The aim of this article was to quantify improvements in external beam treatment plans for early prostate cancer, going from standard four-field conformal radiotherapy (CRT4) to multi-segment, inverse-planned intensity-modulated radiotherapy (IMRTinv). We selected 18 low-, medium- and high-risk early prostate cancer patients requiring external beam radiotherapy and generated standard CRT4 plans. We compared this with five-field conformal radiotherapy (CRT5) plans with beam angles 45°, 100°, 180°, 260° and 315°, five-field plans combining an open beam and rectal shielding segment (forward-planned IMRT (IMRTfor)) and a five-field inverse-planned multi-segment solution (IMRTinv) with planning target volume and bladder dose volume histogram characteristics similar to IMRTfor. The CRT5 plans showed significant rectal sparing compared with CRT4 producing 10–22% reductions in rectal volume receiving 95, 85, 67 and 55% prescription dose (V95, V85, V67 and V55) depending on patient risk group and conforming better to the planning target volume. The IMRTfor plans showed a concave dose distribution, further reducing rectal V95, V85, V67 and V55 between 6 and 50%. We did not find further reductions in rectal doses with IMRTinv compared with IMRTfor. The benefit of IMRT over CRT was achieved by increasing the number of beams, changing beam weights and adding a rectal shielding segment to each beam.