A comparison of conformal and intensity modulated treatment planning techniques for early prostate cancer.

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 degrees, 100 degrees, 180 degrees, 260 degrees and 315 degrees, five-field plans combining an open beam and rectal shielding segment (forward-planned IMRT (IMRT(for))) and a five-field inverse-planned multi-segment solution (IMRT(inv)) with planning target volume and bladder dose volume histogram characteristics similar to IMRT(for). 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 (V(95), V(85), V(67) and V(55)) depending on patient risk group and conforming better to the planning target volume. The IMRT(for) plans showed a concave dose distribution, further reducing rectal V(95), V(85), V(67) and V(55) between 6 and 50%. We did not find further reductions in rectal doses with IMRT(inv) compared with IMRT(for). 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.