title: Using histopathology breast cancer data to reduce clinical target volume margins at radiotherapy.
abstract: OBJECTIVE
  This study aimed to quantify the incidence and extension of microscopic disease around primary breast tumors in patients undergoing breast-conserving therapy (BCT), focusing on a potential application to reduce radiotherapy boost volumes.
  
  
  METHODS
  An extensive pathology tumor-distribution study was performed using 38 wide local excision specimens of BCT patients. Specimen orientation was recorded and microscopic findings reconstructed to assess the incidence of microscopic disease around the macroscopic tumor. A model of disease spread was built, showing probability of disease extension outside a treated volume (P(out,vol)). The model was applied in 10 new BCT patients. Taking asymmetry of tumor excision into account, new asymmetric margins for the clinical target volume of the boost (CTV(boost)) were evaluated that minimize the volume without increasing P(out,TTV) (TTV being total treated volume: V(surgery) + CTV(boost)). Potential reductions in CTV(boost) and TTV were evaluated.
  
  
  RESULTS
  Microscopic disease beyond the tumor boundary occurred isotropically at distances > 1 cm (intended surgical margin) and > 1.5 cm (intended TTV margin) in 53% and 36% of the excision specimens, respectively. In the 10 prospective patients, the average P(out,TTV) was, however, only 16% due to larger surgical margins than intended in some directions. Asymmetric CTV(boost) margins reduced the CTV(boost) and TTV by 27% (20 cc) and 12% (21 cc) on average, without compromising tumor coverage.
  
  
  CONCLUSIONS
  Microscopic disease extension may occur beyond the current CTV(boost) in approximately one sixth of patients. An asymmetric CTV(boost) that corrects for asymmetry of the surgical excision has the potential to reduce boost volumes while maintaining tumor coverage.
authors.affiliation: Department of Radiotherapy, The Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands. j.stroom@nki.nl
authors.forename: Joep
authors.initials: J
authors.lastname: Stroom
authors.forename: Angelique
authors.initials: A
authors.lastname: Schlief
authors.forename: Tanja
authors.initials: T
authors.lastname: Alderliesten
authors.forename: Hans
authors.initials: H
authors.lastname: Peterse
authors.forename: Harry
authors.initials: H
authors.lastname: Bartelink
authors.forename: Kenneth
authors.initials: K
authors.lastname: Gilhuijs
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000473:pathology* / Q000532:radiotherapy* / Q000601:surgery; D005260:Female; D006801:Humans; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D018365:Neoplasm, Residual; D011879:Radiotherapy Dosage; D047368:Tumor Burden