Medical Physics Department, Clatterbridge Cancer Centre, Liverpool, UK.
J Appl Clin Med Phys. 2022 Jan;23(1):e13453. doi: 10.1002/acm2.13453. Epub 2021 Nov 24.
Irregular breathing in lung cancer patients is a common contra-indication to 4D computerized tomography (4DCT), which may then limit radiotherapy treatment options. For irregular breathers, we investigated whether 3DCT or 4DCT (1) better represents tumor motion, (2) better represents average tumor densities, and (3) better allows for volumetric modulated arc threarpy (VMAT) plans delivered with acceptable dosimetric accuracy.
Ten clinical breathing traces were identified with irregularities in phase and amplitude, and fed to a programmable moving platform incorporating an anthropomorphic lung tumor phantom. 3DCT and 4DCT data resorted by phase (4DCT-P) and amplitude (4DCT-A) were acquired for each trace. Tumors were delineated by Hounsfield unit (HU) thresholding and apparent motion range assessed. HU profiles were extracted from each image and agreement with calculated expected profiles quantified using area-under-curve (AUC) scoring. Clinically representative VMAT plans were created for each image, delivered to the irregularly moving phantom, and measured with a small-volume ion chamber at the tumor center.
Median difference from expected tumor motion range for 3DCT, 4DCT-P, and 4DCT-A was 2.5 [1.6-3.6] cm, 1.1 [0.1-1.9] cm, and 1.3 [0.4-1.9] cm, respectively (p = 0.005, 4DCT-P vs. 3DCT). Median AUC scores (ideal = 0) for 3DCT, 4DCT-P, and 4DCT-A were 0.25 [0.14-0.49], 0.12 [0.05-0.42], and 0.13 [0.09-0.44], respectively (p = 0.005, 4DCT-P vs. 3DCT). Nine of ten 4DCT-P plans and all 4DCT-A plans measured within 2.5% of expected dose in the treatment planning system (TPS), compared with seven 3DCT plans.
For the cases studied tumor motion range and average density was better represented with 4DCT compared with 3DCT, even in the presence of irregular breathing. 4DCT images allowed for delivery of VMAT plans with acceptable dosimetric accuracy. No significant differences were detected between phase and amplitude resorting. In combination with 4D cone beam imaging at treatment, our findings have given us confidence to introduce 4DCT and VMAT for lung radiotherapy patients with irregular breathing.
肺癌患者不规则呼吸是 4D 计算机断层扫描（4DCT）的常见禁忌，这可能会限制放疗治疗方案。对于不规则呼吸者，我们研究了 3DCT 或 4DCT（1）是否更好地代表肿瘤运动，（2）是否更好地代表平均肿瘤密度，以及（3）是否更好地允许使用可接受的剂量学准确性交付容积调制弧形 threarpy（VMAT）计划。
确定了 10 个具有相位和幅度不规则性的临床呼吸轨迹，并将其输入到包含拟人化肺肿瘤体模的可编程移动平台中。为每个轨迹获取由相位（4DCT-P）和幅度（4DCT-A）排序的 3DCT 和 4DCT 数据。通过体素阈值确定肿瘤，并评估明显的运动范围。从每个图像中提取 HU 轮廓，并使用曲线下面积（AUC）评分量化与计算出的预期轮廓的一致性。为每个图像创建具有临床代表性的 VMAT 计划，并将其传递到不规则移动的体模中，并在肿瘤中心使用小体积离子室进行测量。
3DCT、4DCT-P 和 4DCT-A 与预期肿瘤运动范围的中位数差异分别为 2.5 [1.6-3.6] cm、1.1 [0.1-1.9] cm 和 1.3 [0.4-1.9] cm（p=0.005，4DCT-P 与 3DCT）。3DCT、4DCT-P 和 4DCT-A 的中位数 AUC 评分（理想值为 0）分别为 0.25 [0.14-0.49]、0.12 [0.05-0.42] 和 0.13 [0.09-0.44]（p=0.005，4DCT-P 与 3DCT）。十个 4DCT-P 计划中的九个和所有 4DCT-A 计划在治疗计划系统（TPS）中测量的剂量均在预期剂量的 2.5%以内，而 3DCT 计划只有七个。
对于研究的病例，与 3DCT 相比，4DCT 更好地代表了肿瘤运动范围和平均密度，即使存在不规则呼吸。4DCT 图像允许以可接受的剂量学准确性交付 VMAT 计划。在相位和幅度排序之间未检测到显著差异。结合治疗中的 4D 锥形束成像，我们的研究结果使我们有信心为有不规则呼吸的肺癌患者引入 4DCT 和 VMAT。
