68Ga is a radioactive isotope which is the basis of, among others, the radiopharmaceutical compound 68Ga-DOTA-TATE. This isotope generates positrons in the decay process; the positrons, in the process of annihilation with electrons, transform into gamma radiation with an energy of 511 keV. These photons are the basis of positron emission tomography research. It should also be remembered that the process of annihilation, and more precisely its effect - gamma radiation - constitutes the main exposure to ionizing radiation for the hands of medical personnel working in the production and injection of this radiopharmaceutical.
First is elution, consisting in obtaining a radionuclide from the generator by eluting its column, ending with obtaining an eluate. The next step is the labelling process, i.e. combining the earlier obtained radioisotope with a chemical substance. Last step before injecting the radiopharmaceutical to the patient is the procedure of dispensing the dose of 68Ga-DOTA-TATE. Figure 8 shows the percentage of the total exposure level for each production step of 68Ga-DOTA-TATE for the left and right hand of radiochemists.
The obtained results show that in the case of production of a 68Ga-DOTA-TATE, the procedure of dispensing the dose of 68Ga-DOTA-TATE has the biggest impact on the exposure of the workers’ fingertips. On the other hand, the lowest percentage of the Hp(0.07) value was obtained in the elution process. It bears mentioning that according to Fig. 2, the highest activity values of the radioisotope with which radiochemists work are obtained during the process of generator elution, and the lowest activity during the procedure of dose dispensing. However, taking into account the fact that the radiopharmaceutical dose dispensing procedure is the most time-consuming process, in contrast to elution process which needs the shortest time to proceed, it can be said that the long duration of the procedure (in accordance with the basic principles of radiation protection) affects the higher values of radiation doses received by workers.
Authors compared hand exposure generated by working with isotopes and radiopharmaceuticals made with the use of radionuclide generators. For this purpose, the data of hand exposure resulting from working with the most popular radioisotope from radionuclide generators − 99mTc was used. It is worth noting that compared with 18F or 68Ga, 99mTc is a source of gamma rays with an energy of 144 keV. Nevertheless, its production, as is the case with any generator-derived product, includes the elution process, labelling and procedure of dispensing the dose of 68Ga-DOTA-TATE. In Fig. 9, authors compared the percentage level of the total exposure value of the right and left hand for each procedure for the radiochemists during the production of 68Ga-DOTA-TATE and 99mTc.
In the case of procedures with the use of 99mTc, the biggest percentage impact in Hp(0.07)/A values was registered during the labelling procedure (84%) for the right hand of radiochemists. In the production process of a 68Ga-DOTA-TATE the results are different. In this case the biggest percentage impact in a total Hp(0.07)/A value was registered for the left hand of radiochemists during the procedure of dispensing the dose of 68Ga-DOTA-TATE (61%). It is worth mentioning that in both cases the procedure which has the lowest impact (below 20%) in total exposure is the elution procedure.
Another popular radioisotope used in positron emission tomography is 18F. Similar to 68Ga, the annihilation process of positrons generates gamma rays that are the main source of workers’ radiation exposure. However, 18F-FDG is produced automatically. The only case of direct manual contact of the workers’ hands with an open source of radiation is the quality control procedure of the produced 18F-FDG. Hand exposures during the 68Ga-DOTA-TATE dose dispensing procedure and 18F-FDG routines were also compared. The results are shown in Fig. 10.
The procedure of dosing the radiopharmaceutical in the case of chemical compounds based on Tc-99m is a manual process. Time required to complete the procedure was presented in the publication written by Wrzesień (2018). In the case of 18F-FDG, the procedure of dose dispensing is fully automatic. The small participation of the worker includes placing the syringe in the right place in the dispensing chamber before automatically filling the syringe with the appropriate radiopharmaceutical activity and removing the syringe from the dispenser after the dispensing process. Data presented in the Fig. 10 shows that in the case of the procedure of dose dispensing with use of 18F-FDG, the left hand of the worker is more exposed than the right one, but the mean Hp(0.07) value did not exceed 1mSv/GBq. For radiochemists performing the same procedure with 68Ga-DOTATATE, the situation is quite different. In this case the left hand of workers is significantly more exposed. The mean values of Hp(0.07)/A exceeded 5mSv/GBq. For the right hand, the mean values of Hp(0.07)/A did not exceed 2mSv/GBq.
The final step in preparing the patient for examination with positron emission tomography is the injection of the radiopharmaceutical via intravenous route. The authors of this work compared exposure of the left and right hand fingertips of nurses who inject 68Ga-DOTA-TATE with the results obtained for nurses who inject 18F-FDG. Figures 11 and 12 presents the obtained results.
In this case conclusions are similar to the previous one. The left hand is the one more exposed in the injection process with 68Ga-DOTA-TATE and 18F-FDG. It is worth of mention that all nurses who took part in measurements were right-handed. For nurses during the injection of 68Ga-DOTA-TATE, the average Hp(0.07)/A values were twice as high for the thumb and index finger as for the nurses during 18F-FDG injection. In the case of the left hand, the exposure resulting from working with a radiopharmaceutical based on 68Ga is also higher for the thumb and middle finger.
Assessment of the annual exposure of workers associated with the radiopharmaceutical 68Ga-DOTA-TATE
1. Assessment of exposure of the hands of radiochemists.
Assessment of exposure of fingertips was performed taking into account 1/3 of the number of working days per year (260) and the average exposure of individual measurement points, taking into account the average activity of the radiopharmaceutical estimated for individual procedures performed by staff using 68Ga-DOTA-TATE.
With this assumption, the maximum annual exposure of 1030 mSv was obtained for the index finger of the left hand during the dosing of the 68Ga-DOTA-TATE activity for individual patients. The minimum estimated annual value was 8 mSv for the middle finger of the right hand during generator elution. It is worth emphasizing, above all, that the maximum estimated exposure value is over 2 times higher than the annual dose limit, and moreover, work with the 68Ga radionuclide is only part of the activity of employees who prepare other preparations based on 68Ga (such as PSMA), but work with many other radionuclides, which consequently increases the exposure value on an annual basis.
2. Assessment of exposure of the hands of nurses.
The assessment of the annual exposure of nurses' hands was made based on the same assumptions as for radiochemists, namely 1/3 of the number of working days in a year (260) and the average exposure of individual measurement points, taking into account the average activity of the radiopharmaceutical estimated for individual procedures performed by staff using 68Ga-DOTA -TATE.
As a result of estimating the values of annual exposure of nurses' hands, they range from 22 mSv to 76 mSv (in both cases it concerns the index finger of the left hand).