• Tetsuo Akimoto, Hiroyuki Katoh, Yoshizumi Kitamoto, Katsuyuki Shirai, Mariko Shioya, and Takashi Nakano.
• Department of Radiation Oncology, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan. takimoto@showa.gunma-u.ac.jp
• Int. J. Radiat. Oncol. Biol. Phys. 2006 Apr 1; 64 (5): 1360-6.

PurposeTo evaluate the advantages of anatomy-based inverse optimization (IO) in planning high-dose-rate (HDR) brachytherapy.Methods And MaterialsA total of 114 patients who received HDR brachytherapy (9 Gy in two fractions) combined with hypofractionated external beam radiotherapy (EBRT) were analyzed. The dose distributions of HDR brachytherapy were optimized using geometric optimization (GO) in 70 patients and by anatomy-based IO in the remaining 44 patients. The correlation between the dose-volume histogram parameters, including the urethral dose and the incidence of acute genitourinary (GU) toxicity, was evaluated.ResultsThe averaged values of the percentage of volume receiving 80-150% of the prescribed minimal peripheral dose (V(80)-V(150)) of the urethra generated by anatomy-based IO were significantly lower than the corresponding values generated by GO. Similarly, the averaged values of the minimal dose received by 5-50% of the target volume (D(5)-D(50)) obtained using anatomy-based IO were significantly lower than those obtained using GO. Regarding acute toxicity, Grade 2 or worse acute GU toxicity developed in 23% of all patients, but was significantly lower in patients for whom anatomy-based IO (16%) was used than in those for whom GO was used (37%), consistent with the reduced urethral dose (p <0.01).ConclusionThe results of this study suggest that anatomy-based IO is superior to GO for dose optimization in HDR brachytherapy for prostate cancer.

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