Tumour Volume and Dose Influence Outcome after Surgery and Highdose Photon Radiotherapy for Chordoma and Chondrosarcoma of the Skull Base and Spine

Aims: To evaluate the long-term outcomes of patients with chordoma and low-grade chondrosarcoma after surgery and high-dose radiotherapy. Materials and methods: High-dose photon radiotherapy was delivered to 28 patients at the Neuro-oncology Unit at Addenbrooke's Hospital (Cambridge, UK) between 1996 and 2016. Twenty-four patients were treated with curative intent, 17 with chordoma, seven with low-grade chondrosarcoma, with a median dose of 65 Gy (range 65-70 Gy). Local control and survival rates were calculated using the KaplaneMeier method. Results: The median follow-up was 83 months (range 7-205 months). The 5 year disease-specific survival for chordoma patients treated with radical intent was 85%; the local control rate was 74%. The 5 year disease-specific survival for chondrosarcoma patients treated with radical intent was 100%; the local control rate was 83%. The mean planning target volume (PTV) was 274.6 ml (median 124.7 ml). A PTV of 110 ml or less was a good predictor of local control, with 100% sensitivity and 63% specificity. For patients treated with radical intent, this threshold of 110 ml or less for the PTV revealed a statistically significant difference when comparing local control with disease recurrence (P - 0.019, Fisher's exact test). Our data also suggest that the probability of disease control may be partly related to both target volume and radiotherapy dose. Conclusion: Our results show that refined high-dose photon radiotherapy, following tumour resection by a specialist surgical team, is effective in the long-term control of chordoma and low-grade chondrosarcoma, even in the presence of metal reconstruction. The results presented here will provide a useful source for comparison between high-dose photon therapy and proton beam therapy in a UK setting, in order to establish best practice for the management of chordoma and low-grade chondrosarcoma. (C) 2018 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.