In the field of nuclear medicine, radiation is utilized for diagnostic and therapeutic applications. Because ioniz- ing radiation can cause biological effects, ensuring safety through comprehensive radiation protection programs is critical. International radiation protection guidance is- sued by the IAEA and ICRP classifies radiation exposure in nuclear medicine into three principal categories: medi- cal exposure, occupational exposure, and public exposure. Each type requires distinct safety measures and regulatory control to ensure compliance with international standards.

Medical exposure involves the deliberate application of ionizing radiation to patients for diagnostic imaging, ther- apeutic procedures, or biomedical research activities. For example, patients may receive ⁹⁹mTc-MDP for bone imag- ing or ¹³¹I for thyroid ablation. Both the IAEA and ICRP highlight the importance of justification, whereby each procedure must provide a clinical benefit that exceeds the associated radiation risk (ICRP, 2007).

Occupational exposure refers to radiation doses incurred by workers because of their professional activities, includ- ing nuclear medicine technologists, radio pharmacists, and physicians. Such personnel are subject to continuous mon- itoring and protection through optimization strategies based on the ALARA (As Low as Reasonably Achievable) concept. ICRP Publication 103(ICRP, 2007) defines an oc- cupational effective dose limit of 20 mSv per year, averaged over five years, with a maximum of 50 mSv permitted in any single year. Safety measures include personal dosim- etry, use of shielding, and minimizing time near sources.

Public exposure includes radiation doses received by in- dividuals who are neither occupationally exposed nor un- dergoing medical procedures, such as visitors or members of the public. Regulatory frameworks impose strict limits on public exposure, restricting the annual effective dose to a maximum of 1 mSv. Control measures include waste management, shielding design, and restricting access to radiation-controlled areas.

The IAEA in 1999 emphasized the importance of compre- hensive radiation protection programs in nuclear medicine facilities to ensure safety across all exposure types. Such programs are founded on the three fundamental radiation protection principles: justification, optimization, and dose limitation. They also ensure adherence to local and inter- national safety standards through measures such as facil- ity shielding, worker training, quality assurance, and in- cident reporting. Implementing such programs promotes both patient safety and occupational and public health. In modern nuclear medicine, radiopharmaceuticals play a vital role in diagnosing and treating many diseases. To use these materials safely and effectively, strong radiation protection programs must be established based on the core

principles of justification, optimization, and dose limita- tion. These measures are crucial to maximize the benefits of nuclear medicine while reducing radiation risks to pa- tients, healthcare workers, and the public.

Diagnostic nuclear medicine procedures involve the ad- ministration of radiopharmaceuticals that deposit ionizing radiation energy in patient organs. These internal expo- sures contribute to stochastic risk and are quantified using the effective dose (E), which represents the weighted sum of equivalent doses to individual organs based on tissue ra- diosensitivity (Alnaaimi et al., 2022). ICRP recommends using E to compare and optimize medical exposures. Pa- tient radiation dose depends on administered activity, iso- tope physical half-life, and biokinetics in the body. Inter- national guidance emphasizes justification of each imaging study and optimization of activity (ALARA) (Alnaaimi et al., 2022). Recent compendia (ICRP 128, 2015) provide updated dose coefficients for diagnostic radiopharmaceu- ticals (Cherry et al., 2012).

In clinical practice, administered activities are adjusted ac- cording to patient age and body size, with pediatric pro- tocols commonly scaling activity by body weight or body surface area. Reference values exist for typical adult and pediatric administered activities. However, it is important to verify that these protocols yield effective doses consis- tent with expectations.

Commonly used radiopharmaceuticals such as Techne- tium-99m (⁹⁹mTc), Iodine-131 (¹³¹I), and Fluorine-18 (¹⁸F- FDG) exhibit relatively short physical half-lives (6 hours, 8 days, and 110 minutes, respectively). Each radiophar- maceutical has specific diagnostic and therapeutic appli- cations: ⁹⁹mTc-sulfur colloid is employed for liver, spleen, and bone marrow imaging; ⁹⁹mTc-MIBI is used in cardiac, neuroendocrine tumors, and breast imaging; ¹³¹I is applied in the treatment of thyroid-related disorders and certain cancers; and ¹³¹I-MIBG serves as a targeted radiotherapy agent for neuroendocrine tumors. Additionally, ¹⁸F-FDG PET offers essential insights into tumor metabolism, com- plementing traditional methods. Diagnostic benchmarks have been set for various cancer-related uses (Elhaie et al., 2024). Although technical improvements continue, ¹⁸F- FDG PET increasingly integrates into multimodal cancer diagnosis protocols as recommended by guidelines.

Several studies, including those by Cherry et al. (2012); Ali et al. (2021) and Shin et al. (2025), have focused on dose assessment methodologies, age-specific biokinetics, and occupational exposures during diagnostic and therapeu- tic procedures. These investigations highlight the ongoing need to refine dosimetric techniques and enhance the ac- curacy of radiation dose estimation for both patients and medical personnel.

This study recalculates age-dependent and comparison

with published reference values of effective doses for rep- resentative nuclear medicine diagnostic procedures using updated ICRP-103/106/128-based dosimetric methodol- ogy integrated within RADAR-2017 simulations. Effec- tive doses were estimated for adult and pediatric reference phantoms for four commonly used radiopharmaceuticals:

⁹⁹mTc-sulfur colloid, ¹⁸F-FDG, ⁹⁹mTc-MIBI, and ¹³¹I-MIBG. The objectives were to quantify age-related dose variations, compare recalculated values with published benchmarks, and evaluate optimization strategies for improving radia- tion protection and dose management in routine clinical nuclear medicine practice.

Unlike previous studies that typically evaluate individual radiopharmaceuticals or specific imaging procedures, the present work provides a unified reassessment of effective doses across multiple diagnostic nuclear medicine exami- nations using current ICRP-based dosimetric methodol- ogy. By combining standardized phantom calculations, contemporary biokinetic models, systematic benchmark- ing against published reference values, and age-depen- dent comparisons, the study offers an updated dosimetric framework that supports radiation protection assessments, protocol benchmarking, and future development of pa- tient-specific optimization strategies.

This study was designed as a computational dosimetric reassessment of effective doses associated with commonly performed diagnostic nuclear medicine procedures. No patient-specific imaging data or clinical measurements were collected. Instead, effective doses were calculated us- ing standardized anthropomorphic reference phantoms, published biokinetic models, and internationally recom- mended dose coefficients. The objective was to provide a consistent comparison of age-dependent effective doses across multiple diagnostic radiopharmaceuticals using a unified dosimetric methodology based on current Inter- national Commission on Radiological Protection (ICRP) recommendations.

The effective dose has been calculated based on the ad- ministered activity per body weight for various age groups: adults (73.7 kg), 15-year-olds (56.8 kg), 10-year-olds (33.2 kg), 5-year-olds (19.8 kg), and infants (1 year, 9.7 kg) (Han et al., 2006). Equation (2) describes pediatric activity scal- ing based on linear body-mass proportionality, whereby the administered activity for a child is calculated as the product of the standard adult activity and the ratio of child-to-adult body weight. This approach assumes approximate propor- tionality between patient mass and radiopharmaceutical distribution volume and is widely used for practical op- timization of pediatric administered activities. Although this method reduces injected activity in smaller patients, the resulting effective dose does not decrease proportion- ally because pediatric dose coefficients are generally higher due to smaller organ size, reduced photon attenuation, and increased tissue radiosensitivity (Verganelakis and Lyra- Georgosopoulou, 2022; Fahey et al., 2017).

(2)

99mTc-sulfur colloid (liver–spleen scan): The effective dose from intravenous injection administration of 99mTc sulfur colloid to varies age group patients shown in Table (1). The effective doses from 99mTc-sulfur colloid decrease from 2.1 mSv in adults to 1.1 mSv in 1-year-old patients due to re- duced administered activity. RADAR-2017 estimates agree closely with ICRP-128 reference values, confirming meth- odological validity. Despite lower absolute doses in chil- dren, dose per MBq remains higher due to smaller body mass.

18F-FDG PET scan: The effective dose resulting from the in- travenous administration of 18F-FDG was assessed across var- ious patients age groups (Table 2). Adult effective dose was 4.8 mSv, while pediatric doses reached up to 4.5 mSv despite lower administered activity. For pediatric patients, the administered activity was reduced proportionally according to body-weight scaling, decreasing from 203 MBq in 15-year-olds to 71 MBq in 5-year-olds. Despite this substantial reduction in injected activity, the effective dose decreased only modestly, from 4.5 mSv in 15-year-olds to 3.4 mSv in 5-year-olds. This relatively limited reduction indicates that decreasing administered ac- tivity does not produce a directly proportional reduction in radiation burden. Pediatric patients exhibit higher absorbed fractions because of smaller organ dimensions, shorter pho- ton path lengths, and reduced self-attenuation, which increase energy deposition in radiosensitive tissues. Age-dependent anatomical scaling and biokinetic differences incorporated into ICRP pediatric phantoms collectively increase absorbed dose per unit administered activity (ICRP, 2015; Fahey et al., 2017; Hussin et al., 2017). Results are consistent with pub- lished literature (Cherry et al., 2012; Hussin, et al., 2017) and emphasize pediatric dose optimization.

Table 1. The RADAR estimated effective dose due to intravenous injection administration of 99mTc sulfur colloid to various age groups.

· Route of Intake: Intravenous.

· Radiopharmaceuticals: 99mTc sulfur collide.

· Scan type: (liver- spleen scan).

Table 2. The estimated effective dose due to intravenous injection of 18F-FDG to patients calculated for adults, 15, 10, and 5, respectively.

· Route of Intake: Intravenous.

· Radiopharmaceuticals: 18F-FDG.

· Scan type: (Total body scan).

99mTc-MIBI (myocardial perfusion): The effective dose from the intravenous injection of 99mTc-MIBI (myocardi- al perfusion) was calculated for various age groups using the ICRP-128 biokinetic models, as shown in Table 3. For adult patients, the calculated effective doses were 5.8 mSv for resting studies and 6.0 mSv for stress studies, consistent with published diagnostic reference values (ICRP, 2015; Alnaaimi et al., 2022) and confirming the reliability of the RADAR- 2017 implementation.

In pediatric patients, the effective dose generally decreases with lower administered activity, and this decrease is pro- portional to body mass. However, this does not imply a lower radiation burden per unit of administered activity. In fact, pediatric patients exhibit higher dose coefficients than adults when normalized (mSv/MBq) due to smaller anatomical structures and reduced photon attenuation.

This is especially true for younger children, were smaller organ masses result in greater local energy deposition from emitted photons. Children’s physiological characteristics

can also lead to prolonged tracer retention in critical or- gans, thereby increasing the absorbed dose per unit of ad- ministered activity. Thus, despite lower administered activ- ity, children’ s effective dose efficiency is higher. A 1-year- old phantom received an effective dose of 3.2 mSv during myocardial imaging, using only about 13% of the activity typically administered to adults. This example illustrates that reducing the administered activity does not lead to a proportional decrease in the effective dose. A similar trend was observed during stress imaging, emphasizing the need for stringent weight-based protocol optimization in pedi- atric cases to maintain diagnostic quality while minimiz- ing radiation exposure.

The consistency of these findings with ICRP 128 reference data reinforces the validity of using standardized phantom models for age- dependent dosimetry. This underscores the necessity for individualized pediatric activity scaling rather than simple proportional reductions from adult protocols, aligning with current radiation protection prin- ciples.

Table 3. The effective dose from the intravenous injection of 99mTc-MIBI (myocardial perfusion) was calculated for various age groups using the ICRP-128 biokinetic models.

· Route of Intake: Intravenous.

· Radiopharmaceuticals: 99mTc - MIBI.

· Scan type: Myocardial scan.

131I-MIBG (neuroendocrine tumor imaging): The effective dose associated with intravenous administration of 131I- MIBG for tumor imaging has been evaluated across various age demographics, as illustrated in Table (4). Adult effec- tive dose reached 7.0 mSv, decreasing to 4.4 mSv in infants. The higher doses of iodine-131 are due to its long physical half-life, extended biological retention, and higher emitted radiation energy.

The analysis presented in Table (4) underscores significant age-related trends in radiation exposure associated with various radiopharmaceuticals. Pediatric patients receive

a higher effective dose per administered MBq than adults because of their smaller organ masses, reduced photon at- tenuation, and increased tissue radiosensitivity. This age- dependent increase in dose coefficients necessitates rigor- ous justification of nuclear medicine procedures and careful optimization of administered activity in accordance with es- tablished pediatric dosage guidelines to maintain diagnostic efficacy while minimizing radiation risk (Fahey et al., 2017). The ranges of effective dose (a few mSv) are consistent with published effective dose compendia for diagnostic nuclear medicine (Cherry et al., 2012; SNMMI.org, 2018).

Table 4. Effective dose for 131I-MIBG (neuroendocrine tumor imaging) evaluated across various age demographics.

· Route of Intake: Intravenous Injection.

· Radiopharmaceuticals: 131I-MIBG.

· Scan type: Neuroendocrine Tumor Imaging.

Table (5) provides a detailed overview of effective doses as- sociated with various diagnostic imaging procedures. The table illustrates how radiation exposure varies significantly depending on the radiopharmaceutical used, the adminis- tered activity, and the type of diagnostic procedure.

The recalculated effective dose for the ⁹⁹mTc-sulfur colloid liver–spleen scan was 2.1 mSv, compared with the pub- lished reference value of 2.2 mSv. The observed difference of approximately 4.5% indicates close numerical consisten- cy with the reference dosimetric data. In comparison, the recalculated effective dose for whole-body ¹⁸F-FDG PET was 4.8 mSv, which is lower than the published reference value of 5.8 mSv. This difference is likely attributable to variations in dosimetric methodology, including updates to tissue-weighting factors, biokinetic models, and calcu- lation frameworks adopted in recent ICRP recommenda- tions. For myocardial perfusion imaging, the recalculated effective doses were 5.8 mSv for the resting protocol and

6.0 mSv for the stress protocol, values that are consistent with the range reported in the literature for similar ad- ministered activities. The relatively higher effective doses observed for these procedures primarily reflect the larger administered activities required to achieve adequate image quality for myocardial perfusion assessment. Among the evaluated radiopharmaceuticals, ¹³¹I-MIBG produced the highest effective dose (7.0 mSv). This result is consistent with the radionuclide’s longer physical half-life, prolonged biological retention, and higher emitted radiation energy, which collectively increase radiation exposure compared with the technetium-99m– and fluorine-18–based radio- pharmaceuticals evaluated in this study. These findings emphasize that differences in effective dose among radio- pharmaceuticals are influenced by both radionuclide char- acteristics and administered activity and should therefore be considered when comparing diagnostic procedures and supporting radiation protection practices.

Table 5. Overview of estimated effective doses for different nuclear medicine scan types in adults, alongside corresponding reference values from the literature.

· FDG-18 activity within the patient at start scan..

This study presents a standardized reassessment of age- dependent effective doses for commonly performed diag- nostic nuclear medicine procedures using current ICRP biokinetic models and the SNMMI Nuclear Medicine Ra- diation Dose Tool (RADAR-2017). By applying a unified dosimetric framework across multiple radiopharmaceuti- cals, the study provides consistent comparisons of effec- tive doses between adult and pediatric reference phantoms based on the latest ICRP recommendations. The results demonstrate that pediatric patients receive higher effective doses per unit administered activity than adults, highlight- ing the importance of age-specific dosimetric assessment and adherence to standardized pediatric administered ac- tivity guidelines.

The findings contribute to radiation protection by provid- ing updated reference effective dose estimates that may support benchmarking of clinical practice, comparison with Diagnostic Reference Levels (DRLs), and periodic review of administered activity protocols. Although this study was limited to effective dose calculations using stan- dardized reference phantoms and did not evaluate image quality, organ-specific absorbed doses, or patient-specific biokinetics, the proposed methodology provides a prac- tical framework for standardized dosimetric assessment. Future studies integrating individualized dosimetry, pa- tient-specific biokinetic modeling, and quantitative im- age quality evaluation will further support evidence-based optimization of diagnostic nuclear medicine procedures while maintaining appropriate radiation protection prin- ciples.