Session Item

Despite the favorable outcomes with local control rates of up to 90% after ten years, progression after radiotherapy (RT) of intracranial meningiomas (MS) does occur. In those cases, re-irradiation is often difficult due to the limited radiation tolerance of the surrounding tissue. Aim of this analysis is to report safety and efficacy of proton therapy (PT) for re-irradiation of recurrent MS

Between March 2015 and June 2019, 25 patients (pts) with 29 intracranial MS were re-irradiated with PT at our institution. Location of the primary lesion was skull base (n = 21) and convexity (n = 8). All but two pts had histologically proven diagnosis of MS (80% were WHO grade II). Median age was 66 years (range, 38-83). Median Karnofsky Performance status was 80 (range, 70-100). All pts failed after previous RT: 33% after Gamma-knife, 43% after Cyber-Knife, 10% after Tomotherapy, 14% after Linac-based stereotactic radiotherapy. Median time from initial irradiation to re-irradiation was 36 months (range, 18-60). Treatment planning was based on morphological magnetic resonance imaging (MRI) with contrast enhancement medium administration. All pts received also 68-Ga-DOTATOC-PET to identify the so-called Biological Tumor Volume. Clinical target volume ranged from 7 to 176 cc. All but one pts (who received 60 Gy in 30 fractions) were treated with 54 GyRBE in 30 fractions. All the pts was treated with active beam scanning PT using 3-4 fields with single or multiple field optimization technique. Toxicity was assessed according to Common Terminology Criteria for Adverse Events version 4.0. Median follow-up time was 12 months (range, 3-51)

All the pts completed the treatment without breaks. Registered acute side effects include grade 1 (14%) headache, grade 1 (10%) conjunctivitis, grade 2 (38%) skin erythema, grade 1 (14%) and grade 2 (24%) alopecia, grade 2 (10%) pain, grade 2 (10%) otitis, grade 2 (5%) dizziness, grade 2 (5%) tinnitus. There was no grade 3 or higher acute toxicities. Registered late side effects include grade 1 (5%) and grade 2 (5%) alopecia, grade 1 (10%) skin hyperpigmentation, and grade 1 (5%) headache. There was no grade 3 or higher late toxicities. During follow-up two pts (7%) developed radionecrosis (diagnosed at imaging) with no symptoms and no need of steroids. Another pts (5%) developed hydrocephalus that needed ventriculoperitoneal drain. Currently, absolute treated site tumor control is 80%, while absolute tumor control is 76%. Median time to local or distant tumor progression was 13 months. Disease specific absolute survival after re-irradiation is 95%, while absolute overall survival is 81%: three pts died of other causes than MS after re-irradiation. Moreover, relief of symptoms recorded before irradiation occurred in 35% of pts

Reirradiation with PT of MS progressing after previous RT appears to be feasible with promising clinical outcomes and an acceptable toxicity profile. Longer follow-up is necessary to assess definitive efficacy