ESTRO 2021 Abstract Book

S869

ESTRO 2021

Objectives To assess the relationship of the dose and fractionation with the local control of the disease using the RECIST 1.1 criteria and the degree of acute and late toxicity in patients treated with BRAIN SBRT of extracerebral primary tumors in different locations. Materials and Methods Methods. Data from patients treated with SBRT between October 2017 and January 2021 were analyzed. Final goals included local control, acute and late toxicity. 30 patients received SBRT, the median age was 59 years (range 40-77). 17 were men and 13 women. The median follow-up was 8 months (1-40 months). The main locations of the primary tumor were lung and breast. The most frequent histology was adenocarcinoma, non-special subtype infiltrating adenocarcinoma, and small cell carcinoma. The most used fractionation was 30 Gy / 10 fraction (63% of patients). Fractions of 16-18 Gy in a single fraction and 25 Gy in 5 fractions were also used. Regarding the volume of the treated lesion, 47% had a volume <4 cm³ and received: 30 Gy (57%), 25 Gy (7%), 16-18 Gy (36%). 53% of the treated lesions had a volume> 4 cm³ and received: 30 Gy (69%), 25 Gy (19%), 16-18 Gy (12%). The median follow-up was 8 months. At three months 6 patients (31%) had stable disease (SE), 4 had a partial response (21%) (PR), 7 (37%) had a complete response (CR), and 2 (11%) had disease progression. In 11 patients (36%), the response could not be evaluated due to death (7 patients) or recent treatment (4 patients). At 6 months, 37% of the evaluated patients had progressed, 26% maintained a complete response, 16% a partial response, and 21% were in stable disease. Currently, 56% of treated patients are still alive. Of the 13 patients who died, 20% were due to their CNS tumor. 85% of the patients did not present acute toxicity, 15% presented different degrees of neurological toxicity (headache, bradypsychia). 90% of the patients did not present late toxicity. Conclusion Conclusions. We observed by RECIST criteria a local control at 6 months of 63%. Eighty-five percent of the patients had no acute or late grade 3 RTOG toxicities. Treatment with SBRT in patients with metastatic disease seems feasible and similar in terms of local control, without presenting relevant acute and late toxicity Results Results. PO-1043 The influence of the conformity index of stereotactic radiotherapy for single brain metastasis K. Makita 1 , Y. Hamamoto 2 , O. Nishizaki 3 , M. Kataoka 4 , T. Manabe 4 , T. Kido 1 1 Ehime University Graduate School of Medicine, Department of Radiology, Toon, Japan; 2 National Hospital Organization Shikoku Cancer Center, Departments of Radiation Oncology, Matsuyama, Japan; 3 Saiseikai Imabari Hospital, Department of Neurosurgery,, Imabari, Japan; 4 Saiseikai Imabari Hospital, Department of Radiology, Imabari, Japan Purpose or Objective This study aimed to evaluate the correlation between the conformity index (CI) and local control (LC) of brain metastases (BMs) following stereotactic radiosurgery (SRS) or fractionated stereotactic radiotherapy (FSRT) using CyberKnife (CK). Materials and Methods Fifty-four patients diagnosed with a single BM lesion between January 2014 and December 2019 who received SRS/FSRT using CK were reviewed. The median biologically effective dose (BED 10 ) of SRS/FSRT was 48.0-81.6 Gy (median 39.6 Gy). Gross tumor volume (GTV) was contoured using contrast-enhanced magnetic resonance imaging. A 1-mm GTV margin was added to obtain the clinical target volume or planning target volume. Imaging studies’ median follow-up was 11 months (range, 1–65 months). Results One-year overall survival and LC were 76% and 75%, respectively. In univariate analysis, tumor volume <10 cm3 and CI <0.77 were significant favorable factors for single BM LC (P=0.034 and 0.014, respectively); CI <0.83 was the only significant favorable factor (P<0.0001) for tumors with volume <10 cm3. The LC of single BM did not vary with the prescribed BED 10 and schedule (SRS vs. FSRT) of radiation. Conclusion Despite the small number of cases, this study demonstrated that lower CI of SRS/FSRT using CK was associated with adequate LC of single BM. PO-1044 Stereotactic radiosurgery for meningioma: a single institution retrospective analysis O. Houlihan 1 , G. Rangaswamy 1 , M. Dunne 2 , L. Fennell 3 , C. Skourou 3 , C. Faul 1 , D. Fitzpatrick 4 1 St Luke's Radiation Oncology Network, Radiation Oncology, Dublin, Ireland; 2 St Luke's Radiation Oncology Network, Clinical Trials Unit, Dublin, Ireland; 3 St Luke's Radiation Oncology Network, Medical Physics, Dublin, Ireland; 4 St Luke's Radiation Oncology Network, Radiation Oncology, Dublin , Ireland Purpose or Objective Meningiomas account from 15-25% of all primary brain tumours with an annual incidence of 1-10/100,000. While surgical resection is the preferred treatment for easily accessible meningiomas that can be safely removed, many patients with meningioma are unsuitable or unfit for surgical resection. Stereotactic radiosurgery (SRS) is increasingly used as primary therapy as well as an adjuvant treatment for residual or recurrent meningiomas and has favourable response rates. We present a retrospective analysis of patients with meningiomas treated with SRS at our institution. Materials and Methods Electronic medical records (ARIA) and stereotactic radiosurgery plans (iPlan) were reviewed to gather data on