In whole brain irradiation, where is the inferior border of the treatment field typically placed?

In whole brain irradiation, the inferior border of the treatment field is typically placed at the level of the cervical spine #2 (C2). This placement is chosen to ensure that the entire brain, including the base of the skull and areas critical for potential metastases, is encompassed by the radiation field.

Positioning at C2 is particularly effective because it is located just below the cranial cavity, allowing for coverage of the brainstem and upper cervical structures, which may also be affected by the disease. This approach minimizes the risk of omitting critical areas that could contribute to the patient's clinical condition while maximizing treatment efficacy.

The other potential choices, while relevant anatomical landmarks, do not provide the necessary coverage for the treatment of the whole brain. For instance, placing the inferior border at the base of the skull may leave out parts of the lower brain and brainstem, which are essential in treating conditions like metastatic brain tumors. Similarly, using the mastoid tip or cervical spine #7 would not adequately cover the required areas, leading to incomplete treatment.