P14.75 Active beam scanning proton therapy radiosurgery: early outcomes

Abstract

Abstract BACKGROUND Stereotactic radiosurgery (SRS) is an important treatment option for intracranial lesions and several photon-SRS techniques have been developed. Proton therapy (PT) has special characteristics that allow normal tissues to be spared better as well as greater homogeneity than with the use of photons, but limited data are available for proton-SRS. Nowadays, PT-SRS is delivered only with passive scattering technique while active pencil beam scanning (PBS) that is considered the most advanced proton technique has not been reported for SRS treatments yet. Here we report early clinical outcomes of PBS PT SRS. MATERIAL AND METHODS Between June 2017 and January 2019, 14 patients (pts) with 20 lesions underwent PBS PT SRS at our institution. Median age was 62 years (range, 28–87). Median Karnofsky performance status was 90 (range, 70–100). Six were male. Tumors included 16 meningiomas (MG) and 4 vestibular schwannomas (VS). Median GTV was 1.05 cc (range, 0.2–2.71). Dose prescription was 12 Gy radiobiologic equivalent (RBE) in one fraction for VS and 15 GyRBE in one fraction for MG. Pts were immobilized using a frameless system: Type-S proton overlay and Type-S proton mask (CIVCO medical solutions, Kalona, IA, USA) together with Moldcare headrest (Q-Fix systems, Avondale, PA, USA). All pts were treated with PBS PT using 2–3 fields with single field optimization technique, and using min-max robust robust optimization (2 mm setup errors, 3.5% range uncertainties), with a Monte Carlo algorithm and 1 mm grid size. Toxicity was assessed using Common Terminology Criteria for Adverse Events version 4.0. RESULTS Median follow-up (FU) was 9 months (range, 3–22). All pts completed the treatment with excellent compliance and no side effects were registered during the procedure. Registered acute side effects include grade 1 (14%) fatigue, grade 2 (7%) headache, and grade 2 (28%) alopecia. There were no grade 3 or higher acute toxicities. Registered late side effects include grade 1 (7%) headache, and grade 1 (14%) alopecia. There were no grade 3 or higher late toxicities. Currently, absolute tumor control is 100% regardless the type of tumor. Despite the short FU radiological reduction was registered in 9 lesions (45%). CONCLUSION PBS PT SRS is a feasible and safe treatment in pts with MG or VS. A high radiological response rate was observed. Longer FU is necessary to assess definitive safety and efficacy.