title: Comparison of dose distributions and organs at risk (OAR) doses in conventional tangential technique (CTT) and IMRT plans with different numbers of beam in left-sided breast cancer.
abstract: OBJECTIVE
  Our aim was to improve dose distribution to the left breast and to determine the dose received by the ipsilateral lung, heart, contralateral lung and contralateral breast during primary left-sided breast irradiation by using intensity modulated radiotherapy (IMRT) techniques compared to conventional tangential techniques (CTT). At the same time, different beams of IMRT plans were compared to each other in respect to CI, HI and organs at risk (OAR) dose.
  
  
  BACKGROUND
  Conventional early breast cancer treatment consists of lumpectomy followed by whole breast radiation therapy. CTT is a traditional method used for whole breast radiotherapy and includes standard wedged tangents (two opposed wedged tangential photon beams). The IMRT technique has been widely used for many treatment sites, allowing both improved sparing of normal tissues and more conformal dose distributions. IMRT is a new technique for whole breast radiotherapy. IMRT is used to improve conformity and homogeneity and used to reduce OAR doses.
  
  
  METHODS
  Thirty patients with left-sided breast carcinoma were treated between 2005 and 2008 using 6, 18 or mixed 6/18 MV photons for primary breast irradiation following breast conserving surgery (BCS). The clinical target volume [CTV] was contoured as a target volume and the contralateral breast, ipsilateral lung, contralateral lung and heart tissues as organs at risk (OAR). IMRT with seven beams (IMRT7), nine beams (IMRT9) and 11 beams (IMRT11) plans were developed and compared with CTT and among each other. The conformity index (CI), homogeneity index (HI), and doses to OAR were compared to each other.
  
  
  RESULTS
  ALL OF IMRT PLANS SIGNIFICANTLY IMPROVED CI (CTT: 0.76; IMRT7: 0.84; IMRT9: 0.84; IMRT11: 0.85), HI (CTT: 1.16; IMRT7: 1.12; IMRT9: 1.11; IMRT11: 1.11), volume of the ipsilateral lung receiving more than 20 Gy (>V20 Gy) (CTT: 14.6; IMRT7: 9.08; IMRT9: 8.10; IMRT11: 8.60), and volume of the heart receiving more than 30 Gy (>V30 Gy) (CTT: 6.7; IMRT7: 4.04; IMRT9: 2.80; IMRT11: 2.98) compared to CTT. All IMRT plans were found to significantly decrease >V20 Gy and >V30 Gy volumes compared to conformal plans. But IMRT plans increased the volume of OAR receiving low dose radiotherapy: volume of contralateral lung receiving 5 and 10 Gy (CTT: 0.0-0.0; IMRT7: 19.0-0.7; IMRT9: 17.2-0.66; IMRT11: 18.7-0.58, respectively) and volume of contralateral breast receiving 10 Gy (CTT: 0.03; IMRT7: 0.38; IMRT9: 0.60; IMRT11: 0.68). The differences among IMRT plans with increased number of beams were not statistically significant.
  
  
  CONCLUSIONS
  IMRT significantly improved conformity and homogeneity index for plans. Heart and lung volumes receiving high doses were decreased, but OAR receiving low doses was increased.
authors.affiliation: Department of Radiation Oncology, Anadolu Medical Center, Gebze, Kocaeli, Turkey.
authors.forename: Hande Bas
authors.initials: HB
authors.lastname: Ayata
authors.affiliation: Department of Radiation Oncology, Anadolu Medical Center, Gebze, Kocaeli, Turkey.
authors.forename: Metin
authors.initials: M
authors.lastname: Güden
authors.affiliation: Department of Radiation Oncology, Anadolu Medical Center, Gebze, Kocaeli, Turkey.
authors.forename: Cemile
authors.initials: C
authors.lastname: Ceylan
authors.affiliation: Department of Radiation Oncology, Anadolu Medical Center, Gebze, Kocaeli, Turkey.
authors.forename: Nadir
authors.initials: N
authors.lastname: Kücük
authors.affiliation: Department of Radiation Oncology, Anadolu Medical Center, Gebze, Kocaeli, Turkey.
authors.forename: Kayihan
authors.initials: K
authors.lastname: Engin
keywords: Breast cancer; Conventional techniques comparison; IMRT; Left breast; Whole breast radiotherapy