Objectives:

Traditional stereotactic radiation therapy (SRT) with individual isocenter plans for each lesion may not be tolerated in patients with multiple brain metastases due to discomfort of long treatment times or co‐morbidities. To significantly shorten overall treatment time, and improve patient comfort, compliance, and clinic efficiency, SRT using a single‐isocenter/multi-lesion (SIML) HyperArc volumetric modulated arc therapy (VMAT) plan with flattening filter free (FFF) beam has been implemented. Our early clinical results of treating multiple brain metastases with SIML HyperArc SRT are reported.

Methods:

Patients were treated using highly conformal SIML VMAT-SRT plans via non-coplanar fully-automated HyperArc geometry. Based on tumor size, location and proximity of the lesions, common prescriptions were 25–30 Gy in 5 fractions, 24–27 Gy in 3 fractions, and 20 Gy in 1 fraction prescribed to each planning target volume (PTV) using 2 mm margin around standard gross tumor volume (GTV) delineated on contrasted-enhanced high-definition MP-RAGE MRI co-registered with the planning CT images. Treatment was delivered every other day with conebeam CT-guidance, adjustments made with 6DOF PerfectPitch couch corrections on TrueBeam, and treatment delivery time within 15 minutes. Encompass support, Q-fix mask and mouth piece bite were implemented for patient immobilization. Acuros-based dose calculation for 6MV-FFF beam (1400 MU/minute) was used for tissue heterogeneity corrections. Alliance A071801 brain SRS/SRT trial criteria were used for dose constraints to adjacent organs-at-risk (OAR) and target conformality. RANO-BM criteria was used to assess treatment response. Tumor local control rates were reported, and toxicity profile rated based on CTCAE v5.0 for brain radionecrosis, optic neuropathy, and brainstem dysfunction.

Results:

Total of 165 brain metastatic lesions from 44 patients were treated. 33 patients (75%) had post-treatment MRI imaging to assess local control and toxicity profile. Mean GTV and PTV volume were 10.2 cc (range, 0.3–54.8 cc) and 16.8 cc (range, 1.0–80.2 cc), respectively. Mean tumor distance-to-isocenter was 5.3 cm, maximum up to 7 cm. All HyperArc SRS/SRT plans met Alliance A071801 protocol requirements for each tumor coverage, dose to OAR including optic apparatus, brainstem, and spinal cord. Mean follow up interval was 7.3 months (range, 0.0–23.5 months). Tumor local control was achieved in 132/140 (94%) of treated and followed up lesions. Brain radionecrosis grade 2 occurred in 3 patients who were managed with dexamethasone. In this cohort, no other CTCAE grade 3+ events of radiation-induced toxicity, optic pathway dysfunction, or brainstem toxicity were observed.

Conclusion(s):

Use of SIML HyperArc for brain SRT for multiple brain metastases has shown excellent tumor local control and low toxicity profile in our patients. Compared to traditional multiple-isocenter brain SRT or chronologically separate treatment courses, it significantly reduces treatment delivery time and thus improves patient comfort, compliance, ease of care, and overall clinic workflow. Longer median follow up results and larger patient cohorts of SIML brain SRT is warranted. To provide the high quality of patient care to underserved populations, we recommend other cancer clinics to commission and implement HyperArc brain SRT programs in their practices, including community centers.