ESTRO 36 Abstract Book

S359 ESTRO 36 _______________________________________________________________________________________________

Purpose or Objective To analyze local control (LC), liver and distant progression free survival (liver PFS, DFS), overall survival (OS) and toxicity in a cohort of patients treated by stereotactic body radiotherapy (SBRT) with fiducial tracking for oligorecurrent liver lesions (Niibe Y, Hayakawa K. Jpn J Clin Oncol. 2010 Feb) from primary colorectal (55.6%), breast (20.4%) and other (24.0%) origins. Influence of lesion size, systemic treatment, physical and biological effective dose (BED with α/β =10) were also evaluated. Material and Methods Hepatic oligorecurrent patients ineligible for surgery and with sufficient liver function were included in this study. During the treatment preparation, 18FDG-PET-CT and liver MRI were used to confirm the oligorecurrent nature of the disease and to delineate the gross target volume (GTV), which were expanded to CTV and with a tracking- based margin to the planning target volume (PTV). Intended prescribed dose was 45Gy in 3 fractions on the 80% isodose. Organs at risk dose constraints were respected, if required at the cost of altered fractionation and/or lowered target coverage. All treatments were executed with the CyberKnife platform using fiducials tracking. Patient and treatment data were processed using Kaplan-Meier method and log-rank test for survival analysis. Results Between 2010 and 2015, 42 patients (55 lesions) were irradiated. The mean CTV and PTV were 67.5 cc and 96.8 cc. Treatments were delivered 3fr/week in a median of three fractions to a PTV median dose of 54.6 Gy. The mean CTV and PTV D98% were 51.5 Gy and 51.2Gy. After median follow-up of 18.9 months, the 1 and 2-year LC/liver PFS/DFS/OS were 81.3/55/62.4/86.9% and 76.3/42.3/52/78.3% respectively. Performance status (p=0.005) and histology (p=0.040) had significant impact on LC, while age (>65y, p=0.074) marginally influenced liver PFS. Physical dose of V45Gy>95% for CTV and V43Gy>95% for PTV showed statistically significant effect on the LC (figure 1), similarly to gEUD(a=-30)>45 Gy (p=0.015), BED-V105Gy>96% (p=0.045) and gEUD(a=- 30)>40Gy (p=0.040), BED85Gy>98% (p=0.037) for CTV and PTV respectively. Acute grade 3 gastrointestinal (GI) and late grade 2 GI and fatigue toxicity were found in 5% and 11% patients. Figure 1 : Kaplan-Meier curves and log-rank test for LC with target dose coverage parameters.

bevacizumab (-77% ± 22%, p=0.048) and had a smaller further decrease after SBRT (-34% ± 34%, p=0.18). With limited number of patients, there were no differences in changes in any perfusion parameters between patients with and without local failure. Conclusion To our knowledge, this is the first study in humans that evaluates quantitative CT and US perfusion measures of CRC liver metastases treated with bevacizumab and SBRT. Changes in different measures of perfusion can be detected with these imaging biomarkers. Further study in a larger cohort are needed to better understand temporal changes in perfusion and determine if these changes can be used to predict response to treatment. PO-0687 Spleen dosimetry are associated with lymphopenia during radiotherapy for hepatocellular carcinoma Q. Zhao 1 , R. Wang 1 , T. Liu 2 , J. Yue 1 1 Shandong Cancer Hospital affiliated to Shandong University, Department of radiation oncology, Jinan, China 2 Shandong Cancer Hospital affiliated to Shandong University, Department of radiology, Jinan, China Purpose or Objective The decline of peripheral blood lymphocytes induced by radiation would lessen the antitumor effect of the immune response, which might cause immunosuppressive. We aim to investigate the correlation between the decline of peripheral blood lymphocyte and spleen irradiation dose in patients with hepatocellular carcinoma (HCC) during radiotherapy (RT). Material and Methods Subjects were 59 patients with HCC who had received RT from 2005 to 2014. Min ALC (minimum value of absolute counts for peripheral blood lymphocyte) was collected from the routine workup for each patient before and weekly during RT. Spleen dose-volume variables including mean spleen dose (MSD) and V n Gy (V n , the percentage of organ volume receiving ≥ n Gy) were calculated from Eclipse Treatment Planning. Potential associations between dosimetric variables and Min ALC were assessed by regression analysis. Results White blood cells, neutrophil cells, lymphocyte cells and monocyte cells were all declined during RT (all P < 0.001). Min ALC were correlated with spleen dosimetric parameters but the other blood cells did not. Min ALC were correlated with MSD (P = 0.005), spleen V 5Gy (P = 0.001), spleen V 25Gy (P = 0.026) and spleen V 30Gy (P = 0.018). Controlling patients karnofsky performance status, gender, age, Child-grades and total dose, multivariate linear regression model showed that only spleen V 5Gy were correlated with the decline of Min ALC (HR= 1.504, P = 0.003). Conclusion Higher spleen irradiation dose were significantly correlated with lower Min ALC during RT for HCC. Maximum sparing for spleen irradiation during RT is recommended to preserve peripheral blood lymphocytes, which may potentially decease immunosuppression. PO-0688 Unresectable hepatic oligorecurrence SBRT of 55 lesion: Adequate dose coverage improves local control P. Berkovic 1 , A. Gulyban 1 , P. Viet Nguyen 1 , D. Dechambre 1 , P. Martinive 1 , N. Jansen 1 , F. Lakosi 2 , L. Janvary 3 , P.A. Coucke 1 1 C.H.U. - Sart Tilman, Radiotherapy department, Liège, Belgium 2 Health Science Center- University of Kaposvar, Radiation Oncology, Kaposvar, Hungary 3 University of Debrecen - Medical Center, Oncology Clinic, Debrecen, Hungary