Radiation Dose Associated With CT in the Watch the Spot Trial: A Pragmatic Trial of Less Versus More Intensive Strategies for Active Follow-Up of Patients With Small Pulmonary Nodules.

Abstract

Watch the Spot is a cluster-randomized pragmatic clinical trial comparing less versus more intensive surveillance strategies for small pulmonary nodules. This article describes radiation doses from screening and follow-up imaging. In all, 34,686 patients with small nodules were enrolled across 24 US sites (March 2017 to July 2019). Dose estimates were available from 21 sites and reported as size-adjusted CT dose index-volume (CTDI_vol), dose-length product (DLP), and effective dose standardized to an 80-kg patient. Mean (SD) doses for screening and follow-up CTs and the proportion exceeding ACR/AAPM dose thresholds were calculated. Two-year cumulative follow-up imaging doses (excluding baseline scans) were estimated from 22 sites and compared between study arms. Radiation doses varied substantially across sites. For screening, mean size-adjusted CTDI_vol ranged from 1.6 mGy (SD = 0.43) to 8.0 mGy (SD = 2.5), DLP from 62 mGy-cm (SD = 16) to 301 mGy-cm (SD = 102), and effective dose from 1.7 mSv (SD = 0.46) to 11 mSv (SD = 3.7). Follow-up scans had higher mean doses and wider variation: CTDI_vol ranged from 4.0 mGy (SD = 3.5) to 14 mGy (SD = 9.8), DLP from 157 mGy-cm (SD = 143) to 443 mGy-cm (SD = 395), and effective dose from 5.1 mSv (SD = 5.4) to 16 mSv (SD = 14). Overall, 44% of screening and 61% of follow-up scans exceeded ACR/AAPM CTDI_vol thresholds, and 81% and 88% exceeded DLP thresholds. Cumulative follow-up doses were similar between study arms (18.6 versus 19.0 mSv, P = .90). Two-year cumulative radiation dose was similar for patients in the less and more intensive surveillance arms; however, patient size-adjusted doses both for screening and follow-up CTs varied widely within and across sites and frequently exceeded recommended thresholds.