ESTRO 2024 - Abstract Book

S954

Clinical - CNS

ESTRO 2024

Of the 26 metastases, 6 metastases were thought to have shown evidence of tumour progression at 3 months, as per RANO-BM, with at least 30% growth demonstrated radiologically and clinically with increasing dose of steroids. Three of these were surgically resected and histological diagnosis of malignancy was confirmed. The remaining 3 metastases were in patients who died at 3-, 4-, and 5-months following SRS, all of which were neurological deaths, suggesting that increase in size identified using the 3-month diagnostic MRI was true progression. Median CBF of the metastases was 26.35, 31.18, 34.93 ml/100g/min at baseline, 1- and 3-months respectively. Baseline CBF in the metastases was significantly lower in patients who demonstrated evidence of stable disease or partial response at their first standard post treatment MRI at 3 months compared to patients who had progressive disease, (20 vs 104 ml/100g/min, p-value = 0.03), Figure 1. This was also reflected in the BM:GM ratio. There was no statistically significant difference in CBF at 1 month and 3 months between the two groups based on tumour progression. However, the BM:GM ratio of the BM 1 month following SRS was significantly higher in patients who demonstrated evidence of stable disease or partial response compared to the group who had progressive disease. There was no significant different in the BM:GM ratio between the 2 groups at 3 months.

Conclusion:

Perfusion of brain metastases can be performed routinely using standard MRI scanners using the ASL technique, which doesn’t require the use of exogenous contrast. It is increasingly being performed after SRS treatment to assess response, however, at baseline it may have utility in predicting response to SRS. We demonstrate an association between higher baseline CBF within the metastasis and tumour progression at 3 months. Increased CBF may signify presence of hypoxia (3). Studies have shown that CBF can increase up to two-fold in presence of hypoxia (3). Hypoxia is an important factor in radioresistant disease and hypoxia modifiers have been tested in clinical trials in non-neurological tumours (4). For those patients where surgery and SRS may have equivalent outcomes, e.g. accessible location, anaesthetic fitness and good prognosis, such information from non invasive imaging can guide treatment decision-making. These findings need to be validated in larger studies.

Keywords: perfusion, biomarker, stereotactic radiosurgery

References:

1. NICE 2018. Brain tumours (primary) and brain metastases in adults. UK.