Category: Imaging & Image Guided Therapy: Radiation Safety
Introduction & Objective : Patients with nephrolithiasis are exposed to high levels of ionizing radiation through both diagnostic and therapeutic modalities; however, the associated risk of secondary malignancy and subsequent mortality has never been assessed. The Biological Effects of Ionizing Radiation (BEIR) VII Phase 2 report commissioned by the National Academy of Sciences provides a framework for estimating the lifetime attributable risk (LAR) of cancer incidence associated with radiation exposure. We present the first known study applying this framework to model the risk of malignancy and associated mortality due to ionizing radiation from the evaluation and management of nephrolithiasis.
Methods : A PUBMED-based literature search was performed to identify model inputs, specifically annual incidence of nephrolithiasis sub-stratified by age and gender, average stone episodes per effected patient, and radiation exposure associated with nephrolithiasis episodes. Only new diagnosis of symptomatic nephrolithiasis in adult patients were included. Estimates of age and gender specific radiation induced secondary malignancy and mortality rates were obtained from the BEIR VII Phase 2 report with dose extrapolation using the linear no-threshold model. Measurements of the USA population stratified by age and gender were obtained from the 2010 Census report.
Results : Incidence of new diagnoses of nephrolithiasis ranged from 42/100,000 in males aged 20-30 to 248/100,000 in males aged 60-70. Radiation exposure per nephrolithiasis episode was 37.3mSv over a 2-year period. Data regarding average stone episodes per patient with nephrolithiasis was limited and conservatively estimated at 1.5. Modeled LAR of secondary malignancy and subsequent mortality in individual stone patients ranged from 0.096% and 0.085%, respectively, in males over the age of 70 to 0.59% and 0.39% in females aged 20-30. In the USA, overall incidence of secondary malignancy and associated mortality related to nephrolithiasis management was calculated to be 862.7 and 545.3 cases/year, respectively.
Conclusions : This model suggests that ionizing radiation from the diagnosis and management of nephrolithiasis carries a small but not insignificant risk of causing secondary malignancy and associated mortality. This knowledge, as well as awareness of the disproportionate risk burden of ionizing radiation on younger and/or female patients must be considered when using modalities that involve radiation in the management of nephrolithiasis.
Dr. Todd Yecies is a resident physician at UPMC. He is originally from the Bay Area in California. His research interests include assessment and management of the risks of ionizing radiation in urology and cost-effectiveness in the field of endourology.