Rectal spacer hydrogel in 1.5T MR-guided and daily adapted SBRT for prostate cancer: dosimetric analysis and preliminary patient-reported outcomes

Bladder Cancer

Br J Radiol. 2020 Oct 23:20200848. doi: 10.1259/bjr.20200848. Online ahead of print.


OBJECTIVE: The main aim of the current analysis was to explore the hypothetical advantages using rectal spacer during 1.5T MR-guided and daily-adapted PC SBRT compared to a no-rectal spacer hydrogel cohort of patients.

METHODS: The SBRT-protocol consisted of a 35 Gy schedule delivered in five fractions. Herein we present a dosimetric analysis between spacer and no-spacer patients. Furthermore, treatment tolerability and feasibility were preliminarily assessed according to clinicians-reported outcomes at the end of treatment and patient-reported outcomes measures (PROMs) in both arms. Toxicity and quality of life were assessed at baseline and after treatment using the Common Terminology Criteria for Adverse Events v5.0, International Prostatic Symptoms Score, ICIQ-SF, IIEF-5, and EORTC-QLQ-C30 and PR-25 questionnaires.

RESULTS: 120 plans (pre- and daily adaptive SBRT planning) were analyzed in 20 patients (10 patients in spacer group and 10 patients in no-spacer group) treated using 1.5T MR-guided adaptive SBRT. Statistically significant dosimetric advantages were observed in favor of the spacer insertion, improving the PTV coverage in terms of V33.2Gy >95% and PTV 37.5 Gy <2% mainly during daily-adapted SBRT. Also, rectum V32, V28 and V18Gy and bladder V35Gy <1 cc were significantly reduced in the spacer cohort. Concerning the PROMS, all questionnaires showed no difference between the pre- and post-SBRT evaluation in both arms, excepting the physical functioning item of EORTC QLQ-C30 questionnaire that was declined in the no-spacer group.

CONCLUSION: These preliminary results strongly suggest the adoption of peri-rectal spacer due to dosimetric advantages not only for rectal sparing but also for target coverage. Longer follow-up is required to validate the clinical impact in terms of Clinicians-reported toxicity and PROMs.

ADVANCES IN KNOWLEDGE: This the first experience reporting preliminary data concerning the potential dosimetric impact of rectal hydrogel spacer on MR-guided SBRT for prostate cancer.