Session Item

Skull base chordomas are radio-resistant tumors requiring high-dose, high-precision radiotherapy as can be delivered by Proton- or Carbon Ion therapy (= Particle Therapy). We analyzed clinical outcome of Particle Therapy of the initial 4-years.  

Between August 2017 and October 2021, 44 patients were treated with proton- (89%) or carbon-ion therapy (11%). Average prescription dose was 75.2Gy RBE in 37 fractions for protons and 66Gy RBE in 22 fractions for Carbon Ions. Chordomas were located either in upper (68%), or lower clivus (32%). Gross total resection was accomplished in 21% of lesions, subtotal resection in 57% and 12% of patients underwent biopsy only or decompression (10%)

At median follow up of 30.3 months (range: 1-51), two-, and three-year actuarial local control rates were 95.5% and 90.9%, respectively. Two-, and three-year overall and progression-free survival rates were 97.7%, 93.2%, 95.5% and 90.9%, respectively. Detailed analysis of risk factors will be presented and included tumor location, and volume, vascular involvement, intradural invasion, critical structure compression, type of particle and radiation dose delivered. Postoperative tumor volume was highly predictive of local failure (p<0.01). No recurrence was observed in postoperative tumors measuring <49cc. Median volume of 5 recurrent tumors was 110.6cc compared to 31.7cc for controlled tumors. No Grade ≥3 toxicities were observed. Five patients (11.4%) experienced transient Grade ≤2 radiation-induced brain changes.

First analysis suggests safety and efficacy of Particle Therapy. Excellent control of small to mid- residual disease underlines the importance of maximum debulking of large lesions. Longer follow up and larger sample size are needed to establish the potentially superior therapeutic role of carbon-ions and to define additional predictors of local failure.