Assessment of occupational exposure from shielded and unshielded syringes for clinically relevant positron emission tomography (PET) isotopes—a Monte Carlo approach using EGSnrc

Abstract

18F has been the most widely used radionuclide in positron emission tomography (PET) facilities over the last few decades. However, increased interest in novel PET tracers, theranostics and immuno-PET has led to significant growth in clinically used positron-emitting radionuclides. The decay schemes of each of these radioisotopes are markedly different from 18F, with different endpoint energies for the emitted positrons and, in some cases, additional high energy gamma radiation. This has implications for the occupational exposure of personnel involved in the manipulation and dispensing of PET radiopharmaceuticals. The EGSnrc Monte Carlo simulation software was used to estimate the doses to extremities in contact with unshielded and shielded syringes containing 64Cu, 18F, 11C, 13N, 15O, 68Ga and 89Zr, respectively. Dose rates at various distances from the syringe were also modelled, with dose rates reported in terms of eye (Hp(3)), skin equivalent (Hp(0.07)) and deep (Hp(10)) doses. The composition and geometry of the simulated syringe shields were based on a selection of commercially available PET shields. Experimental dose rate measurements were performed for validation purposes where possible. Contact skin dose rates for all isotopes, except for 64Cu, were found to be higher than 18F for the unshielded syringe. The addition of a shield resulted in approximately equal contact skin dose rates for nearly all isotopes, for each shield type, with the exception of 89Zr which was notably higher. Dose rate constants (µGy/MBq.hr) for a range of PET isotopes and shields are presented and their significance discussed.

Personal dosimetry for positron emitters, and occupational exposures from clinical use of gallium-68

“…The standard deviations on each dataset are generally large, implying that for a given clinical procedure the position of the contact is likely to be an important parameter in determining the measured dose. This result is generally commensurate with findings presented elsewhere (McCann et al 2021) for contact H p (0.07) skin doses from unshielded syringes: those data extended from 1.2 to 570 (µSv min −1 ) MBq −1 , which encompasses the narrower current span of 55-184 (µSv min −1 ) MBq −1 . The syringe in (McCann et al 2021) contained ∼2 ml of radionuclide solution rather than 6 ml, leading to a less spatially extended source that causes a higher maximum and a wider range of doses.…”

“…However, these are relatively new radiopharmaceuticals, and as a consequence there is currently a paucity of data on the occupational doses resulting from their routine use, both to the technicians drawing it and the clinicians administering it. Indeed, the authors of the current work were able only to find a limited number of citations relating to its dosimetry (Dwivedi et al 2011, Grosser et al 2020, with a very recent publication (McCann et al 2021) also aiming to address some of these gaps. Moreover, the relative importance of skin (from β + ≲ 1.9 MeV), eye (from 0.8 ≲ β + ≲ 1.9 MeV and 0.511 MeV γ) and body (from 0.511 MeV γ) dose equivalents is also to be further established.…”

Finger doses due to 68Ga-labelled pharmaceuticals in PET departments—results of a multi-centre pilot study

“…The addition of the syringe and vial shielding would have reduced these exposures significantly. In a study by McCann et al [8], H p (0.07) skin dose rate in direct contact with the active volume of an unshielded syringe containing 68 Ga was found to be 34.3 mSv MBq −1 h −1 . The addition of a 7.5 mm W/Cu/Ni syringe shield reduced the skin dose rate at this location to 0.2 mSv MBq −1 h −1 , a factor of approximately 180.…”

“…Centre 4 used a thinner syringe shield (5 mm W) compared to all other centres, whose shields were of the order of 7.5-10 mm W. The thickness and composition of the syringe shield used is known to have a significant impact on the potential occupational exposure [8]. A comparison of the effectiveness of a 5 mm and 7.5 mm W/Ni/Cu syringe shield was performed by the Institute of Radiation Physics, Lausanne, Switzerland [19].…”

“…The use of a syringe shield can significantly reduce the contact skin dose rate for both radionuclides. The thickness and composition of the shield employed has a strong influence on the magnitude of the resultant contact skin dose rate [8,9]. A syringe shield with sufficient thickness to absorb all the high energy positrons from 68 Ga will result in comparable skin exposure for both 18 F and 68 Ga. 68 Ga may require additional manipulation and the handling of much larger activities than routinely seen with the dispensing tasks of 18 F radiopharmaceuticals.…”