Probable causes of recurrence in patients with chordoma and chondrosarcoma of the base of skull and cervical spine
141 patients with chordoma and chondrosarcoma of the base of skull and cervical spine were treated with proton and photon irradiation between 1980 and 1989. The local disease was controlled in 111 of these patients. This study reviews the 26 patients who have had their disease recur, and who have evaluable diagnostic studies to examine for probable causes of recurrence. The histologies of the recurrent tumors were 21 non-chondroid chordomas, two chondroid chordomas, and three chondrosarcomas. The prescribed doses ranged from 67 Cobalt-Gray-Equivalent (CGE) to 72 CGE (average of 69 CGE). Doses to small regions of the tumor were deliberately reduced where they abutted certain normal tissues (brain stem, spinal cord, optic chiasm, and optic nerves) in order to keep these structures at acceptance dose levels. The first study, CT or MR scan, on which there was evidence of increase in tumor was carefully evaluated and that volume transferred to the CT scan on which the treatment plan had been developed. The 3D dose distribution in the region of recurrence was carefully analyzed and a judgement made as to the most probable cause of recurrence. Approximately one quarter (6 of 26) of the cases failed in the prescribed dose region. More than half (15 of 26) failed in regions where tumor dose was limited by normal tissue constraints. Approximately 10% of the patients recurred in the surgical pathway and 10% were judged to be marginal misses. Overall, 75% of the patients failed in regions receiving less than the prescribed dose. All tumors which failed in the high dose region had volume greater than 75 cc. Patients with cervical spine disease had a higher rate of recurrence (10 or 26) and larger tumors (average volume of 102 cc) than those with base of skull disease (16 of 115) with an average volume of 63 cc.