Two posterior spine photon fields are matched at a depth of…

Two posterior spine photon fields are matched at a depth of 7 cm. One field measures 8 × 23 cm at an SSD of 112 cm. The adjacent field measures 8 × 19 cm at an SSD of 110 cm. Both fields use 6 MV photons. What skin gap should be placed between the fields to achieve proper matching at 7 cm depth?

Two posterior-anterior (PA) photon fields are matched at a d…

Two posterior-anterior (PA) photon fields are matched at a depth of 5 cm. Both fields are treated at 100 cm SSD. The superior field length is 20 cm, and the inferior field length is 24 cm. The beam energy is 10 MV. What skin gap should be placed between the fields to achieve a match at 5 cm depth?