Burmeister Jay, Alvarado Nicole, Way Sarah, McDermott Patrick, Bossenberger Todd, Jaenisch Harriett, Patel Rajiv, Washington Tara
Karmanos Cancer Institute, Gershenson Radiation Oncology Center and Wayne State University, Detroit, MI 48201, USA.
Med Dosim. 2008 Spring;33(1):6-13. doi: 10.1016/j.meddos.2007.04.003.
Breast radiotherapy is associated with an increased risk of contralateral breast cancer (CBC) in women under age 45 at the time of treatment. This risk increases with increasing absorbed dose to the contralateral breast. The use of intensity modulated radiotherapy (IMRT) is expected to substantially reduce the dose to the contralateral breast by eliminating scattered radiation from physical beam modifiers. The absorbed dose to the contralateral breast was measured for 5 common radiotherapy techniques, including paired 15 degrees wedges, lateral 30 degrees wedge only, custom-designed physical compensators, aperture based (field-within-field) IMRT with segments chosen by the planner, and inverse planned IMRT with segments chosen by a leaf sequencing algorithm after dose volume histogram (DVH)-based fluence map optimization. Further reduction in contralateral breast dose through the use of lead shielding was also investigated. While shielding was observed to have the most profound impact on surface dose, the radiotherapy technique proved to be most important in determining internal dose. Paired wedges or compensators result in the highest contralateral breast doses (nearly 10% of the prescription dose on the medial surface), while use of IMRT or removal of the medial wedge results in significantly lower doses. Aperture-based IMRT results in the lowest internal doses, primarily due to the decrease in the number of monitor units required and the associated reduction in leakage dose. The use of aperture-based IMRT reduced the average dose to the contralateral breast by greater than 50% in comparison to wedges or compensators. Combined use of IMRT and 1/8-inch-thick lead shielding reduced the dose to the interior and surface of the contralateral breast by roughly 60% and 85%, respectively. This reduction may warrant the use of IMRT for younger patients who have a statistically significant risk of contralateral breast cancer associated with breast radiotherapy.
在接受治疗时年龄小于45岁的女性中，乳房放疗与对侧乳腺癌（CBC）风险增加相关。这种风险随着对侧乳房吸收剂量的增加而升高。调强放疗（IMRT）的应用有望通过消除来自物理射束修正器的散射辐射，大幅降低对侧乳房的剂量。对5种常见放疗技术测量了对侧乳房的吸收剂量，这些技术包括成对的15度楔形板、仅外侧30度楔形板、定制的物理补偿器、由计划者选择射野段的基于孔径（野中野）的IMRT，以及在基于剂量体积直方图（DVH）的通量图优化后由叶序算法选择射野段的逆向计划IMRT。还研究了通过使用铅屏蔽进一步降低对侧乳房剂量的情况。虽然观察到屏蔽对表面剂量影响最为显著，但放疗技术在确定内部剂量方面被证明是最重要的。成对楔形板或补偿器导致对侧乳房剂量最高（在内侧表面接近处方剂量的10%），而使用IMRT或去除内侧楔形板会使剂量显著降低。基于孔径的IMRT导致的内部剂量最低，主要是由于所需监测单位数量减少以及相关的泄漏剂量降低。与楔形板或补偿器相比，基于孔径的IMRT使对侧乳房的平均剂量降低了超过50%。IMRT与1/8英寸厚铅屏蔽的联合使用分别使对侧乳房内部和表面的剂量降低了约60%和85%。这种剂量降低可能使IMRT适用于那些因乳房放疗而具有统计学显著对侧乳腺癌风险的年轻患者。
