| Objective This research studies the relation between CT scanning of pancreatic cancer primary tumor and its pathological size after surgical operation as well as the area of pancreatic cancer nidus microscopically, aiming to determine the outline of clinical target volume(CTV) while delineating target volume in radiation therapy. Methods We selected 19 consecutive patients with resected pancreatic cancer from department of hepatobiliary surgery both in PLA General Hospital and PLA Air Force General Hospital for case study. The reconstructed slice thickness in the pancreatic area reached2~4mm. In case of special requirement, slice thickness can be only 1 mm. Then our imaging experts compared the cross sectional CT scanning pictures of the pancreatic cancer primary tumor slice by slice in order to examine the maximum diameter of the cross-sectional pancreatic cancer primary tumor by sitting and observing through a window, the width of which measures 150 Hu and the level of which reaches40~60Hu.Given the position of primary tumor and its anatomical relationship with the resected normal tissue at the periphery, imitate the spatial position of the pancreas in vitro in abdominal cavity. Aiming at the CT scanning levels, cut along the transaction of pancreas in vitro at a fixed slice thickness of 2~4mm into histological sections and keep observing until the occurrence of the maximum cross-sectional slice with radial lines of pancreatic tumor, hereafter is called the interesting slice in this study. Then measure the maximum diameter in the cross-sectional slices of primary tumor.While pathologists read every pathological section, they firstly glance over the whole section through a low power view and draw the edging line of the primary tumor. If the primary tumor edges are invaded with burrs, then the researchers draw the line closely along the root of the burrs. Secondly, the observing focus transfers to the micro nidus which exists within the pancreatic tissue outside the primary tumor by means of a high power view.Meanwhile, the farthest invaded micro nidus is marked and located under the view of microscope. Next, connect the shortest straight line between the marked furthest micro nidus and the edging line of primary tumor and measure that distance, which is called measuring distance, by a vernier caliper. At last, considering the pre- and post-fixation tissue retraction rate, the practical distance between this micro nidus and the edge of primary tumor can be identified, which means the practical distance equals measuring distance divided by retraction rate. Results Of the patients, fifteen possessed preoperative MDR-CT scans which were available for us. The difference between their pathology and the maximum diameter of CT scan-measured primary tumor was of statistical significance(33.6、30.1mm,t=6.969,P<0.001). The median and mean value of the difference proved respectively to be 3.1mm(range, 1.2 to 8mm)and 3.6±2.0mm.Besides, 95% confidence interval of that difference was calculated to be(1.2~6.0mm).The discrepancy between the actual maximum tumor-invaded distance of the nineteen specimens and the maximum measuring distance was statistically significant(3.50mm、3.19 mm,t=14.835,P<0.001). Correspondingly, the median and mean value of that difference were as follows: 0.31mm(range, 0.15 to 0.50mm)、0.30±0.09 mm. The actual maximum tumor-invaded distance was 5.21 mm, while themedian value was 3.34mm(range, 2.19 to 5.21mm) and the mean value reached3.50±0.88 mm. Besides, 95% confidence interval of the invasive microscopic nidus beyond the marginal area of the primary tumor was calculated to range from 2.19 to5.06(rang, 2.19 to 5.06mm). Conclusions Since computed tomography(CT) scanning has significantly underestimated pancreatic cancer primary tumor size, we assume that in the process of radiation therapy, a 5mm marginal expansion of the clinical target volume(CTV) from the gross target volume(GTV) is probably insufficient in pancreatic cancer’s CT simulation. Based on the result of the microscopic nidus-invaded area from this study, it is suggested that another 1~3mm of CTV expansion is necessary. |
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