Long-term outcomes and prognostic factors of skull-base chondrosarcoma patients treated with pencil-beam scanning proton therapy at the Paul Scherrer Institute.
BACKGROUND
Skull-base chondrosarcoma (ChSa) is a rare disease, and the prognostication of this disease entity is ill defined.


METHODS
We assessed the long-term local control (LC) results, overall survival (OS), and prognostic factors of skull-base ChSa patients treated with pencil beam scanning proton therapy (PBS PT). Seventy-seven (male, 35; 46%) patients with histologically confirmed ChSa were treated at the Paul Scherrer Institute. Median age was 38.9 years (range, 10.2-70.0y). Median delivered dose was 70.0 GyRBE (range, 64.0-76.0 GyRBE). LC, OS, and toxicity-free survival (TFS) rates were calculated using the Kaplan Meier method.


RESULTS
After a mean follow-up of 69.2 months (range, 4.6-190.8 mo), 6 local (7.8%) failures were observed, 2 of which were late failures. Five (6.5%) patients died. The actuarial 8-year LC and OS were 89.7% and 93.5%, respectively. Tumor volume > 25 cm(3) (P = .02), brainstem/optic apparatus compression at the time of PT (P = .04) and age >30 years (P = .08) were associated with lower rates of LC. High-grade (≥3) radiation-induced toxicity was observed in 6 (7.8%) patients. The 8-year high-grade TFS was 90.8%. A higher rate of high-grade toxicity was observed for older patients (P = .073), those with larger tumor volume (P = .069), and those treated with 5 weekly fractions (P = .069).


CONCLUSIONS
This is the largest PT series reporting the outcome of patients with low-grade ChSa of the skull base treated with PBS only. Our data indicate that protons are both safe and effective. Tumor volume, brainstem/optic apparatus compression, and age were prognosticators of local failures.
Center for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland (D.C.W., S.B., R.M., F.A., A.B., A.J.L, R.S.); University of Bern, Bern, Switxerland (D.C.W.); University of Zürich, Zürich, Switzerland (D.C.W.); Department of Physics, ETH, Zürich, Switzerland (A.J.L.).
Damien C
DC
Weber
Center for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland (D.C.W., S.B., R.M., F.A., A.B., A.J.L, R.S.); University of Bern, Bern, Switxerland (D.C.W.); University of Zürich, Zürich, Switzerland (D.C.W.); Department of Physics, ETH, Zürich, Switzerland (A.J.L.).
Shahed
S
Badiyan
Center for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland (D.C.W., S.B., R.M., F.A., A.B., A.J.L, R.S.); University of Bern, Bern, Switxerland (D.C.W.); University of Zürich, Zürich, Switzerland (D.C.W.); Department of Physics, ETH, Zürich, Switzerland (A.J.L.).
Robert
R
Malyapa
Center for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland (D.C.W., S.B., R.M., F.A., A.B., A.J.L, R.S.); University of Bern, Bern, Switxerland (D.C.W.); University of Zürich, Zürich, Switzerland (D.C.W.); Department of Physics, ETH, Zürich, Switzerland (A.J.L.).
Francesca
F
Albertini
Center for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland (D.C.W., S.B., R.M., F.A., A.B., A.J.L, R.S.); University of Bern, Bern, Switxerland (D.C.W.); University of Zürich, Zürich, Switzerland (D.C.W.); Department of Physics, ETH, Zürich, Switzerland (A.J.L.).
Alessandra
A
Bolsi
Center for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland (D.C.W., S.B., R.M., F.A., A.B., A.J.L, R.S.); University of Bern, Bern, Switxerland (D.C.W.); University of Zürich, Zürich, Switzerland (D.C.W.); Department of Physics, ETH, Zürich, Switzerland (A.J.L.).
Antony J
AJ
Lomax
Center for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland (D.C.W., S.B., R.M., F.A., A.B., A.J.L, R.S.); University of Bern, Bern, Switxerland (D.C.W.); University of Zürich, Zürich, Switzerland (D.C.W.); Department of Physics, ETH, Zürich, Switzerland (A.J.L.).
Ralf
R
Schneider
D000293:Adolescent; D000328:Adult; D000368:Aged; D001859:Bone Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D002648:Child; D002813:Chondrosarcoma / Q000473:pathology / Q000532:radiotherapy*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D060787:Neoplasm Grading; D011379:Prognosis; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D019292:Skull Base Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D015996:Survival Rate; D047368:Tumor Burden; D055815:Young Adult
chondrosarcoma; pencil beam scanning; prognostic factors; proton therapy; skull-base tumors