Han-Oh Sarah, Hill Colin, Kang-Hsin Wang Ken, Ding Kai, Wright Jean L, Alcorn Sara, Meyer Jeffrey, Herman Joseph, Narang Amol
Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University of School of Medicine, Baltimore, Maryland.
Radiation Medicine, Zucker School of Medicine at Hofstra/Northwell, Lake Success, New York.
Adv Radiat Oncol. 2021 Jan 22;6(2):100655. doi: 10.1016/j.adro.2021.100655. eCollection 2021 Mar-Apr.
In patients undergoing stereotactic body radiation therapy (SBRT) for pancreatic adenocarcinoma, the reproducibility of tumor positioning between deep-inspiration breath holds is unclear. We characterized this variation with fiducials at simulation and treatment and investigated whether a patient-specific breath-hold (PSBH) margin would help account for intrafraction variation at treatment.
We analyzed 20 consecutive patients with pancreatic cancer who underwent SBRT with deep-inspiration breath holds. At simulation, 3 additional breath-hold scans were acquired immediately after the contrast-enhanced planning computed tomography (CT) scan and used to quantify the mean and maximum variations in the simulation fiducial position ( and ), as well as to design the internal target volume (ITV) incorporating a PSBH margin.
At treatment, a mean of 5 breath-hold cone beam CT (CBCT) scans were acquired per fraction for each patient to quantify the mean and maximum variations in the treatment fiducial position ( and ). Various planning target volume (PTV) margins on the gross tumor volume (GTV) versus ITV were evaluated using CBCT scans, with the goal of >95% of fiducials being covered at treatment. The and were 0.9 ± 0.5 mm and 1.5 ± 0.8 mm in the left-right (LR) direction, 0.9 ± 0.4 mm and 1.4 ± 0.4 mm in the anteroposterior (AP) direction, and 1.5 ± 0.9 mm and 2.1 ± 1.0 mm in the superoinferior (SI) direction, respectively. The and were 1.2 ± 0.4 mm and 2.0 ± 0.7 mm in the LR direction, 1.1 ± 0.4 mm and 1.8 ± 0.6 mm in the AP direction, and 1.9 ± 1.0 mm and 3.1 ± 1.4 mm in the SI direction, respectively. The ITV was increased by 21.0% ± 8.6% compared with the GTV alone. The PTV margin necessary to encompass >95% of the fiducial locations was 2 mm versus 4 mm in both LR and AP and 4 mm versus 6 mm in SI for the ITV and the GTV, respectively.
The interbreath-hold variation is not insignificant, especially in the SI direction. Acquiring multiple breath-hold CT scans at simulation can help quantify the reproducibility of the interbreath hold and design a PSBH margin for treatment.
在接受立体定向体部放射治疗（SBRT）的胰腺癌患者中，深吸气屏气之间肿瘤定位的可重复性尚不清楚。我们通过模拟和治疗时的基准标记来表征这种变化，并研究患者特异性屏气（PSBH）边界是否有助于解释治疗时的分次内变化。
我们分析了20例连续接受SBRT深吸气屏气的胰腺癌患者。在模拟时，在对比增强计划计算机断层扫描（CT）扫描后立即获取另外3次屏气扫描，用于量化模拟基准标记位置的平均和最大变化（ 和 ），以及设计包含PSBH边界的内部靶区（ITV）。
在治疗时，每位患者每次分次平均采集5次屏气锥形束CT（CBCT）扫描，以量化治疗基准标记位置的平均和最大变化（ 和 ）。使用CBCT扫描评估了在大体肿瘤体积（GTV）与ITV上的各种计划靶区（PTV）边界，目标是在治疗时>95%的基准标记被覆盖。左右（LR）方向上的 和 分别为0.9±0.5毫米和1.5±0.8毫米，前后（AP）方向上为0.9±0.4毫米和1.4±0.4毫米，上下（SI）方向上为1.5±0.9毫米和2.1±1.0毫米。LR方向上的 和 分别为1.2±0.4毫米和2.0±0.7毫米，AP方向上为1.1±0.4毫米和1.8±0.6毫米，SI方向上为1.9±1.0毫米和3.1±1.4毫米。与单独的GTV相比，ITV增加了21.0%±8.6%。对于ITV和GTV，在LR和AP方向上涵盖>95%基准标记位置所需的PTV边界分别为2毫米对4毫米，在SI方向上为4毫米对6毫米。
屏气间变化并非微不足道，尤其是在SI方向。在模拟时采集多次屏气CT扫描有助于量化屏气间的可重复性，并为治疗设计PSBH边界。
