單一中心初步經驗：
SpaceOAR置入後水凝膠分佈與直腸壁浸潤之真實世界分析

陳聖凱、邱士庭

台灣大學醫學院附設醫院 泌尿部

Real-World Analysis of Hydrogel Spacer Distribution and Rectal Wall Infiltration After SpaceOAR Placement: Initial Experience from a Single Center

Shen-Kai Chen, Shih-Ting Chiu

Department of Urology, National Taiwan University Hospital, Taipei, Taiwan

Purpose: Rectal hydrogel spacer (SpaceOAR) is widely used to reduce rectal radiation dose during prostate radiotherapy. However, real-world data on spacer distribution patterns and rectal wall infiltration (RWI) remain limited, and the clinical significance of RWI is not well characterized. This study aimed to evaluate the distribution patterns of SpaceOAR, RWI incidence and grading, and procedure-related complications in a prospective cohort from a single tertiary center.

Materials and Methods: This prospective study included 16 consecutive patients who underwent SpaceOAR placement at National Taiwan University Hospital between August 2025 and March 2026. All procedures were performed by a single urologist using a transperineal approach under transrectal ultrasound guidance. Patients underwent pelvic MRI within two weeks after spacer implantation. Hydrogel distribution and symmetry were assessed on T2-weighted MRI using a semiqualitative scoring system evaluated at three levels: midgland, 1 cm superior, and 1 cm inferior to the midgland. RWI was identified and categorized by grade based on imaging findings. Clinical outcomes, including early complications and adverse events, were prospectively recorded. Descriptive analyses were performed to evaluate spacer distribution patterns, RWI incidence, and complication rates.

Results: The mean prostate–rectum separation achieved was 1.13 cm (IQR: 0.91–1.44). Symmetric hydrogel distribution at the midline was observed in 81.25% of patients, while symmetry at 1 cm superior and inferior to the midgland was achieved in 87.5% and 81.25%, respectively. Overall, complete symmetry across all levels was noted in 68.75% of cases. One patient (6.25%) demonstrated far lateral distribution (>2 cm), which occurred in the first case. Notably, after the initial 10 cases, all subsequent patients achieved symmetric distribution at all evaluated levels, suggesting a procedural learning curve. RWI was identified in 5 patients (31.25%), including 4 cases of grade 1 and 1 case of grade 3 involvement. Despite the relatively high incidence of RWI, no major clinical sequelae were observed. Other complications included one case of prostatic venous intravasation and one case of urinary retention. No patients developed fever, abscess, or Clavien–Dindo grade ≥3 adverse events.

Conclusions: In this prospective single-center experience, SpaceOAR placement achieved adequate prostate–rectum separation with a high rate of symmetric distribution, which improved with operator experience, suggesting a learning curve of approximately 10 cases. Although RWI was observed in a substantial proportion of patients, most cases were low grade and not associated with clinically significant complications. These findings suggest that, in real-world practice, spacer distribution is operator-dependent, while RWI may not necessarily translate into adverse clinical outcomes.