Hou Wei-Hsien, Wang Chun-Wei, Tsai Chiao-Ling, Hsu Feng-Ming, Cheng Jason Chia-Hsien
Department of Radiation Oncology, City of Hope National Medical Center, Duarte, California, United States of America.
Division of Radiation Oncology, Departments of Oncology, National Taiwan University College of Medicine and Hospital, Taipei, Taiwan, Province of China.
Radiol Oncol. 2016 Sep 8;50(4):427-432. doi: 10.1515/raon-2016-0047. eCollection 2016 Dec 1.
Changes in head and neck anatomy during radiation therapy (RT) produce setup uncertainties of nasopharyngeal cancer (NPC) irradiation. We retrospectively analyzed image guidance data to identify clinical predictors of setup errors.
The data of 217 NPC patients undergoing definitive RT on a helical tomotherapy (HT) unit were analyzed. Factors including tumor stage, body mass index, weight loss, and planning target volume (PTV) were assessed as predictors of daily megavoltage computed tomography (MVCT) setup displacements, which were automatically registered using software.
Mean daily setup displacements (in mm) were 1.2 ± 0.6, 1.8 ± 0.8, 3.4 ± 1.4 in the medial-lateral (ML), superior-inferior (SI), and anterior-posterior (AP) directions, respectively. Mean weight loss was 4.6 ± 3.3 kg (6.8 ± 4.9%). Patients with weight loss > 5% had significantly larger setup displacements in the AP (3.6 ± 1.5 . 2.9 ± 1.1 mm, p < 0.001) and SI (1.6 ± 0.7 . 1.9 ± 0.9 mm, p = 0.01) direction, but not in the ML direction (p = 0.279). The AP setup error increased 0.06 mm (y = 0.055x + 2.927, x: percentage of weight loss/PTV, y: AP displacement) per one percent increase in weight loss normalized to PTV.
Patients with weight loss > 5% and smaller PTVs, possibly because of small body frame or neck girth, were more likely to have increased setup errors in the AP direction.
放射治疗（RT）期间头颈部解剖结构的变化会导致鼻咽癌（NPC）照射的摆位误差。我们回顾性分析图像引导数据以确定摆位误差的临床预测因素。
分析了在螺旋断层放疗（HT）设备上接受根治性放疗的217例NPC患者的数据。评估了包括肿瘤分期、体重指数、体重减轻和计划靶区（PTV）等因素作为每日兆伏级计算机断层扫描（MVCT）摆位位移的预测因素，这些位移通过软件自动配准。
内侧-外侧（ML）、头侧-尾侧（SI）和前后（AP）方向的平均每日摆位位移（单位：mm）分别为1.2±0.6、1.8±0.8、3.4±1.4。平均体重减轻为4.6±3.3 kg（6.8±4.9%）。体重减轻>5%的患者在AP方向（3.6±1.5对2.9±1.1 mm，p<0.001）和SI方向（1.6±0.7对1.9±0.9 mm，p = 0.01）的摆位位移明显更大，但在ML方向无差异（p = 0.279）。体重减轻相对于PTV每增加1%，AP摆位误差增加0.06 mm（y = 0.055x + 2.927，x：体重减轻百分比/PTV，y：AP位移）。
体重减轻>5%且PTV较小的患者，可能由于身材瘦小或颈部周长较小，在AP方向更易出现摆位误差增加。
