ESTRO 2021 Abstract Book

S882

ESTRO 2021

Purpose or Objective To retrospectively investigate clinical and dosimetric predictors of acute lymphopenia and its association with overall survival (OS) in a series of GBM patients treated with postoperative chemo-RT. Materials and Methods Between 2015 and 2019, 64 patients, median age 62.5 years (range 53.3-69.8), were treated at the same Institution with postoperative chemo-RT. Peripheral lymphocyte count (PLC) data and RT dose-volume histogram (DVH) parameters were collected. RT schedule consisted in standard total dose of 60 Gy in 30 daily fractions, with concomitant and adjuvant temozolomide (TMZ) administered as per standard protocol. Post- treatment acute absolute lymphopenia (nadir AAL) was calculated as a PLC lower than 1.0×10³/mm³, while acute relative lymphopenia (nadir ARL) was expressed by the nadir-PLC/pre-PLC ratio. Survival rates were estimated with Kaplan-Meier curves. Clinical and dosimetric variables related to AAL/ARL and OS were identified by univariate and multivariate analyses. Results The median PLC was significantly decreased following CT-RT (2200/mm³ Vs 900/mm³) and did not recover during the adjuvant TMZ treatment. OS was 16 months (range: 3-55 months), with no significant difference between patients who developed AAL and those who did not (16 months vs 16.5 months; p= 0.304, respectively). The 18 months-OS rate was 41.3% for the entire population, with no significant difference between the former and the latter group (43.3% vs 46.2%; p= 0.479, respectively). However, median OS was 14 months vs 26 months (p= 0.013) in nadir ARL vs non-ARL group. Likewise, the 18 months-OS rate was 28.6% vs 60.7% respectively (p= 0.012). At multivariate analysis gross total resection was the most significant predictive factor (OR 4.74; p= 0.042), and a trend in favor of nadir ARL (OR 2.09; p= 0.291) was showed. Conclusion Our data show that treatment-related lymphopenia might adversely affect GBM survival, adding evidence that iatrogenic immunosuppression could be associated with inferior clinical outcomes. Prospective studies are required to confirm these findings. 1 St.Lukes Radiation Oncology Network, Radiation Oncology, Dublin, Ireland; 2 St.Lukes Radiation Oncology Network, Clinical Trials Unit, Dublin, Ireland; 3 St.Lukes Radiation Oncology Network, Medical Physics, Dublin, Ireland Purpose or Objective Renal Cell Carcinoma (RCC) is one of the common sources of metastasis to the brain. Between 4% and 17% of all patients with RCC develop brain metastases. The median survival (MS) after radiotherapy is between 2 and 8 months. Whole Brain Radiotherapy (WBRT) plays an important role in the management of RCC brain metastasis but is limited by its potential neurotoxic effects and the relative radio-resistance of RCC as well as poorer overall survival (OS) and local control rates. Stereotactic radiosurgery (SRS) delivers a conformal and high dose of radiation and is being increasingly used with favorable response rates. We present a retrospective analysis of the outcomes in RCC patients with metastases to the brain treated with SRS at our institution Materials and Methods Patient medical records were reviewed on patients who received SRS for brain metastases secondary to primary RCC between 2013 and 2018 in our institution. We obtained patient data and tumour characteristics. Gadolinium enhanced planning MRI images were fused with CT scan obtained in a stereotactic immobilization mask. Image fusion and treatment planning were done on iPlan radiotherapy planning software. SRS dosimetry on each patient was obtained and follow-up neuro-imaging in the form of MRI scans that was done to evaluate treatment response were reviewed and results recorded. The Kaplan-Meier method was used to estimate survival times for individual patients Results A total number of twenty-four patients were identified (n=24). Sixteen of these patients were male and 8 were female. The median age at diagnosis was 60.4 years. A total of 50 metastases were treated. Forty-five of these metastases were in-situ metastases; 5 were resected and the post-operative cavity was treated in these patients. Ten patients had a solitary metastasis and 6 had > 3 metastases. A single fraction was used to treat 40 metastases. Eight patients were treated with 3 fractions and 2 patients with 5 fractions. The median single fraction dose used was 20 Gray (range 16 – 24 Gy). For in-situ metastases the median planning target volume (PTV) margin was 1 mm and median PTV volume was 1.05 cc. The median duration of imaging follow-up was 14.7 months. The median overall survival (OS) was 14.5 months and the median local progression free survival (PFS) was 16.8 months Conclusion Stereotactic radiosurgery for brain metastases from RCC has been shown to prolong overall survival when compared to WBRT with median survival rates in the order of between 5.1 and 17.8 months. Our retrospective analysis has showed that SRS is an effective treatment option and results in comparable OS rates as per reported literature. Further randomized control trials are required to further evaluate the effectiveness of SRS when compared to other treatment modalities PO-1063 Multicenter study for breast cancer brain metastasis: Role of whole-brain radiotherapy (KROG 1612) J.S. Kim 1 , K. Kim 2 , W. Jung 2 , K.H. Shin 1 , S. Im 3 , H. Kim 4,6 , Y.B. Kim 5 , J.S. Chang 5 , J.H. Kim 3,16 , D.H. Choi 6 , Y.H. Park 7 , D.Y. Kim 8 , T.H. Kim 8 , B.O. Choi 9 , S. Lee 9 , S. Kim 10 , J. Kwon 11 , K.M. Kang 12 , W. Chung 13 , K.S. Kim 14,2 , W.S. Yoon 15 , J. Cha 17 , Y.K. Oh 18 , I.A. Kim 1,19 PO-1062 Stereotactic Radiosurgery for Brain Metastases from Renal Cell Carcinoma: A retrospective study G. Rangaswamy 1 , O. Houlihan 1 , J. Nicholson 1 , H. O'Driscoll 1 , M. Dunne 2 , C. Skourou 3 , C. Faul 1 , D. Fitzpatrick 1