Quantifying Decreased Radiation Exposure From Modern CT Scan Technology and Surveillance Programs of Germ Cell Tumors.

Abstract

Upgrading computerized tomography (CT) scanners to iterative reconstruction techniques (IRT) decreases radiation dose. This reduction, combined with changes in surveillance protocols in clinical stage I testicular cancer (CS1TC) measurably decrease the lifetime attributable risk (LAR) of dying of radiation-associated cancer. This IRB-approved study enrolled 24 CS1TC patients who had CT scans on the same Toshiba Aquilion 64 CT before and after IRT software installation. Dose-length product and CT dose index volume were recorded. A physicist calculated effective doses. Radiation doses were compared using the Wilcoxon signed rank test. Median effective dose per scan was multiplied by scan number based on 16 versus 7 scans in 5-year AS protocols to calculate estimated cumulative dose (ECD). LAR of dying of radiation-associated solid tumor was estimated using ECD for a single exposure at age 35 with the excess absolute risk transport model from the BEIR VII analysis of long-term atomic bomb survivors. Median preupgrade and postupgrade effective doses were 12.5 and 7.7 mSv, respectively (P<0.0001). A linear regression model with a constrained zero intercept fit to the data found that IRT dose was estimated as 61% of filtered back projection dose (95% confidence interval, 0.56-0.66). The IRT upgrade reduced the LAR of the 16-scan protocol 35%. Combination of IRT upgrade and 7-scan protocol reduced surveillance LAR 72%. Modern CT technology combined with reduced scanning strategies can markedly decrease lifetime radiation exposure, further lowering the already small potential mortality of imaging-associated cancers.