DISCUSSION
toxicities, V50 reduction, prostate, prostate RT.The SpaceOAR
SEPARATION, PROSTATE CANCER, PROSTATE
To our knowledge, the current study is the first multicenter central core lab report comparing two biodegradable perirectal spacers in terms of their defining function: the ability to reduce radiation exposure in the rectum of patients undergoing prostate RT.The SpaceOAR has been approved by the FDA and used successfully worldwide. Clinical trials in Europe and the USA have demonstrated that the hydrogel is safe, and that the space created significantly reduces the radiation delivered to the rectum.An earlier comparison of these two spacersIt is noteworthy that among our report, the two spacers performed similarly in the V80 reduction, and UH corresponding V36.25 reduction with ∼5% difference between the spacers, but at 87.5%, 75%, and 62.5% of the full dose (V70, V60, and V50), a significant gap emerged: relative V70 reduction was 17% higher with the balloon spacer, V60 reduction was 28% higher for the balloon spacer, and V50 reduction was 33% higher with the balloon spacer.Our findings comparable with the first results of the French multicenter open‐label study (BioPro‐RCMI‐1505) using the balloon spacer.Future long term‐controlled studies should investigate whether more complete and consistent reduction in rectal radiation translates to better long‐term clinical outcomes.This report has several limitations: Prior spacer implantation experience is inconsistent across study arms; specifically, the experience level was consistently higher in the SpaceOAR arm, ahead of the sets of patients reported. Notwithstanding, the nonrandomized nature of our analysis precludes us from ruling out hidden advantages (unrelated to experience) that may have favored the users of the balloon spacer technology. Such advantages are possibly related to the balloon pre‐defined shape, size, and symmetry. These technological characteristics of the balloon may contribute to the significant dose reduction as shown in our study compared to the gel, as previously demonstrated by Fischer‐Valuck which evaluated the symmetry correlation to rectal dose reduction.Although baseline DVH values tended slightly to be higher in the SpaceOAR group compared to baseline DVHs values in the balloon spacer group, these differences differ insignificantly (Given that the mean baseline characteristics were found to be similar between the two study arms, and the use of a central core lab, it is tempting to conclude that rectal dose reduction was higher among subjects receiving the balloon spacer. The superiority of the balloon, achieving greater rectal dose reduction may be attributed to the (1) larger perirectal separation provided by the balloon (typically 18 mm)Going forward, prospective randomized trials of the two technologies should be carried out to further assess physician satisfaction with symmetry attained, degree of control of the spacing achieved, ease of use as well as acute and chronic toxicities experienced by men treated for prostate cancer. Only by meticulous assessment of the respective approaches will clinicians gain confidence with the use of spacer technologies to neutralize the dosimetric challenges created by the intricate anatomic relationship between the prostate and rectum.