Sankar Arumugam1, Aitang Xing2, Tony Young2, Lois Holloway3. 1. Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute, Sydney, NSW, Australia. Electronic address: Sankar.Arumugam@sswahs.nsw.gov.au. 2. Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute, Sydney, NSW, Australia. 3. Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute, Sydney, NSW, Australia; Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia; South West Clinical School, University of New South Wales, Sydney, NSW, Australia; Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW, Australia.
Abstract
PURPOSE: To study the sensitivity of an ArcCHECK dosimeter in detecting delivery errors during the delivery of Volumetric Modulated Arc Therapy (VMAT). METHODS: Three types of errors in Multi Leaf Collimator (MLC) position and dose delivery were simulated separately in the delivery of five prostate and five head and neck (H&N) VMAT plans: (i) Gantry independent: a systematic shift in MLC position and variation in output to the whole arc; (ii) Gantry dependent: sag in MLC position and output variation as a function of gantry angle; (iii) Control point specific MLC and output errors introduced to only a specific number of Control Points (CP). The difference in local and global gamma (γ) pass rate between the no-error and error-simulated measurements with 2%/2 mm and 3%/3 mm tolerances was calculated to assess the sensitivity of ArcCHECK. The clinical impact of these errors was also calculated. RESULTS: ArcCHECK was able to detect a minimum 3 mm MLC error and 3% output error for Gantry independent errors using either local or global gamma with 2%/2 mm tolerance. For the Gantry dependent error scenario a minimum 3 mm MLC error and 3% dose error was identifiable by ArcCHECK using either global or local gamma with 2%/2 mm tolerance. In errors introduced to specific CPs a MLC error of 10 mm and dose error of 100% introduced to 4CPs were detected by ArcCHECK. CONCLUSION: ArcCHECK used with either local or global gamma analysis and 2%/2 mm criteria can be confidently used in the clinic to detect errors above the stated error values.
PURPOSE: To study the sensitivity of an ArcCHECK dosimeter in detecting delivery errors during the delivery of Volumetric Modulated Arc Therapy (VMAT). METHODS: Three types of errors in Multi Leaf Collimator (MLC) position and dose delivery were simulated separately in the delivery of five prostate and five head and neck (H&N) VMAT plans: (i) Gantry independent: a systematic shift in MLC position and variation in output to the whole arc; (ii) Gantry dependent: sag in MLC position and output variation as a function of gantry angle; (iii) Control point specific MLC and output errors introduced to only a specific number of Control Points (CP). The difference in local and global gamma (γ) pass rate between the no-error and error-simulated measurements with 2%/2 mm and 3%/3 mm tolerances was calculated to assess the sensitivity of ArcCHECK. The clinical impact of these errors was also calculated. RESULTS: ArcCHECK was able to detect a minimum 3 mm MLC error and 3% output error for Gantry independent errors using either local or global gamma with 2%/2 mm tolerance. For the Gantry dependent error scenario a minimum 3 mm MLC error and 3% dose error was identifiable by ArcCHECK using either global or local gamma with 2%/2 mm tolerance. In errors introduced to specific CPs a MLC error of 10 mm and dose error of 100% introduced to 4CPs were detected by ArcCHECK. CONCLUSION: ArcCHECK used with either local or global gamma analysis and 2%/2 mm criteria can be confidently used in the clinic to detect errors above the stated error values.