ESTRO 2024 - Abstract Book

S2000

Clinical - Mixed sites, palliation

ESTRO 2024

Results:

45 patients who received SABR for liver oligometastatic disease between 2016 and 2022 at a single UK centre were assessed. All treated metastases (n=52) were less than 5cm in greatest dimension and median patient age was 71 years (IQR 63-78.5 years). The majority of patients had colorectal liver metastases treated (62.2%) with other primary sites including urothelial (2.2%), breast (6.7%), melanoma (4.4%), lung (4.4%), anal (2.2%), renal cell carcinoma (2.2%), gastrointestinal stromal tumour (2.2%), pancreas (6.7%), cholangiocarcinoma (4.4%) and oesophageal cancer (2.2%). Radiotherapy planning CT scans were performed with active breathing control (ABC) in exhale position for 95.6% of patients with 4D-CT imaging used to assess tumour motion for the remainder who were unable to tolerate ABC. 77.8% of patients had their response to SABR assessed radiologically with liver CT/MRI imaging at least 3 months following completion of treatment. The remainder did not go on to have follow-up imaging post completion of SABR or were lost to follow-up and were not included in analysis of treatment response. With respect to treatment response, 74.3% of all patients had sustained local tumour control following SABR with no radiological progression of the treated metastasis at any stage, whilst 25.7% of patients (n=9) subsequently developed local progression of the treated metastasis at some stage following SABR. Median time to local disease progression for these patients was 12 months (IQR 5-26 months) and 77.8% of this patient cohort had colorectal liver metastases. Of the 9 patients with local progression post-SABR, pattern of relapse was assessed following fusion of follow-up diagnostic imaging with radiotherapy planning CT scan for 7 patients (2 patients had poor fusion of scans and were not included in this assessment). All assessed patients with local tumour progression had relapse within the ablative dose volume and 57.1% also had marginal relapse (adjacent to ablative dose volume). 34.9% of patients had a complete response (CR) to SABR as best radiological response (BRR); however 13.3% of patients who had prior complete radiological response subsequently developed progressive disease at the treated site. 37.2% of patients had a partial response (PR) to treatment, 20.9% had stable disease (SD) and 7% had progressive disease (PD) as BRR (no recorded radiological response to treatment). Median time to BRR for patients who achieved local control (SD, PR or CR) was 4 months (IQR 3-7months). Median delivered BED 10 for the entire patient cohort was 112.5Gy (IQR 100-132Gy) whilst median delivered BED 10 for those who developed local progression of liver metastasis post-SABR was lower at 100Gy (IQR 85.5-132Gy). Median overall survival post-SABR for the entire cohort was 20 months (IQR 15.5-27) with a 1-year overall survival rate of 80.5% and 1-year local control rate of the treated metastasis of 90.3%. Outcomes of this single centre analysis support published data with respect to high local control rates following SABR for liver metastases 1 . To date, the majority of the published data relates to colorectal liver metastases whereas all primary tumour sites were included in this review. Median time to progression for the 25.7% of patients who did ultimately develop local progression post-SABR was 12 months which suggests that there is still some local progression free survival benefit for these patients. Delivered BED 10 was lower at 100Gy in those who progressed post-SABR due to metastasis location/organ at risk constraints which is likely to have been a contributing factor in this regard. All patients assessed who had local relapse post-SABR relapsed within an ablative dose volume and 57.1% also had marginal relapse. This suggests that higher biologically effective doses may be required to achieve ablative effect in such patients and consideration should be given to increased clinical target volume margins to reduce marginal relapse rate. Conclusion: