Nihei K, Mitsumori M, Ishigaki T, Fujishiro S, Kokubo M, Nagata Y, Sasai K, Hiraoka M
Division of Radiation Oncology, National Cancer Center Hospital East, 6-5-1 Kashiwanoha, Kashiwa, Chiba 277-0882, Japan.
Breast Cancer. 2000;7(3):231-6. doi: 10.1007/BF02967465.
The purpose of this study is to determine and recommend the optimal radiation source according to breast size for tangential irradiation in breast conserving therapy.
Twenty-eight patients treated at our department from January 1994 to January 1996 were studied. The dose distribution within the irradiated breast was calculated using a (60)Co-gamma ray and 6 MV-X ray. Then we compared 3-D dose distributions of the (60)Co-gamma ray and 6 MV-X ray in different-sized breasts. Three parameters (breast volume, chest wall separation, and breast height) were adopted as representative of breast size. We also examined correlations among the three parameters.
When the breast size was large (breast volume >400 cm(3), chest wall separation > 19.5 cm, or breast height > 6.5 cm), the average volume of normal tissue which received more than 110% of the isocenter dose ("hot spot") was significantly greater with the (60)Co-gamma ray than with the 6 MV-X ray (p < 0.05). A similar result was obtained with regard to hot spots in the clinical target volume. The cold area that received less than 95% of the isocenter dose was greater using a 6 MV-X ray when the breast size was small (breast volume <200 cm(3), chest wall separation <17.5 cm, or breast height <5.0 cm). However, the difference was not significant. There was a significant correlation between breast volume and chest wall separation (r =0.849, p <0.001). Breast volume and breast height were also significantly correlated (r =0.813, p <0.001).
Since breast volume and shape are different in each patient, the optimal energy should be selected for each case to obtain uniform dose distribution in breast-conserving therapy. Chest wall separation or breast height, which are measurable without a 3-D planning system, can substitute for breast volume as parameters for breast size. We recommend that the (60)Co-gamma ray not be used for treating large breasts, those with chest wall separation > or =19.5 cm or breast height > or =6.5 cm.
本研究的目的是根据乳房大小确定并推荐保乳治疗中切线照射的最佳放射源。
对1994年1月至1996年1月在我科接受治疗的28例患者进行研究。使用钴 - 60伽马射线和6兆伏X射线计算受照射乳房内的剂量分布。然后我们比较了不同大小乳房中钴 - 60伽马射线和6兆伏X射线的三维剂量分布。采用三个参数（乳房体积、胸壁间距和乳房高度）作为乳房大小的代表。我们还研究了这三个参数之间的相关性。
当乳房较大时（乳房体积>400立方厘米，胸壁间距>19.5厘米，或乳房高度>6.5厘米），接受超过等中心剂量110%的正常组织平均体积（“热点”），钴 - 60伽马射线组显著大于6兆伏X射线组（p<0.05）。临床靶区内热点情况也得到类似结果。当乳房较小时（乳房体积<200立方厘米，胸壁间距<17.5厘米，或乳房高度<5.0厘米），使用6兆伏X射线时接受小于等中心剂量95%的冷区更大。然而，差异不显著。乳房体积与胸壁间距之间存在显著相关性（r = 0.849，p<0.001）。乳房体积与乳房高度也显著相关（r = 0.813，p<0.001）。
由于每位患者的乳房体积和形状不同，在保乳治疗中应针对每个病例选择最佳能量以获得均匀的剂量分布。在没有三维计划系统的情况下可测量的胸壁间距或乳房高度，可替代乳房体积作为乳房大小的参数。我们建议，对于胸壁间距≥19.5厘米或乳房高度≥6.5厘米的大乳房，不应使用钴 - 60伽马射线进行治疗。
