Prospective Evaluation of Response to Treatment, Survival Functions, Recurrence Pattern and Toxicity Profile in Indian Patients with Oligo-Brain Metastasis Treated with Only SRS.

Background: Prospective analysis of oligo-brain metastasis in Indian patients treated with SRS-only treatment. Methods: Between January 2017 and May 2022, 235 patients were screened and 138 histologically proven and radiologically confirmed. One to five brain metastasis patients aged more than 18 years with good Karnofsky performance status (KPS >70) accrued in ethical and scientific committee-approved prospective observational study protocol for treatment with only radiosurgery (SRS) with robotic radiosurgery (CyberKnife, CK) [AIMS IRB: 2020-071; CTRI No: REF/2022/01/050237]. Immobilization was performed with a thermoplastic mask, contrast CT simulation was performed with 0.625 mm slices, fused with T1 contrast/T2 FLAIR MRI images for contouring. Planning target volume (PTV) margin of 2-3 mm and a dose of 20-30 Gy in 1-5 fractions. Response to treatment, new brain lesions free survival, overall survival, and toxicity profile after CK were evaluated. Results: In total,: 138 patients with 251 lesions were accrued (median age 59 years (interquartile range [IQR] 49-67 years; female 51%; headache in 34%, motor deficit in 7%, KPS >90 in 56%; lung primary in 44%, breast in 30%; oligo-recurrence in 45%; synchronous oligo-metastases in 33%; adenocarcinoma primary in 83%). One hundred seven patients (77%) received upfront Stereotactic radiotherapy (SRS), 15 (11%) received postoperative SRS, 12 (9%) received whole brain radiotherapy (WBRT) before SRS, and 3 (2%) received WBRT plus SRS boost. The majority had solitary (56%) brain metastasis, 28% had two to three lesions, and 16% had four to five brain lesions. Frontal (39%) was the most common site. Median PTV was 15.5 mL (IQR - 8.1-28.5 mL). Seventy-one (52%) patients were treated with single fractions, 14% with three, and 33% with five fractions. Fraction schedules were 20-2 4 Gy/1fr; 27 Gy/3fr, and 25 Gy/5 fractions (mean BED 74.6 Gy [SD ± 48.1; mean MU 16608], mean treatment time was 49 min (range 17-118 min]. Twelve Gy normal brain volume was 40.8 mL (3.2%) (range 19.3-73.7 mL). At a mean follow-up of 15 months (SD 11.9 months; max 56 months), the mean actuarial OS after SRS-only treatment was 23.7 months (95% confidence interval [CI] 20-28). Further 124 (90%) patients had >3 months, 108 (78%) had >6 months, 65 (47%) had >12 months, and 26 (19%) had >24 months follow-up. Intracranial disease and extracranial disease were controlled in 72 (52.2%) and 60 (43.5%), respectively. "In-field" recurrence, "out-of-field," and "both in and out-of-field" recurrences were in 11%, 42%, and 46%, respectively. At the last follow-up, 55 patients (40%) were alive, 75 (54%) died due to disease progression, and the status of 8 (6%) patients was not known. Among 75 patients who died, 46 (61%) had extracranial disease progression, 12 (16%) had only intracranial progression, and 8 (11%) had unrelated causes. Also, 12/117 (9%) had radiological confirmation of radiation necrosis. Prognostication based on western patients (primary tumor type, number of lesions extracranial disease) showed similar outcomes. Conclusions: SRS alone in brain metastasis is feasible in the Indian subcontinent with similar survival outcomes, recurrence patterns, and toxicity as published in the western literature. Patient selection, dose schedule, and planning need to be standardized to have similar outcomes. WBRT can be safely omitted in Indian patients with oligo-brain metastasis. Western prognostication nomogram is applicable in the Indian patient population.