Atkins Katelyn M, Chen Yiyi, Elliott David A, Doshi Tulsee S, Ognjenovic Sanja, Vachhani Arjun S, Kishore Monica, Primack Steven L, Fuss Martin, Deffebach Mark E, Kubicky Charlotte Dai, Tanyi James A
Department of Medicine, Providence St. Vincent Medical Center, 9205 SW Barnes Rd, Portland, OR 97225, USA.
Department of Public Health & Preventive Medicine, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd, Portland, OR 97239, USA.
J Radiosurg SBRT. 2015;3(3):203-213.
Narrow PTV margins and steep dose gradients underscore the importance of evaluating breathing-associated tumor motion for lung SBRT. The specific aim of this study was to determine the impact of anatomic tumor location on inter-fraction tumor motion.
Forty-one patients underwent standard free-breathing 4DCT simulation and daily image-guidance 4DCTs during lung SBRT. Absolute tumor motion amplitude in the mediolateral (ML), anterior-posterior (AP), and superior-inferior (SI) directions was analyzed from 159 total 4DCT scans (simulation and daily pre-treatment).
Overall, the inter-fraction tumor motion amplitude in the ML, AP, and SI directions was small (mean ≤2.5 mm). Similarly, while both upper lobe (UL) and lower lobe (LL) tumors exhibited limited inter-fraction motion in both the ML and AP directions (mean ≤2.2 mm), tumors in the LL had increased inter-fraction motion in the SI direction compared to UL tumors (mean 4.3±4.0 mm vs. 1.7±1.7 mm, p=0.008). Moreover, 28.6% (n=4) of LL tumors exhibited mean inter-fraction motion along the SI direction >5 mm (all of which resided in the supra-diaphragmatic basal segments of the LL).
Mean inter-fraction tumor motion amplitude along the SI direction exceeded our PTV margins (an isotropic 5 mm expansion of the ITV) in 28.6% of LL tumors (all of which resided in the basal segments). These results suggest that typical ITV-to-PTV margins may be insufficient for a subset of LL lesions and that increased PTV margins, daily breathing motion re-assessment and/or adaptive re-planning may benefit patients with supra-diaphragmatic tumors in the LL.
窄的计划靶区（PTV）边界和陡峭的剂量梯度凸显了评估与呼吸相关的肿瘤运动对肺癌立体定向体部放疗（SBRT）的重要性。本研究的具体目的是确定肿瘤的解剖位置对分次间肿瘤运动的影响。
41例患者在肺癌SBRT期间接受了标准的自由呼吸4DCT模拟以及每日图像引导4DCT扫描。从总共159次4DCT扫描（模拟扫描和每日治疗前扫描）中分析肿瘤在内外侧（ML）、前后（AP）和上下（SI）方向的绝对运动幅度。
总体而言，肿瘤在ML、AP和SI方向的分次间运动幅度较小（平均≤2.5 mm）。同样，虽然上叶（UL）和下叶（LL）肿瘤在ML和AP方向的分次间运动均有限（平均≤2.2 mm），但与UL肿瘤相比，LL肿瘤在SI方向的分次间运动增加（平均4.3±4.0 mm对1.7±1.7 mm, p = 0.008）。此外，28.6%（n = 4）的LL肿瘤在SI方向的平均分次间运动>5 mm（所有这些肿瘤均位于LL的膈上基底段）。
28.6%的LL肿瘤（所有这些肿瘤均位于基底段）在SI方向的平均分次间肿瘤运动幅度超过了我们的PTV边界（ITV各向同性扩展5 mm）。这些结果表明，对于一部分LL病变，典型的ITV到PTV边界可能不足，增加PTV边界、每日呼吸运动重新评估和/或适应性重新计划可能使LL膈上肿瘤患者受益。
