Figure 1
Magnified view of the computational phantom’s lower abdomen and pelvis viewed as rendered polygon mesh in the computer 3D modeling software, showing the position of the 18-week-old fetus (in RST position) and placenta in relation to the uterus and the body of the mother. The fetus is shown in light gray colour, the amniotic fluid in transparent blue, the placenta in green, the uterus in transparent purple, and the body of the mother in olive green color.
Figure 2
The mesh version of the Tena phantom without skin and soft tissues (A) and with the skin and soft tissues that are shown in transparent light brown color (B). The uterus is shown in transparent purple for a better view of the fetus and its position in space and in relation to other organs.
Table 1
List of the tissues and organs in our developed mesh pregnant female phantom in 2nd trimester (Tena), including volume, mass (calculated as the product of tissue density according to ICRP 89 and segmented organ volume) and surface area
| Tissue/organ | Volume (cm3) | Mass (g) | Surface area (cm2) |
|---|---|---|---|
| Adrenal glands | 5.1 | 5.2 | 40.2 |
| Amniotic fluid | 423.4 | 423.4 | 381.7 |
| Blood vessels/blood | 806.4 | 854.8 | 1739.3 |
| Bones, cortex (including | |||
| proximal humerus and femoral | 2443.4 | 4691.4 | 10667.3 |
| heads) | |||
| Bone marrow (including proximal humerus and femoral | 723.4 | 724.4 | 2365.7 |
| heads) | |||
| Central nervous system (brain and spinal cord) | 1156.3 | 1214.1 | 752.4 |
| Colon, content | 454.2 | 472.4 | 825.5 |
| Colon, wall | 287.2 | 298.7 | 1914.3 |
| Esophagus, content | 4.4 | 0 | 42.0 |
| Esophagus, wall | 12.2 | 12.5 | 123.3 |
| Eyeballs | 12.4 | 13.1 | 32.9 |
| Fetus, 17 week old | 123.0 | 129.2 | 200.6 |
| Gall bladder, content | 15.5 | 15.9 | 42.3 |
| Gall bladder, wall | 15.6 | 16.1 | 104.1 |
| Kidneys | 312.3 | 327.9 | 340.4 |
| Liver | 1780.4 | 1869.5 | 1133.2 |
| Lungs | 3937.1 | 1515.8 | 2385.4 |
| Myocardium | 221.6 | 232.7 | 804.1 |
| Pancreas | 85.2 | 89.4 | 161.3 |
| Parotid glands | 24.1 | 24.9 | 64.8 |
| Placenta | 142.7 | 145.5 | 216.8 |
| Soft tissue tissues and (skin) muscles, adipose | 36080.41 | 36802.02 | 39186.9 |
| Spleen | 391.2 | 406.9 | 345.0 |
| Stomach, duodenum and small intestine, content | 570.3 | 593.1 | 1176.1 |
| Stomach, duodenum and small intestine, wall | 425.2 | 442.2 | 2717.9 |
| Submandibular glands | 5.3 | 5.5 | 22.0 |
| Thyroid gland | 10.0 | 10.4 | 3990.0 |
| Upper airways (nasal cavity, | |||
| pharynx and larynx) and | 136.9 | 0.1 | 426.7 |
| trachea/air | |||
| Urinary bladder, content | 11.1 | 11.6 | 38.6 |
| Urinary bladder, wall | 21.5 | 22.2 | 104.7 |
| Uterus (myometrium) | 552.5 | 580.1 | 917.6 |
[i] 1 obtained by subtracting the sum of the volumes of all segmented organs and the total volume of the body;
2 product of volume and 1.02 g/cm3 which is the average value of muscle tissue density (1.050 g/cm3), adipose tissue density (0.950 g/cm3) and skin density (1.060 g/cm3)
Figure 3
Voxelized phantom displayed using MCNP plotter.
Figure 4
Beam arrangements in Eclipse.
Figure 5
Beam Eye View of Field F1, where leafs are represented as transparent rectangles with blue edges. And PTV is colored in green.
Table 2
Tena phantom formats and their characteristics
| Mesh format | DICOM | Voxelized |
|---|---|---|
| N° vertices1: 2889437 N° faces1: 5777800 | Slice thickness: 0.625 mm Distance between slices: 1.867 mm Matrix: 512 x 512 Pixel dimensions: 0.82 mm | Grid size: 219 x 148 x 479 N° voxels: 1.55*10-7 Isovoxel size: 0.186 cm |
[i] 1 variable, could be decimated and adjusted to the computing power of the used computer
Table 3
Contribution of each field to the fetal dose. Fetus and breast doses are normalized per source particle, field contribution to the breast dose is obtained from treatment planning system (TPS), and the breast/fetus ratio is calculated from normalized breast and fetus doses
| Field | Fetus dose per source particle [Gy/SP] 10-19 | Breast dose per source particle [Gy/SP] 10-19 | Field contribution to breast dose1 | Fetus dose normalized to field contribution [Gy/SP] 10-19 | Breast dose normalized to field contribution [Gy/SP] 10-19 | Ratio fetus / breast dose [mGy/Gy] |
|---|---|---|---|---|---|---|
| F1 | 1.45 ± 0.12 | 1000 ± 90 | 0.437 | 0.634 ± 0.054 | 437 ± 37 | 1.44 |
| F2 | 1.05 ± 0.09 | 1070 ± 90 | 0.378 | 0.399 ± 0,035 | 404 ± 36 | 0.99 |
| F3 | 1.03 ± 0.08 | 993 ± 80 | 0.064 | 0.066 ± 0,005 | 63.5 ± 5 | 1.03 |
| F4 | 0.270 ± 0.02 | 1010 ± 80 | 0.057 | 0.015 ± 0.001 | 57.3 ± 4 | 0.27 |
| F5 | 0.854 ± 0.07 | 449 ± 40 | 0.064 | 0.055 ± 0,005 | 28.7 ± 2 | 1.91 |
| Total | 1.169 ± 0.064 | 992.5 ± 52 | ||||
| Total normalized | to prescribed dose | 58.9 ± 3.7 mGy | 50 Gy* |
[i] 1 obtained from TPS
Table 4
Relative contribution to the absorbed dose in the fetus (%) originating in the linac or the phantom. The ratio for each field of photons originating in linac or phantom is given in the last row
| F1 | F2 | F3 | F4 | F5 | Overall | |
|---|---|---|---|---|---|---|
| Linac (%) | 6.0 | 2.1 | 0.8 | 0.3 | 0.3 | 9.5 |
| Phantom (%) | 37.7 | 35.7 | 5.6 | 5.4 | 6.1 | 90.5 |
| Contribution ratio | 16.12 | 5.8 | 14.3 | 5.5 | 4.9 |
Figure 6
Spectra for F1 of the photons coming from the accelerator head and all the photons reaching the fetus (A); Photon spectra in fetus for each field (B).