Patient external dose rate after 177Lu-DOTATATE therapy: factors affecting its decrease and predictive value.

Rationale: Peptide receptor radionuclide therapy (PRRT) with 177Lu-DOTATATE (oxodotreotide) results in external radiation exposure from the patient. In the PREELU observational prospective study, we determined the equivalent dose rate at 1 m of the patient (EDR-1m) for a period following PRRT. The main objective was to predict which patients could be discharged from the hospital at approximately 3 h after the administration of 177Lu-DOTATATE, i.e. at the end of the infusion of amino-acids according to our PRRT protocol. As presenting no undue risk of radiation exposure for the public, those patients could be treated as outpatients or day patients, rather than inpatients. Methods: We sequentially measured EDR-1m facing the sternum and then the pelvis during 50 PRRT in 24 patients with metastatic neuroendocrine tumours, each 30 minutes after ending administration of Lutathera, over at least 180 minutes. Results: 180 minutes after the administration of ca. 7400 MBq of Lutathera, EDR-1m was <40 µSv/h in all cases, and <25 µSv/h in 32 cases (64%). After an overnight hospital stay, EDR-1m was <25 µSv/h in all cases. The EDR-1m value measured facing the sternum was the greatest in about one-fourth of paired measurements. In patients whose creatinine clearance was >96 mL/min/1.73m2, the EDR-1m was most likely (predictive value=90%) to drop below 25 µSv/h within 180 minutes after the administration of Lutathera. In 16 patients who benefited from several PRRT cycles, the creatinine clearance did not decrease significantly from one cycle to the next, probably due to the kidney protection by the amino-acid infusion. The patients whose EDR-1m dropped below 25 µSv/h at 180 minutes during their first PRRT cycle were unlikely (predictive value= 88%) to decease during the following two years. Conclusion: All patients could have been discharged 3 h after administration according to the criterion EDR-1m <40 µSv/h. Using EDR-1m <25 µSv/h as criterion, an extended hospital stay beyond 3 h would have been necessary in around one-third of the PRRT treatments and could be anticipated based on creatinine clearance ≤96 mL/min/1.73m2. EDR-1m <25 µSv/h at 180 min during the first PRRT yielded a strong predictive value on the patient's survival at two years, a finding that should be confirmed in future studies.

[Potential radiation hazard in nuclear medicine]. / Risques liés à la médecine nucléaire diaqnostique et thérapeutique.

Nuclear medicine uses unsealed radioisotopes. The potential radiation hazards depend on the amount of radioactivity administered and the type of radionucleide. Thus, radiation safety instructions will minimize radiation exposure and contamination as low as reasonably achievable. National nuclear safety authority requires rules, regulations and exposure limits for both patients and workers. Good practices and training staff contribute to optimize the radioprotection.

Thyroid cancer patients treated with 131I: radiation dose to relatives after discharge from the hospital.

BACKGROUND: Thyroid cancer patients treated with radioiodine are potential source of radiation exposure for other individuals. Thus, we evaluated the radiation dose received by family members of thyroid cancer patients treated with (131)I after hospital discharge. MATERIALS AND METHODS: Seventy-six family members of 56 thyroid cancer patients were included in the study. Thyroid cancer patients were given 3.7 GBq of (131)I and remained in a radiation protection ward for 3 days. Radiation protection recommendations were given to patients and relatives. Life conditions were recorded and radiation doses were monitored using a personal dosimeter. RESULTS AND DISCUSSION: At discharge, the mean residual activity was 188 MBq. The mean radiation dose delivered to relatives during the 7 days after discharge was low (51.5 µSv) and was similar with either recombinant human thyrotropin (rhTSH) (59 µSv) or withdrawal (50 µSv) (p = 0.37). CONCLUSION: With our current practice, radiation doses to relatives are low and well below international recommendations.

131I effective half-life and dosimetry in thyroid cancer patients.

UNLABELLED: (131)I treatment in thyroid cancer patients may induce side effects, including extrathyroidal cancer and leukemia. There are still some uncertainties concerning parameters that may influence the effective half-life of (131)I and the absorbed doses by extrathyroidal organs. METHODS: Whole-body retention of radioiodine was measured in 254 patients, and repeated quantitative whole-body scans and measurements of the urinary excretion of (131)I were performed on 30 of these patients. RESULTS: The mean effective half-life (10.5 h) was shorter by 31%, with little difference between patients, in the 36 patients who received recombinant human thyroid-stimulating hormone than in the 218 patients who underwent thyroid hormone withdrawal (15.7 h). The residence times in the stomach and in the rest of the body were significantly shorter in patients who received recombinant human thyroid-stimulating hormone than in patients who underwent withdrawal, but the residence times were similar in the colon and bladder. CONCLUSION: In patients who undergo thyroid hormone withdrawal, the longer mean effective half-life is mainly due to delayed renal excretion of (131)I and results in dose estimates higher than the data in report 53 of the International Commission on Radiological Protection, which were obtained from healthy, euthyroid subjects.