IMPROVEMENT OF STEREOTACTIC RADIOSURGERY PLAN QUALITY WITH MULTIPLE NON-COPLANAR VMAT BEAMS

Stereotactic radiosurgery (SRS) is a promising treatment option for patients with multiple brain metastases (BM). Optimal SRS plan quality is important to minimize the risk of severe side effects such as radionecrosis.1,2 We studied if multiple non-coplanar VMAT beams are beneficial over one non-coplonar VMAT beam in terms of SRS plan quality. Three artificially contoured scenarios of brain metastases on an anonymized cerebral planning-CT were used. The first case had 10 BM, the second case 5 BM, and the third case 7 BM. Treatment plans were made in 3 institutions: a single non-coplanar SRS VMAT plan (MAASTRO Clinic=M), HyperArc (multiple non-coplonar beams, Zuerich=Z), and HyperArc (Birmingham, Alabama=A). MAASTRO Clinic and Zuerich used 1 mm GTV-PTV margin, and Alabama 0 mm GTV-PTV margin. The presciption dose was 21 Gy in a single fraction for case 1 and 18 Gy in a single fraction for case 2 and case 3. All plans were normalized that 99% of the comulative planning target volumes (PTVsum) were covered with 100% of the prescription dose. Multiple non-coplanar VMAT beams (e.g. HyperArc) and avoidance of a GTV-PTV margin resulted in better conformity in the high dose region. For case 1 the Paddick GI was 7.2 (M), 3.5 (Z), and 3.8 (A) respectively. For case 2 the Paddick GI was 4.1 (M), 2.9 (Z), and 3.0 (A). For case 3 the Paddick GI was 5.5 (M), 3.2 (Z), and 3.1 (A). The mean brain dose for case 1 was 6.5 Gy (M), 4.8 Gy (Z), and 4.0 Gy (A). The mean brain dose for case 2 was 2.8 Gy (M), 2.2 Gy (Z), and 2.0 Gy (A). The mean brain dose for case 3 was 4.7 Gy (M), 2.8 Gy (Z), and 2.6 Gy (A). The cumulative V12Gy for case 1 was 133 cc (M), 54 cc (Z), and 35 cc (A). The cumulative V12Gy for case 2 was 25 cc (M), 18 cc (Z), and 12 cc (A). The cumulative V12Gy for case 3 was 71 cc (M), 30 cc (Z), 20 cc (A). Optimal SRS plan quality with sparing of healthy brain tissue was achieved with usage of multiple non-coplanar beams (e.g. HyperArc) and avoidance of a GTV-PTV margin. 1) Plan Quality and Treatment Efficiency for Radiosurgery to Multiple Brain Metastases: Non-Coplanar RapidArc vs. Gamma Knife. Liu H et al. Front Oncol. 2016 Feb 11;6:26 2) Comparison of plan quality and delivery time between volumetric arc therapy (RapidArc) and Gamma Knife radiosurgery for multiple cranial metastases. Thomas E et al. Neurosurgery. 2014 Oct;75(4):409–17