title: Dose escalation in brachytherapy for cervical cancer: impact on (or increased need for) MRI-guided plan optimisation.
abstract: OBJECTIVE
  The aim of this study was to assess the impact of dose escalation on the proportion of patients requiring MR image-guided optimisation rather than standard Manchester-based CT-guided planning, and the level of escalation achievable.
  
  
  METHODS
  30 patients with cervical cancer treated with external beam radiotherapy and image-guided brachytherapy (IGBT) had MR images acquired at the first fraction of IGBT. Gross tumour volume and high-risk clinical target volume (HR CTV) were contoured and treatment plans retrospectively produced for a range of total 2-Gy equivalent (EQD2) prescription doses from 66 Gy(α/β=10) to 90 Gy(α/β=10) (HR CTV D90). Standard Manchester system-style plans were produced, prescribed to point A and then optimised where necessary with the aim of delivering at least the prescription dose to the HR CTV D90 while respecting organ-at-risk (OAR) tolerances.
  
  
  RESULTS
  Increasing the total EQD2 from 66 Gy(α/β=10) to 90 Gy(α/β=10) increased the number of plans requiring optimisation from 13.3% to 90%. After optimisation, the number of plans achieving the prescription dose ranged from 93.3% (66 Gy(α/β=10)) to 63.3% (90 Gy(α/β=10)) with the mean ± standard deviation for HR CTV D90 EQD2 from 78.4 ± 12.4 Gy(α/β=10) (66 Gy(α/β=10)) to 94.1 ± 19.9 Gy(α/β=10) (90 Gy(α/β=10)).
  
  
  CONCLUSIONS
  As doses are escalated, the need for non-standard optimised planning increases, while benefits in terms of increased target doses actually achieved diminish. The maximum achievable target dose is ultimately limited by proximity of OARs.
  
  
  CONCLUSIONS
  This work represents a guide for other centres in determining the highest practicable prescription doses while considering patient throughput and maintaining acceptable OAR doses.
authors.affiliation: Radiotherapy Physics Unit, Bristol Haematology and Oncology Centre, University Hospitals Bristol NHS Foundation Trust, UK.
authors.forename: A M
authors.initials: AM
authors.lastname: Paton
authors.forename: K E
authors.initials: KE
authors.lastname: Chalmers
authors.forename: H
authors.initials: H
authors.lastname: Coomber
authors.forename: A L
authors.initials: AL
authors.lastname: Cameron
mesh_terms: D000328:Adult; D000368:Aged; D001918:Brachytherapy / Q000379:methods*; D002277:Carcinoma / Q000532:radiotherapy*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D053783:Magnetic Resonance Imaging, Interventional / Q000379:methods*; D008875:Middle Aged; D058958:Organs at Risk / Q000528:radiation effects; D015641:Radiography, Interventional; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*