Abstract 118P
Background
Treatment of chordoma generally involves surgical resection followed by post-op radiotherapy (RT). Definitive RT can be considered, if resection would result in significant morbidity. However, the incidence of local recurrence (LR) remains high. The purpose of this study is to investigate the influence of RT dose on the pattern of LR for clival and spinal chordoma treated with proton/photon RT.
Methods
A retrospective analysis was performed on 18 patients diagnosed with chordoma and treated with RT from 2010 to 2022. Previous RT treatment plans were merged with diagnostic scans showing the LR. The LR was then mapped out and previous RT delivered to this area was analysed. X2 test was used to investigate the relationship between dose delivered and LR. Local control (LC), disease-free survival (DFS) and overall survival (OS) were estimated using the Kaplan-Meier survival function.
Results
Majority of patients were male (61.1%). Mean age was 58 years (range 30-82). Sacrum was the commonest site of disease (38.8%). 5 patients had pre-op, 8 had post-op, 4 had definite RT and one patient had both pre and post op RT. Majority of patients (72.2%) had surgery. Median RT dose for pre-op was 50.0Gy, post-op was 72.0Gy RBE and definite RT was 76.7Gy RBE With a median follow up period of 60 months (range 9-115), the OS was 87.5%, LC was 62.7% and DFS was 56.9% at 5 years respectively 10 patients (55.5%) developed LR. There were 46.2% of patients with planned R1/2 margin and this was associated with risk of LR (38.5% vs 7.7% for an R0 resection, p = 0.04). Median time to LR was 41 months (range 16-111). There were 3 cases of LR outside the RT field and 3 unresected patients developed local progression after definite RT Within the post-op RT group, 2 patients had LR within the CTV1 volume and 3 patients within the CTV2 volume. No relationship between CTV1 (median dose 50.4Gy) and CTV2 (median dose 72.0Gy) volumes and LR was found (p=0.46). However, for patients who had post-op and definite RT, a dose of <74Gy was strongly associated with risk of LR (87.5% vs 12.5%, p = 0.03).
Conclusions
LR is common in clival and spinal chordoma even after surgery and radiotherapy. There is a strong trend for better LC for patients who received dose of >74Gy in the post-op and definite setting.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.