A COMPARISON OF PROTON AND MEGAVOLTAGE X-RAY TREATMENT PLANNING FOR PROSTATE-CANCER

Conformal photon and proton therapy plans for prostate cancer have bee n compared in an attempt to quantify the potential advantages of using protons. Two X-ray plans (3-field, 6-field) and a 2-field proton plan were made and compared for each of 20 T3 prostate patients with the a id of the 3D planning system VOXELPLAN. Dose distributions were analys ed in terms of dose-volume histograms (DVH). Tumour control probabilit y (TCP) and normal tissue complication probability (NTCP) were compute d using our own and the Lyman-Kutcher-Burman models, respectively. The study shows that on average the proton technique results in the best dose distribution, giving the lowest rectal complication probability, and also that the 3-field X-ray technique is more effective than the 6 -field X-ray technique in sparing the rectum. At 5% rectal NTCP, the p redicted proton average TCP for the 20 patients is 2% (in absolute ter ms) greater than that obtained using 3-field X-ray therapy. For 7 of t he patients the gain in TCP is more than 3%. For the same rectal NTCP as the 3-field X-ray plan with a 64 Gy mean target dose, the use of pr otons increases the TCP by 2% on average, but for 5 of the patients th e increases are greater than 4%. The result is in general positive tow ards the use of protons but a few patients do not benefit from it and this indicates the importance of patient selection for maximum clinica l benefit.