Should organs at risk (OARs) be prioritized over target volume coverage in stereotactic ablative radiotherapy (SABR) for oligometastases? A secondary analysis of the population-based phase II SABR-5 trial
Abstract
BACKGROUND AND PURPOSE
Stereotactic ablative radiotherapy (SABR) for oligometastases may improve survival, however concerns about safety remain. To mitigate risk of toxicity, target coverage was sacrificed to prioritize organs-at-risk (OARs) during SABR planning in the population-based SABR-5 trial. This study evaluated the effect of this practice on dosimetry, local recurrence (LR), and progression-free survival (PFS).
METHODS
This single-arm phase II trial included patients with up to 5 oligometastases between November 2016 and July 2020. Theprotocol-specified planning objective was to cover 95% of the planning target volume (PTV) with 100% of the prescribed dose, however PTV coverage was reduced as needed to meet OAR constraints. This trade-off was measured using the coverage compromise index (CCI), computed as minimum dose received by the hottest 99% of the PTV (D99) divided by the prescription dose. Under-coverage was defined as CCI < 0.90. The potential association between CCI and outcomes was evaluated.
RESULTS
549 lesions from 381 patients were assessed. Mean CCI was 0.88 (95% confidence interval [CI], 0.86-0.89), and 196 (36%) lesions were under-covered. The highest mean CCI (0.95; 95%CI, 0.93-0.97) was in non-spine bone lesions (n=116), while the lowest mean CCI (0.71; 95% CI, 0.69-0.73) was in spine lesions (n=104). On multivariable analysis, under-coverage did not predict for worse LR (HR 0.48, p=0.37) or PFS (HR 1.24, p=0.38). Largest lesion diameter, colorectal…
How strong is the evidence?
Evidence Hub reads this as a secondary / pooled analysis, done in people. Its evidence level is 3 of 5 (Moderate · trial / cohort / secondary analysis). Trials without a large randomized design, cohorts and secondary analyses give moderate evidence. Reported size: 381 participants or records.
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