title: Skin dose in breast brachytherapy: Defining a robust metric.
abstract: OBJECTIVE
  To define a simple, robust, and relevant metric for measuring skin dose in breast brachytherapy.
  
  
  METHODS
  Postoperative treatment plans (Day 0) for 15 permanent breast seed implant (PBSI) and 10 multicatheter high-dose-rate (MC-HDR) brachytherapy patients were included. Retrospectively, three skin structures were contoured: 2 mm external from the body; and subsurface layers 2 mm and 4 mm thick. Maximum point dose (Dmax), doses to small volumes (e.g., D0.2cc), and the volumes receiving a percentage of the prescription dose (V%, e.g., V66) were calculated. D0.2cc was investigated as a surrogate to the dose given to 1 cm(2) of skin (D1cm(2)). Pearson product-moment correlation (R(2)) was computed between metrics.
  
  
  RESULTS
  Observed trends were consistent across brachytherapy technique. V% did not correlate well with any other metrics: median (range) R(2), 0.63 (0.43, 0.77) and 0.69 (0.3, 0.89) for PBSI and MC-HDR, respectively. Dmax was inconsistently correlated across contours and not well correlated with doses to small volumes: median (range) R(2), 0.85 (0.76, 0.93) and 0.88 (0.83, 0.93) for PBSI and MC-HDR, respectively. In contrast, doses to small volumes were consistently well correlated, even across skin layers: D0.1cc vs. D0.2cc median (range) R(2), 0.98 (0.97, 0.99) and 0.97 (0.94, 0.99) for PBSI and MC-HDR, respectively.
  
  
  CONCLUSIONS
  Doses to small volumes are robust measures of breast skin dose and given skin's strong area effect, D0.2cc for a 2 mm thick skin layer, a simple surrogate of D1cm(2), is recommended for recording skin dose in any breast brachytherapy. Dmax is not robust and should be avoided.
authors.affiliation: Medical Physics, BC Cancer Agency, Centre for the Southern Interior, British Columbia, Canada; Department of Physics and Astronomy, University of Victoria, British Columbia, Canada. Electronic address: mhilts@bccancer.bc.ca.
authors.forename: Michelle
authors.initials: M
authors.lastname: Hilts
authors.affiliation: Medical Physics, BC Cancer Agency, Centre for the Southern Interior, British Columbia, Canada.
authors.forename: Heather
authors.initials: H
authors.lastname: Halperin
authors.affiliation: Medical Physics, BC Cancer Agency, Centre for the Southern Interior, British Columbia, Canada; Department of Physics and Astronomy, University of Victoria, British Columbia, Canada.
authors.forename: Dan
authors.initials: D
authors.lastname: Morton
authors.affiliation: Medical Physics, BC Cancer Agency, Centre for the Southern Interior, British Columbia, Canada.
authors.forename: Deidre
authors.initials: D
authors.lastname: Batchelar
authors.affiliation: Radiation Oncology, BC Cancer Agency, Centre for the Southern Interior, British Columbia, Canada.
authors.forename: Francois
authors.initials: F
authors.lastname: Bachand
authors.affiliation: Radiation Oncology, BC Cancer Agency, Centre for the Southern Interior, British Columbia, Canada.
authors.forename: Rezwan
authors.initials: R
authors.lastname: Chowdhury
authors.affiliation: Radiation Oncology, BC Cancer Agency, Centre for the Southern Interior, British Columbia, Canada.
authors.forename: Juanita
authors.initials: J
authors.lastname: Crook
mesh_terms: D001918:Brachytherapy / Q000379:methods; D001940:Breast / Q000528:radiation effects; D001943:Breast Neoplasms / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D008875:Middle Aged; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012189:Retrospective Studies; D012867:Skin / Q000528:radiation effects*
keywords: Breast brachytherapy; Breast permanent seed implants; Dosimetry; HDR brachytherapy; Postoperative; Skin dose; Skin toxicity