Pancreatic cancer tumor size on CT scan versus pathologic specimen: implications for radiation treatment planning

Abstract

Purpose: Pancreatic cancer primary tumor size measurements are often discordant between computed tomography (CT) and pathologic specimen after resection. Dimensions of the primary tumor are increasingly relevant in an era of highly conformal radiotherapy.

Methods and materials: We retrospectively evaluated 97 consecutive patients with resected pancreatic cancer at two Boston hospitals. All patients had CT scans before surgical resection. Primary endpoints were maximum dimension (in millimeters) of the primary tumor in any direction as reported by the radiologist on CT and by the pathologist for the resected gross fresh specimen. Endoscopic ultrasound (EUS) findings were analyzed if available.

Results: Of the patients, 87 (90%) had preoperative CT scans available for review and 46 (47%) had EUS. Among proximal tumors (n = 69), 40 (58%) had pathologic duodenal invasion, which was seen on CT in only 3 cases. The pathologic tumor size was a median of 7 mm larger compared with CT size for the same patient (range, -15 to 43 mm; p < 0.0001), with 73 patients (84%) having a primary tumor larger on pathology than CT. Endoscopic ultrasound was somewhat more accurate, with pathologic tumor size being a median of only 5 mm larger compared with EUS size (range, -15 to 35 mm; p = 0.0003).

Conclusions: Computed tomography scans significantly under-represent pancreatic cancer tumor size compared with pathologic specimens in resectable cases. We propose a clinical target volume expansion formula for the primary tumor based on our data. The high rate of pathologic duodenal invasion suggests a risk of duodenal under-coverage with highly conformal radiotherapy.

Figure 1

(a) Axial and (b) coronal slices of an example patient's pancreatic primary tumor on pre-operative CT scan. (c) Pathologic gross fresh specimen from that same patient. Maximum dimension in any direction on CT scan was 31 mm, and on pathologic specimen was 46 mm.

Figure 1

(a) Axial and (b) coronal slices of an example patient's pancreatic primary tumor on pre-operative CT scan. (c) Pathologic gross fresh specimen from that same patient. Maximum dimension in any direction on CT scan was 31 mm, and on pathologic specimen was 46 mm.

Figure 1

(a) Axial and (b) coronal slices of an example patient's pancreatic primary tumor on pre-operative CT scan. (c) Pathologic gross fresh specimen from that same patient. Maximum dimension in any direction on CT scan was 31 mm, and on pathologic specimen was 46 mm.

Figure 2

Primary tumor size on pre-operative CT scan vs. pathologic specimen (n = 87).

Figure 3

Primary tumor size on pre-operative EUS vs. pathologic specimen (n = 46). Abbreviation: EUS = endoscopic ultrasound.

Figure 4

CTV primary expansion formula for margin required to cover 97.5% of pathologic tumors vs. tumor size on CT or EUS. Abbreviation: CTV = clinical target volume.