What is the quality of hydrogel spacer insertions? and which patients will benefit? A literature review

Validation of a Quality Metric Score to Assess the Placement of Hydrogel Rectal Spacer in Patients Treated With Prostate Stereotactic Radiation Therapy

Purpose

To evaluate the quality of the interspace between the prostate and rectum and assess the effect on the dose to the rectum by measuring the spacer quality score (SQS) before and after implanting a hydrogel rectal spacer.

Methods and Materials

Thirty patients with prostate cancer were treated with stereotactic ablative body radiation therapy as part of the SPORT clinical trial. Each patient had a 10 mL polyethylene glycol hydrogel spacer inserted transperineally. Computed tomography scans were acquired before and after spacer insertion, 10MV flattening filter free (FFF) stereotactic ablative body radiation therapy (SABR) treatment plans were generated using each image set. To calculate the SQS, the prostate-rectal interspace (PRI) was measured in the anterior-posterior orientation, parallel to the anatomic midline at the prostate base, apex, and midgland on the prespacer and postspacer computed tomography. Measurements were taken in 3 transverse positions between the prostate and the rectum, and PRI scores of 0, 1, and 2 were assigned if the interspace between prostate and rectum was <0.3, 0.3 to 0.9, or ≥1 cm, respectively. The overall SQS was the lowest of the PRI scores. Differences between prespacer and postspacer PRIs and SQS were investigated by performing Fisher's exact test and differences between doses to the rectum were investigated by performing the paired samples Wilcoxon rank-sum test and Student t test.

Results

Statistically significant differences between prespacer versus postspacer patients were found when grouping patients according to their overall SQS. The PRI summary score did not reach statistical significance between prespacer and postspacer at the base but was significantly higher for the prostate midline and apex. Statistically significant differences in some rectum dose-volume metrics were found when grouping patients according to their PRIs and SQS.

Conclusions

SQS before and after the spacer insertion was evaluated and was found to be correlated with pre- and postspacer rectal dosimetry. Sources of improvement of the SQS scoring metric and limitations are discussed.

Effect of Transperineal Versus Transrectal Prostate Biopsy on the Quality of Hydrogel Spacer Placement in Men Prior to Radiation Therapy for Prostate Cancer

OBJECTIVE

To determine whether prostate biopsy type affects spacer placement quality using a large sample of patients treated in the ambulatory setting.

METHODS

A retrospective cohort study was conducted on patients diagnosed with prostate cancer who underwent hydrogel spacer placement before primary radiation treatment between 2018 and 2023 after transperineal (TP) or transrectal (TR) prostate biopsy. Study outcomes were Spacer Quality Score (SQS) (0-2, with greater values indicating better placement), Rectal Wall Infiltration (RWI) (0-3, with lower values indicating lack of RWI), and the occurrence of other hydrogel complications.

RESULTS

A total of 395 patients were included. A pre-hydrogel TR biopsy was performed in 273 patients (69.1%), while TP biopsy was performed in 122 (30.9%). A SQS ≥1 occurred in 308 (77.9%) patients. A greater proportion of TP patients had a favorable SQS (≥1) compared to those who underwent TR (87.7 vs 73.5%, P <.002). An RWI score ≥2 was found in 180 (45.6%) patients. The proportion of patients with an unfavorable RWI score (≥2) did not differ significantly by type of biopsy performed. Patients who had an interval of >70 days between biopsy and hydrogel placement had significantly decreased odds of an RWI score ≥2 (odds ratio = 0.42, 95% confidence interval: 0.21-0.83). Only one infection was found after hydrogel placement.

CONCLUSION

The quality of hydrogel placement was significantly better in men who had undergone TP biopsy. Rectal wall infiltration was more common than previously reported but did not differ between TP and TR biopsies.