To date neither the optimal radiotherapy dose nor the existence of a dose-response has been established for salvage RT (SRT).
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A systematic review from 1996 to 2015 and meta-analysis was performed to identify the pathologic, clinical and treatment factors associated with relapse-free survival (RFS) after SRT (uniformly defined as a PSA>0. 2ng/mL or rising above post-SRT nadir). A sigmoidal dose-response curve was objectively fitted and a non-parametric statistical test used to determine significance.
71 studies (10,034 patients) satisfied the meta-analysis criteria. SRT dose (p=0.0001), PSA prior to SRT (p=0.0009), ECE+ (p=0.039) and SV+ (p=0.046) had significant associations with RFS. Statistical analyses confirmed the independence of SRT dose-response. Omission of series with ADT did not alter results. Dose-response is well fit by a sigmoidal curve (p=0.0001) with a TCD50 of 65.8Gy, with a dose of 70Gy achieving 58.4% RFS vs. 38.5% for 60Gy. A 2.0% [95% CI 1.1-3.2] improvement in RFS is achieved for each Gy. The SRT dose-response remarkably parallels that for definitive RT of localized disease.
This study provides level 2a evidence for dose-escalated SRT>70Gy. The presence of an SRT dose-response for microscopic disease supports the hypothesis that prostate cancer is inherently radio-resistant.
Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology. 2016 Nov 15 [Epub ahead of print]
Christopher R King
Department of Radiation Oncology, UCLA School of Medicine, Los Angeles, United States. Electronic address: .