engleski

Intratherapeutic measurements of I-131 in patients with thyroid disease

Therapeutic activity of I-131 in the neck and whole body of patients with benign or malignant thyroid disease may require measurements for 1) control of diagnostic dosimetric planning, 2) radiation protection, and 3) scientific investigations. Thyroid uptake system Capintec Captus 2000 (CC2000) and the survey meter Eberline ESP-1 with HP270 probe (ESP1HP270) were used for the measurements. Geometric uniformity and counting efficiency were studied with I-131 source in the air and phantom using 100 keV and wide energy window in CC2000 and ESP1HP270, respectively, and with calibration sources of Co-57, Ba-133, Cs-137 and Co-60. A standing patient is measured at 4 m distance from a detector placed at half of patient’s height (CC2000), or at 1 m distance from a detector placed at 1.3 m height (ESP1HP270). Each measurement is completed after 100 seconds or >10000 collected counts. The activity accumulated in the neck is calculated as a difference of whole body measurement without and with special shielding over the neck. The measurement of patient without any shielding performed 2 h after oral administration of known therapeutic I-131 and no voiding in the meantime represents 100% of whole-body activity. The patients with empty bladder are measured again 4-12 hour and 4-8 day post-administration, and particularly on the day of discharge from the hospital. This work included 28 patients treated with I-131 for thyrotoxicosis or thyroid cancer. The measurements performed by CC2000 (cpm) and ESP1HP270 (uSv/h) correlated excellently (r=0.99, p<0.01). The average dose rate and count rate in patients was about 0.04 uSv/h/MBq I-131 and 0.2 kcpm/MBq I-131, respectively, with the standard variation of about 15%. The higher was the body mass index the lower were detector responses. One patient was blindly intended to be discharged from the hospital against local radiation protection rules. The average effective whole body half-lives determined from the measurements at 2 h and at the time of discharge from the hospital were about 113 h and 16 h in 6 hyperthyroid and 5 thyroid cancer patients, respectively. The measurements of whole body activity with thyroid uptake system and survey meter are simple, fast and may be interchangeably applied. Systematic intratherapeutic measurements of I-131 activity in patients with thyroid disease may improve predictability and efficacy of radioiodine treatment forced to be occurring in concordance with radiation protection rules. A comparison of diagnostic and therapeutic radioiodine biokinetics may reveal novel scientific evidences on the treatment of thyroid diseases.

thyroid disease; radionuclide therapy; radioiodine-131; in vivo measurements

DOI: 10.1007/s00259-005-1947-0