A dosimetric study comparing three-, four-, and six- field plans for treatment of carcinoma of the prostate.

We present a three-dimensional dosimetric analysis of 3-, 4-, and 6-field plans using 24 MV photon beams for treatment of carcinoma of the prostate. We compare isodose distributions on a transverse plane through the center of the target as well as differential and integral dose volume histograms for the target and critical structures, respectively. An extensive study on a representative case led to the development of a technique where two complementary 3-field daily plans deliver the same daily target dose as the standard 4-field box while affording sparing of the bladder and rectum similar to that achieved with a 6-field plan. This technique was shown to yield the same results on a sample of four additional patients representing a range of target and patient sizes. We conclude that the combined two-day, 3-field method for treatment of the prostate may be a better choice than the standard 4-field box or the 6-field daily plan for dose escalation studies.