水固化头枕对提高乳腺托架固定下乳腺癌放疗锁骨上野摆位准确性的研究

Study on improving accuracy of setup errors of supraclavicular field in radiotherapy for breast cancer by breast bracket and moisture-cured resin cushion

目的 利用水固化头枕对乳腺托架固定下乳腺癌患者下颈部固定进行改良，观察其对锁骨上野（supraclavicular field，SCF）摆位误差及临床靶区（CTV）外放边界的影响。方法 选取13例乳腺癌改良根治术后放疗患者，在原有乳腺托架定位的基础上增加使用水固化垫，将其固定于圆形头枕上并保证填充颈部与托架间的间隙，同时支撑头部偏转。再利用锥形束CT（cone-beam CT，CBCT） 于第1、10和20次治疗前采集CT图像，记录SCF靶区的摆位误差并与前期研究对比分析，计算其CTV外放值及其外放体积的变化。结果 全组患者摆位误差在左右（x）、上下（y）、前后（z）方向分别为（2.16±1.25）、（1.50±1.28）和（1.94±1.12）mm，俯仰（θ）、滚转（Ф）、偏转（ψ）角度分别为（1.76±1.87）°、（1.82±1.12）°和（0.99±0.58）°。与前期研究数据进行非参数秩和检验（Mann-Whitney U test），在y、z方向及θ角度上摆位误差差异具有统计学意义（Z=4.152、3.415、2.053，P〈0.05）。CTV在x、y、z方向分别需外放4.07、4.03和3.73 mm，较前期研究x、y、z方向外放8、8和6 mm的体积平均减少32.73%。结论 个性化头枕配合乳腺托架的定位方法降低了单一圆枕定位下颈部SCF靶区的摆位误差，并将其CTV的外放缩减至在x、y、z方向上不少于4.07、4.03和3.73 mm。

Objective To explore the effects of improvements on setup error（SE） and clinical target （CTV） margin of supraclavicular field （SCF） by using moisture-cured resin cushion and breast bracket for lower neck fixation in breast cancer patients who underwent post-mastectomy radiotherapy.Methods Totally 13 patients with breast cancer who underwent post-mastectomy radiotherapy were enrolled. All patients were immobilized by breast bracket and moisture-cured resin cushion. Firstly, each patient＇s lower neck and head was fixed well by moisture-cured resin cushion, filling the gap between the neck and breast bracket. Secondly,each patient underwent the cone-beam CT （CBCT） at the first, tenth and twentieth treatment after positioning. Then these CBCT images were registered to the planning CT to determine setup errors in translational and rotational directions, and SCF CTV margins by the systematic and random errors were evaluated.Results The setup errors in x （left-right）, y （superior-inferior）, z （anterior-posterior） translational directions were （2.16±1.25）, （1.50±1.28）, （1.94±1.12） mm and （1.76±1.87）°, （1.82±1.12）°, （0.99±0.58）°, respectively in θ （pitch degree）, Ф （roll degree）, ψ （yaw degree） rotational directions. Non-parametric rank test （Mann-Whitney U test）was performed with previous data, the differences of the setup error in y, z,θ directions were statistically significant （Z=4.152, 3.415, 2.053, P〈0.05）.The margins from CTV were 4.07, 4.03 and 3.73 mm in x, y and z directions, respectively. Compared with the previous study on SCF, CTV margin required 8, 8 and 6 mm in x, y and z axis directions, the volume of CTV to PTV were decreased by 32.73%on average.Conclusions Compared with plastic circular pillow alone, moisture-cured resin cushion with breast bracket locating method could reduce setup errors in SCF target region. The margins from CTV to PTV were decreased to 4.07, 4.03 and 3.73 mm in x, y and z axis directions at least.