Department of Medical Physics, British Columbia Cancer Agency, Vancouver Centre, Vancouver, British Columbia, Canada.
Int J Radiat Oncol Biol Phys. 2012 Oct 1;84(2):527-32. doi: 10.1016/j.ijrobp.2011.11.060. Epub 2012 Feb 16.
Contouring variability of the seroma can have important implications in the planning and delivery of accelerated partial breast irradiation (APBI). This study aimed to quantify the dosimetric impact of these interobserver and intraobserver contouring variations by construction of a representative seroma contour (RSC).
Twenty-one patients with a seroma suitable for APBI underwent four computed tomography (CT) scans: one planning CT and three additional CTs on the first, third, and fifth days of treatment. Three radiation oncologists contoured the seroma on each CT scan. For 3 patients, oncologists repeated contouring twice to assess intraobserver variations. Seroma contour variability was quantified by construction of an RSC. In addition, the percent volume overlap (PVO) was calculated. Root-mean-square (RMS) differences in seroma volume, size, and center of mass position compared to those of the RSC were calculated. Treatment fields from the original plan were applied to the repeated CTs by using the same isocenter shifts as the original plan. The dosimetric impact of the contour variations was assessed using V(95) (volume receiving at least 95% of the prescribed dose) and equivalent uniform dose (EUD).
Interobserver RMS volume differences were, on average, 5.6 times larger than intraobserver differences. The median interobserver RMS seroma volume difference was 1.48 cm(3). The median PVO was 51.6%. V(95) and EUD of the seroma contours were similar for all patients. The median RMS differences of the seroma V(95) and EUD were 0.01% (range, 0%-3.99%) and 0.05 Gy (range, 0-0.98 Gy).
Construction of the RSC showed that interobserver variations were most responsible for contour variations of the seroma. Current planning margins provided adequate dose coverage of the seroma despite these contour variations.
在加速部分乳房照射（APBI）的计划和实施中，对浆液肿的轮廓变化进行描绘具有重要意义。本研究旨在通过构建代表性浆液肿轮廓（RSC）来量化这些观察者间和观察者内轮廓变化的剂量学影响。
21 名适合 APBI 的浆液肿患者接受了四次 CT 扫描：一次计划 CT 和三次额外的 CT 扫描，分别在治疗的第一天、第三天和第五天进行。三位放射肿瘤学家在每次 CT 扫描上勾画了浆液肿轮廓。对于 3 名患者，医生重复了两次轮廓勾画以评估观察者内的变化。通过构建 RSC 来量化浆液肿轮廓的变化。此外，还计算了体积重叠百分比（PVO）。与 RSC 相比，计算了浆液肿体积、大小和质心位置的均方根（RMS）差异。通过使用与原始计划相同的等中心移位，将原始计划的治疗场应用于重复的 CT 扫描。使用 V95（接受至少 95%处方剂量的体积）和等效均匀剂量（EUD）评估轮廓变化的剂量学影响。
观察者间 RMS 体积差异平均是观察者内差异的 5.6 倍。观察者间 RMS 浆液肿体积差异的中位数为 1.48cm3。中位数 PVO 为 51.6%。所有患者的浆液肿轮廓 V95 和 EUD 相似。浆液肿 V95 和 EUD 的 RMS 差异中位数分别为 0.01%（范围，0%-3.99%）和 0.05Gy（范围，0-0.98Gy）。
RSC 的构建表明，观察者间的变化是浆液肿轮廓变化的主要原因。尽管存在这些轮廓变化，但当前的计划边缘仍为浆液肿提供了足够的剂量覆盖。
