Dosimetric analysis of intact breast irradiation in off-axis planes
Dosimetric analysis of intact breast irradiation in off-axis planes
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DOI：
10.1016/s0360-3016(97)00292-7
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发表时间：
1997-08-01
影响因子：
7
通讯作者：
Prestidge, BR
中科院分区：
文献类型：
--
作者：
Buchholz, TA;Gurgoze, E;Prestidge, BR
目的：研究完整乳腺放射治疗的剂量不均匀性，以确定不同乳腺大小和乳腺解剖区域的剂量不均匀性。方法：对11例完整乳腺放射治疗的患者进行了L-cm断层扫描。在每个CT切片上确定乳腺组织的面积。使用二维治疗计划系统执行带有肺校正因子的治疗计划，该系统在逐个切片的基础上计算离轴剂量分布。每个计划都使用切向光束，具有匹配的无发散的后缘，并带有准直器旋转以匹配胸壁斜度。在治疗计划期间，通过在侧切线场上使用楔形和通过场的不同加权来最小化中心平面内的剂量不均匀。剂量归一化在乳房和胸大肌正中分离的中央平面的界面上。在优化治疗方案时没有考虑离轴剂量的不均匀。绘制每个I-cm切片的剂量分布图，并计算每个CT切片上乳房内每条等剂量曲线的面积。结果：在整个人群中，平均有10%的乳房体积(范围1-40%)接受了110%或更多的处方剂量。剂量不均匀性的增加与乳房大小呈正相关(r=0.72，p=0.01-矛兵等级检验)。剂量与乳房内位置的关系分析显示，乳房下部解剖象限的剂量不均匀程度最大(p=0.003-Kruskal-Wallis检验)。对于接受110%或更大剂量的组，平均乳房体积在中轴线以下6 cm处为30%，中轴线以下4 cm处为14%，中轴线以下为6%，中轴线以上4 cm处为5%，中轴线以上6 cm处为7%。结论：我们的研究表明，相当数量的乳腺组织获得了规定剂量的110%或更大剂量。这种不均一性在乳房较大的女性中最为明显，这可能解释了与乳房较小的女性相比，这部分患者的美容效果更差的原因。此外，我们的结果显示乳房下象限的剂量不均匀程度最大。对于患有下象限肿瘤的女性，在计划肿瘤床强化时，应考虑离轴剂量的不均匀。(C)1997年爱思唯尔科学公司。
Purpose/Objective: The purpose of this investigation is to quantify dose inhomogeneity of intact breast irradiation in off-axis planes, and determine how dose inhomogeneity varies according to patient breast size and anatomical region of the breast.Methods and Materials: Eleven patients treated with intact breast radiation underwent a treatment-planning computer tomography (CT) scan with l-cm slices through the entire breast. The area of breast tissue was defined on each CT slice. Treatment planning with lung correction factors was performed using a two-dimensional treatment-planning system that calculates off-axis dose distributions on a slice-by-slice basis. Each plan utilized tangential beams with matched nondivergent posterior borders and, with collimator rotation to match the chest wall slope. Dose inhomogeneity within the central plane was minimized during treatment planning by the use of a wedge on the lateral tangent field and by the differential weighting of fields. Dose was normalized at the breast and pectoralis major interface at midseparation in the central plane. Off-axis dose inhomogeneity was not considered in the optimization of the treatment plan. Dose distributions were plotted for each I-cm slice, and the area of each isodose curve within the breast on each CT slice was calculated. The results of each slice mere summed to give an approximation of dose-volume relationships.Results: For the entire population, an average of 10% of the breast volume (range 1-40%) received 110% or greater of the prescribed dose. Increasing dose inhomogeneity was positively correlated with increasing breast sizes (r = 0.72, p = 0.01-Spearmen rank test). Analysis of dose as a function of location within the breast, revealed that the greatest dose inhomogeneity occurred in the lower anatomical quadrants of the breast (p = 0.003-Kruskal-Wallis test). For the group, the mean breast volume that received a 110% or greater dose was: 30% at 6 cm below central axis, 14% at 4 cm below central axis, 6% at central axis, 5% at 4 cm above central axis, and 7% at 6 cm above central axis.Conclusion: Our study demonstrates that a significant volume of breast tissue receives 110% or greater of the prescribed dose. This inhomogeneity is greatest in women with larger breast sizes, providing a possible explanation for the poorer cosmetic result seen in this subset of patients compared to women with small breast sizes. In addition, our results show the greatest dose inhomogeneity in the lower quadrants of the breast. Off-axis dose inhomogeneity should be considered in the planning of tumor bed boosts in women with lower quadrant tumors. (C) 1997 Elsevier Science Inc.