Introduction: Nuclear medicine techniques have been widely employed in the assessment of gastroesophageal dysfunction. Gastroesophageal reflux (GER) is a common, self-limited process in infants and children that usually resolves at 12 to 18 months of age. Clinical management of GER includes conservative treatment, thickened feedings, positional therapy and parental reassurance. On the other hand, GER disease (GERD) is a less common, more serious pathological process that is manifested by poor weight gain, signs of esophagitis and persistent respiratory symptoms that usually warrant medical management and diagnostic evaluation.
photon sources are used for many applications, especially in medicine imaging. Milk scan is used as a sensitive and accurate method for diagnosing GERD in children. The aim of this study is to estimate the amount of absorbed doses in the organs of the stomach, esophagus, and heart of children and infants, who suffer from GERD, using the nuclear imaging.
 
Materials and Methods: By using the computational phantoms of (ORNL) and the MCNPX code in the Monte Carlo method, the absorbed dose of the 99mTc source was calculated as for different age groups. In this test, a certain radiopharmaceutical, which is often Tc99m colloid sulfur, is mixed with the breast milk or milk powder and will be given to the child. After entering the stomach, this radiopharmaceutical will go to an area in the esophagus and will be detected and imaged using the gamma camera.
 
Results: Results from the gamma dosimeter calculation, in which stomach has the highest absorbed dose from photon radiation because this radiopharmaceutical has the maximum accumulation in this organ. it is noteworthy that all the results in this study haven't exceeded the recommended ICRP standards.
The obtained results revealed that the absorbed energy fraction in the organs of the esophagus and heart has an inverse relationship with the distance the source organ. The organ, which absorbs the most dose from gamma radiation is stomach and this is expected because we defined the organ in the calculation code as the radiation source. Our study also shows a correlation between the age of the patients investigated and the rate of their absorbed dose, older children showing a absorbed dose is decreased than younger children.
 
Conclusion: The major objective of the present study is to diagnose GERD, using the labeled colloid sulfur radiopharmaceutical with 99mTc, to take the maximum absorbed dose in the stomach and the minimum dose in the organs of the esophagus and heart to create the maximum of effect for imaging and the minimum of complications.