Universal evaluation of MLC models in treatment planning systems based on a common set of dynamic tests

• Published in: Radiotherapy and oncology Vol. 186; p. 109775
• Main Authors: Saez, Jordi, Bar-Deroma, Raquel, Bogaert, Evelien, Cayez, Romain, Chow, Tom, Clark, Catharine H., Esposito, Marco, Feygelman, Vladimir, Monti, Angelo F., Garcia-Miguel, Julia, Gershkevitsh, Eduard, Goossens, Jo, Herrero, Carmen, Hussein, Mohammad, Khamphan, Catherine, Kierkels, Roel G.J., Lechner, Wolfgang, Lemire, Matthieu, Nevelsky, Alexander, Nguyen, Daniel, Paganini, Lucia, Pasler, Marlies, Fernando Pérez Azorín, José, Ramos Garcia, Luis Isaac, Russo, Serenella, Shakeshaft, John, Vieillevigne, Laure, Hernandez, Victor
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier B.V 01.09.2023
• Subjects: Audits; Comissioning; IMRT; MLC; Standardization; VMAT; Audits; VMAT; IMRT; Comissioning; MLC; Standardization
• ISSN: 0167-8140; 1879-0887
• DOI: 10.1016/j.radonc.2023.109775

•The feasibility of using a universal procedure based on synchronous and asynchronous sweeping gap tests for assessing the dosimetric characteristics of MLC models (transmission, radiation field offset, and tongue-and-groove effects) was demonstrated.•Measured dosimetric characteristics for each MLC type were nearly identical, with minimal differences between centres.•MLC models configured in TPSs, on the contrary, produced an enormous variability in calculated doses and large discrepancies in measured doses.•The proposed procedure facilitates a simple, comprehensive, and universal assessment of MLC models in treatment planning systems.•The procedure can be readily applied in radiotherapy departments and can be a valuable tool for IMRT and credentialing audits. To demonstrate the feasibility of characterising MLCs and MLC models implemented in TPSs using a common set of dynamic beams. A set of tests containing synchronous (SG) and asynchronous sweeping gaps (aSG) was distributed among twenty-five participating centres. Doses were measured with a Farmer-type ion chamber and computed in TPSs, which provided a dosimetric characterisation of the leaf tip, tongue-and-groove, and MLC transmission of each MLC, as well as an assessment of the MLC model in each TPS. Five MLC types and four TPSs were evaluated, covering the most frequent combinations used in radiotherapy departments. Measured differences within each MLC type were minimal, while large differences were found between MLC models implemented in clinical TPSs. This resulted in some concerning discrepancies, especially for the HD120 and Agility MLCs, for which differences between measured and calculated doses for some MLC-TPS combinations exceeded 10%. These large differences were particularly evident for small gap sizes (5 and 10 mm), as well as for larger gaps in the presence of tongue-and-groove effects. A much better agreement was found for the Millennium120 and Halcyon MLCs, differences being within ± 5% and ± 2.5%, respectively. The feasibility of using a common set of tests to assess MLC models in TPSs was demonstrated. Measurements within MLC types were very similar, but TPS dose calculations showed large variations. Standardisation of the MLC configuration in TPSs is necessary. The proposed procedure can be readily applied in radiotherapy departments and can be a valuable tool in IMRT and credentialing audits.