What primarily affects the shape of the isodose curves?

The shape of the isodose curves is primarily influenced by field size and flattening filters.

Field size plays a crucial role because it directly affects the distribution of radiation dose across the treatment area. Larger fields tend to provide a more uniform dose distribution, whereas smaller fields can lead to greater dose gradients and non-uniformity in the isodose curves. This relationship illustrates how varying the field size alters the way radiation spreads out in the tissue.

Flattening filters are used in linear accelerators to create a more uniform beam profile across larger treatment areas. Without these filters, the radiation beam would be non-uniform, typically peaking at the center and diminishing towards the edges. The introduction of flattening filters helps shape the intensity of the beam, which in turn affects the isodose curves by smoothing out the dose distribution, making it more amenable for treatment planning.

Understanding the interaction between field size and flattening filters allows practitioners to optimize treatment plans in radiation therapy, ensuring effective tumor coverage while minimizing exposure to surrounding healthy tissues.