A urinary bladder patient is being treated with an isocentri…
A urinary bladder patient is being treated with an isocentric four-field box portal plan on a linear accelerator calibrated to 100 cm SAD . The AP/PA separation is 25.3 cm. The RT/LT lateral separation is 36.9 cm. The isocenter of the planned target volume is located at a depth of 18.7 cm from the anterior aspect of the patient and midline from the right and left lateral aspect of the patient. The treatment portal for the AP and PA portals are 7.2 cm x 9.8 cm to mirror each other. What would be the field size on the patient’s posterior skin surface?