**7.2 Dosimetry aspects in hybrid molecular imaging applications in paediatric patients**

Dose reduction in PET/CT and SPECT/CT studies with children can be achieved by optimized CT parameters and the administered activity of the radiopharmaceutical,

#### **Figure 10.**

*Effective doses for ages between 1 and 10 years old.*

#### **Figure 11.**

*(A) Administered Activity (MBq) to patient. Weight in Kg/from neonates to adolescents. (B) Positive relation of the effective dose (mSv) with patients' age (0–26 years). No differences were observed between boys and girls of the same age [18].*

*Nuclear Medicine Dosimetry in Paediatric Population DOI: http://dx.doi.org/10.5772/intechopen.105346*

without compromising the diagnostic information needed for high-quality examination. Effective doses to the paediatric patient examined by PET/CT or SPECT/CT depend on the CT protocol of the accompanying CT scan. The co-registered CT scan can be optimized to meet the patient's diagnostic needs and may be performed either as a diagnostic-type CT scan or as an attenuation-correction only [21].

The hybrid molecular imaging examination by PET or SPECT and the CT should be acquired without child-patient movement. Attention to the respiratory phase during the CT imaging for PET/CT is also of a semantic point.

High-quality biokinetic data must be known for the calculation of dose estimates of new PET radiopharmaceuticals. Then, standardized dosimetry codes as OLINDA/ EXM can provide information of doses to organs and effective doses [22].

In addition to the molecular imaging agents 18F-FDG (PET) and 123I-MIBG (SPECT) that are frequently used in children, other PET and SPECT imaging agents may have promise for molecular imaging in children.


PET/MRI use in children with systemic malignancies may benefit from the reduced radiation exposure offered by PET/MRI. The effective dose of a PET/MRI scan is only about 20% that of the equivalent PET/CT examination. Simultaneous acquisition of PET and MRI data combines the advantages of the two previously separate modalities. One disadvantage of PET/MRI is that in order to have an effect, a significantly longer examination time is needed than with PET/CT. PET/MRI has turned out to be a stable hybrid imaging modality, which generates paediatric safe diagnostic studies [23].

#### **7.3 Foetal doses from nuclear medicine examinations**

Doses are provided for "early pregnancy" (dose to the nongravid uterus in the RADAR reference adult female model) and doses to the foetus at 3, 6, and 9 months of gestation (OLINDA/EXM 2.0 software).

Uncertainties in using these estimates for a specific subject are noteworthy, both in the physiology of the radiopharmaceutical kinetics and in the assumed geometry of the maternal and foetal organs [23].

Foetal whole-body doses from common nuclear medicine examinations in early pregnancy as well as at terms have been calculated by Russell and Stabin using ICRP 53 and ICRP 80.

For Example:

1.A pregnant woman at 4 months' gestation is administered 370 MBq of 18FDG. The estimated foetal dose at 3 months is 4.8 mGy and at 6 months is 3.1mGy. An estimate of 5 mGy is reasonable and conservative [24].


**Figure 12.**

*Foetal thyroid doses for 30MBq 123I or 0.55 MBq 131I in early pregnancy and at 9 months.*

2.Foetal thyroid doses are much higher than foetal whole-body doses, 5–15 mGy/ MBq for 123I and 0.5–1.1 Gy/MBq for 131I (**Figure 12**).
