Evaluation of the optimal co-planar field arrangement for use in the boost phase of dose escalated conformal radiotherapy for localized prostate cancer

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Abstract
The aim of this study was to determine the optimal co-planar beam arrangement from a variety of three-field (3F), four-field (4F) and six-field (6F) plans for the boost phase of a dose escalated conformal radiotherapy schedule. Three selected plans (3F 0°, 90°, 270° plan, 4F 45°, 90°, 270°, 315° plan and 6F 40°, 90°, 115°, 245°, 270°, 320° plan) were compared with reference plans (3F 0°, 120°, 240° plan, 4F 0°, 90°, 180°, 270° plan, 6F 55°, 90°, 125°, 235°, 270°, 305° plan and 6F 50°, 90°, 130°, 230°, 270°, 310° plan) in 10 patients. Doses of 64 Gy and 74 Gy were prescribed to the isocentre using 6 MV photons. The boost planning target volume comprised the prostate gland alone without a margin. Plans were compared by means of rectal volumes irradiated to >50% (V50), >80% (V80) and >90% (V90) of the prescribed dose. Irradiated volumes were also measured for the bladder (V90) and the femoral heads (V70). All optimal 3F, 4F and 6F plans gave lower irradiated rectal V80 and V90 levels than their corresponding...