Health effects of Chernobyl.

Abstract

<b>2244</b> <h3><b>Objectives</b></h3> To estimate the error in ⁹⁰Y microsphere delivery vial exposure rate measurement, and assess its impact on the percent of activity delivered calculation. <h3><b>Methods</b></h3> Linear correlation analysis of background-corrected exposure rate (mR/h) at 30 cm from the vial (V), measured with a calibrated ion chamber survey meter, versus activity (GBq) from a dose calibrator calibrated for assaying ⁹⁰Y vials, was performed using the data from our first fifty-seven hepatocellular carcinoma (HCC) ⁹⁰Y microspheres liver brachytherapy treatments. Employing the mR/h computed from the linear correlation function as the correct value, the difference between measured and true (ΔV) was calculated. The resulting difference (Δ%D) in estimated percent of activity delivered (%D=100 × [V - residual waste jar mR/h] / V), using measured versus true V, was then computed. A p value ≤ 0.05 was considered statistically significant. <h3><b>Results</b></h3> Excellent correlation of mR/h vs. GBq was observed (y=1.682x, r=0.993, p&lt;0.0001), over a range of GBq from 0.51 to 6.98 and corresponding mR/h from 0.90 to 11.97. The ΔV was not significant (Mean %ΔV: -1.42±6.70, Range: -34.12 to 10.11, p=0.34). The corresponding Δ%D was also not significant (Mean: -0.06±0.27, Range: -1.43 to 0.73, p=0.094), over the range of %D (Mean: 96.8±6.4, Range: 64.0 to 100%). <h3><b>Conclusions</b></h3> Based on measured - fit residuals, the ⁹⁰Y microspheres vial activity mR/h "assay" appears to be within 10% of true. Since the estimated %D tends to be very high in HCC patients (e.g., 49 of 57 ≥ 95% and 53 of 57 ≥ 90% in this cohort), the equation approaches V/V most of the time, and thus the effect of an error in V is generally negligible. On the other hand, the one ΔV outlier (-34.1%) suggests a large error is possible. If the true %D was 80 for that treatment, the error would have resulted in a %D of 70 and thus an apparent misadministration (&gt; 20% difference from prescribed), suggesting that minimizing inaccuracy in V is prudent (e.g. by minimizing variation in the measurement geometry)