title: Clinical implementation of an electron monitor unit dosimetry system based on task group 71 report and a commercial calculation program.
abstract: Many clinics still use monitor unit (MU) calculations for electron treatment planning and/or quality assurance (QA). This work (1) investigates the clinical implementation of a dosimetry system including a modified American Association of Physicists in Medicine-task group-71 (TG-71)-based electron MU calculation protocol (modified TG-71 electron [mTG-71E] and an independent commercial calculation program and (2) provides the practice recommendations for clinical usage. Following the recently published TG-71 guidance, an organized mTG-71E databook was developed to facilitate data access and subsequent MU computation according to our clinical need. A recently released commercial secondary calculation program - Mobius3D (version 1.5.1) Electron Quick Calc (EQC) (Mobius Medical System, LP, Houston, TX, USA), with inherent pencil beam algorithm and independent beam data, was used to corroborate the calculation results. For various setups, the calculation consistency and accuracy of mTG-71E and EQC were validated by their cross-comparison and the ion chamber measurements in a solid water phantom. Our results show good agreement between mTG-71E and EQC calculations, with average 2% difference. Both mTG-71E and EQC calculations match with measurements within 3%. In general, these differences increase with decreased cutout size, increased extended source to surface distance, and lower energy. It is feasible to use TG71 and Mobius3D clinically as primary and secondary electron MU calculations or vice versa. We recommend a practice that only requires patient-specific measurements in rare cases when mTG-71E and EQC calculations differ by 5% or more.
authors.affiliation: Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, USA.
authors.forename: Huijun
authors.initials: H
authors.lastname: Xu
authors.affiliation: Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, USA.
authors.forename: Mariana
authors.initials: M
authors.lastname: Guerrero
authors.affiliation: Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, USA.
authors.forename: Shifeng
authors.initials: S
authors.lastname: Chen
authors.affiliation: Radiation Oncology Center, Good Sam Hospital, MedStar RadAmerica, Baltimore, MD, USA.
authors.forename: Xiaocheng
authors.initials: X
authors.lastname: Yang
authors.affiliation: Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, USA.
authors.forename: Karl
authors.initials: K
authors.lastname: Prado
authors.affiliation: Department of Medical Physics, Tom Baker Cancer Centre, Calgary, AB, Canada.
authors.forename: Colleen
authors.initials: C
authors.lastname: Schinkel
keywords: Electron monitor unit calculation; Mobius3D Electron Quick Calc; Task Group 71