Abstract

Sruthi K¹, Ramakrishna Kamath¹, Ajinkya Gupte¹, Ajay Sasidharan¹, Pushpaja K U¹, Anoop R¹, Haridas Nair¹, Annex E H², Debnarayan Dutta¹

¹Amrita Institute of Medical Sciences, Radiation Oncology, Kochi, India; ²Amrita Institute of Medical Sciences, Medical Physics, Kochi, India

To evaluate the outcome, probability and patterns of recurrence, retreatment incidence and toxicities in patients treated for brain metastases with linac based robotic radiosurgery in Indian patient population.

Between May 2017 and February 2021, 100 patients with 167 brain metastases were accrued prospectively and treated with robotic radiosurgery (CK) (M6, Multiplan, VOLO). Patients with small volume oligo brain metastases (<3 sites) with good performance status (PS 0-1) and controlled primary were accrued. Frameless stereotactic based immobilization was ensured with a thermoplastic mask, a contrast CT simulation was done with 0.625 mm slices and fused with T1 contrast/T2 Flair MRI images for contouring. PTV margin of 2-3 mm and a dose of 20-30Gy in 1-5 fractions was decided based on the treatment volume. 12Gy normal brain volume and marginal dose was considered for dose prescription. Response to treatment, new brain lesion free survival, overall survival and toxicity profile after CK was evaluated. Normogram for Indian patient population for ‘new lesion free’ survival was considered.

In 100 accrued patients with 167 brain lesions [mean age 57 yrs(29-82yrs), female 54%, primary cancer- lung 42 %,breast 32%, RCC 9 % ,other primary site 17%]. 15% received previous WBRT. Solitary metastasis was in 59%, upto 3 in 32% and >3 in only 9% patients. One, 3 & 5 fraction SRS was done in 61%, 15% and 24%. SRS dose was 12 Gy in 4%,13-18Gy in 19%,20-24Gy in 42% and 25-30Gy in 35%. Mean PTV was 22 cc. Mean 12Gy normal brain volume was 5.1cc,Brainstem max dose 643cGy, Optic chiasm max dose 229cGy,Mean HI 1.16,CI 1.23.Mean monitor units 18749, treatment time 52 minutes and  number of beams was 203. At mean follow up 58.8 wks (4-164 wk), 86 had follow up evaluation (39 patients were alive, 47 expired). Among 32 patients who had recurrent brain metastases, 20 underwent treatment (12 received re-SRS, 5 WBRT, 3 had surgery) while 12 had progressive systemic and intracranial recurrence and were treated with only palliative/ supportive care. Only ‘Out of field’ and only ‘in-field’ recurrence noted in 13% and 5% respectively. Both in/out of field recurrences was in 14%.Long term steroid usage was noted in 19%. Radiological radiation necrosis was diagnosed in 11 % and 3 patients required surgery. 

In selected patient cohort, SRS in Indian patients with brain metastasis is similar to published literature. Recurrence rate at 6 months is 20% and 80% of recurrent cases are re-treated with SRS. Radiation necrosis rate is 11% and only 3% require surgical intervention.