Basic Treatment Planning

Penumbra • Penumbra is often defined as the distance between the 20% and the 80% (10% and 90%) isodose lines • The penumbra is the region near the edge of the field where the dose falls off rapidly  Width depends on  Size of ‘source’

 SSD/FSD (Lower SSD, higher penumbra)  Energy (Increasing penumbra with increasing energy: increased field size)