In radiotherapy, what is the purpose of dose fractionation?

• A. To deliver the entire dose in a single session for speed.
• B. To minimize total treatment time at all costs.
• C. To avoid any normal tissue exposure.
• D. To maximize tumor control while allowing normal tissues to repair and reduce toxicity.

Answer: (D)

Fractionation balances tumor control with normal-tissue safety by delivering the total dose in several smaller fractions over time. This approach takes advantage of differences in how tumor and normal tissues repair sublethal radiation damage. Normal tissues, especially late-responding ones, can repair between sessions more effectively, so the accumulated damage to them is reduced, while tumor cells—often more vulnerable to repeated exposing and less able to repair quickly—accumulate lethal damage. The result is a higher therapeutic ratio: you maximize tumor control while allowing normal tissues to repair and thereby reduce toxicity. In more advanced terms, the different radiosensitivities of tissues (often described by the α/β ratio) mean that smaller dose per fraction tends to spare late-responding normal tissues without compromising much the tumor kill. That’s why delivering the dose in fractions is preferred over a single large dose.