S Dufreneix1, J Bellec2, S Josset3, L Vieillevigne4. 1. Institut de Cancérologie de l'Ouest, Angers, Saint-Herblain, France. Electronic address: stephane.dufreneix@ico.unicancer.fr. 2. Centre Eugène Marquis, Rennes, France. 3. Institut de Cancérologie de l'Ouest, Angers, Saint-Herblain, France. 4. Institut Claudius Régaud, Institut Universitaire du Cancer de Toulouse, France; Centre de Recherche et de Cancérologie de Toulouse, UMR1037 INSERM - Université Toulouse 3 - ERL5294 CNRS, Oncopole, Toulouse, France.
Abstract
PURPOSE: The determination of output factors in small field dosimetry is a crucial point, especially when implementing stereotactic radiotherapy (SRT). Herein, a working group of the French medical physicist society (SFPM) was created to collect small field output factors. The objective was to gather and disseminate information on small field output factors based on different detectors for various clinical SRT equipment and measurement configurations. METHOD: Participants were surveyed for information about their SRT equipment, including the type of linear particle accelerator (linac), collimator settings, measurement conditions for the output factors and the detectors used. Participants had to report both the ratio of detector readings and the correction factors applied as described in the IAEA TRS-483 code of practice for nominal field sizes smaller or equal to 3 cm. Mean field output factors and their associated standard deviations were calculated when data from at least 3 linacs were available. RESULTS: 23 centres were enrolled in the project. Standard deviations of the mean field output factors were systematically smaller than 1.5% for field sizes larger or equal to 1 cm and reached 5% for the smallest field size (0.5 cm). Deviations with published data were smaller than 2% except for the 0.5 cm circular fixed aperture collimator of the CyberKnife where it reached 3.5%. CONCLUSION: These field output factor values obtained via a large multicentre study can be considered as an external cross verification for any radiotherapy centre starting a SRT program and should help minimize systematic errors when determining small field output factors.
PURPOSE: The determination of output factors in small field dosimetry is a crucial point, especially when implementing stereotactic radiotherapy (SRT). Herein, a working group of the French medical physicist society (SFPM) was created to collect small field output factors. The objective was to gather and disseminate information on small field output factors based on different detectors for various clinical SRT equipment and measurement configurations. METHOD:Participants were surveyed for information about their SRT equipment, including the type of linear particle accelerator (linac), collimator settings, measurement conditions for the output factors and the detectors used. Participants had to report both the ratio of detector readings and the correction factors applied as described in the IAEA TRS-483 code of practice for nominal field sizes smaller or equal to 3 cm. Mean field output factors and their associated standard deviations were calculated when data from at least 3 linacs were available. RESULTS: 23 centres were enrolled in the project. Standard deviations of the mean field output factors were systematically smaller than 1.5% for field sizes larger or equal to 1 cm and reached 5% for the smallest field size (0.5 cm). Deviations with published data were smaller than 2% except for the 0.5 cm circular fixed aperture collimator of the CyberKnife where it reached 3.5%. CONCLUSION: These field output factor values obtained via a large multicentre study can be considered as an external cross verification for any radiotherapy centre starting a SRT program and should help minimize systematic errors when determining small field output factors.
Authors: Wolfgang Lechner; Rodolfo Alfonso; Mehenna Arib; M Saiful Huq; Anas Ismail; Rajesh Kinhikar; José M Lárraga-Gutiérrez; Karthick Raj Mani; Nkosingiphile Maphumulo; Otto A Sauer; Shaima Shoeir; Sivalee Suriyapee; Karen Christaki Journal: Med Phys Date: 2022-07-08 Impact factor: 4.506