[Low-dose spiral CT versus standard dose CT in detection of pulmonary metastasis from gestational trophoblastic tumor].

Objective The purpose of this study is to investigate whether low-dose spiral chest CT scan can replace standard-dose CT scan in detecting pulmonary metastases for patients with gestational trophoblastic tumor ( GTT). Methods Totally, 34 GTT patients underwent 56 chest CT scans for the assessment of pulmonary metastasis. All patients received CT examination both at standard-dose (120 KV, 150 mAs, pitch 1 , and a standard reconstruction algorithm) and low-dose CT( 120 KV, 40 mAs, pitch 2, and a bone reconstruction algorithm) simultaneously each time. The images were interpreted by two radiologists independently. A metastasis by CT image was defined as a nodule within lung parenchyma that could not be attributed to a pulmonary vessel. The number of lesions detected at each dose protocol was recorded. The size of each lesion was measured and categorized as 5 mm, 5 - 10 mm or ^ 10 mm. The differences in detection of the lesions between the standard- and low-dose CT protocols were compared using Wilconxon signed rank test. Results 1417 lesions were detected at the standard-dose, whereas 1214 lesions were found by low-dose CT. Lesions 5 mm detected by low-dose CT were fewer than that detected by standard-dose CT (Z = - 3. 368, P = 0. 000) , though there was no statistically significant difference between the standard- and low-dose CT in detecting lesion ≥5 mm (Z = -0. 055,P =0. 957). Moreover, the risk score of the patients was not affected either. The sensitivity of low-dose CT was 69. 16% for all size of lesions, 58. 50% for 5 mm, 87. 07% for 5-10 mm, and 97. 01% for ≥ 10 mm. The positive predictive value for different sizes of lesion was 80. 71% ( all sizes) , 73. 82% (5 mm) , 88. 86% (5-10 mm) , and 98.48% ( ≥10 mm) , respectively. Conclusion Low-dose chest CT can replace the standard-dose chest CT as a screening and follow-up examination to assess the change in pulmonary metastasis for patients with gestational trophoblastic tumor.