hyperfractionation

Hyperfractionation is a radiotherapy schedule in which the total prescribed dose is delivered in smaller doses per fraction but with more fractions per day than conventional schedules. Typically, two fractions per day, each about 1.1 to 1.2 Gy, are given with a minimum interval of six hours, enabling a higher total dose, usually around 70 to 72 Gy, over about six weeks.

Rationale centers on radiobiological principles: smaller fraction sizes reduce late normal-tissue toxicity while permitting dose escalation to improve tumor control. Although tumors may have a higher alpha/beta ratio than late-responding tissues, the reduced per-fraction dose keeps late effects low and allows a higher cumulative dose than standard regimens.

Clinical use has historically focused on cancers such as head and neck squamous cell carcinomas, where randomized trials in the 1980s and 1990s reported improvements in local control with acceptable toxicity compared with conventional fractionation. With advances in conformal radiotherapy and intensity-modulated radiotherapy, hyperfractionation has become less common, though it remains part of some protocols and is used in certain pediatric regimens.

Practical considerations include the need for precise scheduling and increased daily treatment sessions, placing greater demands on patients and radiotherapy facilities. Common acute toxicities include mucositis and dermatitis; long-term toxicity depends on tumor site and technique.

Hyperfractionation is a form of altered fractionation and is distinct from hypofractionation, which uses larger doses per fraction and fewer treatments. Current practice often prioritizes IMRT with either conventional or altered fractionation rather than true hyperfractionation.