What determines the total dose received by a point in the patient outside the treatment field?

The total dose received by a point in the patient outside the treatment field is determined by the combination of the transmitted primary dose and the scattered dose. When radiation is delivered during treatment, some of it passes through the targeted area, contributing to the transmitted primary dose, while a portion of the radiation interacts with the surrounding tissues and structures, leading to secondary scatter.

The primary dose refers to the radiation beam aimed directly at the tumor, while scattered radiation originates from interactions of primary radiation with matter, which can include both the patient’s body and the treatment apparatus. As the primary radiation passes through and interacts with these materials, it scatters in various directions, increasing the dose that can be received outside the direct path of the primary beam.

The significant aspect of this combination of doses is essential for accurately assessing how much radiation a patient receives outside of the treatment area, which is crucial for understanding both the effectiveness of the treatment targeting and the potential for unwanted side effects in healthy tissues. Different types of radiation may influence the relative contributions of these components, but the overall dose received outside the treatment field is a factor of both the transmitted and scattered doses.