title: Geometric and dosimetric approach to determine probability of late cardiac mortality in left tangential breast irradiation: comparison between wedged beams and field-in-field technique.
abstract: OBJECTIVE
  To evaluate the probability of late cardiac mortality resulting from left breast irradiation planned with tangential fields and to compare this probability between the wedged beam and field-in-field (FIF) techniques and to investigate whether some geometric/dosimetric indicators can be determined to estimate the cardiac mortality probability before treatment begins.
  
  
  METHODS
  For 30 patients, differential dose-volume histograms were calculated for the wedged beam and FIF plans, and the corresponding cardiac mortality probabilities were determined using the relative seriality model. As a comparative index of the dose distribution uniformity, the planning target volume (PTV) percentages involved in 97-103% of prescribed dose were determined for the two techniques. Three geometric parameters were measured for each patient: the maximal length, indicates how much the heart contours were displaced toward the PTV, the angle subtended at the center of the computed tomography slice by the PTV contour, and the thorax width/thickness ratio.
  
  
  RESULTS
  Evaluating the differential dose-volume histograms showed that the gain in uniformity between the two techniques was about 1.5. With the FIF technique, the mean dose sparing for the heart, the left anterior descending coronary artery, and the lung was 15% (2.5 Gy vs. 2.2 Gy), 21% (11.3 Gy vs. 9.0 Gy), and 42% (8.0 Gy vs. 4.6 Gy) respectively, compared with the wedged beam technique. Also, the cardiac mortality probability decreased by 40% (from 0.9% to 0.5%). Three geometric parameters, the maximal length, angle subtended at the center of the computed tomography slice by the PTV contour, and thorax width/thickness ratio, were the determining factors (p = .06 for FIF, and p = .10 for wedged beam) for evaluating the cardiac mortality probability.
  
  
  CONCLUSIONS
  The FIF technique seemed to yield a lower cardiac mortality probability than the conventional wedged beam technique. However, although our study demonstrated that FIF technique improved the dose coverage of the PTV, the restricted number of patients enrolled and the short follow-up did not allow us to evaluate and compare the breast cancer survival rates of the patients.
authors.affiliation: Department of Medical Physics, "A. Perrino" Hospital, Brindisi, Italy.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Pili
authors.forename: Luca
authors.initials: L
authors.lastname: Grimaldi
authors.forename: Christian
authors.initials: C
authors.lastname: Fidanza
authors.forename: Elena T
authors.initials: ET
authors.lastname: Florio
authors.forename: Maria F
authors.initials: MF
authors.lastname: Petruzzelli
authors.forename: Maria P
authors.initials: MP
authors.lastname: D'Errico
authors.forename: Cristina
authors.initials: C
authors.lastname: De Tommaso
authors.forename: Francesco
authors.initials: F
authors.lastname: Tramacere
authors.forename: Francesca
authors.initials: F
authors.lastname: Musaio
authors.forename: Roberta
authors.initials: R
authors.lastname: Castagna
authors.forename: Maria C
authors.initials: MC
authors.lastname: Francavilla
authors.forename: Emilio A L
authors.initials: EA
authors.lastname: Gianicolo
authors.forename: Maurizio
authors.initials: M
authors.lastname: Portaluri
mesh_terms: D000328:Adult; D000368:Aged; D001940:Breast / Q000473:pathology; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D003331:Coronary Vessels / Q000528:radiation effects; D005260:Female; D006321:Heart / Q000528:radiation effects*; D006331:Heart Diseases / Q000401:mortality* / Q000517:prevention & control; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000528:radiation effects; D008875:Middle Aged; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects; D011336:Probability; D011832:Radiation Injuries / Q000401:mortality* / Q000517:prevention & control; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D047368:Tumor Burden / Q000528:radiation effects