Definition of a source region for the lacrimal glands based on the ICRP adult reference voxel phantoms for use in internal dosimetry

Objectives: The lacrimal gland is an exocrine gland, which releases it secretions directly into the eyeball. Lacrimal glands play an essential role in maintaining the normal anatomy and function of the eye and are an important part of the lacrimal system. Dacryoscintigraphy or lacrimal scintigraphy is a nuclear medicine procedure to image the lacrimal system to diagnose abnormalities that cause epiphora (pathological overflow of tear). It has also been shown that diagnostic examinations with ⁶⁷Ga-citrate have an increased lacrimal gland uptake also in patients without ocular pathology. Other radiopharmaceuticals that have been reported to show lacrimal gland uptake are ⁶⁸Ga-PSMA and ^99mTc-HMPAO as well as sodium iodide and pertechnetate. The lacrimal glands have not been considered to be a radiosensitive organ for stochastic effects and thus it has not been included as a source or target region in the ICRP/ICRU adult reference voxel phantoms. To be able to estimate the absorbed dose contribution from the lacrimal glands to other organs and tissues, a computer program developed. The purpose of the computer program was to create a source region for the lacrimal glands in the adult reference phantoms to facilitate absorbed dose estimations from specific uptake in the lacrimal glands.

Methods: A computer program was developed for the adult male and female reference voxel phantoms where each transaxial slices was shown in color. The lacrimal glands were created based on the information given by Bingham et al. (Ophtal Plast Reconstr Surg 29, 157-159, 2013). The data was saved as a source file in the Monte Carlo simulation program MCNP, allowing a uniform distribution of activity within the lacrimal glands. The lacrimal glands were just created as a source region without changing the anatomy of the reference phantoms. Specific absorbed fractions were generated for photons, electrons and alpha particles enabling the use for arbitrary radionuclides.

Results: For gallium-68 the absorbed dose was estimated for 30 different organs and tissues from homogeneously distributed decays in the lacrimal glands. The organ and tissue which received the highest absorbed doses was extrathoracic region, lenses of the eyes, oral mucosa, brain, red bone marrow and salivary glands, respectively

Conclusions: A source region for the lacrimal glands was developed to estimate the absorbed doses to other organs and tissues. Creating a source region for the lacrimal glands based on the adult reference phantoms enables more realistic absorbed dose estimations than before.

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