ABSTRACT
Objective To investigate the impacts of the CT value-electron density transformation curves on radiotherapy dosage for different scanning sites.Methods The CT value-electron density transformation curves under head,chest and abdomen modes were obtained with CIRS062 nonuniform equivalent phantom,a CT simulator and the same scanning parameters.Totally 8 patients with glioma,lung cancer or gastric cancer had the radiotherapy dosages calculated with Pinnacle 9.8 TPS and CT value-electron density transformation curve under the three modes,so as to analyze the dosage deviation involving in hop value as well as the dose volume histogram (DVH) for the target area and organs at risk (OAR).Results With the scanning parameters kept the same,the head area had no significant differences in the CT value-electron density transformation curve and exposure dosage with the abdomen area (P＞0.05),while the head and abdomen areas had statistical differences in the CT value-electron density transformation curve with the chest area (P＜0.05).CT values varied greatly at the high-density tissue,while the dosage deviations at the target area and OAR were both less than 2％.Conclusion CT value-electron density transformation curve for different scanning sites has influences on radiotherapy dosage,and head and chest tumors should have the dosage calculation based on the CT value-electron density transformation curve with corresponding scanning modes to ensure dosage computation precision during treatment planning.
ABSTRACT
Objective To compare the diagnostic value 18F-fluorothymidine (FLT) and 18F-fluorodeoxyglucose (FDG) PET/CT in detecting lymph node metastases of untreated thoracic esophageal carcinoma. Methods Twenty-two patients with thoracic esophageal squamous cell carcinoma underwent both 18F-FLT and 18F-FDG PET/CT before surgery. The imaging results of the two modalities in detecting regional lymph node metastases were compared prospectively with the pathologic findings. The X2-test was used with SPS S 13.0. Results All patients underwent esophagectomy and lymphadenectomy. The metastatic lymph nodes were found in 16 patients, from which 47 of 424 excised nodes were positive by pathologic examination. False positive results were 14 while false negative 8 on 18F-FDG PET/CT. In contrast, false positive results were only 3 but false negative were 12 on 18 F-FLT PET/CT. The sensitivity, specificity, accuracy,negative predictive value, and positive predictive value were 74.47% ( 35/47 ), 99.20% ( 374/377 ),96.46% (409/424), 96.89% ( 374/386 ) and 92.11% ( 35/38 ) respectively for 18 F-FLT PET/CT, whereas the corresponding values were 82.98% (39/47), 96.29% (363/377), 94.81% (402/424), 97.84%(363/371 ) and 73.58% (39/53) respectively for 18 F-FDG PET/CT (X2 = 0.572, 6.018, 1.017, 0.348,3.852, P＞0. 05, ＜0.05, ＞0.05, ＞0.05 and ＞0.05). Conclusions Compared with 18F-FDG PET/CT, 18F-FLT PET/CT may be less sensitive but more specific for the detection of lymph node metastases of thoracic esophageal carcinoma.