RADIATION ASSOCIATED WITH CT-GUIDED ABLATION OF RENAL TUMORS: EFFECTS ON PROJECTED LIFE EXPECTANCY

Purpose:    Minimally invasive imaging-guided cancer therapies are increasingly used for cancer control and cure.  These therapies frequently require extensive pre- and post-procedure CT studies, and there is growing concern about the associated radiation exposure to patients.  Our purpose was to estimate the effects of radiation exposure associated with CT-guided radiofrequency ablation (RFA) - a commonly used imaging-guided therapy - on the life expectancy (LE) of patients with renal tumors who opt for RFA over surgery.

Method:    We developed a decision-analytic Markov model to estimate LE for 65-year-olds with a single, ≤4cm renal cancer, comparing two treatment strategies: (1) CT-guided RFA; and (2) surgery, the current standard.  The model incorporated treatment effectiveness, renal cancer-related mortality, age-specific mortality (all cause), and radiation-induced cancer mortality.  Organ-specific radiation doses were estimated for the RFA procedure, and for CT scans following RFA and surgery.  The Biological Effects of Ionizing Radiation (BEIR) VII report was adapted to estimate excess mortality associated with radiation exposure.  We estimated and compared LE for each strategy, and quantified the contribution of radiation-induced cancer mortality to the LE difference between strategies.  Effects of changes in key model parameters upon model results were evaluated in sensitivity analysis. 

Result:    Cumulative radiation exposure associated with RFA (up to 516 mSv) was considerably greater than surgery (up to 112 mSv).  Under base-case assumptions, RFA yielded a minimally lower LE (15.38 yrs) compared to surgery (15.43 yrs, 17 day difference).  Radiation-induced cancer mortality accounted for 12/17 days of this difference.  Our results - in particular, the scope of this estimated LE difference - were stable over changes in most model parameters tested in sensitivity analysis.  Our results were notably sensitive to variation in patient age at initial treatment.  For example, for 35-year-olds, the estimated LE difference was 70 days; for 75-year-olds, it was 6 days.  To a lesser degree, our results were sensitive to variability in the assumed latent periods that defined when radiation-induced cancer mortality could occur after an exposure, and to CT radiation dose per scan. 

Conclusion:     In elderly patients, RFA remains a safe alternative to surgery despite higher radiation exposure.  In younger patients, potential LE reductions resulting from RFA-related radiation exposure are relatively greater, and merit explicit consideration when determining therapeutic choice.