title: Quantification of cold spots caused by geometrical uncertainty in field-in-field techniques for whole breast radiotherapy.
abstract: OBJECTIVE
  To quantify the cold spot under geometrical uncertainties in field-in-field techniques for whole breast radiotherapy.
  
  
  METHODS
  Ten consecutive patients from both the left- and right-sided treatment site groups who received whole breast radiotherapy with the field-in-field technique were included. Virtual plans were made with moving isocenters to the posterior direction having two amplitudes (5 and 10 mm) and prescribing the same monitor unit as the original plan (FIF_5 and FIF_10). The planning target volume for evaluation was defined by subtracting the areas within 5 mm from the skin and within 5 mm from the lung from the whole breast. The differences in V90, V95 and D98 of planning target volume for evaluation were measured between the original and virtual plans. As a reference, the same measurements were taken for the wedge techniques (Wedge_5 and Wedge_10).
  
  
  RESULTS
  The differences in V95 were -0.2% on FIF_5, -1.7% on FIF_10, -0.5% on Wedge_5 and -1.5% on Wedge_10. The differences in V90 were -0.02% on FIF_5, -0.3% on FIF_10, -0.05% on Wedge_5 and -0.1% on Wedge_10. The differences in D98 were 0 Gy on FIF_5, -0.1 Gy on FIF_10, -0.2 Gy on Wedge_5 and -0.4 Gy on Wedge_10. The differences in D98 between the original plans and virtual scenarios for field-in-field techniques were significantly smaller than those for wedge techniques, but there were no statically significant differences in V90 and V95.
  
  
  CONCLUSIONS
  The quantity of the cold spots caused by the geometrical uncertainties in field-in-field techniques was similar to that for the wedge techniques and was acceptable.
authors.affiliation: Department of Radiation Oncology, St Luke's International Hospital, 9-1, Akashicho, Chuoh-ku, Tokyo 104-8560, Japan. naokinak@luke.or.jp
authors.forename: Naoki
authors.initials: N
authors.lastname: Nakamura
authors.forename: Shogo
authors.initials: S
authors.lastname: Hatanaka
authors.forename: Naoto
authors.initials: N
authors.lastname: Shikama
authors.forename: Keiko
authors.initials: K
authors.lastname: Akahane
authors.forename: Kenji
authors.initials: K
authors.lastname: Sekiguchi
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D008875:Middle Aged; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D035501:Uncertainty