MLC positional accuracy evaluation through the Picket Fence test on EBT2 films and a 3D volumetric phantom

Abstract

The accuracy of MLC positions during radiotherapy is important as even small positional deviations can translate into considerable dose delivery errors. This becomes crucial when radiosensitive organs are located near the treated volume and especially during IMRT, where dose gradients are steep. A test commonly conducted to measure the positional accuracy of the MLCs is the Picket Fence test. In this study two alterations of the Picket Fence test were performed and evaluated, the first one using radiochromic EBT2 films and the second one the Delta4PT diode array phantom and its software. Our results showed that EBT2 films provide a relatively fast, qualitative visual inspection of the significant leaf dispositions. When slight inaccuracies need to be revealed or precise numerical results for each leaf position are needed, Delta4PT provides the desired accuracy of 1 mm. In treatment modalities where a higher accuracy is required in the delivered dose distribution, such as in IMRT, precise numerical values of the measurements for the MLC positional inspection are required.PACS number: 87.55.Qr, 87.56.bd, 87.56.Fc, 87.56.nk

Characterization of positional accuracy of a double‐focused and double‐stack multileaf collimator on an MR‐guided radiotherapy (MRgRT) Linac using an IC‐profiler array

“…Visual inspection of a picket fence has been shown to be sensitive to 1 mm. 9 Our test particularly the HBB QA procedure is highly sensitive up to 0.5 mm (i.e., À14.1% AE 4.1% and 10.8% AE 2.4%). Yan et al compared the sensitivity of IMRT QA for detection of MLC random and systematic errors through introduction of errors of 1 and 2 mm.…”

“…In comparison to other proposed routine MLC QA methods, our method may allow for improved sensitivity for detection of systematic MLC positional errors. Visual inspection of a picket fence has been shown to be sensitive to 1 mm . Our test particularly the HBB QA procedure is highly sensitive up to 0.5 mm (i.e., −14.1% ± 4.1% and 10.8% ± 2.4%).…”

“…However, the lack of real‐time information combined with the time to process or scan film for readout limits its utility, especially in a routine setting. As such, many institutions have adopted the picket fence technique for visual inspection of the MLC performance, at the cost of reduced sensitivity and eliminating quantitative information …”

“…As such, many institutions have adopted the picket fence technique for visual inspection of the MLC performance, at the cost of reduced sensitivity and eliminating quantitative information. 9 More recently, film has been widely replaced with onboard x-ray-based imaging panels such as electronic portal imaging devices (EPID) for C-arm linacs [10][11][12][13][14][15][16][17][18][19][20] and parallel plate CT detectors for helical-based systems. 21 These arrays have proven to be robust, efficient, and sensitive tools for MLC QA by measuring x-ray fluence profiles.…”

Evaluation of intensity modulated radiation therapy delivery system using a volumetric phantom on the basis of the task group 119 report of american association of physicists in medicine

“…[13] These setup corrections were then applied to the rest of the measurements performed with the same phantom position.…”