Stabilised Hyaluronic Acid Gel Rectal Spacers in MRI ‐Guided Brachytherapy for Gynaecological Cancers: A Prospective Feasibility Study

INTRODUCTION: To evaluate insertion feasibility of a stabilised hyaluronic acid (sHA) gel rectal spacer in gynaecological cancer high dose rate brachytherapy (GynBT). METHODS: This single institution prospective study included patients with gynaecological cancers receiving magnetic resonance imaging (MRI)-guided GynBT. Feasibility was assessed by technical success, clinician user experience, spacer visibility on MRI and spacer stability over the GynBT course. RESULTS: Twelve patients were included in this study. Insertion of sHA gel into the rectovaginal space was achieved in all 12 patients without spacer-related complications. Clinicians reported sHA gel as easy to use, with high visibility on TRUS (rated 4-5) and excellent visibility on MRI. Target-to-rectum distance increased with sHA spacer insertion (mean 7.82 mm, 95% CI: 5.27-10.36, p < 0.001). During GynBT, there was a reduction in sHA gel spacer volume (mean 1.75 cc, 95% CI: 0.57-2.93, p = 0.007) and craniocaudal distance (mean -3.87 mm, 95% CI: -7.37 to -0.36, p = 0.034). However, there were no significant changes in target-to-rectum distance (p = 0.490) and spacer level measurements (p > 0.2). CONCLUSION: Insertion of sHA gel rectal spacer is technically feasible and safe in GynBT, increasing the separation between the target and rectum. The sHA gel spacer is easy to use, highly visible on both TRUS and MRI, and stable during the entire GynBT course. Further studies are required to ascertain patient suitability, dosimetric comparison, patient-reported outcomes, toxicities, and optimal technique. TRIAL REGISTRATION: The study was registered with the Australian New Zealand Clinical Trials Registry (ACTRN12625000167460).