Anatomy-based inverse optimization in high-dose-rate brachytherapy combined with hypofractionated external beam radiotherapy for localized prostate cancer: comparison of incidence of acute genitourinary toxicity between anatomy-based inverse optimization and geometric optimization.
OBJECTIVE
To evaluate the advantages of anatomy-based inverse optimization (IO) in planning high-dose-rate (HDR) brachytherapy.


METHODS
A 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.


RESULTS
The 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).


CONCLUSIONS
The results of this study suggest that anatomy-based IO is superior to GO for dose optimization in HDR brachytherapy for prostate cancer.
Akimoto
Tetsuo
T
Department of Radiation Oncology, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan. takimoto@showa.gunma-u.ac.jp
Katoh
Hiroyuki
H
Kitamoto
Yoshizumi
Y
Shirai
Katsuyuki
K
Shioya
Mariko
M
Nakano
Takashi
T
D000368:Aged; D000369:Aged, 80 and over; D001918:Brachytherapy / Q000379:methods*; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D007496:Iridium Radioisotopes / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000209:etiology; D011859:Radiography; D020266:Radiotherapy, Conformal / Q000379:methods; D012007:Rectum / Q000000981:diagnostic imaging / Q000528:radiation effects; D014521:Urethra / Q000000981:diagnostic imaging / Q000528:radiation effects*; D014566:Urogenital System / Q000528:radiation effects*
D007496:Iridium Radioisotopes