Conroy Leigh, Quirk Sarah, Smith Wendy L
Department of Medical Physics, Tom Baker Cancer Centre, Calgary, Alberta T2N 4N2, Canada and Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
Department of Medical Physics, Tom Baker Cancer Centre, Calgary, Alberta T2N 4N2, Canada; Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, Canada; and Department of Oncology, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
Med Phys. 2015 Sep;42(9):5404-9. doi: 10.1118/1.4928141.
Respiratory margins for partial breast irradiation (PBI) have been largely based on geometric observations, which may overestimate the margin required for dosimetric coverage. In this study, dosimetric population-based respiratory margins and margin formulas for external beam partial breast irradiation are determined.
Volunteer respiratory data and anterior-posterior (AP) dose profiles from clinical treatment plans of 28 3D conformal radiotherapy (3DCRT) PBI patient plans were used to determine population-based respiratory margins. The peak-to-peak amplitudes (A) of realistic respiratory motion data from healthy volunteers were scaled from A = 1 to 10 mm to create respiratory motion probability density functions. Dose profiles were convolved with the respiratory probability density functions to produce blurred dose profiles accounting for respiratory motion. The required margins were found by measuring the distance between the simulated treatment and original dose profiles at the 95% isodose level.
The symmetric dosimetric respiratory margins to cover 90%, 95%, and 100% of the simulated treatment population were 1.5, 2, and 4 mm, respectively. With patient set up at end exhale, the required margins were larger in the anterior direction than the posterior. For respiratory amplitudes less than 5 mm, the population-based margins can be expressed as a fraction of the extent of respiratory motion. The derived formulas in the anterior/posterior directions for 90%, 95%, and 100% simulated population coverage were 0.45A/0.25A, 0.50A/0.30A, and 0.70A/0.40A. The differences in formulas for different population coverage criteria demonstrate that respiratory trace shape and baseline drift characteristics affect individual respiratory margins even for the same average peak-to-peak amplitude.
A methodology for determining population-based respiratory margins using real respiratory motion patterns and dose profiles in the AP direction was described. It was found that the currently used respiratory margin of 5 mm in partial breast irradiation may be overly conservative for many 3DCRT PBI patients. Amplitude alone was found to be insufficient to determine patient-specific margins: individual respiratory trace shape and baseline drift both contributed to the dosimetric target coverage. With respiratory coaching, individualized respiratory margins smaller than the full extent of motion could reduce planning target volumes while ensuring adequate coverage under respiratory motion.
部分乳腺照射（PBI）的呼吸边界很大程度上基于几何观察，这可能高估了剂量覆盖所需的边界。在本研究中，确定了基于剂量学的群体呼吸边界以及外照射束部分乳腺照射的边界公式。
使用来自28例三维适形放疗（3DCRT）PBI患者计划的临床治疗计划中的志愿者呼吸数据和前后（AP）剂量分布来确定基于群体的呼吸边界。将健康志愿者真实呼吸运动数据的峰峰值幅度（A）从A = 1毫米按比例缩放至10毫米，以创建呼吸运动概率密度函数。剂量分布与呼吸概率密度函数进行卷积，以生成考虑呼吸运动的模糊剂量分布。通过测量模拟治疗与原始剂量分布在95%等剂量水平处的距离来确定所需边界。
覆盖90%、95%和100%模拟治疗群体的对称剂量学呼吸边界分别为1.5毫米、2毫米和4毫米。患者在呼气末设置时，前方所需边界大于后方。对于呼吸幅度小于5毫米的情况，基于群体的边界可以表示为呼吸运动范围的一部分。在前后方向上，针对90%、95%和100%模拟群体覆盖的推导公式分别为0.45A/0.25A、0.50A/0.30A和0.70A/0.40A。不同群体覆盖标准的公式差异表明，即使对于相同的平均峰峰值幅度，呼吸轨迹形状和基线漂移特征也会影响个体呼吸边界。
描述了一种使用真实呼吸运动模式和AP方向剂量分布来确定基于群体的呼吸边界的方法。发现目前在部分乳腺照射中使用的5毫米呼吸边界对于许多3DCRT PBI患者可能过于保守。仅幅度不足以确定患者特定的边界：个体呼吸轨迹形状和基线漂移都对剂量学靶区覆盖有影响。通过呼吸指导，小于运动全范围的个体化呼吸边界可以减少计划靶体积，同时确保在呼吸运动下有足够的覆盖。
