TY - JOUR T1 - <strong>Simplifying thryoid cancer <sup>131</sup>I maximum permissible activity estimation</strong> JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 1317 LP - 1317 VL - 61 IS - supplement 1 AU - Kenneth Nichols AU - Gene Tronco AU - Maria-Bernadette Tomas AU - Kuldeep Bhargava AU - Christopher Palestro Y1 - 2020/05/01 UR - http://jnm.snmjournals.org/content/61/supplement_1/1317.abstract N2 - 1317Background: Prior to administering 131I for the treatment of thyroid cancer, blood samples are taken every day over several days following administration of small activities of 131I, from which total dose (D) to blood per administered mCi of 131I is estimated. 131I maximum permissible administered activity (MPAA) is derived from D so as not to exceed 200 cGy to blood. We conducted this investigation to determine whether it is possible to determine MPAA from only 3 blood samples collected over 4 days, &amp; to evaluate whether MPAA estimates are affected by impaired renal function (IRF). Methods: Data were examined retrospectively for 121 pts (63 female pts; 58 male pts; age = 58±17 yrs), including 26 with compromised renal function (defined as pts for whom both BUN &amp; creatinine values exceeded normal limits established by each of the laboratories that analyzed their blood samples) evaluated for MPAA before 131I treatment. On the 1st day, 3-4 mL blood was withdrawn prior to 131I administration &amp; counted in a well counter for baseline background activity determination. Pts then were administered an activity of 37-148 MBq 131I, &amp; the 1st sample of 3-4 mL of blood was withdrawn 4 hrs later. Blood samples were repeated at 24, 48, 72 &amp; 96-144 hrs. At the end of all counting sessions, 1-mL aliquots of blood collected throughout the week were counted for 1 min in a well counter. Method1 computed D1 from counts measured for the 5 blood samples (J Nucl Med 2017;58:1588-95). Method2 computed the effective half-life of 131I clearance from only the 1st &amp; last well counter measurements &amp; the baseline blood sample; for intervening time periods exponentially interpolated counts were substituted for actual well counter measurements to estimate blood dose (D2). MPAA1 = 200 cGy/D1 &amp; MPAA2 = 200 cGy/D2. Results: D1 was greater for pts with IRF than pts with NRF (1.08±0.37 versus 0.62 ±0.45 rad/mCi, p &lt; 0.001), as was D2 (1.09±0.36 versus 0.65 ±0.45 rad/mCi, p &lt; 0.001). D2 correlated strongly with D1 for all pts (r = 1.00, p &lt; 0.0001), pts with IRF (r = 1.00, p &lt; 0.0001), &amp; pts with NRF (r = 0.94, p &lt; 0.0001). Similarly, MPAA2 correlated strongly with MPAA1 for all pts (r = 0.95, p &lt; 0.0001), pts with IRF (r = 1.00, p &lt; 0.0001), &amp; pts with NRF (r = 0.94, p &lt; 0.0001). MPAA1 was not normally distributed (Kolmogorov-Smirnov D = 0.12, p = 0.0001), with median = 348 mCi &amp; mean = 413±250 mCi. MPAA2 was lower than MPAA1 (380±215 versus 412±250 mCi, Wilcoxon p &lt; 0.0001), but for activities below the median value of 348 mCi, differences were small (6±12 mCi; 2±4% per cent difference). For activities &lt; 348 mCi, differences between MPAA2 &amp; MPAA1 were similar for pts with IRF and NRF (3±5 versus 8±14 mCi, p = 0.07; 1±2% versus 3±5% per cent difference, p = 0.06). Conclusions: We conclude that maximum permissible administered activity can be accurately determined with as few as 3 blood samples collected over 4 days, regardless of pts' renal function. ER -