Dose fractionation

Dose Fractionation

Illustration of the effect of self-repair in dose fractionation

Dose fractionation is a radiation therapy technique used in the treatment of cancer. It involves dividing the total dose of radiation into multiple smaller doses, or fractions, which are administered over a period of time. This approach allows for the delivery of a higher total dose of radiation to the tumor while minimizing damage to surrounding healthy tissue.

Principles of Dose Fractionation

The primary principle behind dose fractionation is the biological concept of repair, repopulation, redistribution, and reoxygenation, often referred to as the "4 Rs" of radiobiology. These principles help to maximize the damage to cancer cells while allowing normal cells to recover.

Repair

Normal cells have the ability to repair sub-lethal damage caused by radiation. By fractionating the dose, there is time between treatments for normal cells to repair themselves, reducing the risk of side effects.

Repopulation

During the intervals between fractions, normal cells can repopulate, which helps to maintain the integrity of normal tissues. However, cancer cells can also repopulate, which is why the timing and scheduling of fractions are critical.

Redistribution

Radiation is more effective at certain phases of the cell cycle. Fractionation allows for redistribution of cells into more sensitive phases, increasing the likelihood of cell death in cancer cells.

Reoxygenation

Tumor cells that are well-oxygenated are more sensitive to radiation. Fractionation allows time for reoxygenation of hypoxic tumor areas, making subsequent doses more effective.

Types of Dose Fractionation

There are several types of dose fractionation schedules used in clinical practice:

Conventional Fractionation

Conventional fractionation typically involves daily doses of 1.8 to 2.0 Gy per fraction, given five days a week over several weeks.

Hyperfractionation

Hyperfractionation involves giving smaller doses of radiation more than once a day. This approach aims to increase the total dose delivered to the tumor while sparing normal tissue.

Hypofractionation

Hypofractionation uses larger doses per fraction and fewer fractions overall. This approach is often used in palliative care or in certain types of cancer where a shorter treatment course is beneficial.

Accelerated Fractionation

Accelerated fractionation shortens the overall treatment time by increasing the number of fractions per week. This approach aims to reduce the time for tumor repopulation.

Clinical Applications

Dose fractionation is used in the treatment of various types of cancer, including breast cancer, prostate cancer, lung cancer, and head and neck cancer. The choice of fractionation schedule depends on the type of cancer, the stage of the disease, and the overall treatment goals.

Advantages and Disadvantages

Advantages

• Allows for higher total doses of radiation to be delivered safely.
• Reduces the risk of late radiation-induced side effects.
• Provides time for normal tissue repair.

Disadvantages

• Requires multiple visits to the treatment center.
• Prolonged treatment duration can be inconvenient for patients.
• Potential for tumor repopulation between fractions.

Related Pages

• Radiation therapy
• Radiobiology
• Cancer treatment
• Radiation dose