Comprehensive comparison of Bioprotect balloon and Barrigel hydrogel rectal spacers in proton therapy for prostate cancer

BACKGROUND: To compare the geometric consistency, dosimetric performance, and early clinical outcomes of the BioProtect balloon spacer versus the Barrigel hydrogel spacer in patients receiving proton therapy for prostate cancer. METHODS: This retrospective study analyzed 50 prostate cancer patients treated with proton therapy: 25 with BioProtect and 25 with Barrigel. Anatomical displacement, rectal dose (V70/V60/V50), rectal wall infiltration (RWI), and early gastrointestinal (GI) toxicity were assessed. Two treatment plans per patient (prostate-only and whole-pelvis) were generated using identical optimization workflows. Geometric and dosimetric comparisons were performed using t-tests, and correlations between anatomy and dose were evaluated. RESULTS: BioProtect achieved greater midgland (18.28 mm vs. 14.52 mm, p < 0.01) and apical (12.8 mm vs. 8.3 mm, p < 0.001) separation. Prostate-only plans with BioProtect showed significantly lower rectal V60 (2.02% vs. 6.69%) and V50 (4.28% vs. 10.16%) (p < 0.01). Whole-pelvis plans showed V70/V60/V50 reductions of 72.8%, 66.1%, and 66.7%, respectively (all p < 0.01). No RWI events occurred in the BioProtect arm, compared to three with Barrigel. Acute grade ≥ 2 GI toxicity was observed in 0% of BioProtect vs. 17.4% of Barrigel patients at 3 months. CONCLUSION: BioProtect demonstrated superior and more consistent rectal sparing in proton therapy compared to Barrigel. The fixed geometry balloon design yielded enhanced separation, reduced rectal dose, and fewer early GI toxicities. These findings suggest an dosimetric and clinical advantage of BioProtect in the proton therapy setting.