Obtaining the national metrological traceability chain
associated to the dosimetry of the eye lens by creating high-precision dosimetry phantoms,
using state-of-the-art 3D printing techniques

As it is known, the public health sector is strongly supported and addressed by all the member states of the European Union (EU). One of the very important aspects related to the public health that must be carefully addressed, is the one related to the exposure to ionizing radiation. In order to provide support in this matter for all the member states, EU issued the Council Directive 2013/59/Euratom, which lays down basic safety standards (BSS) for protection against the dangers arising from exposure to ionizing radiation. The practical implementation of the provisions of the Council Directive 2013/59/EURATOM (transposed at the national level by the Ministry Order no. 752/3978/136 from 2018) is a challenging task for all the EU member states. Due to this fact, the technical support of as many as possible international experts, from different institutions and organizations is strongly needed. Many international organizations, institutes and professional associations are fully involved in this matter. In this project, we intend to focus specifically on a subject that still did not reach its maturity level, the one related to the exposure of the human eye to ionizing radiation fields. As it is known, the human eye is exposed to ionizing radiation in many situations as: in medical procedures (both patients and medical staff), in industry, in applied nuclear physics research, etc. One of the most radiation-sensitive parts of the human eye is the eye lens, which starts to show degradations when being exposed to low dose levels (e.g., radio-induced cataract). Latest studies showed even lower threshold values that it was thought before . As a consequence, the dose limitation for eye lens recommended by International Commission on Radiation Protection (ICRP) was set to a conservative safer value of 20 mSv/year (occupational exposure, over 18 years old), which was lowered from the previous value of 150 mSv/year. For under 18 years old professionals, the new threshold was recommended to be set at 15 mSv/year, rather than 50 mSv/year (previous value). For general public exposure, the recommended value remains at 15 mSv/year. Even so, the ALARA (“As Low As Reasonable Achievable”) concept is the essence of the radiation protection culture. It means one must avoid being exposed to ionizing radiation as much as possible, first due to the fact that the dose is a cumulative quantity and secondly that the damaging effect to the human cells must be considered not only from the deterministic point of view, but also from the stochastic one. The exposure to ionizing radiation could not always be avoided by for example, the professionals who are working in ionizing radiation related fields. In this situation, in order to take the best possible radiation protection measures, knowing the dose rates that a person deals with, as precise as it can be determined, is a very important task that needs to be fulfilled. In order to develop proper and metrological traceable methods for making these kinds of determinations, involvement of the national metrology institutes is strongly required. In Romania, at the national level, all the ionizing radiation-related metrology activities are performed within IFIN-HH.

As it is well known, cataract is defined as the “loss of transparancy of the eye lens” and starts with lens opacity. Cataract is the most frequent cause for blindness worldwide. When the eye lens starts to lose its transparency, some optical phenomena occure, which lead to the scattering of the light, when it enters into the eye. The scattering of the light means that only a part of the incident light will reach the sensitive part of the eye where the image is actually forming, the retina. The associated symptoms are a foggy sight that by the time goes by, will lead to blindness.

Trying to provide support for monitoring the dose to the eye lens, the International Organization for Standardization issued ISO 15382:2015 "Radiological protection - Procedures for monitoring the dose to the lens of the eye, the skin, and the extremities". Its practical implementation is still difficult and a challenge, mostly due to the limitation of the actual dose-measuring devices and even more important, due to the lack of the calibration protocols [4]. At this moment, for measuring the dose uptaken by the eye lens, few external devices are used.

The quantity related to the exposure of eye lens to ionizing radiation that needs to be known is HT,eyelens (equivalent dose at the eye lens). Also, Hp(3) (equivalent dose at 3 mm depth) needs to be considered, but only as an operational quantity. Only few dosimeters are designed for Hp(3). Therefore Hp(3) is rarely used, but their availability is now started to increase. None of HT,eyelens and Hp(3) are directly measurable quantities (expressed in Sieverts [Sv]), being calculated from the directly measured quantity called absorbed dose (using constants). Absorbed dose (D, expressed in Gray [Gy]) is basically defined as the energy deposited by the ionizing radiation (E, expressed in Joules [J]) divided by the the mass of the exposed material (m, expressed in kg).

In order to provide precise measurements of the absorbed dose, the used devices need to be appropriately calibrated and to be traceable to national and international dosimetry standards (national metrology institutes). Reliable calibration factors must be provided, mainly taking into account the fact that the used dosimeters are not exactly positioned as the eye lens and also the measured value must be correlated to both eyes (the uniformity of the ionizing radiation field must be precisely determined).

By solving the above mentioned issues, the scientific research related to the eye lens dosimetry will be strongly addressed: metrology research, detectors research, radiobiology research, radiation protection research and medical research. From the technological and socio-economic point of view, new metrology services will be available.