Critical appraisal of RapidArc radiosurgery with flattening filter free photon beams for benign brain lesions in comparison to GammaKnife: a treatment planning study

Background: To evaluate the role of RapidArc (RA) for stereotactic radiosurgery (SRS) of benign brain lesions in comparison to GammaKnife (GK) based technique. Methods: Twelve patients with vestibular schwannoma (VS, n = 6) or cavernous sinus meningioma (CSM, n = 6) were planned for both SRS using volumetric modulated arc therapy (VMAT) by RA. 104 MV flattening filter free photon beams with a maximum dose rate of 2400 MU/min were selected. Data were compared against plans optimised for GK. A single dose of 12.5 Gy was prescribed. The primary objective was to assess treatment plan quality. Secondary aim was to appraise treatment efficiency. Results: For VS, comparing best GK vs. RA plans, homogeneity was 51.7 +/- 3.5 vs. 6.4 +/- 1.5%; Paddick conformity Index (PCI) resulted 0.81 +/- 0.03 vs. 0.84 +/- 0.04. Gradient index (PGI) was 2.7 +/- 0.2 vs. 3.8 +/- 0.6. Mean target dose was 17.1 +/- 0.9 vs. 12.9 +/- 0.1 Gy. For the brain stem, D-1cm3 was 5.1 +/- 2.0 Gy vs 4.8 +/- 1.6 Gy. For the ipsilateral cochlea, D-0.1cm3 was 1.7 +/- 1.0 Gy vs. 1.8 +/- 0.5 Gy. For CSM, homogeneity was 52.3 +/- 2.4 vs. 12.4 +/- 0.6; PCI: 0.86 +/- 0.05 vs. 0.88 +/- 0.05; PGI: 2.6 +/- 0.1 vs. 3.8 +/- 0.5; D-1cm3 to brain stem was 5.4 +/- 2.8 Gy vs. 5.2 +/- 2.8 Gy; D-0.1cm3 to ipsi-lateral optic nerve was 4.2 +/- 2.1 vs. 2.1 +/- 1.5 Gy; D-0.1cm3 to optic chiasm was 5.9 +/- 3.1 vs. 4.5 +/- 2.1 Gy. Treatment time was 53.7 +/- 5.8 (64.9 +/- 24.3) minutes for GK and 4.8 +/- 1.3 (5.0 +/- 0.7) minutes for RA for schwannomas (meningiomas). Conclusions: SRS with RA and FFF beams revealed to be adequate and comparable to GK in terms of target coverage, homogeneity, organs at risk sparing with some gain in terms of treatment efficiency.