A. Chaikh et al.: Radioprotection 2025, 60( 1), 50 – 56 53 Fig. 2. Experimental setup to measure and compare linear attenuation coefficient using RW3 plates( left) and VeroWhite resin( right) with a 6 MV Elekta beam.
Fig. 3. Pictures of the printed bellies over the ATOM phantom and the printed plates( white color) to simulate the 2 nd( on the left) and 3 rd( on the right) trimesters.
where( e) represents the given thickness. The beam size at the isocenter was 3 3cm 2 in order to meet the minimum required size according to the documentation of the ionization chamber used and to always be smaller than the dimensions of the crossed VeroWhite plates.
3 Results
3.1 Modeling bellies for different stages of pregnancy
The ATOM phantom alone represents the first trimester of pregnancy. For a 2-month pregnancy, the fundal height is 8 cm. The printed bellies simulate the 6th and 8th months of pregnancy with fundal heights of 24 and 30 cm, respectively. They were printed to be complementary, that means that the belly of the 3rd trimester is placed above the one of the second trimester. Furthermore, to meet the size constraints of the 3D printer, the belly corresponding to the last trimester is cut into two parts, as well as the printed plates.
For the first trimester, one plate was modeled at the uterus level( ATOM plate number 30) and printed using the dimension of the ATOM ® phantom. For 2 nd, and 3 rd trimesters, two bellies and one other plate( ATOM plate number 25) were modeled and printed, as visualized in Figure 3.
The defined holes were modeled to insert the Farmer( PTW 30013) ionization chamber( 0.6 cc). Note that, each hole has a rod to be plugged in case of non-use. To prevent any difficulty to insert the ionization chamber in the dedicated holes, the rod created for the ionization chamber was cut in half lengthwise.
3.2 Chemical composition and physical density
The chemical composition of the resin, determined by the CHONS analyzer is indicated in Table 1.
The remaining proportion unidentified by the CHONS method( 0.4 %) is attributed to oxygen for the calculated linear attenuation coefficients because the proportion of oxygen was determined subsequently to the other atoms and thus after the calculation of the attenuation coefficients. Thus, the oxygen proportion used was 23,65 % which stay inside the associated uncertainties. Sulfur is below the quantification limit( 0.91 mg ofsulfurforthemassweighed in the analyses).
The density of the resin obtained by the helium pycnometry method was 1.190 ± 0.001 g / cm 3.
3.3 Calculated linear attenuation coefficients
Figure 4a presents the calculated total attenuation coefficients( derived from mass attenuation coefficient using the obtained resin density r = 1.19 g / cm 3) and relative differences for the resin compared to water( H 2 O), as a function of photon energy. The chemical composition of the resin was taken into consideration, as described previously with 23,65 % of oxygen. The relative difference between water and VeroWhite resin attenuation coefficients is within 15 % for photon beams delivered by radiotherapy equipment’ s( between 0.1 and 10 MeV).