Possibility of limiting the un-justified irradiation in (131)I therapy of Graves' disease: a thyroid mass-reduction based method for the optimum activity calculation.
OBJECTIVE
In Graves' disease therapy, the amount of (131)I is usually decided following two different modalities: the administration of a fixed activity or of an activity individually calculated based on a fixed value of target absorbed dose. Although the effectiveness of each of these approaches is good (about 80% of patients cured), the ALARA principle must be applied avoiding the un-justified radioactivity to the patient himself, the people living/working near him and the environment. In this paper a new approach to the (131)I therapy in Graves' disease, based on the optimum value of the final thyroid mass, is presented.


METHODS
97 Graves' disease patients (29 males) were randomly assigned into three groups (GR1, GR2, GR3). In two of them (GR1, GR3) the radioiodine administering activity was calculated based on two fixed thyroid absorbed dose values (100 Gy for GR1; 400 Gy for GR3), in GR2 it was calculated based on the desired final optimum thyroid mass value m(f)=0.24 m(0)/U(0)


RESULTS
The rate of cured patients are 48% (GR1), 97% (GR2) (z-test, p<0.001) and 97% (GR3). The average activity administered to GR2 (393 + or - 157 MBq) is lower than that administrered to GR3 patients (524 + or - 201 MBq) (p=0.007, two-tails unpaired t-test); the thyroid absorbed dose in GR2 (262 + or - 78 Gy) is lower than in GR3 patients (407 + or - 23 Gy) (p<0.001, two-tails unpaired t-test).


CONCLUSIONS
Our results demonstrate that the thyroid-mass based approach optimizes the treatment avoiding an un-justified excess or a not-effective too low activity without time and resources consuming.
Sezione di Fisica Medica, U.O.Fisica Sanitaria, Azienda Ospedaliero-Universitaria Pisana, via Roma 67, I56125 Pisa, Italy. c.traino@ao-pisa.toscana.it
Antonio C
AC
Traino
Mariano
M
Grosso
Giuliano
G
Mariani
D000465:Algorithms; D005260:Female; D006111:Graves Disease / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D007457:Iodine Radioisotopes / Q000008:administration & dosage / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D009929:Organ Size; D011829:Radiation Dosage; D019275:Radiopharmaceuticals / Q000008:administration & dosage / Q000627:therapeutic use*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D013961:Thyroid Gland / Q000473:pathology / Q000528:radiation effects; D016896:Treatment Outcome
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals