Paul M. Yonover, MD
Par Mehta, MD
Dr. Yonover is chief analytics officer at UroPartners, LLC and assistant clinical professor of urology at University of Illinois Medical School, Chicago, and Dr. Mehta is medical director of radiation oncology at UroPartners.
Disclosures: Dr. Yonover is a consultant and speaker for Augmenix, Astellas, and MDxHealth. Dr. Mehta is a consultant for Augmenix and trains/proctors physicians on SpaceOAR placement technique.
For urologists and radiation oncologists alike, when treating prostate cancer, one recurring theme is “protect the rectum.” As surgeons, we learn meticulous techniques to avoid rectal injuries, and our radiation colleagues have long strategized on how to optimally deliver the maximum dose of tolerable radiation while minimizing radiation exposure to “organs at risk” such as the bladder, rectum, urethra, and penile bulb. In this era of dose escalation and hypofractionation, rectal toxicity is of paramount consideration.
In this article, we discuss one particular new product and how it may herald a significant change in the landscape of radiation therapy for prostate cancer.
A novel solution to reduce rectal dosing is to physically push the rectum away from the prostate during radiation treatment, which can be achieved with the transperineal injection of a hydrogel “spacer” that solidifies in seconds and stays in place through radiation therapy before fully resorbing in approximately 6 months. The concept is not new, but the first product of its kind to receive FDA approval, SpaceOAR hydrogel, was introduced by Augmenix in April 2015 and is now widely available for routine use.
Our large single-specialty urology group, UroPartners in Chicago, has been utilizing SpaceOAR hydrogel since its introduction, and we now have one of the largest series with the product in the United States. When we looked at our own experience with SpaceOAR, we reported on a retrospective series of 105 men receiving intensity-modulated radiation therapy (IMRT) monotherapy for low- and intermediate-risk prostate cancer (81Gy, 45 fractions) who received SpaceOAR hydrogel. We examined the dose-volume histograms (DVHs) with respect to rectal dosing and compared them to the non-spacer control arm in the SpaceOAR randomized clinical trial (Huang et al. Poster presentation, AUA annual meeting [Engineering in Urology], May 2016).
With the spacer hydrogel, we were able to achieve a mean rV70 (the percent volume of rectum that received 70 Gy) of 1.1% +/- 1.7% (0-8.3), which represents a 94% reduction in rectal dose compared to a published control arm and markedly below the recommended limit of 20% by QUANTEC safety guidelines. Likewise, we also saw large dose reductions to the penile bulb in our cohort (9.0 +/- 5.2 Gy), which is 82% lower than dosing guidelines.
After more than 250 SpaceOAR applications to date at the UroPartners Radiation Center in Chicago, we have not experienced any complications directly related to SpaceOAR placement. In one patient, SpaceOAR injection was well tolerated, but the patient then developed significant irritative voiding issues upon starting radiotherapy from what appeared to be exquisite bladder radiosensitivity. He stopped radiotherapy and instead underwent an uneventful robot-assisted laparoscopic radical prostatectomy. We do not feel the SpaceOAR hydrogel was responsible for his voiding issues and the gel placement did not complicate the surgery.
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