This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: NEET Jan 2020, Subject name: Gynaecology & Obstetrics
A 55 year old woman diagnosed with ca cervix stage IIb is adviced for chemoradiation. Which of the following is true statement regarding radiation use ? 
Select and explain. 
A. Dose/Intensity of radiation is inversely propoional to the square of distance of source, B. Rapidly proliferating cells are radioresistant, C. small blood vessels are radioresistant, D. small bowel is radioresistant
A: Dose/Intensity of radiation is inversely propoional to the square of distance of source
Answer: A: Dose/Intensity of radiation is inversely propoional to the square of distance of source 
Explanation: - Inverse square law:- Dose /Intensity of radiation is inversely propoional to the square of distance of source - Other options: If tissues with a rapid proliferation rate such as epithelium of the small intestine or oral cavity are irradiated, acute clinical symptoms develop within a few days to weeks The small bowel is paicularly vulnerable to acute early damage from radiation therapy Susceptibility of Selected Tissues to Radiation-Induced Cancer Susceptibility Tissues High Bone marrow, female breast, thyroid Moderate Bladder, colon, stomach, liver, ovary Low Bone, connective tissue, muscle, cervix, uterus, rectum