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Imaging metrics predicted OS in NSCLC treated with stereotactic ablative radiotherapy
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Pretreatment PET/CT imaging metrics provided potential predictors of OS and cancer-specific survival in patients with non–small cell lung cancer treated with stereotactic ablative radiotherapy.
“Stereotactic ablative radiotherapy for early-stage lung cancer is a highly promising new treatment modality and, based on excellent outcomes in numerous phase 2 clinical trials, has rapidly become a de facto standard of care for patients unable to tolerate standard surgical therapy,” Billy W. Loo Jr., MD, PhD, DABR, thoracic radiation oncology program leader at Stanford University and Stanford Cancer Institute, told HemOnc Today. “It is now being actively investigated in ‘high-risk’ patients who are borderline surgical candidates because of poor pulmonary function or other comorbidities, and also in selected cohorts of surgical candidates.”
Billy W. Loo Jr.
Loo and colleagues retrospectively reviewed records of 54 patients with early-stage NSCLC who were treated with sterotactic ablative radiotherapy to investigate the association between metabolic metrics on pre- and post-treatment PET/CT imaging and primary tumor control, PFS, OS and cancer-specific survival.
Among the study cohort, 45 patients were considered medically inoperable and nine patients declined surgery. A thoracic surgeon evaluated all patients considered inoperable, except one patient with a guarded prognosis from rectal cancer, bilateral pulmonary emboli and atrial fibrillation.
“As with surgery, because of the high rates of primary tumor control achieved with [stereotactic ablative radiotherapy], the most common pattern of recurrence after treatment is metastasis to regional or distant sites,” Loo said. “Particularly in patients who are unable to have surgery, non-invasive prognostic factors for metastatic recurrence would be an important selector for patients who might benefit from systemic therapy, possibly in the adjuvant setting.”
Median follow-up time for the study cohort was 13.2 months. The researchers estimated that 1-year primary tumor control was 100%, PFS was 83%, OS was 87% and cancer-specific survival was 94%.
According to study results, pretreatment maximum standardized uptake value (SUV; P=.014), metabolic tumor volume (MTV) threshold 7 (P=.0077) and MTV threshold 10 (P=.0039) correlated significantly with OS. Patients in the low-MTV threshold 7 subgroup had higher 1-year estimated OS (100% vs. 78%; P=.0077) and cancer-specific survival (100% vs. 88%; P=.082) than patients in the high-MTV threshold 7 subgroup.
The researchers observed that multiple pretreatment PET/CT metrics correlated with OS on univariate analysis. Nine of 13 deaths were due to intercurrent illness; however, these were almost evenly distributed among the high- and low-MTV subgroups. The link between MTV and cancer-specific survival indicates that the relationship is cancer specific, as all cancer specific deaths occurred in the high-MTV population.
“Although there have been some discordant findings in the literature, our study demonstrated that analysis of pretreatment [18F-fluorodeoxyglucose]-PET scans yielded prognostic factors for OS, namely maximum SUV and MTV,” Loo said. “This is appealing because the information is readily available from scans routinely done for initial cancer staging. Ultimately, imaging metrics such as these will probably be combined with other noninvasive assays such as blood-based biomarkers to improve the predictive potential.”
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