Re-irradiation with VMAT for progressive brain metastases after previous whole brain radiation for radionecrosis risk avoidance. Marilena Theodorou, MD 1, , Andriana Peratikou, MSc, DABR, 2 , Stefani Stefanou MSc,CSci, MIPEM, 2, , Lora Ioannou, MSc, CSci, MIPEM, 2,, Efthymiou Themos MSc, 2, Erato Stylianou MSc, 2,,Ali Vehbi Artikan MSc, DABR, 2 Aristotelis Giannos MSc 2, Kyriaki Michailidou, PhD, 4 Demetrios Andreopoulos, MD,PhD 1 1 Radiation Oncology Department, Bank of Cyprus Oncology Center, 2 Medical Physics Department, Bank of Cyprus Oncology Center, 3 Department of electron microscopy/molecular pathology and the Cyprus School of molecular medicine, the Cyprus Institute for Genetics and Neurology Contact: marilena.theodorou@bococ.org.cy Radiation Oncology and Radiodiagnostics, Bank of Cyprus Oncology Center, Nicosia, Cyprus , www.bococ.org.cy Introduction The risk of radionecrosis is a main problem in radiotherapy oncology, especially for re-irradiation of the brain. Whole brain radiotherapy is indicated for multiple brain metastases (3 or more lesions),whereas local radiotherapy such as radiosurgery or stereotactic fractionated radiotherapy is indicated for oligometastatic disease (1- 3 lesions). Many patients with multiple brain metastases from breast cancer are irradiated with whole brain radiotherapy. Local radiotherapy is indicated if there is further disease progression or new brain metastases. With the advances in radiotherapy oncology and the new radiotherapy techniques available, re-irradiation is possible with high dose to the target and reduced risk for the organs at risk, reducing the risk of radionecrosis. . Methods In September 2014, a 35-year old patient was diagnosed with metastatic breast cancer presenting multiple brain metastases. She received 30Gy in 10 fractions to the whole brain. In February 2017, 2,5 years later, the patient developed acute palsy in the left arm and disease progression in the brain with 5 metastases appearing on MRI in the following locations: 1.Right temporal parietal ca. 7mm 2.Right occipital central compress posterior Horn of lateral Ventricle ca. 2,5 cm 3. Right cerebellum peripheral ca. 9mm 4. Right parietal central lateral the biggest metastasis, ca. 1cm 5. Left temporal ca. 8mm 03/2017 she received external beam radiation using VMAT (volumetric rapid arc radiotherapy) with Cone-Beam-CT verification, receiving a total dose 45Gy in 15 fractions (daily dose 3Gy/fraction) for the five metastases separately using one isocentre. This dose corresponds to a biological effective dose (BED) of stereotactic radiotherapy for brain metastases. For clinical target definition, the MRI was fused with the planning CT. The GTV (gross tumor volume) included the macroscopic metastases separately and the CTV (clinical target volume) included the GTV + 5mm safe margin. Immobilization of the head occurred with stereotactic thermoplastic mask. In order to evaluate the total dose to the organs at risk from both treatments, the previous plan for the whole brain treatment from September 2014 was added with the new VMAT plan. Results The table below shows the dose received by the organs at risk from both treatments. All doses received were well within the tolerance levels as per Quantec. The treatment was well tolerated by the patient without significant side effects or complications and she could continue working at the supermarket during her treatment. The further FU did not give late side effects and the MRIs showed complete response for the 4 small metastases, and partial response with necrotic changes for the largest metastasis. The latest MRI showed no evidence of necrosis. B VMAT Plan for the 5 metastases after previous whole brain radiation OAR Dose received Brainstem Max. dose: 46Gy, Mean dose: 26Gy Optic chiasm Max. dose: 22Gy Right optic nerve Max. dose: 11Gy Left optic nerve Max. dose: 12Gy Right lens Max. dose: 5,8Gy, Mean dose: 5Gy Left lens Max. dose: 6,5Gy, Mean dose: 5,5Gy Right internal ear Max. dose:25,8Gy, mean dose: 19,8Gy Left internal ear Max. dose: 16,6Gy, mean dose: 16Gy Conclusion and summary VMAT-technique (volumetric modulated arc therapy) for Re-irradiation of the brain for progressive brain metastases after previous radiation specially whole brain radiotherapy is indicated due to the good safety for the organ at risk in order to avoid radionecrosis risk. DEGRO 2018, Leipzig