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Abstract：
BACKGROUND: In pediatric radiotherapy treatment planning of abdominal tumors, dose constraints to the pancreatic tail/spleen are applied to reduce late toxicity. In this study, an analysis of inter- and intrafraction motion of the pancreatic tail/spleen is performed to estimate the potential benefits of online MRI-guided radiotherapy (MRgRT).
METHODS: Ten randomly selected neuroblastoma patients (median age: 3.4 years), irradiated with intensity-modulated arc therapy at our department (prescription dose: 21.6/1.8 Gy), were retrospectively evaluated for inter- and intrafraction motion of the pancreatic tail/spleen. Three follow-up MRIs (T2- and T1-weighted ± gadolinium) were rigidly registered to a planning CT (pCT), on the vertebrae around the target volume. The pancreatic tail/spleen were delineated on all MRIs and pCT. Interfraction motion was defined as a center of gravity change between pCT and T2-weighted images in left-right (LR), anterior-posterior (AP) and cranial-caudal (CC) direction. For intrafraction motion analysis, organ position on T1-weighted ± gadolinium was compared to T2-weighted. The clinical radiation plan was used to estimate the dose received by the pancreatic tail/spleen for each position.
RESULTS: The median (IQR) interfraction motion was minimal in LR/AP, and largest in CC direction; pancreatic tail 2.5 mm (8.9), and spleen 0.9 mm (3.9). Intrafraction motion was smaller, but showed a similar motion pattern (pancreatic tail, CC: 0.4 mm (1.6); spleen, CC: 0.9 mm (2.8)). The differences of Dmean associated with inter- and intrafraction motions ranged from - 3.5 to 5.8 Gy for the pancreatic tail and - 1.2 to 3.0 Gy for the spleen. In 6 out of 10 patients, movements of the pancreatic tail and spleen were highlighted as potentially clinically significant because of ≥ 1 Gy dose constraint violation.
CONCLUSIONS: Inter- and intrafraction organ motion results into unexpected constrain violations in 60% of a randomly selected neuroblastoma cohort, supporting further prospective exploration of MRgRT.
METHODS: Ten randomly selected neuroblastoma patients (median age: 3.4 years), irradiated with intensity-modulated arc therapy at our department (prescription dose: 21.6/1.8 Gy), were retrospectively evaluated for inter- and intrafraction motion of the pancreatic tail/spleen. Three follow-up MRIs (T2- and T1-weighted ± gadolinium) were rigidly registered to a planning CT (pCT), on the vertebrae around the target volume. The pancreatic tail/spleen were delineated on all MRIs and pCT. Interfraction motion was defined as a center of gravity change between pCT and T2-weighted images in left-right (LR), anterior-posterior (AP) and cranial-caudal (CC) direction. For intrafraction motion analysis, organ position on T1-weighted ± gadolinium was compared to T2-weighted. The clinical radiation plan was used to estimate the dose received by the pancreatic tail/spleen for each position.
RESULTS: The median (IQR) interfraction motion was minimal in LR/AP, and largest in CC direction; pancreatic tail 2.5 mm (8.9), and spleen 0.9 mm (3.9). Intrafraction motion was smaller, but showed a similar motion pattern (pancreatic tail, CC: 0.4 mm (1.6); spleen, CC: 0.9 mm (2.8)). The differences of Dmean associated with inter- and intrafraction motions ranged from - 3.5 to 5.8 Gy for the pancreatic tail and - 1.2 to 3.0 Gy for the spleen. In 6 out of 10 patients, movements of the pancreatic tail and spleen were highlighted as potentially clinically significant because of ≥ 1 Gy dose constraint violation.
CONCLUSIONS: Inter- and intrafraction organ motion results into unexpected constrain violations in 60% of a randomly selected neuroblastoma cohort, supporting further prospective exploration of MRgRT.
摘要：
背景：在腹部肿瘤的儿科放射治疗计划中，应用胰尾/脾的剂量限制来减少晚期毒性。在这项研究中,我们对胰尾/脾脏的运动间和运动内进行了分析,以评估在线MRI引导放射治疗(MRgRT)的潜在益处.
方法：10名随机选择的神经母细胞瘤患者（中位年龄：3.4岁），在我们部门用强度调节电弧疗法照射（处方剂量：21.6/1.8Gy），回顾性评估胰尾/脾的运动间和运动内。三个随访MRI（T2和T1加权±g）与计划CT（pCT）严格配准，在目标体积周围的椎骨上。在所有MRI和pCT上描绘胰腺尾部/脾脏。分数运动定义为pCT和T2加权图像之间的重心变化在左右（LR），前后（AP）和颅尾（CC）方向。对于帧内运动分析，将T1加权±钆上的器官位置与T2加权进行比较。临床放射计划用于估计每个位置的胰尾/脾接收的剂量。
结果：LR/AP的中位（IQR）分数运动最小，CC方向最大;胰尾2.5mm(8.9),和脾脏0.9毫米（3.9）。内交运动较小，但表现出类似的运动模式(胰腺尾巴，CC:0.4mm(1.6);脾脏,CC：0.9毫米（2.8））。与运动间和运动内运动相关的Dmean差异在胰腺尾部为-3.5至5.8Gy，在脾脏为-1.2至3.0Gy。在10个病人中有6个，由于违反≥1Gy的剂量限制,胰尾和脾的运动被强调为潜在的临床意义.
结论：在随机选择的神经母细胞瘤队列中，在60％的神经母细胞瘤队列中，支持MRgRT的进一步前瞻性探索。
方法：10名随机选择的神经母细胞瘤患者（中位年龄：3.4岁），在我们部门用强度调节电弧疗法照射（处方剂量：21.6/1.8Gy），回顾性评估胰尾/脾的运动间和运动内。三个随访MRI（T2和T1加权±g）与计划CT（pCT）严格配准，在目标体积周围的椎骨上。在所有MRI和pCT上描绘胰腺尾部/脾脏。分数运动定义为pCT和T2加权图像之间的重心变化在左右（LR），前后（AP）和颅尾（CC）方向。对于帧内运动分析，将T1加权±钆上的器官位置与T2加权进行比较。临床放射计划用于估计每个位置的胰尾/脾接收的剂量。
结果：LR/AP的中位（IQR）分数运动最小，CC方向最大;胰尾2.5mm(8.9),和脾脏0.9毫米（3.9）。内交运动较小，但表现出类似的运动模式(胰腺尾巴，CC:0.4mm(1.6);脾脏,CC：0.9毫米（2.8））。与运动间和运动内运动相关的Dmean差异在胰腺尾部为-3.5至5.8Gy，在脾脏为-1.2至3.0Gy。在10个病人中有6个，由于违反≥1Gy的剂量限制,胰尾和脾的运动被强调为潜在的临床意义.
结论：在随机选择的神经母细胞瘤队列中，在60％的神经母细胞瘤队列中，支持MRgRT的进一步前瞻性探索。
