Top Line: What is the optimal 5-fraction stereotactic radiation therapy (SRT) dose for brain metastases
The Study: In this study from Sunnybrook, 334 brain metastases in 220 patients were treated with hypofractionated stereotactic radiotherapy (HSRT). Targets were defined using MRI with 1.5 mm slice thickness. A 2-3 mm margin was added to create the PTV (3 mm for targets 1 cm or smaller). Brain mets were typically treated with 22.5 to 35 Gy prescribed to 99% of the PTV in 5 daily fractions using a multi-arc VMAT technique. Most (70%) had multiple mets (although only 36% received HSRT to multiple targets) and 22% had received prior whole brain radiation. Most mets were < 2 cm (60%) while 20% were 2-3 cm and 10% were > 3 cm. The most common prescription was 30 Gy (46%) followed by 25 Gy (24%). A dose > 30 Gy was prescribed to 15% of targets. Local failure occurred in 8% at 6 months, 15% at 9 months, and 24% at 12 months. Local failure was significantly lower among those who received ≥ 30 Gy at 6 months (13→ 5%), 9 months (22.4→ 10%), and 12 months (33→ 19%). And while we know that larger lesions often get lower doses but have a higher recurrence risk, dose ≥ 30 Gy was still associated with less local failure among the 200 lesions that were < 2 cm. In addition, dose ≥ 30 Gy was a significant predictor of local control on multivariable analysis. Radiation necrosis occurred in 15.6% with 9.5% having symptomatic necrosis.
TBL: When delivering LINAC-based 5-fraction SRT for brain metastases, a dose of 30-35 Gy prescribed to a 2-3 mm margin is associated with a low rate of adverse events and improved local control compared to < 30 Gy. | Myrehaug, Int J Radiat Oncol Biol Phys 2021