Background: To demonstrate how adaptive hypofractionated radiosurgery by gamma knife (GK) can be successfully utilized to treat a large brainstem metastasis - a novel approach to a challenging clinical situation.
Case description: A 42-year-old woman, diagnosed with metastatic nonsmall cell lung cancer in July 2011, initially treated with chemotherapy and tyrosine kinase inhibitors, developed multiple brain metastases March 2013, with subsequent whole brain radiotherapy, after which a magnetic resonance imaging (MRI) showed a significant volume regression of all brain metastases. A follow-up MRI in October 2013 revealed a growing brainstem lesion of 26 mm. Linear accelerator-based radiotherapy and microsurgery were judged contraindicated, why the decision was made to treat the patient with three separate radiosurgical sessions during the course of 1 week, with an 18% tumor volume reduction demonstrated after the last treatment. Follow-up MRI 2.5 months after her radiosurgical treatment showed a tumor volume reduction of 67% compared to the 1(st) day of treatment. Later on, the patient developed a radiation-induced perilesional edema although without major clinical implications. An MRI at 12 months and 18-fluoro-deoxyglucose positron emission tomography of the brain at 13 months showed decreased edema with no signs of tumor recurrence. Despite disease progression during the last months of her life, the patient's condition remained overall acceptable.
Conclusion: GK-based stereotactic adaptive hypofractionation proved to be effective to achieve tumor control while limiting local adverse reactions. This surgical modality should be considered when managing larger brain lesions in critical areas.
Keywords: Biological equivalent dose; Karnofsky scale; brainstem metastasis; nonsmall cell lung cancer; peripheral/prescription dose; recursive partitioning analysis; stereotactic adaptive hypofractionated radiosurgery.