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CTPA versus V-Q lung scan in pregnant women
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Third study endpoint: radiation exposure
Eleven clinically based studies were selected to com- pare radiation exposure during CTPA and V-Q lung scan- ning.16,18,20,21,24,28,33,34,52,54,57 The mean maternal effective dose ranged from 0.9 to 5.85 milliSievert (mSv) with V-Q lung scanning and from 0.23 to 9.7 mSv with CTPA (Table 4). The fetal/uterus absorbed dose ranged from 0.2 to 0.7 milliGray (mGy) with V-Q lung scanning and from 0.002 to 0.51 mGy with CTPA.28 Direct comparisons between V-Q lung scanning and CTPA were not possible because of variations in the imaging protocols used and the meth- ods of measuring or calculating radiation exposure. The dose-length product (DLP) was available in four stud- ies:16,20,21,57 it ranged from 69.34±10.95 mGy/cm57 to 397.54±100.4 mGy/cm.16 Because of the large differences in the applied, mostly unstandardized CTPA protocols among these studies, we refrained from data pooling.
A total of 11 relevant studies assessing CTPA radiation exposure in female phantoms showed that the mean maternal effective dose ranged from 2.5 mSv58 to 4.9 mSv59 (Table 5). The fetal/uterus absorbed dose ranged from 0.003 mGy66 to 0.73 mGy.67 These results from the phantom studies should be interpreted with caution and may not be directly extrapolated to clinical practice because of the wide variations in scan techniques and methods of measuring and/or calculating the radiation exposure. No phantom studies with V-Q lung scanning were available.
Discussion
Our systematic review and meta-analysis provides an overview of all published literature on diagnostic accura- cy, scan efficiency and radiation exposure dose of V-Q lung scans versus CTPA in pregnant patients with suspect- ed acute PE. The negative predictive value and rates of non-diagnostic tests were comparable between V-Q lung scans and CTPA, although significant heterogeneity, over- all high risk of bias and absence of direct comparisons prevent definite conclusions. Moreover and importantly, studies included in the meta-analysis are mostly outdated and none of the available studies evaluated state-of-the- art imaging techniques as currently used in clinical prac- tice. Maternal and fetal radiation exposure with CTPA and V-Q lung scanning could not be compared because of lack of homogeneity in radiation calculation methods and large differences between the scan protocols used. However, all reported radiation measurements for both imaging techniques were clearly below the established harmful threshold of 100 mGy.69
The pooled failure rate for both imaging modalities was negligible, suggesting that both CTPA and V-Q lung scan- ning can equally safely exclude PE during pregnancy. Our findings are concordant with those recently reported.70 Indeed, in the Cochrane review including 11 studies with 695 CTPA and 665 V-Q lung scan results, the median neg- ative predictive value for both imaging techniques was
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