LOCL-02 DOSIMETRIC AND CLINICAL ANALYSIS OF PSEUDO-PROGRESSION VS. RECURRENCE AFTER HYPER-FRACTIONATED RADIOTHERAPY FOR BRAIN METASTASES BASED ON ENHANCED MAGNETIC RESONANCE IMAGING

PURPOSE: The main challenge in follow-up duration of patients with brain metastases after stereotactic radiotherapy is to distinguish between pseudo-progression and tumor recurrence. The objective of this study is to retrospectively analyze the predictive factors. METHODS: The study included 123 patients with enlarged brain metastases after hyper-fractionated radiotherapy in our center from 2009 to 2019, and the baseline clinical features, radiotherapy planning parameters, and enhanced magnetic resonance imaging before and after radiation therapy were analyzed. Logistic regression was performed to compare the differences between groups. independent risk factors with P < 0.05 and associated with recurrence was used to establish a predicting nomogram and validated by Bootstrap in internal cohort. RESULTS: The median volume of lesions was 8.4 cc. The median follow-up time was 68.4 months (interquartile range [IQR], 30.4 – 63.2 months). A total of 76 (61.8%) patients were evaluated as pseudo-progression, 47 patients (38.2%) were evaluated as tumor recurrence. The median time to tumor recurrence and pseudo-progression were 12.9 months (IQR, 8.7 – 19.6 months) and 18.3 months (IQR, 9.4 – 27.8 months) respectively. Variables associated with tumor recurrence included: gross tumor volume ≥ 6 cc, biological effective dose < 60 Gy, target coverage < 96% and no targeted therapy. The area under curve value was 0.730 and mean absolute error in calibration curve was 0.041. Sixty-one patients received salvage therapy, including re-irradiation (n = 32, 26.0%), surgical resection (n = 22, 17.9%) or systemic therapy (n = 22, 17.9%). The survival time in pseudo-progression and tumor recurrence groups were 66.3 months (95% CI, 56.8 – 75.9 months) and 39.6 months (95% CI, 29.2 – 50.0 months, respectively; P = 0.001). CONCLUSIONS: Clinical and dosimetry features of hyper-fractionated radiation therapy based on enhanced brain magnetic resonance can help distinguish pseudo-progression from tumor recurrence after hyper-fractionated radiotherapy for brain metastases. And the individual risk could be estimated by the nomogram effectively.