Improved rectal dosimetry with the use of SpaceOAR during high-dose-rate brachytherapy.
PURPOSE
Hydrogel spacers have been suggested to limit rectal radiation dose with improvements in clinical outcomes in patients undergoing external beam radiation treatment for prostate cancer. No studies to date have assessed the utility and dosimetric effect of SpaceOAR (Augmenix, Inc, Waltham, MA), the only Food and Drug Administration-approved hydrogel rectal spacer, for high-dose-rate (HDR) brachytherapy.


METHODS
Eighteen consecutive patients scheduled for HDR brachytherapy in the treatment of prostate cancer underwent transperineal ultrasound-guided placement of 10 cc of SpaceOAR hydrogel following catheter implantation. Treatment plans were generated using an inverse planning simulated annealing algorithm. Rectal dosimetry for these 18 patients was compared with the 36 preceding patients treated with HDR brachytherapy without SpaceOAR.


RESULTS
Fifty-four plans were analyzed. There was no difference in age, pretreatment prostate-specific antigen, Gleason score, clinical stage, prostate volume, or contoured rectal volume between those who received SpaceOAR and those who did not. Patients who received SpaceOAR hydrogel had significantly lower dose to the rectum as measured by percent of contoured organ at risk (median, V80 < 0.005% vs. 0.010%, p = 0.003; V75 < 0.005% vs. 0.14%, p < 0.0005; V70 0.09% vs. 0.88%, p < 0.0005; V60 = 1.16% vs. 3.08%, p < 0.0005); similar results were seen for rectal volume in cubic centimeters. One patient who received SpaceOAR developed a perineal abscess 1 month after treatment.


CONCLUSIONS
Transperineal insertion of SpaceOAR hydrogel at the time of HDR brachytherapy is feasible and decreases rectal radiation dose. Further investigation is needed to assess the clinical impact of this dosimetric improvement and potential toxicity reduction.
['Wu|Susan Y|SY|', 'Boreta|Lauren|L|', 'Wu|Ashley|A|', 'Cheung|Joey P|JP|', 'Cunha|J Adam M|JAM|', 'Shinohara|Katsuto|K|', 'Chang|Albert J|AJ|']
D000368:Aged D000465:Algorithms D001918:Brachytherapy D005240:Feasibility Studies D006801:Humans D020100:Hydrogels D008297:Male D008875:Middle Aged D058958:Organs at Risk D011471:Prostatic Neoplasms D011829:Radiation Dosage D011832:Radiation Injuries D011879:Radiotherapy Dosage D011880:Radiotherapy Planning, Computer-Assisted D012007:Rectum
Dosimetry Brachytherapy Hydrogel Prostate cancer Rectal protection