52 A. Chaikh et al.: Radioprotection 2025, 60( 1), 50 – 56 Fig. 1. Representation of the 3D modeling bellies placed over the ATOM ® phantom. The fundal heights value and its representation are shown in red, and the green points present the holes used to place the ionization chamber and measured dose.
dosimetry( Mayer et al., 2015) and to assess the thyroid dose to children using 131 I( Beaumont et al., 2017).
2.4.1 Chemical composition and physical density
The chemical composition of the resin was determined by a CHONS( Flashsmart model, Thermoscientific) analyzer. Few milligrams of resin sample is weighed with a microbalance into a tin capsule, which is then introduced into an oxidation / reduction reactor heated to 950 ° C. A controlled supply of oxygen causes the tin to oxidize, an exothermic reaction that raises the temperature to 1800 ° C. At this temperature, organic and inorganic substances are converted into gases( CO 2, N 2, H 2 O, SO 2) which, after reduction, are separated on a gas chromatography column and finally detected by a thermal conductivity detector. The oxygen is quantified in a special pyrolysis reactor heated to 1065 ° C in an oxygen-free environment. A catalyst ensures the conversion of oxygen into CO, which is separated and detected with the gas chromatography with thermal conductivity detector.
The density of the resin was measured using the helium pycnometry method. Gas pycnometry( AccuPyc II 1340 model, MICROMERITICS) is used to determine the true – or skeletal – density of solid materials, which is the mass of solid material divided by its volume minus the free volume. A sample is placed in a chamber of known volume, which is sealed and pressurized. The gas fills the empty spaces within and between the sample particles. The sample chamber is then expanded to an adjoining reference chamber of known volume. The change in pressure is used to calculate the volume of the sample. Skeletal density is calculated from the sample mass and the volume it occupies. This method is useful for determining the skeletal density of materials, even those with small pores and irregular shapes.
2.4.2 Calculated and measured attenuation coefficients
To assess the water dosimetric equivalence of the VeroWhite resin, two distinct methods were used: by calculation means using the chemical composition and by measurements of the attenuation.
In the first method, the percentage of each chemical element is used to determine the linear attenuation coefficients( m) as a function of photon energy. The linear attenuation coefficients of each chemical element were taken from data available on the NIST( National Institute of Standards and Technology) website 5.
In the second method, the measurements were carried out using Synergy Elekta accelerator with 6 MV photon beam whom quality index is 0.685. In this case, a semiflex ionization chamber 31010( 0.125 cc) was positioned at a depth of 3 cm within a block of 5 cm RW3 plates, as described in Figure 2. Then, various thicknesses( up to 21 cm) of RW3 plates or VeroWhite printed plates were placed above the block to measure the attenuation of the beam. The measured charge( I 0) without added plates was taken as the reference one. Then, for each thickness( x) of RW3 or printed plates, the collected charge( I) was measured. The attenuation coefficient can be calculated, as the collected charge is directly proportional to the incident fluence, assuming that the beam spectrum is identical for the various measurements performed. The linear attenuation coefficient in cm �1( m) was calculated as given by the Beer – Lambert’ s law( Alshipli et al., 2018) using the following equation: m ¼ 1 x ln I
0 ð1Þ
I
However, it should be noted that the experimental conditions differ slightly between the two sets of measurements due to the difference in dimensions between the RW3 plates and the available VeroWhite resin elements( Fig. 2). The RW3 plates have a volume of 30 30 1cm 3 whereas the printed plates of VeroWhite have a volume of 3 3 e cm 3,
5 https:// physics. nist. gov / PhysRefData / FFast / html / form. html.