Intensity Modulated Neutron Radiotherapy for the Treatment of Adenocarcinoma of the Prostate

Purpose: This study investigates the enhanced conformality of neutron dose distributions obtainable through the application of intensity modulated neutron radiotherapy (IMNRT) to the treatment of prostate adenocarcinoma. Methods and Materials: An in-house algorithm was used to optimize individual segments for IMNRT generated using an organ-at-risk (OAR) avoidance approach. A number of beam orientation schemes were investigated in an attempt to approach an optimum solution. The IMNRT plans were created retrospectively for 5 patients previously treated for prostate adenocarcinoma using fast neutron therapy (FNT), and a comparison of these plans is presented. Dose distributions and dose-volume histograms (DVHs) were analyzed and plans were evaluated based on percentage volumes of rectum and bladder receiving 95%, 80%, and 50% (V₉₅, V₈₀, V₅₀) of the prescription dose, and on V₆₀ for both the femoral heads and GM_muscle group. Results: Plans were normalized such that the IMNRT DVHs for prostate and seminal vesicles were nearly identical to those for conventional FNT plans. Use of IMNRT provided reductions in rectum V₉₅ and V₈₀ of 10% (2-27%) and 13% (5-28%), respectively, and reductions in bladder V₉₅ and V₈₀ of 12% (3-26%) and 4% (7-10%), respectively. The average decrease in V₆₀ for the femoral heads was 4.5% (1-18%), with no significant change in V₆₀ for the GM_muscle group. Conclusions: This study provides the first analysis of the application of intensity modulation to neutron radiotherapy. The IMNRT technique provides a substantial reduction in normal tissue dose in the treatment of prostate cancer. This reduction should result in a significant clinical advantage for this and other treatment sites.