title: The effect of image guidance on dose distributions in breast boost radiotherapy.
abstract: OBJECTIVE
  To determine the effect of image-guided radiotherapy on the dose distributions in breast boost treatments.
  
  
  METHODS
  Computed tomography images from a cohort of 60 patients treated within the IMPORT HIGH trial (CRUK/06/003) were used to create sequential and concomitant boost treatment plans (30 cases each). Two treatment plans were created for each case using tumour bed planning target volume (PTV) margins of 5 mm (achieved with image-guided radiotherapy) and 8 mm (required for bony anatomy verification). Dose data were collected for breast, lung and heart; differences with margin size were tested for statistical significance.
  
  
  RESULTS
  A median decrease of 29 cm(3) (range 11-193 cm(3)) of breast tissue receiving 95% of the prescribed dose was observed where image-guided radiotherapy margins were used. Decreases in doses to lungs, contralateral breast and heart were modest, but statistically significant (P < 0.01). Plan quality was compromised with the 8 mm PTV margin in one in eight sequential boost plans and one third of concomitant boost plans. Tumour bed PTV coverage was <95% (>91%) of the prescribed dose in 12 cases; in addition, the required partial breast median dose was exceeded in nine concomitant boost cases by 0.5-3.7 Gy.
  
  
  CONCLUSIONS
  The use of image guidance and, hence, a reduced tumour bed PTV margin, in breast boost radiotherapy resulted in a modest reduction in radiation dose to breast, lung and heart tissues. Reduced margins enabled by image guidance were necessary to discriminate between dose levels to multiple PTVs in the concomitant breast boost plans investigated.
authors.affiliation: Joint Department of Physics, The Royal Marsden/Institute of Cancer Research, Sutton, Surrey, UK. Electronic address: ellen.donovan@icr.ac.uk.
authors.forename: E M
authors.initials: EM
authors.lastname: Donovan
authors.affiliation: Joint Department of Physics, The Royal Marsden/Institute of Cancer Research, Sutton, Surrey, UK.
authors.forename: C
authors.initials: C
authors.lastname: Brooks
authors.affiliation: Joint Department of Physics, The Royal Marsden/Institute of Cancer Research, Sutton, Surrey, UK.
authors.forename: R A
authors.initials: RA
authors.lastname: Mitchell
authors.affiliation: Oncology Centre, Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK.
authors.forename: M
authors.initials: M
authors.lastname: Mukesh
authors.affiliation: Oncology Centre, Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK.
authors.forename: C E
authors.initials: CE
authors.lastname: Coles
authors.affiliation: Centre for Vision Speech and Signal Processing, University of Surrey, Guildford, UK.
authors.forename: P M
authors.initials: PM
authors.lastname: Evans
authors.affiliation: Joint Department of Physics, The Royal Marsden/Institute of Cancer Research, Sutton, Surrey, UK.
authors.forename: E J
authors.initials: EJ
authors.lastname: Harris
mesh_terms: D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D019583:Dose Fractionation, Radiation; D005260:Female; D005500:Follow-Up Studies; D006321:Heart / Q000528:radiation effects*; D006801:Humans; D008168:Lung / Q000528:radiation effects*; D059351:Organ Sparing Treatments; D058958:Organs at Risk; D011379:Prognosis; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D014057:Tomography, X-Ray Computed
keywords: Breast boost; image-guided radiotherapy; margin reduction; organs at risk; treatment planning