NRG Oncology International Consensus Contouring Atlas on Target Volumes and Dosing Strategies for Dose-Escalated Pancreatic Cancer Radiotherapy.

Purpose/objective(s): Dose-escalated radiotherapy is increasingly used in the treatment of pancreatic cancer, however approaches to target delineation vary widely. We present the first North American cooperative group consensus contouring atlas for dose-escalated pancreatic cancer radiotherapy.

Materials/methods: An expert international panel comprising 15 radiation oncologists, 2 surgeons and 1 radiologist were recruited. Participants used MimCloud software to contour high and low risk clinical target volumes (CTV) on three pancreatic cancer cases: a borderline resectable head tumor, a locally advanced head tumor, and a medically inoperable tail tumor. Simultaneous truth and performance level estimation (STAPLE) volumes were created, and contours were analyzed using Dice similarity coefficients.

Results: The contoured gross tumor volume (GTV) for the borderline head, locally advanced head, and unresectable tail tumor cases were 156.7, 58.2 and 9.0 cc, respectively, and the Dice similarity coefficients (SD) for the high- and low-risk CTV ranged from 0.45 to 0.82. Consensus volumes were agreed upon by authors. High-risk CTVs comprised the tumor plus abutting vessels. Low-risk CTVs started superiorly at (tail tumors) or 1 cm above (head tumors) the celiac takeoff and extended inferiorly to the superior mesenteric artery (SMA) at the level of the first jejunal takeoff. For head, neck, and proximal body tumors, the lateral volume encompassed the entire pancreas head and 5-10 mm around the celiac, superior mesenteric artery (SMA), superior mesenteric vein (SMV), including the common hepatic artery and medial portal vein, consistent with a "Triangle" volume-based approach. For distal body and tail tumors, the entire tail was included, along with the splenic vessels and the takeoffs of celiac artery.

Conclusion: Through multidisciplinary collaboration, we created consensus contouring guidelines for dose-escalated pancreatic cancer radiotherapy. These volumes include not only gross disease, but also routine elective coverage, and can be used to standardize practice for future trials seeking to define the role of dose escalated radiotherapy in pancreatic cancer.