Proton therapy with a fixed beamline for skull-base chordomas and chondrosarcomas: outcomes and toxicity.

This study presents an analysis (efficacy and toxicity) of outcomes in patients with skull-base chordomas or chondrosarcomas treated with a fixed horizontal pencil proton beam. Chordomas (CAs) and chondrosarcomas (CSAs) are rare tumours that are usually located near the base of the skull and very close to the brain's most critical structures. Proton therapy (PT) is often considered the best radiation treatment for these diseases, but it is still a limited resource. Active scanning PT delivered via a fixed pencil beamline might be a promising option. This is a single-centre experience describing the results of proton therapy for 31 patients with CA (n = 23) or CSA (n = 8) located near the base of the skull. Proton therapy was utilized by a fixed pencil beamline with a chair to position the patient between May 2016 and November 2020. Ten patients underwent resection (32.2%), 15 patients (48.4%) underwent R2 resection, and 6 patients had unresectable tumours (19.4%). In 4 cases, the tumours had been previously irradiated. The median PT dose was 70 GyRBE (relative biological efficacy, 1.1) [range, 60 to 74] with 2.0 GyRBE per fraction. The mean GTV volume was 25.6 cm3 [range, 4.2-115.6]. Patient demographics, pathology, treatment parameters, and toxicity were collected and analysed. Radiation-induced reactions were assessed according to the Common Terminology Criteria for Adverse Events (CTCAE) v 4.0. The median follow-up time was 21 months [range, 4 to 52]. The median overall survival (OS) was 40 months. The 1- and 2-year OS was 100%, and the 3-year OS was 66.3%. Four patients died due to non-cancer-related reasons, 1 patient died due to tumour progression, and 1 patient died due to treatment-related injuries. The 1-year local control (LC) rate was 100%, the 2-year LC rate was 93.7%, and the 3-year LC rate was 85.3%. Two patients with CSA exhibited progression in the neck lymph nodes and lungs. All patients tolerated PT well without any treatment interruptions. We observed 2 cases of ≥ grade 3 toxicity, with 1 case of grade 3 myelitis and 1 case of grade 5 brainstem injury. Treatment with a fixed proton beam shows promising disease control and an acceptable toxicity rate, even the difficult-to-treat subpopulation of patients with skull-base chordomas or chondrosarcomas requiring dose escalation.

Gordon K ，Gulidov I ，Koryakin S ，Smyk D ，Makeenkova T ，Gogolin D ，Lepilina O ，Golovanova O ，Semenov A ，Dujenko S ，Medvedeva K ，Mardynsky Y ... -  《Radiation Oncology》

Effectiveness and safety of spot scanning proton radiation therapy for chordomas and chondrosarcomas of the skull base: first long-term report.

Ares C ，Hug EB ，Lomax AJ ，Bolsi A ，Timmermann B ，Rutz HP ，Schuller JC ，Pedroni E ，Goitein G ... -  《-》

Dosimetric analysis of local failures in skull-base chordoma and chondrosarcoma following pencil beam scanning proton therapy.

Basler L ，Poel R ，Schröder C ，Bolsi A ，Lomax A ，Tanadini-Lang S ，Guckenberger M ，Weber DC ... -  《Radiation Oncology》

Proton radiation therapy for chordomas and chondrosarcomas of the skull base.

Hug EB ，Slater JD 《NEUROSURGERY CLINICS OF NORTH AMERICA》

Long term outcomes of patients with skull-base low-grade chondrosarcoma and chordoma patients treated with pencil beam scanning proton therapy.

To evaluate the long term tumor control and toxicity of skull base tumors treated with pencil beam scanning proton therapy (PT). PT was delivered to 151 (68%) and 71 (32%) chordoma and chondrosarcoma (ChSa) patients, respectively. Mean age of patients was 40.8±18.4years and the male to female ratio was 0.53. The postoperative tumor was abutting the brainstem or optic apparatus in 71 (32.0%) patients. The postoperative mean gross tumor volume (GTV) was 35.7±29.1cm(3). The delivered mean PT dose was 72.5±2.2GyRBE. After a mean follow-up of 50 (range, 4-176) months, 35 local (15.8%) failures were observed between 10.9 and 85.4months. The estimated 7-year LC rate for chordoma (70.9%; CI95% 61.5-81.8) was significantly lower compared to the LC rate for ChSa patients (93.6%; 95%CI 87.8-99.9; P=0.014). The estimated 7-year distant metastasis-free- and overall survival rate was 91.6% (95%CI 91.6-98.6) and 81.7% (95%CI 74.7-89.5), respectively. On multivariate analysis, optic apparatus and/or brainstem compression, histology and GTV were independent prognostic factors for LC and OS. The 7-year high grade toxicity-free survival was 87.2 (95%CI 82.4-92.3). PBS PT is an effective treatment for skull base tumors with acceptable late toxicity. Optic apparatus and/or brainstem compression, histology and GTV allow independent prediction of the risk of local failure and death in skull base tumor patients.

Weber DC ，Malyapa R ，Albertini F ，Bolsi A ，Kliebsch U ，Walser M ，Pica A ，Combescure C ，Lomax AJ ，Schneider R ... -  《-》