comparison of conventional and 3d conformal treatments using linac energies for prostate cancer

background: to evaluate the dosimetric difference between conventional and three-dimensional conformal radiotherapy (3d-crt) using 6 and 18 mv x-ray photons. materials and methods: computed tomography scans of 26 pelvic patients were acquired and transferred to the 3d treatment planning system. for each patient, 8 conventional plans (3, 4, 5 and 6 fields) and one 3d-crt plan were prepared using 6 and 18 mv photon energies. the minimum dose (dmin), maximum dose (dmax) and mean dose (dmean) to target (ptv) and organs at risk (oar), integral dose, homogeneity index and conformity index were compared for each plan. also, experimental measurements were performed using farmer ionization chamber on a patient based pelvic phantom. results: on average, six-field (6f1) plans, offer minimum dose to critical organs and sufficient dose to prostate. increasing the beam energy lead to a decrease in dmean of the bladder and femoral heads, as well as dmax of ptv. the ci and id were decreased by 4% and 11% respectively with increasing the energy and the number of beams. experimental measurements were also in good agreement with calculations. 3d-crt reduced dmean of bladder, rectum and femoral heads and also ci and id were significantly improved by 44.6% and 30.8%, respectively. conclusion: increasing the photon energy and number of beams, improve the treatment parameters of bladder, femoral heads and ptv, except the rectum. 3d-crt offered the most conformity in the delivery doses to the prostate while sparing dose to oars, uninvolved structures with lower integral dose. iran. j. radiat. res., 2012 10(3‐4): 145‐150