title: Effects of geometrical uncertainties on whole breast radiotherapy: a comparison of four different techniques.
abstract: OBJECTIVE
  The purpose of this study was to quantify the target coverage, homogeneity, and robustness of the dose distributions against geometrical uncertainties associated with four whole breast radiotherapy techniques.
  
  
  METHODS
  The study was based on the planning-computed tomography-datasets of 20 patients who underwent whole breast radiotherapy. A total of four treatment plans (wedge, field-in-field [FIF], hybrid intensity-modulated radiotherapy [IMRT], and full IMRT) were created for each patient. The hybrid IMRT plans comprised two opposed tangential open beams plus two IMRT beams. Setup errors were simulated by moving the beam isocenters by 5 mm in the anterior or posterior direction.
  
  
  RESULTS
  With the original plan, the wedge technique yielded a high volume receiving ≥107% of the prescription dose (V107; 7.5%±4.2%), whereas the other three techniques yielded excellent target coverage and homogeneity. A 5 mm anterior displacement caused a large and significant increase in the V107 (+5.2%±4.1%, p<0.01) with the FIF plan, but not with the hybrid IMRT (+0.4%±1.2%, p=0.11) or full IMRT (+0.7%±1.8%, p=0.10) plan. A 5-mm posterior displacement caused a large decrease in the V95 with the hybrid IMRT (-2.5%±3.7%, p<0.01) and full IMRT (-4.3%±5.1%, p<0.01) plans, but not with the FIF plan (+0.1%±0.7%, p=0.74). The decrease in V95 was significantly smaller with the hybrid IMRT plan than with the full IMRT plan (p<0.01).
  
  
  CONCLUSIONS
  The FIF, hybrid IMRT, and full IMRT plans offered excellent target coverage and homogeneity. Hybrid IMRT provided better robustness against geometrical uncertainties than full IMRT, whereas FIF provided comparable robustness to that of hybrid IMRT.
authors.affiliation: Department of Radiation Oncology, St. Luke's International Hospital, Tokyo, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Nakamura
authors.affiliation: Division of General Internal Medicine, Department of Medicine, St. Luke's International Hospital, Tokyo, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Takahashi
authors.affiliation: Department of Radiology, St. Luke's International Hospital, Tokyo, Japan.
authors.forename: Minobu
authors.initials: M
authors.lastname: Kamo
authors.affiliation: Department of Radiation Oncology, St. Luke's International Hospital, Tokyo, Japan.
authors.forename: Shogo
authors.initials: S
authors.lastname: Hatanaka
authors.affiliation: Department of Radiation Oncology, St. Luke's International Hospital, Tokyo, Japan.
authors.forename: Haruna
authors.initials: H
authors.lastname: Endo
authors.affiliation: Department of Radiation Oncology, St. Luke's International Hospital, Tokyo, Japan.
authors.forename: Norifumi
authors.initials: N
authors.lastname: Mizuno
authors.affiliation: Department of Radiation Oncology, Saitama Medical University International Medical Center, Hidaka, Japan.
authors.forename: Naoto
authors.initials: N
authors.lastname: Shikama
authors.affiliation: Department of Radiation Oncology, St. Luke's International Hospital, Tokyo, Japan.
authors.forename: Mami
authors.initials: M
authors.lastname: Ogita
authors.affiliation: Department of Radiation Oncology, St. Luke's International Hospital, Tokyo, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Sekiguchi
keywords: Breast neoplasms; Intensity-modulated radiotherapy