Residual Postoperative Tumour Volume Predicts Outcome after High-dose Radiotherapy for Chordoma and Chondrosarcoma of the Skull Base and Spine

Abstract

Aims High-dose radiotherapy after surgical debulking is the treatment of choice for chordomas and chondrosarcomas. This study reviewed our outcomes, in relation to residual tumour volume and radiation dose, in order to inform our future practice. Patients and methods Nineteen patients referred to the Neuro-Oncology Unit at Addenbrooke’s Hospital (Cambridge, UK) between 1996 and 2009 and treated with photon radiotherapy were reviewed. Seventeen of the 19 were treated with curative intent. The median follow-up was 53 months. The tumours in the study had a mean gross tumour volume (GTV) of 17.2 cm 3 (median 10.5 cm 3) and a range of 0–76.3 cm 3. The median dose was 65 Gy in 39 fractions. Results The 5 year cause-specific survival for radically treated patients with chordomas was 92% and the 5 year local control rate was 83%. The 5 year cause-specific survival and local control rates with chondrosarcomas were both 100%. A planning target volume (PTV) below 90 cm 3 is predictive of local control, but volumes above this are not. The GTV seems to be a better predictor of outcome: among the 17 of 19 patients treated curatively, a GTV threshold of 30 cm 3 distinguished local failures from the 15 patients with local control, with sensitivity to detect local control of 100% (95% confidence interval 78–100%), specificity 100% (95% confidence interval 16–100%) and positive predictive value 100% (95% confidence interval 78–100%). Conclusions Our results show a high level of efficacy for fractionated photon radiotherapy after surgery, in keeping with other series. In addition, we found that although surgical debulking is essential, a small residual tumour volume may still be controlled with high-dose photon radiotherapy. This information may be relevant during neurosurgical planning, possibly allowing a reduction in risk of serious neurological deficits. This should encourage the further development of sophisticated photon radiotherapy, for patients unsuitable for proton therapy.