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Bone metastases occur in approximately one third of patients with cancer and 70% of these originate in the spine. Radiotherapy (RT) is an important tool in the multidisciplinary management of spinal metastases (SM). Stereotactic ablative body radiation therapy (SABR) uses a highly conformal and image-guided approach to deliver higher radiation doses accurately. Studies have shown that SABR is effective in treating SM. However, selecting the most appropriate patients remains challenging. Our aim was to analyse patients who received SABR for SM since its implementation at our institution and determine local control, toxicity and survival.

We retrospectively analysed data on patients who were referred for SABR for SM between October 2018 and April 2021. We obtained patient data and tumour characteristics including histology, size, number and location of SM; and presence of extra-cranial disease. Treatment planning with the aid of a planning MRI was done on Eclipse and all patients were treated using a volumetric modulated arc therapy (VMAT) plan. SABR dosimetry was obtained. Kaplan-Meier method was used to estimate survival times for individual patients from the day SABR was completed to the date of last follow up or death.

A total of 32 SM were treated in 30 patients. The median age at initial diagnosis was 57.4 years and the median age at first fraction was 65.5 years. Seventeen patients had breast cancer, 9 had prostate cancer, 2 had lung cancer, 1 had oesophageal cancer and 1 had head and neck cancer. Six SM were confirmed on histology. Nine patients had extra-cranial disease and 22 patients were on systemic treatment. Back pain was the presenting symptom in 18 out of the 32 SM. The spinal levels treated were cervical (1), thoracic (23), lumbar (7) and sacral (1). The median performance status was 1. Eight SM were treated with 3 fractions and 24 were treated with 5 fractions. The median dose was 30 Gy. The median distance to cord was 2.1mm. The median D 0.035cc to cord for 3 fractions was 16.94 Gy and for 5 fractions was 23.6 Gy. The median time to first fraction from date of referral was 2 months. Twenty five out of 32 (78%) cases had improvement in pain levels or controlled pain at follow up. There were 11 reports of acute toxicity, most commonly pain flare (n=7). One patient had a vertebral fracture post SABR. Twenty five out of 32 SM (78%) were stable on follow up MRI, 2 had progressed in the radiotherapy field, and 5 cases did not have imaging available for review. Median overall survival was not reached. Cumulative proportion surviving at 2 years was 77%.

Our retrospective study demonstrates that the use of SABR is an effective treatment option for SM and offers symptomatic relief and acceptable disease control with low levels of toxicity. Larger, multicentre prospective trials are warranted to determine appropriate patient selection, optimal dose and fractionation, and follow up protocols.