Department of Radiation Oncology, The University of Texas Southwestern Medical Center, Dallas, TX, 75390, USA.
Department of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, 510515, China.
Radiat Oncol. 2017 Sep 11;12(1):151. doi: 10.1186/s13014-017-0889-6.
Recently developed stereotactic partial breast irradiation (S-PBI) allows delivery of a high biologically potent dose to the target while sparing adjacent critical organs and normal tissue. With S-PBI tumoricidal doses, accurate and precise dose delivery is critical to achieve high treatment quality. This study is to investigate both rigid and non-rigid components of target geometric error and their corresponding margins in S-PBI and identify correlated clinical factors.
Forty-three early-stage breast cancer patients with implanted gold fiducial markers were enrolled in the study. Fiducial positions recorded on the orthogonal kV images on a Cyberknife system during treatment were used to estimate intra-fraction errors and composite errors (including intra-fraction errors and residual errors after patient setup). Both rigid and non-rigid components of intra-fraction and composite errors were analyzed and used to estimate rigid and non-rigid margins, respectively. Univariate and multivariate linear regressions were conducted to evaluate correlations between clinical factors and errors.
For the study group, the intra-fraction rigid and non-rigid errors are 2.0 ± 0.6 mm and 0.3 ± 0.2 mm, respectively. The composite rigid and non-rigid errors are 2.3 ± 0.5 mm and 1.3 ± 0.8 mm, respectively. The rigid margins in the left-right, anterior-posterior, and superior-inferior directions are estimated as 2.1, 2.4, and 2.3 mm, respectively. The estimated non-rigid margin, assumed to be isotropic, is 1.7 mm. The outer breast quadrants are more susceptible to composite errors occurrence than the inner breast quadrants. The target to chest wall distance is the clinical factor correlated with target geometric errors.
This is the first comprehensive analysis of breast target geometric rigid and non-rigid errors in S-PBI. Upon the estimation, the non-rigid margin is comparable to rigid margin, and therefore should be included in planning target volume as it cannot be accounted for by the Cyberknife system. Treatment margins selection also need to consider the impact of relevant clinical factor.
最近发展的立体定向部分乳房照射（S-PBI）允许在靶区给予高生物有效剂量，同时保护相邻的关键器官和正常组织。S-PBI 中的肿瘤杀伤剂量，精确和准确的剂量输送对于实现高质量的治疗至关重要。本研究旨在调查 S-PBI 中靶区几何误差的刚性和非刚性成分及其相应的边界，并确定相关的临床因素。
43 例早期乳腺癌患者接受植入金质基准标记物。在 Cyberknife 系统上的正交千伏图像上记录的基准位置用于估计分次内误差和复合误差（包括分次内误差和患者摆位后的残余误差）。分析分次内和复合误差的刚性和非刚性成分，并分别用于估计刚性和非刚性边界。进行单变量和多变量线性回归，以评估临床因素与误差之间的相关性。
对于研究组，分次内刚性和非刚性误差分别为 2.0±0.6mm 和 0.3±0.2mm。复合刚性和非刚性误差分别为 2.3±0.5mm 和 1.3±0.8mm。左右、前后和上下方向的刚性边界分别估计为 2.1、2.4 和 2.3mm。假设各向同性的非刚性边界为 1.7mm。外乳房象限比内乳房象限更容易发生复合误差。靶区到胸壁的距离是与靶区几何误差相关的临床因素。
这是首次对 S-PBI 中乳房靶区的刚性和非刚性几何误差进行全面分析。在估计时，非刚性边界与刚性边界相当，因此应包括在计划靶区体积中，因为 Cyberknife 系统无法考虑到这一点。治疗边界的选择还需要考虑相关临床因素的影响。
