Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Int J Radiat Oncol Biol Phys. 2012 Nov 1;84(3):861-6. doi: 10.1016/j.ijrobp.2012.01.037. Epub 2012 Apr 9.
To evaluate the reproducibility of tumor motion probability distribution function (PDF) in stereotactic body radiation therapy (SBRT) of lung cancer using cine megavoltage (MV) images.
Cine MV images of 20 patients acquired during three-dimensional conformal (6-11 beams) SBRT treatments were retrospectively analyzed to extract tumor motion trajectories. For each patient, tumor motion PDFs were generated per fraction (PDF(n)) using three selected "usable" beams. Patients without at least three usable beams were excluded from the study. Fractional PDF reproducibility (R(n)) was calculated as the Dice similarity coefficient between PDF(n) to a "ground-truth" PDF (PDF(g)), which was generated using the selected beams of all fractions. The mean of R(n), labeled as R(m), was calculated for each patient and correlated to the patient's mean tumor motion rang (A(m)). Change of R(m) during the course of SBRT treatments was also evaluated. Intra- and intersubject coefficient of variation (CV) of R(m) and A(m) were determined.
Thirteen patients had at least three usable beams and were analyzed. The mean of R(m) was 0.87 (range, 0.84-0.95). The mean of A(m) was 3.18 mm (range, 0.46-7.80 mm). R(m) was found to decrease as A(m) increases following an equation of R(m) = 0.17e(-0.9Am) + 0.84. R(m) also decreased slightly throughout the course of treatments. Intersubject CV of R(m) (0.05) was comparable to intrasubject CV of R(m) (range, 0.02-0.09); intersubject CV of A(m) (0.73) was significantly greater than intrasubject CV of A(m) (range, 0.09-0.24).
Tumor motion PDF can be determined using cine MV images acquired during the treatments. The reproducibility of lung tumor motion PDF decreased exponentially as the tumor motion range increased and decreased slightly throughout the course of the treatments.
使用电影 MV 图像评估肺癌立体定向体放射治疗（SBRT）中肿瘤运动概率分布函数（PDF）的可重复性。
回顾性分析了 20 例患者在三维适形（6-11 束）SBRT 治疗期间采集的电影 MV 图像，以提取肿瘤运动轨迹。对于每个患者，使用三个选定的“可用”束生成每个分次的肿瘤运动 PDF（PDF(n)）。没有至少三个可用束的患者被排除在研究之外。分次 PDF 可重复性（R(n)）计算为 PDF(n)与“真实”PDF（PDF(g)）之间的 Dice 相似系数，该 PDF 使用所有分次的选定束生成。为每个患者计算 R(n)的平均值，标记为 R(m)，并与患者的平均肿瘤运动范围（A(m)）相关联。还评估了 SBRT 治疗过程中 R(m)的变化。确定了 R(m)和 A(m)的 Intra-和 Inter-subject 变异系数（CV）。
对 13 名至少有三个可用束的患者进行了分析。R(m)的平均值为 0.87（范围为 0.84-0.95）。A(m)的平均值为 3.18mm（范围为 0.46-7.80mm）。发现 R(m)随着 A(m)的增加而呈指数下降，遵循 R(m)=0.17e(-0.9Am)+0.84 的方程。在治疗过程中，R(m)也略有下降。R(m)的 Inter-subject CV（0.05）与 Intra-subject CV 的 R(m)（范围为 0.02-0.09）相当；A(m)的 Inter-subject CV（0.73）明显大于 Intra-subject CV 的 A(m)（范围为 0.09-0.24）。
可以使用治疗期间采集的电影 MV 图像确定肿瘤运动 PDF。随着肿瘤运动范围的增加，肿瘤运动 PDF 的可重复性呈指数下降，并且在治疗过程中略有下降。
