AAPM Task Group 198 Report: An implementation guide for TG 142 quality assurance of medical accelerators

Hanley, Joseph; Dresser, Sean; Simon, William E.; Flynn, R; Klein, Eric E.; Létourneau, D.; Liu, Chihray; Yin, Fang‐Fang; Arjomandy, B.; Ma, Lijun; Aguirre, Francisco Ayala; Jones, Jimmy; Bayouth, John E.; Holmes, Todd C.

doi:10.1002/mp.14992

Cited by 95 publications

(88 citation statements)

References 133 publications

(324 reference statements)

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“…In linac QA, one of the many critical parameters which must be monitored is the stability of the mechanical isocentre ( 4 ). 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.…”

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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“…The analysis parameters of leaf position errors were maximum leaf RMS error, 95th percentile error, the number of failed leaves and the percentage of different leaf positioning errors. The first two analysis parameters are recommended in the TG-142 and TG-198 report, and the report believes that these two parameters are helpful for analyzing the state of the MLC performance [ 12 , 13 ]. The maximum leaf RMS error is a single value, which is the maximum RMS error of all leaves in bank A and bank B.…”

Section: Methodsmentioning

confidence: 99%

“…The TG-51 recommends a tolerance of 0.5 mm for static MLC leaf position accuracy, and the values of the maximum leaf root mean square (RMS) and 95th percentile leaf positioning error were not proposed [ 11 ]. In TG-142 and the latest TG-198, the tolerance of MLC leaf position accuracy is ± 1 mm, and the RMS and 95th percentile errors should be < 0.35 cm [ 12 , 13 ]. The above guidelines recommended annual assessments for the both tests.…”

Section: Introductionmentioning

confidence: 99%

Comparison of MLC positioning deviations using log files and establishment of specific assessment parameters for different accelerators with IMRT and VMAT

et al. 2022

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Background and purpose The study evaluated the differences in leaf positioning deviations by the log files of three advanced accelerators with two delivery techniques, and established specific assessment parameters of leaf positioning deviations for different types of accelerators. Methods A total of 420 treatment plans with 5 consecutive treatment log files were collected from the Trilogy, TrueBeam and Halcyon accelerators. Millennium MLC was equipped on the Trilogy and TrueBeam accelerators. A jawless design and dual-layer MLC were adopted on the Halcyon accelerator. 70 IMRT and 70 VMAT plans were selected randomly on each accelerator. The treatment sites of all plans included head and neck, chest, breast, pelvis and other sites. The parsing tasks for 2100 log files were proceeded by SunCheck software from Sun Nuclear Corporation. The maximum leaf root mean square (RMS) errors, 95th percentile errors and percentages of different leaf positioning errors were statistically analyzed. The correlations between these evaluation parameters and accelerator performance parameters (maximum leaf speed, mean leaf speed, gantry and arc angle) were analyzed. Results The average maximum leaf RMS errors of the Trilogy in the IMRT and VMAT plans were 0.44 ± 0.09 mm and 0.79 ± 0.07 mm, respectively, which were higher than the TrueBeam's 0.03 ± 0.01 mm, 0.03 ± 0.01 mm and the Halcyon's 0.05 ± 0.01 mm, 0.07 ± 0.01 mm. Similar data results were shown in the 95th percentile error. The maximum leaf RMS errors were strongly correlated with the 95th percentile errors (Pearson index > 0.5). The leaf positioning deviations in VMAT were higher than those in IMRT for all accelerators. In TrueBeam and Halcyon, leaf position errors above 1 mm were not found in IMRT and VMAT plans. The main influencing factor of leaf positioning deviation was the leaf speed, which has no strong correlation with gantry and arc angles. Conclusions Compared with the quality assurance guidelines, the MLC positioning deviations tolerances of the three accelerators should be tightened. For both IMRT and VMAT techniques, the 95th percentile error and the maximum RMS error are suggested to be tightened to 1.5 and 1 mm respectively for the Trilogy accelerator. In TrueBeam and Halcyon accelerators, the 95th percentile error and maximum RMS error of 1 and 0.5 mm, respectively, are considered appropriate.

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“…Volumetric modulated arc therapy and multiple gantry angle intensity‐modulated radiotherapy are commonly utilized in modern radiotherapy departments, and the requirement for an accurate multi‐leaf collimator (MLC) in these techniques is well documented. [ 1–3 ] Multiple professional guidelines and publications recommend completing MLC quality assurance (QA) at multiple gantry angles to ensure the MLC performance is maintained over the full range of rotational motion. [ 2–6 ]…”

Section: Introductionmentioning

confidence: 99%

“…Volumetric modulated arc therapy and multiple gantry angle intensity-modulated radiotherapy are commonly utilized in modern radiotherapy departments, and the requirement for an accurate multi-leaf collimator (MLC) in these techniques is well documented. [1][2][3] Multiple professional guidelines and publications recommend completing MLC quality assurance (QA) at multiple gantry angles to ensure the MLC performance is maintained over the full range of rotational motion. [2][3][4][5][6] Most modern linacs are fitted with an electronic portal imaging device (EPID) that can produce images from the megavoltage (MV) beam and are an efficient tool for tasks such as MLC QA and patient-specific quality assurance (PSQA).…”

Section: Introductionmentioning

confidence: 99%

Variation in Elekta iView electronic portal imager pixel scale factor with gantry angle, and impact on multi‐leaf collimator quality assurance

Goodall

Norvill²

2022

J Applied Clin Med Phys

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For Elekta Agility linear accelerators, the iViewGT electronic portal imaging device (EPID) is positioned at a nominal X-Ray source-to-panel distance of 1600 mm. For display, image registration, and data processing purposes, the image pixels are scaled to spatial units at the treatment isocenter plane. This is achieved by applying a pixel scaling factor (PSF). During this investigation, the dependence of the PSF at cardinal gantry angles was determined along with the resulting effects on the multi-leaf collimator (MLC) quality assurance (QA) results for three linear accelerators (linacs). The PSF was found to vary by 0.0018-0.0022 mm/pixel during gantry rotation, which resulted in variations in the mean MLC reported error of up to 0.8 mm at 100 mm off -axis with the gantry rotated to 180 • . Measurement and application of a gantry angle-specific PSF is a simple process that can be implemented to improve the accuracy of EPID-based MLC QA at cardinal gantry angles.

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AAPM Task Group 198 Report: An implementation guide for TG 142 quality assurance of medical accelerators

Cited by 95 publications

References 133 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

Comparison of MLC positioning deviations using log files and establishment of specific assessment parameters for different accelerators with IMRT and VMAT

Variation in Elekta iView electronic portal imager pixel scale factor with gantry angle, and impact on multi‐leaf collimator quality assurance

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