title: Lipiodol versus diaphragm in 4D-CBCT-guided stereotactic radiotherapy of hepatocellular carcinomas.
abstract: OBJECTIVE
  The purpose of this work was to investigate the potential of lipiodol as a direct tumor surrogate alternative to the diaphragm surrogate on four-dimensional cone-beam computed tomography (4D-CBCT) image guidance for stereotactic radiotherapy of hepatocellular carcinomas.
  
  
  METHODS
  A total of 29 hepatocellular carcinomas (HCC) patients treated by stereotactic radiotherapy following transarterial chemoembolization (TACE) with homogeneous or partial defective lipiodol retention were included. In all, 4-7 pretreatment 4D-CBCT scans were selected for each patient. For each scan, either lipiodol or the diaphragm was used for 4D registration. Resulting lipiodol/diaphragm motion ranges and position errors relative to the reconstructed midventilation images were analyzed to obtain the motion variations, and group mean (ΔM), systematic (Σ), and random (σ) errors of the treatment setup.
  
  
  RESULTS
  Of the lipiodolized tumors, 55 % qualified for direct localization on the 4D-CBCT. Significant correlations of lipiodol and diaphragm positions were found in the left-right (LR), craniocaudal (CC), and anteroposterior (AP) directions. ΔM and σ obtained with lipiodol and diaphragm were similar, agreed to within 0.5 mm in the LR and AP, and 0.3 mm in the CC directions, and Σ differed by 1.4 (LR), 1.1 (CC), and 0.6 (AP) mm. Variations of diaphragm motion range > 5 mm were not observed with lipiodol and in one patient with diaphragm. The margin required for the tumor prediction error using the diaphragm surrogate was 6.7 (LR), 11.7 (CC), and 4.1 (AP) mm.
  
  
  CONCLUSIONS
  Image-guidance combining lipiodol with 4D-CBCT enabled accurate localization of HCC and thus margin reduction. A major limitation was the degraded lipiodol contrast on 4D-CBCT.
authors.affiliation: Department of Clinical Oncology, TuenMun Hospital, TuenMun, Hong Kong (S.A.R). ckh456@ha.org.hk.
authors.forename: Mark K H
authors.initials: MK
authors.lastname: Chan
authors.affiliation: Department of Clinical Oncology, TuenMun Hospital, TuenMun, Hong Kong (S.A.R).
authors.forename: Venus
authors.initials: V
authors.lastname: Lee
authors.affiliation: Department of Clinical Oncology, TuenMun Hospital, TuenMun, Hong Kong (S.A.R).
authors.forename: C L
authors.initials: CL
authors.lastname: Chiang
authors.affiliation: Department of Clinical Oncology, TuenMun Hospital, TuenMun, Hong Kong (S.A.R).
authors.forename: Francis A S
authors.initials: FA
authors.lastname: Lee
authors.affiliation: Department of Clinical Oncology, TuenMun Hospital, TuenMun, Hong Kong (S.A.R).
authors.forename: Gilbert
authors.initials: G
authors.lastname: Law
authors.affiliation: Department of Diagnostic Radiology, TuenMun Hospital, TuenMun, Hong Kong (S.A.R).
authors.forename: N Y
authors.initials: NY
authors.lastname: Sin
authors.affiliation: Department of Diagnostic Radiology, TuenMun Hospital, TuenMun, Hong Kong (S.A.R).
authors.forename: K L
authors.initials: KL
authors.lastname: Siu
authors.affiliation: Department of Clinical Oncology, TuenMun Hospital, TuenMun, Hong Kong (S.A.R).
authors.forename: Frank C S
authors.initials: FC
authors.lastname: Wong
authors.affiliation: Department of Clinical Oncology, TuenMun Hospital, TuenMun, Hong Kong (S.A.R).
authors.forename: Stewart Y
authors.initials: SY
authors.lastname: Tung
authors.affiliation: Department of Clinical Oncology, TuenMun Hospital, TuenMun, Hong Kong (S.A.R).
authors.forename: Hollis
authors.initials: H
authors.lastname: Luk
authors.affiliation: Department of Radiation Oncology, Saphir Radiosurgery Center, University Clinic Schleswig-Holstein, Kiel, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Blanck
mesh_terms: D006528:Carcinoma, Hepatocellular / Q000473:pathology* / Q000601:surgery*; D016461:Chemoembolization, Therapeutic / Q000379:methods; D003131:Combined Modality Therapy; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D003964:Diaphragm / Q000473:pathology*; D004998:Ethiodized Oil; D057918:Fiducial Markers; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D008113:Liver Neoplasms / Q000473:pathology* / Q000601:surgery*; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies
chemical_list: D004998:Ethiodized Oil
keywords: 4D cone beam CT; Contrast media; Image-guided radiotherapy; Planning techniques; Stereotactic body radiotherapy