Bolus (radiation therapy)

Bolus is a term used in radiation therapy, an area of medicine focused on the treatment of cancer and other diseases by using radiation to kill or control the growth of malignant cells. A bolus is a device or material placed on the skin's surface, or within a body cavity, to alter the depth of dose distribution of radiation. Its primary purpose is to ensure a more uniform dose of radiation is delivered to the tissues being treated, particularly when targeting superficial tumors.

Function and Importance

The bolus acts by mimicking tissue and increasing the skin or superficial tissue's dose, which might otherwise receive a lower dose than intended due to the physical properties of radiation beams. This is particularly important in treatments where the skin itself is the target, or in situations where the tumor is located very close to the skin surface. By using a bolus, radiation oncologists can ensure that the maximum dose of radiation is delivered to the tumor with minimal damage to the underlying healthy tissues.

Types of Bolus

There are various types of bolus materials used in radiation therapy, including:

• Custom-made bolus: Designed specifically for a patient's treatment area, often using materials like gel or wax that can be molded to the shape of the treatment site.
• Commercial bolus: Pre-made sheets of material that can be cut and shaped to fit the patient but are not custom-molded.
• Virtual bolus: Used in planning computer simulations to predict and adjust the dose distribution without a physical bolus.

Application

The application of a bolus in radiation therapy is determined by the treatment plan developed by the radiation oncologist and the medical physicist. The plan considers the type and location of the cancer, the depth of the target tissue, and the type of radiation beam used. The bolus is placed directly on the skin or within a body cavity, such as the mouth or vagina, to ensure that the radiation dose is accurately delivered to the target area.

Challenges and Considerations

While boluses are invaluable in achieving optimal dose distribution, their use comes with challenges. Precise placement is crucial; even slight movements can alter the radiation dose received by the skin or tumor. Additionally, the material and thickness of the bolus must be carefully selected to match the treatment plan's requirements, as different materials and thicknesses can significantly affect the dose distribution.

Conclusion

The use of a bolus in radiation therapy is a critical component in the treatment of cancers located near or at the skin surface. By ensuring a more uniform dose distribution, boluses help maximize the treatment's effectiveness while minimizing damage to healthy tissues. As radiation therapy techniques continue to advance, the role of the bolus remains essential in providing patients with the best possible outcomes.