A 75-year-old man was diagnosed in June 2016 with right-sided pleural desmoplastic mesothelioma. He had a previous history of smoking and exposure to asbestos as well as substantial underlying cardiovascular comorbidity. Curative treatment was deemed not feasible. While awaiting palliative antitumoral treatment, the patient experienced impaired balance, severe rotational vertigo, nausea, and vomiting. Brain CT and MRI in July 2016 revealed a solitary 20-mm metastasis with slight surrounding edema in the left middle cerebellar peduncle and extending along the tentorium (M1). V4 was minimally compressed without hydrocephalus. Corticosteroid therapy was initiated but microsurgery was deemed not feasible due to previous cardiovascular morbidity. Systemic palliative chemotherapy was initiated and he was referred for GKRS as no other treatment options remained available for M1. The patient underwent 3R-intervention for his solitary lesion in August 2016. KPS was estimated as 70–80 and RPA as 2 at GKRS 1 during steroid treatment de-escalation. KPS subsequently improved to 80 at GKRS 2 and 90–100 at GKRS 3 despite decreased steroid dose. M1 underwent a volume reduction of 22% between GKRS 1 and GKRS 3 (10.2 cm3 to 7.9 cm3) while V4 volume increased from 0.79 cm3 to 0.93 cm3 (21%). One-month follow-up with clinical assessment and MRI revealed mild fatigue presumed due to ongoing systemic antitumoral treatment (KPS 90) though without major neurological impairment, and substantial tumor volume reduction of almost 50% (10.2 cm3 at GKRS 1 to 5.6 cm3 at 4 weeks after GKRS 3). V4 volume had also increased significantly (from 0.79 cm3 at GKRS 1 to 1.31 cm3 at 4 weeks) []. A follow-up MRI at 3 months showed a small suspected recurrence with mild surrounding edema at the inferior aspect of the previous radiation field which was successfully treated in December 2016 along with ten new metastases; all eleven lesions were treated with SF-GKRS. No clinical signs of neurological deficits or radiological evidence of ARE were reported. The patient died 6 months after completion of 3R due to an aggressive, drug-resistant pneumonia.
A 41-year-old, nonsmoking female was initially diagnosed with metastatic TTF-1 positive lung adenocarcinoma in 2011. She underwent radiotherapy for her primary lesion as well as several lines of systemic treatments with initially positive but later mixed response. In March 2013, the patient reported symmetric sensory symptoms with numbness and tingling around her lips and limbs which eventually caused impaired balance. Brain MRI revealed more than 20 supra and infratentorial metastases including one to the left in the pons (M1) and signs of leptomeningeal carcinomatosis. The lesion in the pons (M1) had central necrosis and measured 25 × 30 × 26 mm at the time of diagnosis. The patient started high-dose systemic corticosteroid therapy and was treated the same month with whole brain radiation therapy (WBRT) with a dose fractionation of 4 Gy delivered over 5 consecutive days (4 Gy × 5). A follow-up MRI in July 2013 revealed volume reduction of all intracranial metastases including the pontine lesion (M1). The ensuing follow-up MRI in October 2013 demonstrated progression of M1 from 19 mm to 27 mm and slight V4 floor compression without hydrocephalus. A previously known small metastasis in the left lateral occipital lobe (M2) showed signs of progression as well. All other metastases were deemed under control at this point. To avoid further neurological impairment and V4 obstruction due to tumor growth and/or posttreatment ARE, M1 was treated by 3R in November 2013 [].\nAt the time of GKRS 1, M1 proved larger (9.2 cm3) with further perilesional edema and more apparent V4 floor compression, though still without signs of hydrocephalus. M2 had also grown slightly (from 10 to 12 mm in diameter) and was treated by SF-GKRS with 21 Gy to the 50% isodose prescription line. Apart from slight fatigue, left-sided facial numbness, and tingling the patient reported no other symptoms at the time of GKRS 1; at this stage, her KPS was estimated to be 90 and the RPA to be 1–2.\nDespite ongoing cortisone treatment, the perilesional edema remained nearly unchanged between GKRS 1 and GKRS 3; cortisone treatment was discontinued shortly after completion of GKRS 3. Nevertheless, V4 proved slightly wider at the time of GKRS 3 (from 0.9 cm3 at GKRS 1 to 1.2 cm3 at GKRS 3) and the tumor had decreased approximately 18% in volume (from GKRS 1 to GKRS 3). At 1-month follow-up, the patient was almost asymptomatic (KPS 90–100); the corresponding MRI revealed a significant reduction of tumor volume of approximately 67% (from 9.2 cm3 at GKRS 1 to 3.1 cm3 at the first follow-up) as well as renormalization of V4 boundaries (0.9 cm3 to 1.7 cm3) [; ].\nM1 developed a local ARE radiologically verified by MRI (follow-ups between March and November 2014) as well as 18F-FDG PET-CT (April and December 2014), which subsequently yielded without cortisone 6 months later (October 2014). Despite the above, the patient remained next to asymptomatic from her treated lesion during the follow-up. Unfortunately, systemic treatment eventually failed; the patient underwent SF-GKRS for several metastases (distant to M1 and M2 boundaries) from April to November 2014; her condition deteriorated steadily in December 2014, and she subsequently died in February 2015 (15 months after 3R) mainly due to intrathoracic tumor progression. Her quality of life was overall good from the time of 3R treatment and 12 months onwards.[]