Dose estimates of occupational radiation exposure during radioguided surgery of Tc-99m-PSMA-labeled lymph nodes in recurrent prostate cancer

Aim [99mTc]Tc-PSMA-based radioguided surgery (TPRS) represents a curative approach for localized relapse of prostate cancer. For its simplified regulatory permission, the radiation protection authorities require a 99mTc- activity below the exemption limit of 10 MBq at the time of surgery. Our aim was to determine the optimal amount of radioactivity (OAR) to comply with that limit and to estimate the maximum number of TPRS procedures per year and surgeon without triggering the full monitoring obligations. Methods In this retrospective study, a dose rate meter was calibrated using measurements on phantoms and from recently injected (1 min p. i.) patients to determine the activity in the patient from measured dose rates. The effective half-life of 99mTc-PSMA-I&S in patients was determined from repeated dose rate measurements to estimate dose parameters of relevance for radiation protection. External exposures of the surgeons were measured with personal dosimeters calibrated in Hp(10). The surgeon’s finger dose Hp(0.07) is estimated from radioactivity measured in resected lymph nodes. Potenzial incorporations were estimated for an activity of 10 MBq. Results From the first 6 subsequent patients, an effective half-life of 4.15 h was observed. Assuming an operation time 24 h p. i., the OAR was 550 MBq. Operations lasting in average 2 h in a distance of 0.25 m to the patient imply a body dose for surgeons of 4.16 µSv per procedure. Based on these estimates, the surgeon’s Hp(10) is less than 1 mSv per year with up to 241 operations per year. Hp(0.07) and potential incorporation of activity do not lead to further limitations. Summary All radiation protection regulations are met with adherence to OAR recommended here without triggering the full monitoring obligations from radiation protection regulations.

Effects of 99mTc on the electrochemical properties of thiamazole in vitro

Thiamazole inhibits the thyroid hormone synthesis and does not inactivate the existing thyroxine and triiodothyronine that circulate in the blood. In this paper Thiamazole electrochemical behavior was monitored by cyclic voltammetry on glassy carbon (GC) electrode in the absence and presence of sodium pertechnetate (99mTc). The influence of different Thiamazole concentrations without and in the presence of radiopharmaceutical 99mTc, the effect of the number of scan cycles, and the effect of 99mTc activity on the appearance of cyclic voltammograms were examined. The results show that there is an observed increase in the reduction peak current with an increase of Thiamazole concentration. It was found that the concentration of the tested drug had a significant effect on its redox characteristics. The results obtained show that the application of different concentrations of sodium pertechnetate exhibits the inhibitory properties of the used radiopharmaceutical on the drug in the treatment of thyroid gland disease.

Comparison of 99mTc Injected Activity with Prescribed Activity in Four Types of Nuclear Medicine Exams

Background: 99mTc is a radioactive isotope that is obtained by eluting a 99Mo/99mTc generator. (PINSTECH, Islamabad) and used for radionuclide scanning. Objectives: The objective of this work is to study the uncertainties in 99mTc activity that exist due to time delay between injection preparation and administration to patients, during the process of gamma camera scanning. Methods: Lead canisters were used for storing elution vials and dose calibrator for measuring 99mTc activity in mCi. The activity of preparing 99mTc injection and its administration to patients were compared with the prescribed values of activity recommended in the Society of Nuclear Medicine procedure guidelines. Results: This study showed that uncertainty in the activity existed in one thyroid patient, 38 bone patients, 5 renal patients and 45 cardiac patients. Conclusion: This uncertainty in activity exists due to time delay between injection preparation and administration to patients, as well as due to residual radionuclide that is not injected into patients and remains in the syringe.

Leakage Radiometric Control of Chemical Drugs with Regional Perfusion of Surgical Isolated Limbs

Purpose: Modernization and evaluation of the clinical effectiveness of the technology of continuous radiometric monitoring carried out during high-dose chemotherapy of a surgically isolated limb with tumor foci. Material and methods: A modernized radiometric control technology for regional limb perfusion is proposed. It is based on in vivo labeling of erythrocytes with 99mTc eluate followed by continuous monitoring of the activity of labeled erythrocytes as a simulator of a chemotherapy drug over the heart region. Its distinctive features are intravenous injection of a pyrfotech slice after giving inhalation anesthesia to ensure a sufficient level of red blood cell chelation, as well as using 99mTc activity less than its minimum significant level, which allows working with an open source of ionizing radiation without violating the requirements of radiation safety regulations. Results: The developed technology was successfully used with 106 regional perfusion of the upper and lower extremities in patients with melanoma or sarcoma of soft tissues. In 4 cases, according to the results of radiometric control, the intervention of the surgical team was required to reduce the chemical preparation leakage that was occurring. Conclusion: The technology upgraded by us is characterized by ease of implementation, the ability to take timely measures to prevent or reduce the leakage of a chemotherapy drug from an isolated limb according to the results of continuous in vivo radiometric monitoring of 99mTc-labeled red blood cells over the heart, as well as low radiation load on the patient and staff.