Calculation of equivalent dose for the lens of the eye in a positron field using EGS5

Abstract

The equivalent dose rate per positron fluence for the human eye lens is calculated using a Monte Carlo simulation code, EGS5, with two mathematical models (a computational head voxel phantom and a simple eye model). The eye lens doses for medical staff and carers as received from a radiopharmaceutical such as 18 F-FDG, which is used in PET examinations, when spilled on the floor, and from positrons passing through a thin injection tube are calculated using a simple eye model. At energies less than 1 MeV, the equivalent dose for the eye lens per electron and positron fluence as calculated using the simple eye model was a maximum of three orders of magnitude lower than that for the head voxel phantom. These values for the simple eye model were equal to the calculation results obtained using the eye lens model in ICRP Publication 116 and those reported in past studies. The eye lens dose rates from the point and tube sources of 18 F-FDG as calculated using our simple eye model are about 0.57 and 0.37 Sv min −1 MBq −1 at 5 cm, respectively. The doses at 10 cm were one-third to half of those at 5 cm.

Current situations and discussions in Japan in relation to the new occupational equivalent dose limit for the lens of the eye

“…Knowledge of exposure of the lens during nuclear medicine diagnostics has not yet been accumulated sufficiently to discuss the equivalent dose to the lens in Japan. There are calculated estimations for 18 F-fluorodeoxyglucose ( 18 F-FDG) used for a positron emission tomography (PET) at medical facilities [42,43]. In those studies, it was estimated that the equivalent dose to the skin (H p (0.07)), at 60 cm from an injection tube became 20% of the dose at 20 cm from the tube [42], and the calculated equivalent dose to the lens (H p (3)) was 70 μSv/min at 5 cm from the tube [43].…”

Determination of a reliable assessment for occupational eye lens dose in nuclear medicine

“…The amount of exposure to each radionuclide was determined in triplicate. The source shape does not affect the equivalent dose of the eye lens if the distance is >30 cm 25 . Nuclear medicine procedures have a high risk of occupational abdominal exposure while dispensing and administering radionuclides to patients 26 .…”

“…These results were normalized to 30 cm from the source to clarify differences among the dosimeters according to the square of the distance from it. If the distance exceeded >30 cm, irradiation doses are uniform independently of the source shape 25 . The dose equivalent of Glass Badge and Luminess Badge dosimeters was used at H p (10) because the energy band for nuclear medicine is adopted H p (10) rather than H p (0.07) in principle.…”

“…The source shape does not affect the equivalent dose of the eye lens if the distance is >30 cm. 25 Nuclear medicine procedures have a high risk of occupational abdominal exposure while dispensing and administering radionuclides to patients. 26 Thus, the syringe source was positioned at 30 cm from the abdomen of the phantom.…”

“…If the distance exceeded >30 cm, irradiation doses are uniform independently of the source shape. 25 The dose equivalent of Glass Badge and Luminess Badge dosimeters was used at H p (10) because the energy band for nuclear medicine is adopted H p (10) rather than H p (0.07) in principle. The exposure was analyzed in terms of the position, type of radionuclide, and type of dosimeter.…”