title: Retrospective feasibility study of simultaneous integrated boost in cervical cancer using Tomotherapy: the impact of organ motion and tumor regression.
abstract: BACKGROUND
  Whole pelvis intensity modulated radiotherapy (IMRT) is increasingly being used to treat cervical cancer aiming to reduce side effects. Encouraged by this, some groups have proposed the use of simultaneous integrated boost (SIB) to target the tumor, either to get a higher tumoricidal effect or to replace brachytherapy. Nevertheless, physiological organ movement and rapid tumor regression throughout treatment might substantially reduce any benefit of this approach.
  
  
  OBJECTIVE
  To evaluate the clinical target volume - simultaneous integrated boost (CTV-SIB) regression and motion during chemo-radiotherapy (CRT) for cervical cancer, and to monitor treatment progress dosimetrically and volumetrically to ensure treatment goals are met.
  
  
  METHODS
  Ten patients treated with standard doses of CRT and brachytherapy were retrospectively re-planned using a helical Tomotherapy - SIB technique for the hypothetical scenario of this feasibility study. Target and organs at risk (OAR) were contoured on deformable fused planning-computed tomography and megavoltage computed tomography images. The CTV-SIB volume regression was determined. The center of mass (CM) was used to evaluate the degree of motion. The Dice's similarity coefficient (DSC) was used to assess the spatial overlap of CTV-SIBs between scans. A cumulative dose-volume histogram modeled estimated delivered doses.
  
  
  RESULTS
  The CTV-SIB relative reduction was between 31 and 70%. The mean maximum CM change was 12.5, 9, and 3 mm in the superior-inferior, antero-posterior, and right-left dimensions, respectively. The CTV-SIB-DSC approached 1 in the first week of treatment, indicating almost perfect overlap. CTV-SIB-DSC regressed linearly during therapy, and by the end of treatment was 0.5, indicating 50% discordance. Two patients received less than 95% of the prescribed dose. Much higher doses to the OAR were observed. A multiple regression analysis showed a significant interaction between CTV-SIB reduction and OAR dose increase.
  
  
  CONCLUSIONS
  The CTV-SIB had important regression and motion during CRT, receiving lower therapeutic doses than expected. The OAR had unpredictable shifts and received higher doses. The use of SIB without frequent adaptation of the treatment plan exposes cervical cancer patients to an unpredictable risk of under-dosing the target and/or overdosing adjacent critical structures. In that scenario, brachytherapy continues to be the gold standard approach.
authors.affiliation: Department of Radiation Oncology, Centre Hospitalier Universitaire Vaudois - CHUV, Rue du Bugnon 21, Lausanne 1011, Switzerland. fernanda.herrera@chuv.ch
authors.forename: Fernanda G
authors.initials: FG
authors.lastname: Herrera
authors.forename: Sharon
authors.initials: S
authors.lastname: Callaway
authors.forename: Ela
authors.initials: E
authors.lastname: Delikgoz-Soykut
authors.forename: Mehtap
authors.initials: M
authors.lastname: Coskun
authors.forename: Laetitia
authors.initials: L
authors.lastname: Porta
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Meuwly
authors.forename: Joao
authors.initials: J
authors.lastname: Soares-Rodrigues
authors.forename: Leonie
authors.initials: L
authors.lastname: Heym
authors.forename: Raphael
authors.initials: R
authors.lastname: Moeckli
authors.forename: Mahmut
authors.initials: M
authors.lastname: Ozsahin
mesh_terms: D016477:Artifacts; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D009038:Motion; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*