Gastrointestinal Syndrome (ARS) occurs at a dose threshold of which value?

• A. 0.5 Gray
• B. 1 Gray
• C. 10 Gray
• D. 50 Gray

Answer: (C)

Gastrointestinal syndrome appears when the dose is high enough to severely disrupt the rapidly renewing lining of the gut. At about 10 Gy, the intestinal crypt stem cells are drastically depleted, causing loss of mucosal integrity and barrier function. This leads to rapid onset of severe diarrhea, fluid and electrolyte imbalance, and creates a route for bacteria to enter the bloodstream, resulting in sepsis. Without aggressive supportive care, death can occur within days to a couple of weeks. Doses much lower than this, such as 0.5 or 1 Gy, primarily cause hematopoietic (bone marrow) effects rather than GI-specific damage. A dose as high as 50 Gy would cause widespread, immediate damage and is not the threshold for GI syndrome onset. Therefore, the threshold where GI-ARS starts is around 10 Gy.