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ST 3.3 –
Protección radiológica en medicina nuclear
METROLOGICAL ASPECTS IN EFFECTIVE DOSE ESTIMATION IN
NUCLEAR MEDICINE PATIENTS
Ruzzarin, Anelise1*; Xavier, Ana Maria
2
; Iwahara, Akira
1
; Tauhata, Luiz
1
1
IRD/CNEN. Brasil.
2
CNEN. Brasil.
* Responsible author, email: anelise@bolsista.ird.gov.br
In order to investigate the performance of routine measurements in nuclear medicine services,
LNMRI/IRD has been conducting, since 1998, a comparison program of activity measurements
of radiopharmaceuticals administered to patients in nuclear medicine. Correction factors are
determined from the result of performance analysis in order to determine with better accuracy
the activity to be administered to the patients. The present study shows how the correction
factor is determined by the ratio between the measurement of the activity at the nuclear
medicine center and the activity determined by the LNMRI, which is adopted as reference. It is
essential that the dose calibrator be calibrated with standards traceable to national metrology
laboratories, so that the activity administered to the patient is neither greater nor smaller than
the appropriate value. The corrected values of the activities can be used to calculate with
greater accuracy the effective doses received by the patients as well as the risk of cancer.
Information related to radiopharmaceuticals and administered activities, type of exams and
patient data of three Brazilian hospitals were collected for 1496 adults and 202 children
submitted to diagnostic exams employing
99m
Tc and
131
I. Results showed that a considerable
difference between the administered activity and the activity corrected until 30% and 13% above
the reference value, respectively, for the
131
I and 99mTc was detected. The consequences of
these differences were not very critical in this study since the activity read in dose calibrator
before administration was lower than the activity corrected, thus causing a lower effective dose
in patients. However, this reduction in activity may result in problems in obtaining the image and
consequently, failure diagnosis, delaying correct diagnosis. On the other hand, the
overestimation would be worse, mainly in therapeutic applications, because an unnecessarily
high absorbed dose would be delivered to the patient.