Vasquez Osorio Eliana Maria, McCallum Hazel, Bedair Ahmed, Faivre-Finn Corinne, Haughey Aisling, van Herk Marcel, Iqbal Muhammad Shahid, McWilliam Alan, Price Gareth, Byrne John, Cobben David
Radiotherapy-Related Research, University of Manchester, Manchester, United Kingdom; The Christie NHS Trust, Manchester, United Kingdom.
Radiotherapy Physics, Northern Centre for Cancer Care, Freeman Hospital, Newcastle upon Tyne, United Kingdom.
Int J Radiat Oncol Biol Phys. 2020 Nov 15;108(4):1082-1090. doi: 10.1016/j.ijrobp.2020.06.068. Epub 2020 Jul 4.
Emerging evidence suggests that the heart is more radiosensitive than previously assumed; therefore, accounting for heart motion in radiation therapy planning is becoming more critical. In this study, we determined how much heart delineations based on 3-dimensional (3D) computed tomography (CT), 4-dimensional (4D) average projection (AVG), and maximum intensity projection (MIP) images should be extended to represent the full extent of heart motion during 4D imaging acquisition.
The 3D and 4D CT scans of 10 lung cancer patients treated with stereotactic ablative radiation therapy were used. Median surfaces were derived from heart delineations of 3 observers on the 3D CT, AVG, MIP, and 25% exhale scans. Per patient, the 25% exhale contour was propagated on every phase of the 4D scan. The union of all 4D phase delineations (U4D) represented the full extent of heart motion during imaging acquisition. Surface distances from U4D to 3D, AVG, and MIP volumes were calculated. Distances in the most extreme surface points (1.5 cm most superoinferior, 10% most right/left/anteroposterior) were used to derive margins accounting only for systematic (delineation) errors.
Heart delineations on the MIP were the closest to the full extent of motion, requiring only ≤2.5-mm margins. Delineations on the AVG and 3D scans required margins up to 3.4 and 7.1 mm, respectively. The largest margins were for the inferior, right, and anterior aspects for the delineations on the 3D, AVG, and MIP scans, respectively.
Delineations on 3D, AVG, or MIP scans required extensions for representing the heart's full extent of motion, with the MIP requiring the smallest margins. Research including daily imaging to determine the random components for the margins and dosimetric measurements to determine the relevance of creating a planning organ at risk volume of the heart is required.
新出现的证据表明，心脏的放射敏感性比以前认为的更高；因此，在放射治疗计划中考虑心脏运动变得更加关键。在本研究中，我们确定了基于三维（3D）计算机断层扫描（CT）、四维（4D）平均投影（AVG）和最大强度投影（MIP）图像的心脏轮廓应扩展多少，以代表4D成像采集期间心脏运动的全部范围。
使用了10例接受立体定向消融放疗的肺癌患者的3D和4D CT扫描。中位表面由3名观察者在3D CT、AVG、MIP和25%呼气扫描上的心脏轮廓得出。对于每位患者，25%呼气轮廓在4D扫描的每个阶段进行传播。所有4D相位轮廓的并集（U4D）代表成像采集期间心脏运动的全部范围。计算从U4D到3D、AVG和MIP体积的表面距离。在最极端的表面点（最上下1.5 cm、最右/左/前后10%）的距离用于得出仅考虑系统（轮廓）误差的边界。
MIP上的心脏轮廓最接近运动的全部范围，仅需要≤2.5 mm的边界。AVG和3D扫描上的轮廓分别需要高达3.4和7.1 mm的边界。3D、AVG和MIP扫描上轮廓的最大边界分别位于下方、右侧和前方。
3D、AVG或MIP扫描上的轮廓需要扩展以代表心脏运动的全部范围，MIP需要的边界最小。需要进行包括每日成像以确定边界的随机成分以及剂量测量以确定创建心脏计划危及器官体积的相关性的研究。
