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    Interventional procedure overview of biodegradable spacer insertion to reduce rectal toxicity during radiotherapy for prostate cancer

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    Validity and generalisability of the studies

    • Evidence assessments on different biodegradable perirectal spacers (including synthetic hydrogel, and biodegradable balloons) used during different radiotherapy techniques (EBRT or BT alone or in combination) for patients with low to intermediate prostate cancer were included within this overview.

    • Systematic reviews included different types of studies but were predominantly based on 1 RCT done in the USA (Mariados 2015 and related publications) and non-randomised studies (nRCTs). There is overlap of primary studies between included systematic reviews.

    • Hydrogel spacers were compared to no spacers in 3 systematic reviews (Miller 2020, Armstrong 2021, Vaggers 2021), and the RCT which was limited to T1 and T2 tumours (Mariados 2015). Hydrogel spacers were compared to balloons in a HTA (NIPHNO, EUnetHTA 2020) and 1 systematic review (Ardekani 2021). Biodegradable rectal spacers, including hydrogel spacers, balloons, and hyaluronic acid spacers, were compared to each other in one systematic review (Mok 2014).

    • Outcomes assessed were mainly reduction in toxicity, reduction in radiation doses, increase in the distance between the prostate and rectum, quality of life and prostate motion or displacement. Outcomes such as survival, patient satisfaction were not reported in studies.

    • Variations were noted in patient characteristics (tumour stages), radiotherapy techniques and protocols used (either on its own or in combination with other techniques), and follow-up periods across primary studies included within the systematic reviews. These variations might have influenced the performance of spacers and clinical outcomes.

    • Follow-up varied across studies and ranged from 6 to 60 months.

    • Most of the related case series with small sample sizes that assessed biodegradable rectal spacers have been included in the appendix. 3 of these small case series used a substance (DuraSeal) 'off-label' for this procedure.