title: Isocentric integration of intensity-modulated radiotherapy with electron fields improves field junction dose uniformity in postmastectomy radiotherapy.
abstract: BACKGROUND
  In postmastectomy radiotherapy (PMRT), the dose coverage of the planning target volume (PTV) with additional margins, including the chest wall, supraclavicular, interpectoral, internal mammary and axillar level I-III lymph nodes, is often compromised. Electron fields may improve the medial dose coverage while maintaining organ at risk (OAR) doses at an acceptable level, but at the cost of hot and cold spots at the electron and photon field junction. To improve PMRT dose coverage and uniformity, an isocentric technique combining tangential intensity-modulated (IM)RT fields with one medial electron field was implemented.
  
  
  METHODS
  For 10 postmastectomy patients isocentric IMRT with electron plans were created and compared with a standard electron/photon mix and a standard tangent technique. PTV dose uniformity was evaluated based on the tolerance range (TR), i.e. the ratio of the standard deviation to the mean dose, a dice similarity coefficient (DSC) and the 90% isodose coverage and the hot spot volumes. OAR and contralateral breast doses were also recorded.
  
  
  RESULTS
  IMRT with electrons significantly improved the PTV dose homogeneity and conformity based on the TR and DSC values when compared with the standard electron/photon and tangent technique (p < 0.02). The 90% isodose coverage improved to 86% compared with 82% and 80% for the standard techniques (p < 0.02). Compared with the standard electron/photon mix, IMRT smoothed the dose gradient in the electron and photon field junction and the volumes receiving a dose of 110% or more were reduced by a third. For all three strategies, the OAR and contralateral breast doses were within clinically tolerable limits.
  
  
  CONCLUSIONS
  Based on these results two-field IMRT combined with an electron field is a suitable strategy for PMRT.
authors: Department of Medical Physics, Turku University Hospital , Finland.
authors: Pauliina
authors: P
authors: Wright
authors: Sami
authors: S
authors: Suilamo
authors: Paula
authors: P
authors: Lindholm
authors: Jarmo
authors: J
authors: Kulmala
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001940:Breast / Q000528:radiation effects*; D001943:Breast Neoplasms / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D004583:Electrons / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D008408:Mastectomy; D008875:Middle Aged; D059351:Organ Sparing Treatments / Q000379:methods*; D058958:Organs at Risk / Q000528:radiation effects*; D017785:Photons / Q000627:therapeutic use; D011832:Radiation Injuries / Q000517:prevention & control; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D018714:Radiotherapy, Adjuvant / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*