HPB P27 Stereotactic Ablative Radiotherapy in Colorectal Liver Metastases: A Systematic Review and Descriptive Summary of Practice
Authors: Maccabe Thomas , Nwogwugwu Obi , Lee Sheila , Blencowe Natalie , Pandanaboyana Sanjay , Pathak Samir 
Published: December 2022

Abstract

Background
Treatment options for unresectable Colorectal Liver Metastases (CRLM) have, until recently, been mostly limited to radiofrequency or microwave ablation though there are some limitations. Stereotactic Ablative Radiotherapy (SABR) is being used increasingly to overcome these limitations with control rates and survival outcomes, reported to be comparable to ablation. However, there are several unknown factors regarding the use of SABR in CRLM, including the criteria for patient selection, optimal dose delivery and target volumes. This systematic review aims to summarise and describe the patient selection, indications, treatment regimens and survival outcomes for SABR in CRLM.

Methods
The literature was searched systematically to identify all articles reporting on SABR for CRLM, from inception until 1st January 2021. Primary research studies were included if they described the patient inclusion criteria, treatment regimens and outcomes from inoperable CRLM. Studies with extra-hepatic colorectal metastases were included if the metastases were deemed treatable with local therapies. Recommendations from the UK SABR consortium was used to categorise radiation dosage and fractionation. Data were collected on patient demographics, selection criteria, radiotherapy delivery and dosage and survival outcomes.

Results
Fifteen studies were included with a total of 522 patients and 770 liver metastases.
Most studies (9/15) included patients with three or fewer metastases, however the tumour size varied from 4–15cm. Eleven studies stipulated that CRLM must be unresectable, with only one study defining unresectability according to patient or disease characteristics. Three quoted inoperability after multidisciplinary or tumour board decision, the remainder did not justify inoperability. Of these eleven, six studies stipulated that they must also be unsuitable for ablation. Patients with extra-hepatic metastases were included in ten studies, but the justification was inconsistent across all studies.
Total radiation dose and fractionation varied across all studies, ranging from 16–75Gy and 3–8 fractions respectively. No studies pre-determined a target dosage for any cohort. Approximately half (149/301) of all patients received regimens in accordance with the UK SABR Consortium recommendations. Immobilisation methods were reported in eleven studies with nine different permutations including moulds, frames, abdominal compressions or breath control techniques.
One year local control was reported at 48–96%, 2 years: 36–91% and 3 years: 26–85%. Overall survival at 1 year ranged from 53–100%, 2 years: 26–81% and 3 years: 21–65%.

Conclusions
There are significant variations in practice for delivering SABR for CRLM. There is no absolute consensus determining patient selection or treatment regimens. Although outcomes may seem promising in a selection of studies, the wide range of results and heterogeneity of studies means that truly reliable conclusions cannot be synthesised. Consensus statements to inform high-quality prospective studies are urgently needed to optimise treatment and improve patient outcomes.