[en] Purpose/Objective: A series of dose-findings studies in prostate cancer have been performed using the physical advantages of 3-D treatment planning and the biological advantages of hyperfractionation and high LET radiation. This study was initiated to determine if prostate doses of > 79 Gy could be delivered without excessive femoral head morbidity. Although rectal and bladder toxicity have been considered dose limiting organs, the dose delivered to the femoral heads became significant at tumor doses > 79 Gy (2 Gy/fraction photon equivalent dose). Materials and Methods: Two hundred patients with prostate cancer have received non-axial photon and/or neutron radiation treatments including (R) and (L) SO/IO/AISO field arrangements. These are accomplished with gantry angles of +/- 35 deg. -90 deg. and pedestal rotation of +/-25 deg. -30 deg. . This new protocol consists of a combination of non-axial neutron fields followed by hyperfractionated axial and non axial photon beams. The scheme of the protocol is as follows: Neutrons, 4 non axial fields, RL, LL, RAISO/LAISO: Right anterior/Left anterior, inferior to superior oblique, 1.1 NGy/fx equivalent to a 2 Gy/fx photon dose, up to 11 NGy, 5 days/week, followed by Photons, 15 MV 4 axial fields, Ant, Post, RL, LL 1.15 Gy/fx up to 23 Gy, morning session. 4 non axial fields, RSO/LSO: R/L, superior to inferior oblique RIO/LIO: R/L, inferior to superior oblique 1.15 Gy/fx up to 23 Gy, afternoon session. The current 2Gy/fx photon equivalent total dose is 79 Gy with an estimated ((α(β)) = 3.0 and RBE = 3.75 for hip injury). The goal of this protocol is to optimize the plan in order to keep the femoral head dose to <50 Gy. CT simulation and 3-D conformal treatment planning was performed for each patient. Plans were evaluated based on dose-volume histograms (DVHs) and NTCP calculated for femoral heads. Results: Based on the DVH analysis, the GTV prostate received 100% of the prescribed dose. NTCP for the femoral heads was favorable with this new beam arrangement. Comparison with axial 4 or 6 field plans will be presented. Conclusions: At the current dose level (79 Gy photon equivalent) it is necessary to utilize non axial beams to avoid femoral head damage. The DVH and NTCP analysis demonstrate that this is possible without compromising the TCP. Long term follow up is necessary to determine whether the observed complication rates will match the NTCP prediction