1 mm. However, this tolerance level has not been well-established for the specific case of small field stereotactic VMAT. This study aims to evaluate the clinical impact of mechanical uncertainty on this treatment modality by modelling systematic gantry sag derived isocentre variance in the Treatment Planning System (TPS).ApproachA previously reported dataset of gantry sag values in the literature served as a starting point for this study. Using an in-house developed VMAT arc splitting algorithm, isocentre shifts were applied at a Control Point (CP) level to DICOM-RT treatment plans. Dose distributions for varying isocentre shift magnitudes were calculated for a set of 29 stereotactic VMAT plans using the Eclipse Acuros XB dose algorithm. These plans had a range of Planning Target Volume (PTV) sizes. A quantitative comparison of each plan was conducted by evaluating five Dose Volume Histogram (DVH)-derived plan quality metrics.ResultsAll metrics exhibited a deterioration in plan quality with increasing magnitudes of isocentre shift. At small PTV sizes, these effects were amplified, exhibiting significant changes at 1 mm of average shift when typical targets and tolerances were considered. For plans with PTVs between 0 and 5 cm3, a 1 mm shift reduced PTV coverage by 6.6 ± 2.2% and caused a 12.1 ± 3.8% deterioration in the conformity index. Based on the results of this study, the prevalent tolerance of 1 mm may not be suitable for treatments of small PTVs with small fields.SignificanceIn contrast to commonly accepted values, an absolute mechanical isocentre of 0.5 mm with action level at 0.75 mm is recommended for stereotactic VMAT of PTV sizes below 10 cm3.

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Section: Introductionmentioning

confidence: 99%

Dosimetric impact of mechanical movements of the Linac gantry during treatments with small fields

et al. 2022

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“…However, the sagging angle could not be measured directly. Rowshanfarzad et al . reported the sag of the collimators and the combination of electronic portal imaging device (EPID) sag and the gantry sag using some ball‐bearing phantoms and the EPID.…”

Section: Introductionmentioning

confidence: 99%

A novel verification method using a plastic scintillator imagining system for assessment of gantry sag in radiotherapy

et al. 2018

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We developed a novel verification system, designated as the "kompeito shot test system," to verify the 3D beam alignment. This system concept works for both verification of the 3D isocentricity and the direct evaluation of the sagging angle. Next, we want to improve the aspects of this system, such as the shape and the type of scintillator, to increase the system accuracy and nonisocentric beam alignment performance.

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“…The result is effectively a blurring of the isocenter position, which negatively influences the accuracy of dose delivery while also causing a geometric misalignment of the electronic portal imaging device (EPID) imaging system . There is a similar angle‐dependent effect on the MLC carriage within the head . Several studies have been performed with the purpose of investigating the influence of gravity on the mechanical performance of linear accelerators, many sharing a common thread of capturing and analyzing x‐ray projections of a phantom (often consisting of one or more ball bearings) …”

Section: Introductionmentioning

confidence: 99%

“…2 There is a similar angle-dependent effect on the MLC carriage within the head. [3][4][5] Several studies have been performed with the purpose of investigating the influence of gravity on the mechanical performance of linear accelerators, many sharing a common thread of capturing and analyzing x-ray projections of a phantom (often consisting of one or more ball bearings). 1,[3][4][5][6][7][8] Due to the obvious clinical implications of suboptimal linac mechanical performance, the magnitude of this isocenter deviation must be tightly bounded.…”

Section: Introductionmentioning

confidence: 99%

“…[3][4][5] Several studies have been performed with the purpose of investigating the influence of gravity on the mechanical performance of linear accelerators, many sharing a common thread of capturing and analyzing x-ray projections of a phantom (often consisting of one or more ball bearings). 1,[3][4][5][6][7][8] Due to the obvious clinical implications of suboptimal linac mechanical performance, the magnitude of this isocenter deviation must be tightly bounded. Denton et al, 9 in a statistically motivated approach, examined the results of 149 Winston-Lutz tests to derive a practical schedule action level of 1.25 mm and an immediate action level of 1.50 mm for stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) treatments.…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of the Impact of the Linac MLC and Gantry Sag in volumetric modulated arc therapy

et al. 2019

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Purpose Mechanical sag in the radiotherapy linear accelerator gantry and multi‐leaf collimator (MLC) carriage effectively causes systematic deviations in the isocenter with respect to gantry angle. To minimize the impact of this error on treatment, a tolerance value of a 1‐mm mechanical isocenter shift is commonly accepted for intensity‐modulated radiation therapy quality assurance (QA). However, this tolerance value has not been firmly established for volumetric modulated arc therapy (VMAT) treatments. The purpose of this study is therefore to evaluate the impact of gantry and MLC carriage sag on VMAT clinical performance. Methods A published dataset of Elekta and Varian sag measurements served as a starting point for the investigation. Typical sag profiles were chosen and modeled as continuous isocenter deviations in three dimensions. The data were then incorporated into existing Digital Imaging and Communications in Medicine protocol, extended for radiotherapy plans via a “beam‐splitting” algorithm. Three treatment sites were investigated in parallel: head and neck, prostate, and prostate with surrounding lymph nodes. Monte Carlo‐simulated dose distributions were obtained for varying magnifications of the modeled sag. The resulting dose distributions, including that for no error, were compared qualitatively and quantitatively, against multiple metrics. Results The dose‐volume histograms (DVHs) for all plans exhibited a decrease in planning target volume (PTV) dose uniformity with increasing sag magnification, whereas dose to organs at risk exhibited no coherent trend. The prostate plan was shown to be the most vulnerable to mechanical sag across all considered metrics. However, all plans with peak isocenter deviation less than 1 mm were well within typical cutoff points for each metric. Conclusions All avenues of investigation presented substantiate the commonly accepted tolerance value of a 1‐mm peak isocenter shift in annual linac QA.

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Investigation of the mechanical performance of Siemens linacs components during arc: gantry, MLC, and electronic portal imaging device

Cited by 7 publications

References 37 publications

Dosimetric impact of mechanical movements of the Linac gantry during treatments with small fields

Dosimetric impact of mechanical movements of the Linac gantry during treatments with small fields

A novel verification method using a plastic scintillator imagining system for assessment of gantry sag in radiotherapy

Evaluation of the Impact of the Linac MLC and Gantry Sag in volumetric modulated arc therapy

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