title: Robustness assessment of a novel IMRT planning method for lung radiotherapy.
abstract: OBJECTIVE
  Conventional radiotherapy treatment planning for lung cancer accounts for tumour motion by increasing the beam apertures. We recently developed an IMRT planning strategy which uses reduced beam apertures in combination with an edge enhancing boost to compensate for loss of coverage due to respiration. Previous results showed that this approach ensures target coverage while reducing lung dose. The current study evaluated the robustness of this boost volume (BV) technique to changes in respiratory motion, including amplitude and time spent in each respiratory phase.
  
  
  METHODS
  ITV and BV plans were generated for one NSCLC patient with respiratory motion amplitude of 0.9cm. Dose was accumulated for three different weightings of the 4DCT phases. Nine numerical phantoms were created with tumour sizes of 3cm, 5cm and 6.5cm and motion amplitudes of 7mm, 10mm and 14mm. The robustness of BV and ITV plans to variations in motion amplitude was assessed. The relative contributions of the width of the boost volume and the boost dose to plans efficacy and robustness were investigated.
  
  
  RESULTS
  The BV plans were robust to typical variations in the time spent at each respiratory phase. Both ITV and BV plans were robust to 3mm amplitude decreases but not to 3mm amplitude increases. Increasing the boost dose from 110% to 120% of the prescription dose had negligible effect in improving tumour coverage.
  
  
  CONCLUSIONS
  To improve the robustness of this technique the width of the boost volume needs to be increased.
authors.affiliation: Department of Physics, Ryerson University, 350 Victoria St, Toronto, ON M5B 2K3, Canada; Department of Radiation Physics, Princess Margaret Cancer Center, 610 University Ave, Toronto, ON M5G 2M9, Canada. Electronic address: mohsen.ahanj@ryerson.ca.
authors.forename: Mohsen
authors.initials: M
authors.lastname: Ahanj
authors.affiliation: Department of Radiation Physics, Princess Margaret Cancer Center, 610 University Ave, Toronto, ON M5G 2M9, Canada; Department of Radiation Oncology, University of Toronto, 150 College St, Toronto, ON M5S 3E2, Canada. Electronic address: jeanpierre.bissonnette@rmp.uhn.on.ca.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Bissonnette
authors.affiliation: Carleton Laboratory for Radiotherapy Physics, Department of Physics, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada. Electronic address: emily.heath@carleton.ca.
authors.forename: Emily
authors.initials: E
authors.lastname: Heath
authors.affiliation: Department of Medical Physics, Odette Cancer Center, Sunnybrook Health Sciences Center, 2075 Bayview Ave, Toronto, ON M4N 3M5, Canada; Department of Radiation Oncology, University of Toronto, 150 College St, Toronto, ON M5S 3E2, Canada. Electronic address: claire.mccann@sunnybrook.ca.
authors.forename: Claire
authors.initials: C
authors.lastname: McCann
mesh_terms: D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000532:radiotherapy*; D009068:Movement; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated; D012119:Respiration
keywords: IMRT; Lung cancer; Respiratory motion; Robustness analysis