A Prospective Outcomes Study of Proton Therapy for Skull-Base Chondrosarcomas

Objective To evaluate the effectiveness of definitive or adjuvant external-beam proton therapy (PT) on local control and survival in patients with skull-base chondrosarcoma.

Methods Between January 2007 and February 2016, a total of 43 patients (median age, 49 years; range, 23–80) with skull-base chondrosarcoma were treated with double-scattered PT. Median total dose was 73.8 Gy (RBE) (range, 64.5–74.4); 33 patients received 1.8 Gy (RBE) once-daily fractionations and 10 received 1.2 Gy (RBE) twice-daily fractionations. Primary site included skull-base tumors involving the clivus, cavernous sinus, petrous bone, and sella, and tumors involving the ethmoid or sphenoid sinuses. Surgical resection and biopsy alone were performed in 36 (83.7%) and 7 (16.3%) patients, respectively. Tumor grade was as follows: 19 (44.2%) Grade I, 22 (51.1%) Grade II, and 2 (4.7%) Grade III. Forty patients had gross disease; 7 were treated for locally recurrent disease following surgery. Distant metastases, overall survival, cause-specific survival, local control, and disease-free survival were calculated. PT-related toxicities were scored using CTCAE v4.0.

Results Median follow-up was 3.7 years (range, 0.7–10.1). The 3-year actuarial overall survival rate was 95%, cause-specific survival was 100%, disease-free survival was 93%, local control was 93%, and freedom from distant metastases was 100%. Three patients experienced local recurrence with no regional or distant recurrence observed. At last follow-up, 38 patients were alive with no evidence of recurrent disease, 2 were alive with recurrent disease, 2 were dead from intercurrent disease, and 1 was dead of recurrent disease. The time to local progression was 2, 2.5, and 3 years (n = 3) following PT. We did not observe any higher than Grade III acute toxicities. 9.3% (n = 4) of patients experienced Grade III or higher late toxicity: Grade III hearing loss (n = 3), and a Grade III radiation-induced tumor (meningioma: 9 years 9 months after treatment). We observed a Grade II temporal lobe and brainstem radiation necrosis, both in the same patient.

Conclusion High-dose conformal PT alone or following surgical resection for skull-base chondrosarcoma is an effective treatment with a high rate of local control and with a relatively low toxicity profile. Further follow-up of this cohort is necessary to better characterize long-term disease control and late toxicities.

No conflict of interest has been declared by the author(s).