Department of Radiation Oncology, MacKay Memorial Hospital, 92, Section 2, Chung-Shan North Road, Taipei, 104, Taiwan.
Department of Medicine, MacKay Medical College, New Taipei City, Taiwan.
Radiat Oncol. 2018 Dec 27;13(1):254. doi: 10.1186/s13014-018-1200-1.
This study aimed to evaluate the inter-fraction set-up error and intra-fraction motion during reverse semi-decubitus (RSD) breast radiotherapy, and to determine a planning target volume (PTV) margin.
Pre- and post-treatment cone-beam computed tomography (CBCT) scans were prospectively acquired at fractions 1, 4, 7, 8, 11, and 14 for 30 patients who underwent RSD breast radiotherapy. Online correction for initial set-up error greater than 5 mm or 2° was performed and post-correction CBCT was acquired. An off-line analysis was performed to quantify initial and residual inter-fraction set-up errors and intra-fraction motion in three-dimensions. Patient inter-fraction errors were analysed for time trends during the course of radiotherapy. PTV margins were calculated from the systematic and random errors.
The initial inter-fraction population systematic errors were 1.8-3.3 mm (translation) and 0.5° (rotation); random errors were 1.8-2.1 mm (translation) and 0.3-0.5° (rotation). After online correction, the residual inter-fraction population systematic errors were 1.2-1.8 mm (translation) and 0.3-0.4° (rotation); random errors were 1.4-1.6 mm (translation) and 0.3-0.4° (rotation). Intra-fraction population systematic and random errors were ≤ 1.3 mm (translation) and ≤ 0.2° (rotation). The magnitude of inter-fraction set-up errors in the anterior-posterior direction, roll, and yaw were significantly correlated with higher body weight and body mass index (BMI). The inter-fraction set-up error did not change significantly as a function of time during the course of radiotherapy. The magnitude of intra-fraction motion was not correlated with patient characteristics and treatment time. The total PTV margins accounting for pre-correction and intra-fraction errors were 6.5-10.2 mm; those accounting for post-correction and intra-fraction errors were 4.7-6.3 mm.
CBCT is an effective modality to evaluate and improve the inter-fraction set-up reproducibility in RSD breast radiotherapy, particularly for patients with higher BMI. Intra-fraction motion was minimal during RSD breast radiotherapy.
本研究旨在评估反向半卧位（RSD）乳腺癌放疗中的分次间摆位误差和分次内运动，并确定计划靶区（PTV）边界。
前瞻性地对 30 例接受 RSD 乳腺癌放疗的患者在第 1、4、7、8、11 和 14 分次时采集治疗前和治疗后锥形束 CT（CBCT）扫描。对于初始摆位误差大于 5mm 或 2°的患者进行在线校正，并获取校正后 CBCT。进行离线分析以在三维方向上量化初始和残余分次间摆位误差和分次内运动。分析患者分次间误差在放疗过程中的时间趋势。从系统和随机误差计算 PTV 边界。
初始分次间人群系统误差为 1.8-3.3mm（平移）和 0.5°（旋转）；随机误差为 1.8-2.1mm（平移）和 0.3-0.5°（旋转）。在线校正后，残余分次间人群系统误差为 1.2-1.8mm（平移）和 0.3-0.4°（旋转）；随机误差为 1.4-1.6mm（平移）和 0.3-0.4°（旋转）。分次内人群系统误差和随机误差均≤1.3mm（平移）和≤0.2°（旋转）。前-后方向、滚转和偏航方向的分次间摆位误差与较高的体重和体重指数（BMI）显著相关。在放疗过程中，分次间摆位误差随时间的变化不明显。分次内运动的幅度与患者特征和治疗时间无关。考虑预校正和分次内误差的总 PTV 边界为 6.5-10.2mm；考虑校正后和分次内误差的总 PTV 边界为 4.7-6.3mm。
CBCT 是评估和提高 RSD 乳腺癌放疗中分次间摆位重复性的有效方法，特别是对于 BMI 较高的患者。在 RSD 乳腺癌放疗中，分次内运动很小。
