Skin dose in breast brachytherapy: Defining a robust metric

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• 作者：Michelle Hilts¹ ; ² ; ^{mhilts@bccancer.bc.ca" class="auth_mail" title="E-mail the corresponding author} ; Heather Halperin¹ ; Dan Morton¹ ; ² ; Deidre Batchelar¹ ; Francois Bachand³ ; Rezwan Chowdhury³ ; Juanita Crook³
• 关键词：Breast brachytherapy ; Breast permanent seed implants ; HDR brachytherapy ; Postoperative ; Dosimetry ; Skin dose ; Skin toxicity
• 刊名：Brachytherapy
• 出版年：2015
• 出版时间：November-December 2015
• 年：2015
• 卷：14
• 期：6
• 页码：970-978
• 全文大小：1205 K

文摘

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 (D_max), doses to small volumes (e.g., D_0.2cc), and the volumes receiving a percentage of the prescription dose (V_%, e.g., V₆₆) were calculated. D_0.2cc was investigated as a surrogate to the dose given to 1 cm² of skin (D_1cm²). Pearson product–moment correlation (R²) was computed between metrics.

Results

Observed trends were consistent across brachytherapy technique. V_% did not correlate well with any other metrics: median (range) R², 0.63 (0.43, 0.77) and 0.69 (0.3, 0.89) for PBSI and MC-HDR, respectively. D_max was inconsistently correlated across contours and not well correlated with doses to small volumes: median (range) R², 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: D_0.1cc vs. D_0.2cc median (range) R², 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, D_0.2cc for a 2 mm thick skin layer, a simple surrogate of D_1cm², is recommended for recording skin dose in any breast brachytherapy. D_max is not robust and should be avoided.