In an isocentric treatment with a 100 cm SAD machine, what is the anterior SSD if the depth of the tumor center is 12 cm?

In an isocentric treatment setup, the Source-to-Axis Distance (SAD) is a fixed distance from the radiation source to the isocenter, which remains constant regardless of the patient's position or the depth of the tumor. In this scenario, the SAD is specified as 100 cm, and the depth of the tumor center is 12 cm.

To determine the anterior Source-to-Skin Distance (SSD), you would subtract the depth of the tumor from the SAD. This approach arises from the basic geometric relationship in radiation therapy concerning the isocenter, which is the point where all treatment beams converge.

Thus, the anterior SSD can be calculated as follows:

1. Start with the SAD: 100 cm.

2. Subtract the depth of the tumor: 100 cm - 12 cm = 88 cm.

This calculation indicates that the anterior SSD is 88 cm. In clinical practice, knowing this distance is crucial for accurate treatment delivery, as it helps to ensure the tumor is appropriately targeted while minimizing dose to surrounding healthy tissues. In this case, the given answer of 88 cm accurately reflects the resulting anterior SSD based on the provided depth of the tumor.