RESUMO
Radiation-induced salivary gland dysfunction is the most frequent side-effect of I-131 thyroid therapy. Here, a novel saliva sampling method with ordinary chewing gums administered to the patients at appropriate time intervals post-treatment (TIPT) was used to relate this effect to chewing gum saliva activity (CGSA) content. Saliva samples were acquired after the oral administration of prescribed I-131 activity (radioactivity administered [RA]) to 19 differentiated thyroid cancer (DTC) and 16 hyperthyroidism patients of the radioisotope unit (RIU) during 2014 and 2015. The error of this saliva collecting process was found to be 1.2%-2.05%, and so, the method was considered satisfactory. For each patient, the CGSA was plotted against the TIPT producing a curve, R(t). On this, two functions were fitted: a linear on the first few rising data points and a gamma variate over the peak of the R(t). From these, several parameters related to the radioactivity oral transit were calculated and the total radioactivity administered (TRA) during all past treatments of each patient was obtained from RIU records. The patients were asked to report any swelling, dry mouth, taste-smell change, or pain and were graded as a morbidity score (MS) describing the quality of life of each. The peak radioactivity in the saliva samples, Rmax, was found to be proportional to RA and was plotted against the CGSA extrapolated at 24 and 36 hours. The linear fits produced were used to estimate the salivary glands' activity average effective half-life (16.3 hours). The MS of DTC patients was found to depend linearly both on Rmax and TRA (MS = 0.0032 × Rmax - 0.7107 and MS = 0.1862 × TRA +0.66, respectively). Both lines were used to extrapolate symptom thresholds. The measurement of Rmax in DTC patients proved very useful for individualized radiation protection, and the dependence of MS on TRA should be used when additional treatments are considered for repeat DTC patients.