Partially wedged radiation beams

To increase dose homogeneity within certain radiotherapy targets, we define d a partially wedged radiation beam as a beam with wedge modification in on e part of the field only. Partially wedged beams may be beneficial in cases with curved surfaces inside parts of the beam only, where they may compens ate for missing tissue and/or for variations in depth to the target region. Possible sites suitable for partially wedged beams include urinary bladder and tangential breast irradiation. Customized partially wedged beams were delivered applying dynamic collimation techniques. Two different linear det ector arrays, a semiconductor diode array and an ionization chamber array, were used independently in the same standard water tank to verify that the partially wedged beams were delivered according to the definition. Dose cal culations of partial wedge fields were implemented in our treatment plannin g system and compared with the measured dose distributions. We re-planned a representative treatment plan for both advanced urinary bladder cancer and tangential breast irradiation using partially wedged beams. For both patie nts the target dose homogeneity was improved, and the doses to surrounding critical normal tissues were reduced. (C) 2000 American Association of Phys icists in Medicine. [S0094-2405(00)00503-4].