title: Clinical significance of treatment delivery errors for helical TomoTherapy nasopharyngeal plans - A dosimetric simulation study.
abstract: OBJECTIVE
  Develop a framework to characterize helical TomoTherapy (HT) machine delivery errors and their clinical significance.
  
  
  METHODS
  Ten nasopharynx HT plans were edited to introduce errors in Jaw width (JW), couch speed (CS), gantry period (GP), gantry start position (GSP), multi leaf collimator leaf open times (MLC LOT). In case of MLC LOT only, both systematic and random delivery errors were investigated. Each error type was simulated independently for a range of magnitudes. Dose distributions for the clinical reference plans and the error simulated plans were compared to establish the magnitude for each error type which resulted in a change in clinical tolerance, defined as 5% variation in D95 of PTV70, D0.1cc of spinal cord, D0.1cc of brainstem and the smallest value of either a 10% or 3.6Gy dose variation in mean parotid dose.
  
  
  RESULTS
  Dose variation from systematic delivery errors in JW ±0.5mm, CS ranges between -1% to 1.5%, GP ±1s, GSP ranges between -20to 2.50and MLC LOT random error up to 2% from the planned value relative to the clinical reference plan was within the set tolerance values for all the patient cohorts. GSP errors and the random MLC LOT errors with up to 10% standard deviation were found to be relatively insensitive compared to other delivery errors.
  
  
  CONCLUSIONS
  This work has established a framework to characterize HT machine delivery errors. This framework could be applied to any patient dataset to determine clinically relevant HT QA tolerances.
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute, Sydney, NSW, Australia; Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia. Electronic address: Shrikant.deshpande@sswahs.nsw.gov.au.
authors.forename: Shrikant
authors.initials: S
authors.lastname: Deshpande
authors.affiliation: Department of Human Oncology, School of Medicine and Public Health, University of Wisconsin-Madison, USA. Electronic address: mwgeurts@humonc.wisc.edu.
authors.forename: Mark
authors.initials: M
authors.lastname: Geurts
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute, Sydney, NSW, Australia; Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW, Australia. Electronic address: Philip.Vial@sswahs.nsw.gov.au.
authors.forename: Philip
authors.initials: P
authors.lastname: Vial
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute, Sydney, NSW, Australia; Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia. Electronic address: metcalfe@uow.edu.au.
authors.forename: Peter
authors.initials: P
authors.lastname: Metcalfe
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute, Sydney, NSW, Australia. Electronic address: Mark.Lee@sswahs.nsw.gov.au.
authors.forename: Mark
authors.initials: M
authors.lastname: Lee
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute, Sydney, NSW, Australia; Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia; Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW, Australia; South West Clinical School, University of New South Wales, Sydney, NSW, Australia. Electronic address: Lois.Holloway@sswahs.nsw.gov.au.
authors.forename: Lois
authors.initials: L
authors.lastname: Holloway
mesh_terms: D006801:Humans; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D011785:Quality Assurance, Health Care; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D061106:Radiotherapy Setup Errors; D050397:Radiotherapy, Intensity-Modulated
keywords: Dosimetric simulation; Helical tomotherapy; QA tolerance