A Multi-Institutional Phase 2 Trial of High-Dose SAbR for Prostate Cancer Using Rectal Spacer
By: Folkert MC, Zelefsky MJ, Hannan R, et al.
High-dose stereotactic ablative radiotherapy (SAbR) for prostate cancer (PCa) offers the radiobiologic potency of the most intensified radiation therapy regimens, but was associated with >90% rates of ulceration of the anterior rectal wall on endoscopic assessment that infrequently progressed to severe rectal toxicity in prior prospective series. A multi-institutional Phase II prospective trial was conducted to assess whether placement of a peri-rectal hydrogel spacer would reduce acute periprostatic rectal ulcer events following high dose (> 40 Gy) SAbR.
|Grade 1||Grade 2||Grade 3||Grade 1||Grade 2||Grade 3|
|Genitourinary (Any)||28 (65.1%)||20 (46.5%)||1 (2.3%)||27 (64.3%)||1 4 (33.3%)||1 (2.4%)|
|Irritative||19 (44.2%)||16 (37.2%)||1 (2.3%)||18 (42.9%)||12 (28.6%)||0 (0.0%)|
|Obstructive||18 (41.9%)||5 (11.6%)||0 (0.0%)||14 (33.3%)||6 (14.3%)||1 (2.4%)|
|Gastrointestinal||25 (58.1%)||10 (23.3%)||0 (0.0%)||14 (33.3%)||6 (14.3%)||0 (0.0%)|
|Reproductive||14 (32.6%)||6 (14.0%)||0 (0.0%)||6 (14.3%)||6 (14.3%)||0 (0.0%)|
- The SpaceOAR Hydrogel pivotal study did not use SBRT so the results may not be comparable.
- This study was not randomized and definitive claims about the benefits of a spacer cannot be made.
- These results may not be achieved with other SBRT protocols.
- Weaknesses of the study are primarily in terms of secondary endpoints, as the patient cohort was small with a median follow-up of 48 months to date.
- While it is early to interpret biochemical control results, and this Phase 2 trial is not powered or structured for rigorous comparison across other prospective trials, they are promising with a 4-year FFBF of 93.8% despite over half the treated patients considered unfavorable IR, and no patients receiving concurrentor adjuvant ADT.
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SBRT was not the method used in the SpaceOAR Hydrogel single-blind Phase III trial performed to evaluate dosimetric and clinical effects of SpaceOAR Hydrogel. IG-IMRT delivered at 79.2 Gy in 1.8-Gy fractions was the method used.
Results from case studies are not necessarily predictive of results in other cases. Results in other cases may vary.
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