鼻咽癌调强放疗中头颈部轮廓变化对摆位误差的影响

Impact of changes in head and neck contours on setup errors in intensity-modulated radiotherapy for nasopharyngeal carcinoma

目的:探讨鼻咽癌调强放疗头颈部轮廓变化与摆位误差的关系。方法:选取32例调强放疗的鼻咽癌患者,均采用头颈肩热塑膜固定,在治疗第15、20、25次采用千伏级锥形束CT扫描,获取的图像与定位CT图像匹配后得到摆位误差数据,同时记录患者头颈部轮廓变化率,用统计学方法分析头颈部变化对摆位误差的影响。结果:摆位误差分别为左右(0.85±1.24)mm、头脚(0.36±1.41)mm、腹背(-1.69±0.97)mm,A、B、C这3个层面上头颈部轮廓平均变化率分别为5.57%、6.13%和4.46%。3个层面上只有头脚方向的摆位误差和头颈部变化率呈线性相关:A层面(r=0.68,P=0.01);B层面(r=0.56,P=0.04);C层面(r=0.67,P=0.01),而左右方向和腹背方向上则无相关性。结论:患者头颈部轮廓均随着放疗的进行而缩小,其变化对摆位误差的影响不明显,当其变化率大于8%时,有必要重新制定放疗计划。

Objective To determine the impact of changes in head and neck contours on the setup errors in intensity modulated radiotherapy（IMRT） for nasopharyngeal carcinoma. Methods Thirty-two nasopharyngeal carcinoma patients treated with IMRT were selected. Patients were immobilized by head and neck thermoplastic mask and scanned by k VCBCT at the 15^th, 20^th and 25^th times of treatment. The obtained images were matched with the localization CT images to obtain the setup errors. Simultaneously, the changes in head and neck contours were recorded and the impact of changes in head and neck contours on setup errors were statistically analyzed. Results The setup errors were（0.85±1.24） mm,（0.36±1.41） mm and（-1.69±0.97） mm in the left-right, head-feet and anterior-posterior direction respectively. The average change rates of head and neck contours at level A, B, C were respectively 5.57%, 6.13% and 4.46%. The change rate of head and neck contours showed linearity correlation to the setup displacements in head-feet direction（r=0.68, P=0.01 at level A; r=0.56, P=0.04 at level B; r=0.67, P=0.01 at level C）. No linear correlations were found in the other two directions.Conclusion The head and neck contours decrease as radiotherapy is performed, without obvious impacts on the setup errors.When the change rate is over 8%, radiotherapy plan should be re-planned.