Wang David, DeNittis Albert, Evans Tracey, Meyer Thomas
Lankenau Medical Center, 100 E Lancaster Ave, Wynnewood, PA 19096, USA.
Lankenau Institute for Medical Research, 100 East Lancaster Avenue, Wynnewood, PA 19096, USA.
J Radiosurg SBRT. 2020;7(2):157-164.
It is crucial to spare lung when treating early stage lung carcinoma with stereotactic body radiotherapy (SBRT) for minimizing the radiation induced toxicities, such as radiation pneumonitis and late fibrosis. A retrospective study was performed with a combination of approaches to determine the optimal range of prescription isodose line (P-IDL) within which lung tissue was best spared in SBRT plans with Volumetric-Modulated Arc Therapy (VMAT) and Monte-Carlo-like dose calculation algorithm. Twenty clinically-delivered SBRT lung plans were optimized using traditional LINAC MLC based approaches: an average P-IDL of (88.8 ± 0.5)% (the error bar of all the data is the 95% confidence interval (CI)). The plans were then re-optimized using a new combination of approaches with variation of P-IDL from 60% to 90% for each case. The combination of approaches included finding and utilizing an optimal P-IDL, implementing tuning ring structures internal and external to the target, as well as normal tissue objective and equivalent. The plans were evaluated with the following indexes: 1. R, the ratio of 50% prescription isodose volume to the plan target volume (PTV); 2. V and V, the volume of lung within 20Gy and 5Gy, respectively; 3. PCI, the Paddick comformity index; 4. D, the maximum dose at 2 cm from PTV in any direction; 5. MLD, the mean dose in total lung volume; 6. Focal Index (FI), an indicator of dose in the core of the target. The optimal P-IDL was found to be in the range of 75-80%. The average optimal P-IDL for the 20 cases was (77.9 ± 0.9)%. With the optimization strategies the average PCI was increased by (10.3 ± 2.1)%; the average R, V, V, D and MLD were decreased by (29.1 ± 4.1)%, (26.9 ± 5.4)%, (13.9 ± 3.5)%, (13.4 ± 4.3)% and (16.7 ± 2.3)%, respectively. The FI was increased by (23.7 ± 1.3)%. The optimal P-IDL range was 75-80% for SBRT VMAT lung treatment plans. The application of the set of optimization approaches can significantly improve the lung sparing in SBRT VMAT plans with AXB dose calculation algorithm and makes treatment plans more conformal in high, intermediate and low dose regions, while higher dose is delivered to the target.
在采用立体定向体部放疗（SBRT）治疗早期肺癌时，为了将放射性肺炎和晚期纤维化等辐射诱发毒性降至最低，保护肺组织至关重要。本研究采用多种方法进行回顾性研究，以确定在容积调强弧形放疗（VMAT）和类蒙特卡洛剂量计算算法的SBRT计划中，肺组织得到最佳保护的处方等剂量线（P-IDL）的最佳范围。使用基于传统直线加速器多叶准直器的方法对20个临床实施的SBRT肺部计划进行了优化：平均P-IDL为(88.8 ± 0.5)%（所有数据的误差线为95%置信区间（CI））。然后，针对每个病例，使用新的方法组合对计划进行重新优化，P-IDL范围从60%到90%不等。这些方法组合包括找到并利用最佳P-IDL、在靶区内外部实施调谐环结构，以及正常组织目标和等效物。通过以下指标对计划进行评估：1. R，50%处方等剂量体积与计划靶区体积（PTV）的比值；2. V和V，分别为20Gy和5Gy范围内的肺体积；3. PCI，帕迪克适形指数；4. D，在任何方向上距PTV 2 cm处的最大剂量；5. MLD，全肺体积的平均剂量；6. 焦点指数（FI），靶区核心剂量的指标。发现最佳P-IDL范围为75 - 80%。20个病例的平均最佳P-IDL为(77.9 ± 0.9)%。通过优化策略，平均PCI提高了(10.3 ± 2.1)%；平均R、V、V、D和MLD分别降低了(29.1 ± 4.1)%、(26.9 ± 5.4)%、(13.9 ± 3.5)%、(13.4 ± 4.3)%和(16.7 ± 2.3)%。FI提高了(23.7 ± 1.3)%。对于SBRT VMAT肺部治疗计划，最佳P-IDL范围为75 - 80%。该组优化方法的应用可显著提高采用AXB剂量计算算法的SBRT VMAT计划中的肺保护效果，并使治疗计划在高、中、低剂量区域更适形，同时向靶区输送更高剂量。
