Radiotherapeutic factors in the management of cervical-basal chordomas and chondrosarcomas.

Abstract

To define prognostic factors for local control and survival in 90 consecutive patients treated by fractionated photon and proton radiation for chordoma or chondrosarcoma of the cranial base and upper cervical spine. Between December 1995 and December 2000, 90 patients (median age, 51.3 yr; range, 10-85 yr; male/female ratio, 3:2) were treated by a combination of high-energy photons and protons. Sixty-four patients had a chordoma, and 26 had a chondrosarcoma. The proton component was delivered by the 201-MeV proton beam of the Centre de Protontherapie d'Orsay. The median total dose delivered to the gross tumor volume (GTV) was 67 cobalt Gray equivalents (range, 22-70 cobalt Gray equivalents). With a median follow-up of 34 months (range, 3-74 mo), treatment of 25 tumors failed locally. The 3-year local control rates were 69.2% (+/-6.0%) and 91.6% (+/-8.4%) for chordomas and chondrosarcomas, respectively. According to multivariate analysis, a small tumor volume excluded from the 95% isodose line (P = 0.032; relative risk [RR], 0.098; 95% confidence interval [CI], 0.01-0.81) and a controlled tumor (P = 0.049; RR, 0.19; 95% CI, 0.04-0.99) were independent favorable prognostic factors for overall survival. On multivariate analysis, a high minimum dose (P = 0.02; RR, 2.8; 95% CI, 1.2-6.6), a high tumor control probability (P = 0.02; RR, 3.8; 95% CI, 1.2-12.5), a high dose delivered to 95% of the GTV (P = 0.03; RR, 3.4; 95% CI, 1.15-10.2), a high GTV encompassed by the 90% isodose line (P = 0.01; RR, 3.29; 95% CI, 1.29-8.44), and a small GTV excluded from the 90% isodose line (P = 0.036; RR, 0.4; 95% CI, 0.1-0.9) were independent favorable prognostic factors for local control. In chordomas and chondrosarcomas of the cranial base and cervical spine treated by surgical resection and then by high-dose photon and proton irradiation, local control is mainly dependent on the quality of radiation, especially dose uniformity within the GTV. Special attention must be paid to minimize underdosed areas because of the close proximity of critical structures and to redefine and possibly escalate dose constraints to tumor targets in future studies in view of the low toxicity observed to date.