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 > 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 > or = 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 > or = 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% (> or = 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.