Estabrook Neil C, Corn Jonathan B, Ewing Marvene M, Cardenes Higinia R, Das Indra J
1 Indiana University Health Arnett Cancer Care , Lafayette, IN , USA.
2 Department of Radiation Oncology, Indiana University School of Medicine , Indianapolis, IN , USA.
Br J Radiol. 2018 Feb;91(1083):20170512. doi: 10.1259/bjr.20170512. Epub 2017 Dec 22.
Dosimetric evaluation of air column in gastrointestinal (GI) structures in intensity modulated radiation therapy (IMRT) of pancreatic cancer.
Nine sequential patients were retrospectively chosen for dosimetric analysis of air column in the GI apparatus in pancreatic cancer using cone beam CT (CBCT). The four-dimensional CT (4DCT) was used for target and organs at risk (OARs) and non-coplanar IMRT was used for treatment. Once a week, these patients underwent CBCT for air filling, isocentre verification and dose calculations retrospectively.
Abdominal air column variation was as great as ±80% between weekly CBCT and 4DCT. Even with such a large air column in the treatment path for pancreatic cancer, changes in anteroposterior dimension were minimal (2.8%). Using IMRT, variations in air column did not correlate dosimetrically with large changes in target volume. An average dosimetric deviation of mere -3.3% and a maximum of -5.5% was observed.
CBCT revealed large air column in GI structures; however, its impact is minimal for target coverage. Because of the inherent advantage of segmentation in IMRT, where only a small fraction of a given beam passes through the air column, this technique might have an advantage over 3DCRT in treating upper GI malignancies where the daily air column can have significant impact. Advances in knowledge: Radiation treatment of pancreatic cancer has significant challenges due to positioning, imaging of soft tissues and variability of air column in bowels. The dosimetric impact of variable air column is retrospectively studied using CBCT. Even though, the volume of air column changes by ± 80%, its dosimetric impact in IMRT is minimum.
评估胰腺癌调强放射治疗（IMRT）中胃肠道（GI）结构内气柱的剂量学情况。
回顾性选取9例连续患者，使用锥形束CT（CBCT）对胰腺癌患者胃肠道内气柱进行剂量学分析。采用四维CT（4DCT）确定靶区和危及器官（OARs），并采用非共面IMRT进行治疗。这些患者每周进行一次CBCT，用于回顾性分析气柱填充、等中心验证和剂量计算。
每周CBCT与4DCT之间腹部气柱变化高达±80%。即使在胰腺癌治疗路径中有如此大的气柱，前后径的变化也很小（2.8%）。使用IMRT时，气柱变化与靶体积的大幅变化在剂量学上无相关性。观察到平均剂量偏差仅为-3.3%，最大为-5.5%。
CBCT显示胃肠道结构中有较大气柱；然而，其对靶区覆盖的影响极小。由于IMRT中分割的固有优势，即给定射束只有一小部分穿过气柱，在治疗上消化道恶性肿瘤时，该技术可能比三维适形放疗（3DCRT）更具优势，因为上消化道恶性肿瘤中每日气柱变化可能有显著影响。知识进展：由于定位、软组织成像和肠道气柱变异性，胰腺癌的放射治疗面临重大挑战。使用CBCT对可变气柱的剂量学影响进行了回顾性研究。尽管气柱体积变化达±80%，但其在IMRT中的剂量学影响最小。
