Which cancer therapy is defined as short-distance therapy, using implanted or nearby radioactive sources?

• A. Brachytherapy
• B. Linear Accelerators
• C. External Beam
• D. Cobalt-60 Unit (Gamma Knife)

Answer: (A)

Short-distance therapy is brachytherapy, where the radioactive source is placed directly inside or very close to the tumor. Being so near the target allows a high dose to be delivered to cancer cells while the radiation intensity drops off quickly with distance, thanks to the inverse square law, which helps spare surrounding healthy tissue. Brachytherapy can use implanted seeds or applicators that stay in place for a set period or deliver radiation from within the body, providing precise dose conformity to irregular tumor shapes. In contrast, external approaches deliver radiation from outside the body, through healthy tissues, so they’re not considered short-distance therapies.