Chaudhari S R, Goddu S M, Rangaraj D, Pechenaya O L, Lu W, Kintzel E, Malinowski K, Parikh P J, Bradley J D, Low D A
Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO 63110, USA.
Phys Med Biol. 2009 Apr 21;54(8):2541-55. doi: 10.1088/0031-9155/54/8/019. Epub 2009 Apr 6.
In their classic paper, Yu et al (1998 Phys. Med. Biol. 43 91) investigated the interplay between tumor motion caused by breathing and dynamically collimated, intensity-modulated radiation delivery. The paper's analytic model assumed an idealized, sinusoidal pattern of motion. In this work, we investigate the effect of tumor motion based on patients' breathing patterns for typical tomotherapy treatments with field widths of 1.0 and 2.5 cm. The measured breathing patterns of 52 lung- and upper-abdominal-cancer patients were used to model a one-dimensional motion. A convolution of the measured beam-dose profiles with the motion model was used to compute the dose-distribution errors, and the positive and negative dose errors were recorded for each simulation. The dose errors increased with increasing motion magnitude, until the motion was similar in magnitude to the field width. For the 1.0 cm and 2.5 cm field widths, the maximum dose-error magnitude exceeded 10% in some simulations, even with breathing-motion magnitudes as small as 5 mm and 10 mm, respectively. Dose errors also increased slightly with increasing couch speed. We propose that the errors were due to subtle drifts in the amplitude and frequency of breathing motion, as well as changes in baseline (exhalation) position, causing both over- and under-dosing of the target. The results of this study highlight potential breathing-motion-induced dose delivery errors in tomotherapy. However, for conventionally fractionated treatments, the dose delivery errors may not be co-located and may average out over many fractions, although this may not be true for hypofractionated treatments.
在他们的经典论文中，Yu等人（1998年，《物理医学与生物学》43卷，91页）研究了呼吸引起的肿瘤运动与动态准直、调强放射治疗之间的相互作用。该论文的分析模型假设了一种理想化的正弦运动模式。在这项工作中，我们基于典型断层放射治疗（射野宽度为1.0厘米和2.5厘米）中患者的呼吸模式，研究肿瘤运动的影响。使用52例肺癌和上腹部癌患者测量的呼吸模式来模拟一维运动。将测量的射束剂量分布与运动模型进行卷积，以计算剂量分布误差，并记录每次模拟的正、负剂量误差。剂量误差随着运动幅度的增加而增加，直到运动幅度与射野宽度相似。对于1.0厘米和2.5厘米的射野宽度，在某些模拟中，即使呼吸运动幅度分别小至5毫米和10毫米，最大剂量误差幅度也超过了10%。剂量误差也随着治疗床速度的增加而略有增加。我们认为，这些误差是由于呼吸运动的幅度和频率的细微漂移以及基线（呼气）位置的变化，导致靶区剂量过高和过低。本研究结果突出了断层放射治疗中潜在的呼吸运动引起的剂量传递误差。然而，对于常规分割治疗，剂量传递误差可能不会集中在同一位置，并且可能在多个分割中平均化，尽管对于大分割治疗可能并非如此。
