ESTRO 38 Abstract book

S670 ESTRO 38

postoperative external beam LBRT. It provides the chance of earlier start of systemic treatment after resection of brain metastasis compared to external beam LBRT. EP-1211 Radiation necrosis after SRS for intracranial metastases from lung cancer: A retrospective review A. Sharma 1 , L. Mountjoy 2 , R. Butterfield 3 , N. Zhang 3 , H. Ross 2 , S. Schild 4 , J. Ashman 4 , T. Daniels 4 , H. Paripati 2 , M. Mrugala 1 , S. Vora 4 , N. Patel 5 , R. Zimmerman 5 , T. Sio 4 , A. Porter 1 1 Mayo Clinic Arizona, Neuro-Oncology, Phoenix, USA ; 2 Mayo Clinic Arizona, Hematology/Oncology, Phoenix, USA ; 3 Mayo Clinic Arizona, Research Biostatistics, Phoenix, USA ; 4 Mayo Clinic Arizona, Radiation Oncology, Phoenix, USA ; 5 Mayo Clinic Arizona, Neurosurgery, Phoenix, USA Purpose or Objective Radiation therapy is the primary treatment of intracranial metastasis (ICM) from lung cancer. Radiation necrosis (RN) occurs post-treatment with an incidence of 5-24%. Radiographically, RN remains a diagnostic quandary that can appear indistinct from tumor progression. We reviewed the spectrum of imaging changes in patients with SRS-treated ICM from lung cancer (LC) in an effort to classify potential risk factors for RN and to identify radiographic differentiators of RN versus tumor progression. Material and Methods Patients with LC and ICM who received stereotactic radiosurgery (SRS) for treatment between 2013 and 2018 at our institution were retrospectively reviewed at our institution. Sixty-three patients were identified. Demographics, tumor type, ICM burden and location, chemotherapy, surgery, and SRS details as well as outcomes were recorded. Magnetic resonance imaging (MRI) was reviewed and evaluated using the Response Assessment in Neuro-Oncology criteria (RANO). Results Of the 63 patients included in this study, clinical and radiographic criteria for RN were seen in 24 (38%) as early as 2 months and as late as 5 years post-RT. Six were taken to the OR because of refractory symptoms and were found to have pathology-proven RN. Patients with RN were significantly more likely to have had resection of an ICM (45.8%) prior to radiation than patients who did not have RN (20.5%, p=0.04). No significant differences were found in location, size, or genetic profile of lesions, but a non- significant trend for RN was seen in younger patients (average age 64 vs 68, p=0.08). Twenty patients received treatments directed towards RN - steroids, surgery, laser ablation or bevacizumab. The 4 remaining Patients who did not receive treatment had clinical/functional decline and lower overall survival (OS) of 13 months, vs 21.5 months if they did receive treatment. 85% of patients treated for RN experienced radiographic and clinical benefit. When steroids were used alone, the rate of improvement was 85.7% (6/7). There was 100% improvement with laser ablation (4/4) and bevacizumab (4/4). Surgical resection of RN resulted in improvement in 4/6 patients (66%), however the remaining two were left with increased neurologic morbidity that likely hastened death. All surgical specimens collected showed necrotic changes with only one revealing a mix of RN and tumor. Conclusion We present one of the larger case series of ICM in LC and their treatment outcomes. Our observation of RN as late as 5 years post-RT for ICM necessitates clinician awareness and early intervention to reduce morbidity. Younger age and prior surgical resection are potential risk factors for RN. Providers should keep a high index of suspicion for RN as development can occur several months after treatment for ICM. Several treatment options showed benefit without increased morbidity and improved survival in this cohort,

type (P=0.0001), PTV>1 cc (P=0.041) and BED<47.2 Gy (P=0.0001) were negative predictive factors of response. Conclusion The present data showed that SFRT/SRS with HyperArc TM is safe and effective for multiple BMs, mostly in appropriately selected patients. The utilization of SFRT/SRS for BMs is promising and should be explored in randomized trial. EP-1210 Local control and toxicity of IORT with low energy X-rays after resection of brain metastasis H. Kahl 1 , S. Sabine 2 , M. Heiko 3 , G. Ute 3 , K. Ina 3 , H. Volkmar 3 , M. Christoph 4 , B. Ansgar 4 , K. Jürgen 2 , S. Georg 1 1 Klinikum Augsburg, Strahlenklinik, Augsburg, Germany ; 2 Klinikum Augsburg, Stabsstelle Medizinphysik, Augsburg, Germany ; 3 Klinikum Augsburg, Neurochirurgische Klinik, Augsburg, Germany ; 4 Klinikum Augsburg, Klinik für Diagnostische Radiologie und Neuroradiologie, Augsburg, Germany Purpose or Objective The paradigm of adjuvant radiotherapy after resection of brain metastasis is changing from whole brain irradiation (WBI) to localized brain radiotherapy (LBRT). Improving survival of stage IV patients, puts neurologic late toxicity more and more into focus. IORT with low energy is a promising method to apply LBRT for brain metastasis as it maximally shortens the resection radiation interval as well as the time to the start of mostly needed systemic treatment compared to external beam radiation. Material and Methods We performed a retrospective analysis of patients treated with low energy X-ray IORT after resection of brain metastasis (mamma carcinoma 6, colorectal cancer 5, melanoma 4, NSCLC 4, renal cell carcinoma 2, other 2) between 2013 and 2018 at the Klinikum Augsburg. In total 25 metastases were resected in 22 patients (9 males/13 females) and treated with IORT using the Intrabeam system. Four patients had recurrent disease, of which 3 were pretreated with WBI. All patients fitted to RPA class 1 and 2 (8 and 14 patients). Median age was 60.8 years (44-82 years), median applied dose 20Gy (16-20Gy) on the surface of the applicator and median applicator size 2.5 cm (1.5 -4cm). None of the patients received additional planned WBI. Actuarial overall survival (OS), local control rate (LC), distant brain control (DC) were calculated by the Kaplan-Meier method and put into context with published and own data of adjuvant LBRT with radiosurgery (SRS) or hypofractionated stereotactic radiotherapy (HSRT). Results With a median follow up (FU) of 12.1 months (1 to 48 months), actuarial overall survival (OS) @ 1 year (2 years) was 73% (60%). The LC (actuarial LC @1year/@2years) of all 25 lesions was calculated 88% (85%/53%). DC of the 22 patients @1year (@2years) was 44% (44%). Only 3 patients received WBI as salvage after IORT (14%), all other distant recurrences were treated and controlled with SRS. We found a symptomatic brain necrosis rate of 4% (1 lesion/ pre-treated with WBI+SRS boost), but found asymptomatic radiotherapy induced MR alterations also in the FU of 2 other patients (8%/cumulative 12%). One air embolism occurred during the IORT procedure. One patient developed a lethal infarction of the a. cerebri media 14 days post surgery. One patient with 2 consecutive resections and IORT procedures developed a bacterial meningoencephalitis and one postoperative thrombopenic bleeding requiring surgery occurred. No other healing complications were observed. There was no increased use of steroids post operatively compared to patients with brain metastasis resection only. Conclusion IORT with low energy is a feasible option to apply LBRT after resection of brain metastasis providing comparable local control with no increased toxicity compared to