**8.1 Dosimetry in paediatric nuclear medicine: from acquisition to image processing, image gently**

The radiation burden in nuclear medicine depends principally on the administered radiopharmaceutical properties and the biological parameters-pharmacokinetics properties of the radiopharmaceutical within the patient. So,


To limit radiation exposure to children from diagnostic nuclear medicine procedures to the lowest levels with reliable qualitative imaging, a correlation of administered activity with weight-effective dose in radiopharmaceutical imaging is valued.

Administered activities in paediatric subjects are distributed over smaller volumes generating higher absorbed doses. In diagnostic examinations, fractions of adult administered amounts and formulae based on child's body parameters are used. Recommended activities could be obtained by EANM dosage-card or North American Guidelines—Paediatric dosage card.

Cumulated activity calculation from the time-activity curve will lead to a total number of disintegrations. Absorbed dose algorithms and image processing determine the radiation transport, energy deposition and the radiation burden of the subject; Advanced approaches such as Monte-Carlo modelling in nuclear medicine for imaging and dosimetry are successfully used.

For newborn subjects, it is necessary to apply the minimum dose, because the activity calculated according to newborn weight is less than the recommended minimum activity, resulting to worsen diagnostic imaging quality.

#### **8.2 Optimization—Conclusion**

Optimization in medical imaging is the balancing of the amount of ionizing radiation and image quality. The minimum radiation dose for the paediatric patient must assure that the image quality provides satisfactory information to meet the clinical requirement. Optimization involves both the imaging systems as testing and quality control as well as imaging body parameters and administered activity [25].

Optimal protocols, with improved image reconstruction methods and advanced instrumentation, facilitate the dosage reduction and provide the maximum image quality at a minimum effective dose. Optimization of imaging protocols and establishment of diagnostic reference levels achieve the goals of good quality images at reduced radiation doses. Standardized methods for performing dose calculations for radiopharmaceuticals by various steps in the process and models for calculating time– activity integrals as urinary bladder or intestines can be used [26].

In hybrid imaging PET/CT or SPECT/CT, deep learning-based reconstruction (DLR) may facilitate CT radiation dose reduction in children. Lower-dose DLR images were compared with standard-dose iterative reconstruction images. DLR use at 80-kVp results in substantial dose reduction with preserved or even improved image quality. So, the use of DLR allows greater dose reduction for paediatric CT than current image reconstruction techniques [27].

Clinical dosimetry in targeted radionuclide therapy in children supports the treatment decisions and should be a strong indication that treatment results are dependent on the absorbed dose delivered to the treated organ as well as to the critical organs.

### **Acknowledgments**

D.A. Verganelakis gratefully acknowledges all support provided by the 'ELPIDA' Association of Friends of Children with Cancer and the Oncology Clinic "Marianna V. Vardinoyiannis" at Children's hospital "Aghia Sophia" in Athens.

*Dosimetry*
