The relative contribution of photons and positrons to skin dose in the handling of PET radiopharmaceuticals.

BACKGROUND: Despite recommendations to use syringe and vial shields to reduce exposure of the hands of staff when manipulating PET radiopharmaceuticals, operators sometimes prefer to work without shields, believing that the faster handling limits the equivalent dose. The aim of this work is to show that this approach does not properly consider the contribution of positrons to the dose. MATERIALS AND METHODS: Using the Varskin+ code, skin doses were calculated for syringes of various sizes, filled with 18F, 11C or 68Ga solution. Syringes without shielding, or shielded with 2 mm and 10 mm of tungsten were considered. RESULTS: Dose rate values in mSv/s per MBq, averaged on a 1 cm2 surface at a depth of 0.07 mm were calculated for all the above conditions. For example, in the case of 3 mL 18F syringe at 1 mm from the skin, the dose rate without shielding is 1.32E-02 and 8.63E-04 for positrons and photons respectively. For 11C, the corresponding dose rates are 4.70E-02 and 8.90E-04 respectively, and for 68Ga, 8.52E-02 and 9.48E-04. CONCLUSIONS: Our results show that the dose due to positrons is the principal component of skin irradiation, by a factor of 3-100, depending on the conditions. The use of shields for syringes and vials is necessary to avoid unjustified skin exposures, that may challenge dose limits. In our opinion, automatic systems for dispensing and allowing injection with shielded syringes, or automatic injectors, are economically justified and should be adopted in PET.

Radiation Safety and Accidental Radiation Exposures in Nuclear Medicine.

Medical radiation accidents and unintended events may lead to accidental or unintended medical exposure of patients and exposure of staff or the public. Most unintended exposures in nuclear medicine will lead to a small increase in risk; nevertheless, these require investigation and a clinical and dosimetric assessment. Nuclear medicine staff are exposed to radiation emitted directly by radiopharmaceuticals and by patients after administration of radiopharmaceuticals. This is particularly relevant in PET, due to the penetrating 511 keV γ-rays. Dose constraints should be set for planning the exposure of individuals. Staff body doses of 1-25 µSv/GBq are reported for PET imaging, the largest component being from the injection. The preparation and administration of radiopharmaceuticals can lead to high doses to the hands, challenging dose limits for radionuclides such as 90Y and even 18F. The risks of contamination can be minimized by basic precautions, such as carrying out manipulations in purpose-built facilities, wearing protective clothing, especially gloves, and removing contaminated gloves or any skin contamination as quickly as possible. Airborne contamination is a potential problem when handling radioisotopes of iodine or administering radioaerosols. Manipulating radiopharmaceuticals in laminar air flow cabinets, and appropriate premises ventilation are necessary to improve safety levels. Ensuring patient safety and minimizing the risk of incidents require efficient overall quality management. Critical aspects include: the booking process, particularly if qualified medical supervision is not present; administration of radiopharmaceuticals to patients, with the risk of misadministration or extravasation; management of patients' data and images by information technology systems, considering the possibility of misalignment between patient personal data and clinical information. Prevention of possible mistakes in patient identification or in the management of patients with similar names requires particular attention. Appropriate management of pregnant or breast-feeding patients is another important aspect of radiation safety. In radiopharmacy activities, strict quality assurance should be implemented at all operational levels, in addition to adherence to national and international regulations and guidelines. This includes not only administrative aspects, like checking the request/prescription, patient's data and the details of the requested procedure, but also quantitative tests according to national/international pharmacopoeias, and measuring the dispensed activity with a calibrated activity meter prior to administration. In therapy with radionuclides, skin tissue reactions can occur following extravasation, which can result in localized doses of tens of Grays. Other relevant incidents include confusion of products for patients administered at the same time or malfunction of administration devices. Furthermore, errors in internal radiation dosimetry calculations for treatment planning may lead to under or over-treatment. According to literature, proper instructions are fundamental to keep effective dose to caregivers and family members after patient discharge below the Dose constraints. The IAEA Basic Safety Standards require measures to minimize the likelihood of any unintended or accidental medical exposures and reporting any radiation incident. The relative complexity of nuclear medicine practice presents many possibilities for errors. It is therefore important that all activities are performed according to well established procedures, and that all actions are supported by regular quality assurance/QC procedures.

Optimization of a Labeling and Kit Preparation Method for Ga-68 Labeled DOTATATE, Using Cation Exchange Resin Purified Ga-68 Eluates Obtained from a Tin Dioxide 68Ge/68Ga Generator.

PURPOSE: The aim of this study was to optimize a radiolabeling method using cationic processed Ga-68 eluates from a SnO2-based 68Ge/68Ga generator, followed by the development of DOTA-Tyr3-Thre8-octreotide (DOTATATE) kits. PROCEDURES: Diluted generator eluates were adsorbed on a SCX resin and desorbed with acidified 5 M NaCl solution. Optimized labeling conditions were determined by variation of pH, using 35 µg DOTATATE and sodium acetate buffer. DOTATATE kits were developed based on optimized radiolabeling conditions, were labeled, and evaluated. RESULTS: Optimized labeling conditions resulted in a radiolabeling efficiency of around 99 % and radiochemical yield of almost 85 %. Different kit preparation methods did not significantly influence the radiolabeling results. Kits were found to be stable over 3 months. CONCLUSION: A labeling method using SCX-processed Ga-68 eluates was optimized. DOTATATE kits specifically for these SCX-processed Ga-68 eluates were successfully formulated. A post-labeling Sep-Pak C18 purification should be optional.

Development and Evaluation of User-Friendly Single Vial DOTA-Peptide Kit Formulations, Specifically Designed for Radiolabelling with 68Ga from a Tin Dioxide 68Ge/68Ga Generator.

PURPOSE: This study was aimed to develop single vial 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-peptide kits to be used with fractionated eluates from a SnO2-based 68Ge/68Ga generator. PROCEDURES: Kits were formulated with 35 µg DOTA-Tyr3-Thre8-octreotide, DOTA-[Tyr3]-octreotide and DOTA-[NaI3]-octreotide (DOTATATE, DOTATOC and DOTANOC) and sodium acetate powder, vacuum-dried and stored at -20 °C for up to 12 months. Labelling of the kits was carried out with 2 ml 68Ga eluate. Comparative labelling was carried out using aqueous DOTA-peptide stock solutions kept frozen at -20 °C for up to 12 months. RESULTS: The quality of the kits was found to be suitable over a 1-year storage period (pH, sterility, endotoxin content, radiolabelling efficiency and radiochemical yields of 68Ga-labelled DOTA-peptides). Radiochemical yields ranged from 73 to 83 %, while those obtained from stock solutions from 64 to 79 %. No significant decline in kit labelling yields was observed over a 12-month storage period. CONCLUSION: The single vial kit formulations met the quality release specifications for human administration and appear to be highly advantageous over using peptide stock solutions in terms of stability and user-friendliness.