Long-term clinical safety of high-dose proton radiotherapy delivered with pencil beam scanning technique for extracranial chordomas and chondrosarcomas in adult patients: Clinical evidence of spinal cord tolerance
Menée auprès de 76 patients atteints d'un chordome de la colonne vertébrale ou d'un chondrosarcome (âge médian : 53 ans ; durée médiane de suivi : 5,5 ans), cette étude évalue la toxicité d'une forte dose de protonthérapie par balayage à faisceau filiforme
Purpose/Objectives : To assess the radiation dose tolerance of the spinal cord, we reviewed our institutional experience regarding the incidence of radiation-induced spinal cord toxicity following high dose, pencil beam scanning proton therapy (PBSPT). Materials/Methods : Seventy-six patients (median age, 53 years; range: 23–79), treated for spinal chordoma (n=55) or chondrosarcoma (n=21) met the following criteria and were retrospectively analyzed: PBSPT only, no re-irradiation or concomitant chemotherapy, maximum dose (Dmax) to the spinal cord of ≥45 Gy(RBE), ≥18 years of age, and follow-up of ≥12 months. The delivered dose was 59.4–75.2 Gy(RBE) (median, 73.9) delivered with conventional fractionation between 2000–2014. The Dmax, D2%, V40–V60 of the surface (sSC) and center (cSC) of the spinal cord were recorded. Toxicity was scored according to the Common Toxicity Criteria of Adverse Events (CTCAE v4.03). Results : Median follow-up was 65.5 months (range, 13–173). Patients received a mean Dmax and D2% to the sSC of 59.0 (median 58.7, range: 48.3 – 75.9), and 55.3 Gy(RBE) (median, 52.7, range: 43.1 – 73.8), respectively. The corresponding values for the cSC were 52.3 (median, 52.7, range: 32.3 – 73.3) and 51.1 Gy(RBE) (median, 52.0, range: 25.3 – 73.1), respectively. Four patients (5%) developed acute radiation-induced neurotoxicity (G1, n=1; G2, n=3). Twelve patients (16%) experienced late neurologic toxicities (G1, n=7; G2, n=4; G4, n=1). One patient with a history of pre-PBSPT symptomatic spinal cord compression redeveloped tetraplegia (G4) after receiving a Dmax of 57.8 Gy(RBE) to the sSC and 54.1 Gy(RBE) to the cSC. No significant correlation was found between sSC Dmax and D2%, cSC Dmax and D2%, or the length of CTV and toxicity. Conclusions : High-dose conformal PBSPT may be delivered safely in close proximity to the spinal cord with minimal neurotoxicity. Dose constraints of 64 Gy(RBE) as D2% for the sSC and 54 Gy(RBE) for the cSC appear appropriate for clinical use.