Pancreatic cancer has poor prognosis and is one of the leading causes of cancer-related deaths worldwide (1). Surgical resection is the standard treatment for early stage pancreatic cancer, but 30–35% of patients are in a locally advanced stage upon diagnosis (2).These patients with locally advanced pancreatic cancer (LAPC) are commonly treated with systemic chemotherapy, but the median overall survival is only 11.9–13.6 months (3).A previous study on LAPC patients treated with first-line chemotherapy reported that 41% of the patients died without developing any distant metastases (4).For such patients without distant metastasis, radiotherapy could contribute to better survival outcomes by control of locoregional tumor.
Delivering high doses to the target organ while avoiding the organs-at-risk (OARs) is important in radiotherapy. In general, three-dimensional conformal radiation therapy (3D-CRT), which is a beam delivery technique without intensity modulation within the field of radiation, based on computed tomography (CT) images of a patient’s internal organs has been used. The pancreas is surrounded by radiosensitive organs, such as the stomach, liver, colon, and kidneys. During irradiation to the irregularly shaped target volume using 3D-CRT, it is inevitable for these radiosensitive organs to be irradiated with high doses, thus causing gastrointestinal (GI) toxicities such as ulcer, hemorrhage, perforation, and stenosis. Conventionally fractionated 3D-CRT combined with chemotherapy has a response rate of 60%, but gastroduodenal ulcers are observed in 42.3% of the patients [5, 6].
Compared with 3D-CRT, high-precision radiotherapy, such as intensity-modulated radiotherapy (IMRT) and volumetric modulated radiotherapy (VMAT), enables dose escalation to the target organs with minimal exposure to the OARs. Further, several reports showed that IMRT combined with chemotherapy improved overall survival (OS) and locoregional progression-free survival (LRPFS) and decreased both acute and late GI toxicities (5–7). A comparison study of 3D-CRT, IMRT, and VMAT for locally advanced cancer of the pancreatic head showed better sparing of the OARs, especially the duodenum, small bowel, and right kidney, and fewer acute GI toxicities in VMAT than that in 3D-CRT or IMRT (8).
A continuous non-coplanar delivery technique, termed dynamic wave arc (DWA), was recently developed (9). It allows simultaneous rotation of both radiation head unit and the O-ring-shaped gantry, thus delivering sequential non-coplanar beams both safely and quickly without the need to rotate the couch. The clinical benefit of DWA was first reported in 15 patients with varying treatment sites, namely, breast boost, prostate, lung stereotactic body radiation therapy, and bone metastases (10). Since then, DWA has been added to noncoplanar VMAT techniques to achieve better flexibility in dose shaping while keeping dosimetrically effective delivery. DWA has been reported to have dosimetric advantages over coplanar VMAT (co-VMAT) in tumors located in the midline of the body, such as skull base tumors and prostate cancers [11, 12]. A study on the application of DWA in cases of LAPC using preclinical versions of the treatment planning system (TPS) concluded that it has comparable dosimetric distributions to co-VMAT (13). However, there are no previous reports focused on the dosimetric advantage of DWA in pancreatic head and body cancer, which is also located in the midline of the body, using the clinically integrated version of RayStation TPS (RaySearch Laboratories, Stockholm, Sweden). Thus, this study aimed to investigate the superiority of DWA to co-VMAT with respect to dose distributions in locally advanced pancreatic head and body cancer, using a TPS.