Gifford Kent A, Pacha Omar, Hebert Adelaide A, Nelson Christopher L, Kirsner Steven M, Ballo Matthew T, Bloom Elizabeth S
Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Brachytherapy. 2013 Mar-Apr;12(2):114-9. doi: 10.1016/j.brachy.2012.05.005. Epub 2012 Aug 9.
Most institutions model breast epidermis with a surface contour and record the maximum dose on the external surface of the patient. The objective of this study was to compare the external surface contour (ext) model of the skin with our current volumetric model for skin for radiation treatment planning in accelerated partial breast irradiation brachytherapy.
A literature search was conducted to identify studies measuring breast epidermal thickness. Clinical plans were performed with a 2-mm contraction of the external surface contour. This 2-mm contraction of the external surface contour was used to approximate breast epidermis thickness. Then, the external surface contour was expanded 5mm outside the external contour of the patient for the second skin model. Maximum doses from the two models were recorded and compared.
The average breast epidermal thickness from five studies was 1.68mm. Mean percent difference between skin and ext+5mm for balloon plans, strut plans, and all plans was 10.1%, 14.5%, and 12.5%, respectively. Differences in doses between the two skin models were statistically significant (p<0.0001).
The volumetric skin model was validated because the average breast epidermal thickness was 1.68mm. The surface model for skin may underestimate the dose delivered to the epidermis by as much as 23.8%. The external surface contour method does not accurately represent the dermatologic skin thickness of the breast as the skin is modeled as a surface rather than a volume. These discrepancies may skew correlations of dose to skin and toxicity determinations.
大多数机构使用具有表面轮廓的乳房表皮模型，并记录患者体表的最大剂量。本研究的目的是比较皮肤的体表轮廓（ext）模型与我们目前用于加速部分乳腺照射近距离放射治疗的皮肤容积模型，以进行放射治疗计划。
进行文献检索以确定测量乳腺表皮厚度的研究。临床计划采用体表轮廓收缩2毫米进行。体表轮廓的这种2毫米收缩用于近似乳腺表皮厚度。然后，将体表轮廓在患者外部轮廓之外扩展5毫米以构建第二个皮肤模型。记录并比较两个模型的最大剂量。
五项研究的平均乳腺表皮厚度为1.68毫米。气囊计划、支柱计划和所有计划中，皮肤与ext+5毫米之间的平均百分比差异分别为10.1%、14.5%和12.5%。两种皮肤模型之间的剂量差异具有统计学意义（p<0.0001）。
由于平均乳腺表皮厚度为1.68毫米，容积皮肤模型得到了验证。皮肤表面模型可能会低估传递到表皮的剂量达23.8%。体表轮廓法不能准确代表乳房的皮肤厚度，因为皮肤被建模为一个表面而非一个容积。这些差异可能会扭曲皮肤剂量与毒性测定之间的相关性。
