# Pediatric Dose Optimization and the Image Gently Campaign

## Introduction

Children are more radiosensitive than adults due to their rapidly dividing cells, longer remaining lifespan for stochastic effects to manifest, and smaller body habitus leading to higher organ doses per unit of administered activity. The Image Gently Campaign, launched in 2008, promotes radiation dose optimization in pediatric imaging, including nuclear medicine, through education, awareness, and evidence-based guidelines.

## Radiobiological Considerations in Pediatric Patients

### Why Children Are More Vulnerable

The higher mitotic rate in growing tissues increases radiation susceptibility. A longer life expectancy provides more time for radiation-induced cancers to develop. Smaller body size means organs are closer to the radiation source, resulting in higher absorbed doses. The thyroid, breast, and gonadal tissues are particularly radiosensitive in children. The effective dose per MBq administered is significantly higher in children than in adults for the same radiopharmaceutical.

### Stochastic Risk Estimates

The lifetime attributable risk of cancer is approximately 2 to 3 times higher for a child compared to an adult receiving the same effective dose. The BEIR VII report estimates a lifetime cancer risk of approximately 5% per Sv for a child under 10 years of age. This risk decreases with increasing age at exposure.

## The Image Gently Campaign

### Origins and Mission

The Image Gently Campaign was founded by the Alliance for Radiation Safety in Pediatric Imaging. It initially focused on CT dose reduction and expanded to nuclear medicine in 2010. The core message is to "child-size the dose" by adjusting administered activity to patient weight. The campaign is a multidisciplinary coalition involving radiology, medical physics, and nuclear medicine societies.

### Image Gently in Nuclear Medicine

The "Go with the Guidelines" initiative promotes standardized pediatric radiopharmaceutical dosing. It endorsed adoption of the North American Consensus Guidelines and the EANM Dosage Card. The campaign promotes minimum administered activities that still yield diagnostic images and encourages technologist and physician education on pediatric-specific protocols.

## Pediatric Administered Activity Guidelines

### North American Consensus Guidelines

The North American approach uses weight-based dosing with a baseline activity multiplied by a weight-dependent factor. Minimum administered activities are specified per radiopharmaceutical to ensure adequate count statistics for diagnostic image quality. For example, Tc-99m DMSA has a baseline of 56 MBq (1.5 mCi) with a minimum of 18.5 MBq (0.5 mCi). Tc-99m MAG3 has a baseline of 37 MBq (1.0 mCi) for direct radionuclide cystography.

### EANM Dosage Card

The European approach uses a class-based system (A, B, C) for activity calculation, with multiples of a baseline activity determined by body weight class. This system generally yields slightly different activities compared to the North American guidelines. Harmonization efforts between North American and European standards are ongoing.

### Key Radiopharmaceuticals and Pediatric Considerations

Tc-99m MDP for bone scanning uses weight-based dosing with a minimum of 40 MBq. Tc-99m DMSA for renal cortical imaging requires a minimum of 18.5 MBq for adequate count statistics. Tc-99m MAG3 for renal function studies requires adequate hydration before and after the examination. F-18 FDG for PET is administered at 3.7 to 5.2 MBq/kg with a minimum of 26 MBq. I-123 MIBG uses weight-based dosing with mandatory thyroid blockade.

| Radiopharmaceutical | Pediatric Dose | Minimum Activity | Special Considerations |
|---|---|---|---|
| Tc-99m MDP (bone) | Weight-based | 40 MBq (1.1 mCi) | Hydration; void before imaging |
| Tc-99m DMSA (renal cortex) | Weight-based | 18.5 MBq (0.5 mCi) | Image at 2–4 hours |
| Tc-99m MAG3 (renal function) | Weight-based | 37 MBq (1.0 mCi) | Hydration; bladder catheter if needed |
| Tc-99m MAA (lung perfusion) | Weight-based; reduce particles | 10–50 MBq | Reduce to 10,000–50,000 particles in neonates |
| F-18 FDG (PET) | 3.7–5.2 MBq/kg | 26 MBq (0.7 mCi) | Fast 4–6 h; sedation protocol if needed |
| I-123 MIBG | 5.2 MBq/kg | 37 MBq (1.0 mCi) | Thyroid blockade mandatory |
| Tc-99m pertechnetate (Meckel) | Weight-based | 9.3 MBq (0.25 mCi) | Pentagastrin or cimetidine pretreatment |

## Technical Strategies for Dose Optimization

### Acquisition Optimization

High-sensitivity collimators should be used when spatial resolution is less critical, as they allow adequate image quality with lower administered activities. Acquisition time can be increased to compensate for reduced administered activity. Iterative reconstruction algorithms improve image quality at lower counts compared to filtered back-projection. Three-dimensional SPECT/CT improves lesion detection and reduces the need for repeat studies.

### Equipment Considerations

Solid-state CZT detectors offer improved sensitivity and energy resolution compared to conventional sodium iodide detectors. Digital PET systems with silicon photomultipliers achieve higher sensitivity, allowing further dose reduction. Low-dose CT protocols should be used for attenuation correction and anatomic localization. Age-appropriate immobilization devices minimize motion artifacts and the need for repeat imaging.

### Sedation and Patient Preparation

The need for sedation should be minimized through child-friendly environments and age-appropriate preparation. When sedation is required, its timing should be coordinated with radiopharmaceutical uptake periods. Adequate hydration and voiding are essential to reduce bladder and gonadal radiation dose. The "feed and wrap" technique is effective for achieving adequate immobilization in infants under 6 months.

## CT Dose Considerations in Hybrid Imaging

The CT component of SPECT/CT and PET/CT contributes additional radiation beyond the radiopharmaceutical dose. Low-dose, non-diagnostic CT should be used for attenuation correction when possible. CT parameters including kVp and mAs should be adjusted based on patient weight. Non-CT alternatives such as transmission sources should be considered when available.

## Quality Assurance and Institutional Protocols

Written pediatric protocols should be established for each radiopharmaceutical. Regular audits of administered activities against published guidelines ensure compliance. Technologist training specific to pediatric nuclear medicine is essential. Participation in dose registries such as the ACR Dose Index Registry supports benchmarking. Communication with referring physicians about the benefits and risks of nuclear medicine studies facilitates appropriate utilization.

## Clinical Pearls

Weight-based dosing with defined minimum activities should always be used for pediatric nuclear medicine studies. Adult doses should never be scaled down arbitrarily.

The Image Gently campaign emphasizes that diagnostic image quality can be maintained with reduced administered activities through technical optimization such as longer acquisition times and iterative reconstruction.

The CT component of hybrid SPECT/CT or PET/CT may contribute significantly to total radiation dose in children and should be minimized using low-dose protocols.

Thyroid blockade is mandatory before I-123 or I-131 MIBG administration in children to protect the highly radiosensitive pediatric thyroid.

## References

1. Gelfand MJ, et al. "Pediatric Radiopharmaceutical Administered Doses: 2010 North American Consensus Guidelines." *J Nucl Med*. 2011;52(2):318-322.
2. Lassmann M, et al. "The New EANM Paediatric Dosage Card." *Eur J Nucl Med Mol Imaging*. 2007;34(5):796-798.
3. Fahey FH, et al. "Dose Estimation in Pediatric Nuclear Medicine." *Semin Nucl Med*. 2017;47(2):118-125.
4. Frush DP, et al. "The Image Gently Campaign: Increasing CT Radiation Dose Awareness Through a National Education and Awareness Program." *Pediatr Radiol*. 2008;38(3):265-269.