Combined intensity-modulated radiation therapy vs. three-dimensional highly conformal radiotherapy after (125)I prostate permanent seed brachytherapy: a comparative treatment planning study.

PURPOSE: A comparative treatment planning study was conducted to analyze combined intensity-modulated radiation therapy (IMRT) vs. three-dimensional highly conformal radiotherapy (3D-hCRT) after (125)I permanent seed brachytherapy in patients with localized prostate cancer.

METHODS AND MATERIALS: We optimized an IMRT and a 3D-hCRT treatment plan to 45Gy in 9 patients 2 months after (125)I seed brachytherapy (110Gy) implant. IMRT and 3D-hCRT were planned using eight and seven nonopposed coplanar fields of 6- and 23-MV. Dose-volume histograms for target volume and organs at risk were compared for both techniques.

RESULTS: IMRT provided similar conformality but better homogeneity (p=0.021) than 3D-hCRT plans, despite slightly higher maximal point dose rates (101.9% vs. 100.9%, p=0.050). 3D-hCRT plans required fewer monitor units than did IMRT (289 vs. 607, p=0.008). Dose to bladder, penile bulb, and femoral heads were lower with IMRT than with 3D-hCRT (p=0.008-0.028). No differences were observed for dose to urethra and the entire rectum. Mean dose to rectal wall was lower with IMRT than with 3D-hCRT (25.1 vs. 26.5Gy, p=0.028).

CONCLUSION: IMRT plans result in more homogeneous dose distribution and in reduced doses to most organs at risk at the expense of needing more than twice the monitor units compared with 3D-hCRT.