Table 2.
Summary of organs in the computer models of the two patients.
| Organ∕structure | Density (g cm−3) h | Material (ICRU 46)h | Mass (g)10 | |
|---|---|---|---|---|
| Newborn (5 weeks, female) | Teenager (12years, male) | |||
| Respiratory system | ||||
| Pharynx-larynxa | 1.03 | Average soft tissuei | 1.6 | 17.3 |
| Trachea-bronchi | 1.03 | Average soft tissue | 1.0 | 13.7 |
| Lungs | 0.26 | Lung (adult, healthy, inflated) | 57.9 | 445.3 |
| Alimentary system | ||||
| Esophagus | 1.03 | Average soft tissue | 1.5 | 18.0 |
| Stomachb | 1.03 | Average soft tissue | 39.4 | 282.9 |
| Pancreas | 1.03 | Average soft tissue | 9.2 | 82.1 |
| Liver | 1.03 | Average soft tissue | 104.5 | 961.5 |
| Gall bladder | 1.03 | Average soft tissue | 4.1 | 24.6 |
| Small intestine | 1.03 | Average soft tissue | 70.7 | 558.3 |
| Large intestine | 1.03 | Average soft tissue | 63.9 | 436.5 |
| Circulatory system | ||||
| Heart | 1.03 | Average soft tissue | 51.2 | 459.8 |
| Urogenital system | ||||
| Kidneys | 1.03 | Average soft tissue | 21.5 | 189.3 |
| Urinary bladder | 1.03 | Average soft tissue | 5.4 | 63.8 |
| Prostatec | 1.03 | Average soft tissue | – | 3.1 |
| Testes | 1.03 | Average soft tissue | – | 3.9 |
| Ovaries | 1.03 | Average soft tissue | 0.5 | – |
| Uterus | 1.03 | Average soft tissue | 3.2 | – |
| Vagina | 1.03 | Average soft tissue | 0.4 | – |
| Skeletal systemd | ||||
| Cranium | 1.4h | Average skeletonh | 257.5 | 941.9 |
| Mandible | 1.4 | Average skeleton | 20.5 | 99.4 |
| Clavicles | 1.4 | Average skeleton | 1.2 | 42.9 |
| Scapulea | 1.4 | Average skeleton | 6.3 | 164.6 |
| Sternum | 1.4 | Average skeleton | 2.5 | 32.1 |
| Ribs | 1.4 | Average skeleton | 25.5 | 302.9 |
| Cervical vertebrae | 1.4 | Average skeleton | 7.1 | 74.4 |
| Thoracic vertebrae | 1.4 | Average skeleton | 23.5 | 233.7 |
| Lumbar vertebrae | 1.4 | Average skeleton | 16.6 | 186.7 |
| Pelvis | 1.4 | Average skeleton | 25.6 | 492.6 |
| Sacrum | 1.4 | Average skeleton | 10.9 | 152.7 |
| Upper humeri | 1.4 | Average skeleton | 5.1 | 175.9 |
| Lower humeri | 1.4 | Average skeleton | 3.7 | 125.1 |
| Radii, ulnae | 1.4 | Average skeleton | 6.1 | 185.9 |
| Wrist and hand bones | 1.4 | Average skeleton | 4.6 | 132.1 |
| Upper femora | 1.4 | Average skeleton | 10.9 | 439.6 |
| Lower femora | 1.4 | Average skeleton | 15.0 | 543.9 |
| Tibiae, fibiae, patellae | 1.4 | Average skeleton | 21.5 | 765.5 |
| Ankle and foot bones | 1.4 | Average skeleton | 12.1 | 420.1 |
| Integumentary system | ||||
| Skin (torso only)e | 1.03 | Average soft tissue | 49.3 | 452.4 |
| Additional organs∕tissues | ||||
| Brain | 1.03 | Average soft tissue | 400.3 | 1488.4 |
| Eyes | 1.03 | Average soft tissue | 6.8 | 14.6 |
| Thyroid | 1.03 | Average soft tissue | 1.6 | 11.2 |
| Breastsf | 0.96 | Breast (50∕50) | 0.7 | 2.2 |
| Thymus | 1.03 | Average soft tissue | 16.3 | 37.5 |
| Spleen | 1.03 | Average soft tissue | 8.1 | 215.1 |
| Adrenal glands | 1.03 | Average soft tissue | 6.5 | 10.6 |
| Residual soft tissuesg | 1.03 | Average soft tissue | 2348.2 | 30 226.5 |
Combined organ of pharynx and larynx, combined organ of trachea and bronchi, and esophagus were modeled as tubular organs with air-fill lumens. The wall thickness of these tubular organs was assumed to be 2 mm for the newborn and 3 mm for the teenager. It was independently verified that, over the range of 1–3 mm, the effect of wall thickness on organ dose was less than 1%. Dose to combined organ of pharynx and larynx was used as a surrogate for dose to salivary glands, oral mucosa, and extrathoracic (ET) region.
Alimentary tract organs (stomach, small intestine, large intestine), heart, gall bladder, and urinary bladder were modeled as single homogenous organs without delineation of walls and contents. For alimentary tract organs, dose to the entire organ (wall and content) was used to approximate the dose to the radiosensitive wall lining. This is a reasonable approximation since the wall and the content are located in parallel to each other.
Prostate, testes, ovaries, uterus, and vagina are gender-specific organs and were included in the models of their respective genders only.
The skeleton was modeled as a homogeneous mixture of its component tissues, namely, cortical bone, trabecular bone, yellow marrow, red marrow, and various connective tissues. The atomic composition and mass density data published by Cristy and Eckerman (Ref. 5) for the skeletons of newborn and adult were used for the newborn and the teenager patients, respectively.
The torso of the NURBS model of each patient was covered with a skin layer to allow dose estimations for the skin. The skin thickness was assumed to be 1 and 2 mm for the newborn and the teenager patients, respectively, resulting in a 1–2 voxel definition of the skin in the Monte Carlo simulations. Whole body skin dose was calculated as torso skin dose multiplied by the ratio of torso skin area to whole body skin area, where skin areas were estimated from the NURBS model of each patient.
The breasts of each patient were located based on the body surface contours of the patient in his∕her CT images and relative to the locations of other organs. They were modeled as homogenous organs with elemental composition defined according to the 50∕50-breast in ICRU Publication 46 (Ref. 18). Since glandular breast tissue only starts developing in puberty (Ref. 46), the breasts of the newborn patient were likely to have little glandular tissue; however, in the BEIR VII report (Ref. 22), the lifetime attributable risk of breast cancer is the highest at age of zero. Thus, even the breast tissue of a newborn has some radiosensitive structure, the dose to which was approximated by the dose to a 50∕50-breast.
Residual soft tissues included skeletal muscle, adipose tissue, cartilage, blood, lymphatic tissues, and connective tissues. Dose to residual soft tissues was used to approximate dose to skeletal muscle and lymphatic nodes.
The atomic composition and mass density data tabulated in ICRU Publication 46 (Ref. 18) were used for all organs and tissues with the exception of the skeleton (see footnote d).
Average soft tissue of adult male was used.
Organ∕tissue mass in the voxel models.