van der Heyden Brent, van Hoof Stefan J, Schyns Lotte E J R, Verhaegen Frank
1 Department of Radiation Oncology (MAASTRO), GROW-School for Oncology and Developmental Biology, Maastricht University Medical Centre, Maastricht, Netherlands.
2 Medical Physics Unit, Department of Oncology, McGill University, Montréal, QC, Canada.
Br J Radiol. 2017 Jan;90(1069):20160419. doi: 10.1259/bjr.20160419. Epub 2016 Oct 24.
During precision irradiation of a preclinical lung tumour model, the tumour is subject to breathing motion and it can partially move out of the irradiation field. This work aimed to perform a quantitative analysis of the impact of respiratory motion on a mouse lung tumour irradiation with small fields.
A four-dimensional digital mouse whole body phantom (MOBY) with a virtual 4-mm spherical lung tumour at different locations in both lungs is used to simulate a breathing anaesthetized mouse in different breathing phases representing a full breathing cycle. The breathing curve is determined by fluoroscopic imaging of an anaesthetized mouse. Each MOBY time frame is loaded in a dedicated treatment planning system (small animal radiotherapy-Plan) and is irradiated by a full arc with a 5-mm circular collimator. Mean and time-dependent organ doses are calculated for the tumour, heart and spinal cord.
Depending on the location of the lung tumour, an overestimation of the mean tumour dose up to 11% is found. The mean heart dose could be both overestimated or underestimated because the heart moves in or out of the irradiation field depending on the beam target location. The respiratory motion does not affect the mean spinal cord dose. A dose gradient is visible in the time-dependent tumour dose distribution.
In the future, new methods need to be developed to track the lung tumour motion before preclinical irradiation to adjust the irradiation plan. Margins, collimator diameter and target dose could be changed easily, but they all have their drawbacks. State-of-the-art clinical techniques such as respiratory gating or motion tracking may offer a solution for the cold spots in the time-dependent tumour dose. Advances in knowledge: A suitable method is found to quantify changes in organ dose due to respiratory motion in mouse lung tumour image-guided precision irradiation.
在临床前肺肿瘤模型的精确照射过程中，肿瘤会受到呼吸运动的影响，可能会部分移出照射野。本研究旨在对呼吸运动对小鼠肺肿瘤小视野照射的影响进行定量分析。
使用一种四维数字小鼠全身体模（MOBY），其双肺不同位置有一个虚拟的4毫米球形肺肿瘤，用于模拟处于不同呼吸阶段（代表一个完整呼吸周期）的麻醉小鼠。呼吸曲线通过对麻醉小鼠的荧光透视成像确定。每个MOBY时间帧被加载到一个专用的治疗计划系统（小动物放射治疗计划）中，并用5毫米圆形准直器进行全弧照射。计算肿瘤、心脏和脊髓的平均器官剂量以及随时间变化的器官剂量。
根据肺肿瘤的位置，发现平均肿瘤剂量高估可达11%。平均心脏剂量可能被高估或低估，因为心脏会根据射束靶点位置移入或移出照射野。呼吸运动不影响脊髓的平均剂量。在随时间变化的肿瘤剂量分布中可见剂量梯度。
未来，需要开发新的方法来在临床前照射前跟踪肺肿瘤运动，以调整照射计划。边缘、准直器直径和靶剂量可以很容易地改变，但它们都有各自的缺点。诸如呼吸门控或运动跟踪等先进的临床技术可能为随时间变化的肿瘤剂量中的冷点提供解决方案。知识进展：找到了一种合适的方法来量化小鼠肺肿瘤图像引导精确照射中由于呼吸运动引起的器官剂量变化。
