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Brachytherapy. 2015 Nov-Dec;14(6):970-8. doi: 10.1016/j.brachy.2015.08.002. Epub 2015 Sep 26.

Skin dose in breast brachytherapy: Defining a robust metric.

Author information

1
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.
2
Medical Physics, BC Cancer Agency, Centre for the Southern Interior, British Columbia, Canada.
3
Medical Physics, BC Cancer Agency, Centre for the Southern Interior, British Columbia, Canada; Department of Physics and Astronomy, University of Victoria, British Columbia, Canada.
4
Radiation Oncology, BC Cancer Agency, Centre for the Southern Interior, British Columbia, Canada.

Abstract

PURPOSE:

To define a simple, robust, and relevant metric for measuring skin dose in breast brachytherapy.

METHODS AND MATERIALS:

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.

KEYWORDS:

Breast brachytherapy; Breast permanent seed implants; Dosimetry; HDR brachytherapy; Postoperative; Skin dose; Skin toxicity

PMID:
26412617
DOI:
10.1016/j.brachy.2015.08.002
[Indexed for MEDLINE]

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