ESTRO 2020 Abstract book

S154 ESTRO 2020

stage III (n=7), stage IV (n=3) and unknown (n=15). The median prescribed dose (peaked for SABR) for the RT1 and RT2 was 57Gy (range: 45-88) and 57Gy (range: 54-60), respectively. Table 1 shows characteristics for the retreatment and matched cohort (n=77). The median OS (measured from RT1) for the retreatment cohort was 51m (95% CI: 45-58); fig1A . The median OS was 51m (95%CI: 49- NA) for patients treated with re-irradiation (n=25) and 58m (95%CI: 51-NA) for patients treated with repeat radiotherapy (n=28). After adjusting for lead time bias (OS measured from RT2), patients who underwent retreatment within 1y of the first radiotherapy had worse OS (median: 20m, 95% CI: 12-36) compared to patients where the inter- radiotherapy gap was >1y (median: 25m, 95% CI: 15-55); p =0.013 ( fig1B ). The type of radiotherapy and performance score were not prognostic in the retreatment cohort. After adjusting for lead time bias, there was no difference in OS for the retreatment (median: 21m, 95% CI: 15-33) and the matched cohort (median: 22m, 95%CI: 17-NA); p=0.436 ( fig1C ).

retreatment dose and investigate toxicity and quality of life.

PH-0282 Phase 2 Study of Novel Partial Tumor Irradiation for Sparing Peri-Tumoral Immune Microenvironment. S. Tubin 1 , M.K. Khan 2 , G. Salerno 3 , W.F. Mourad 4 , W. Yan 5 , B. Jeremic 6 1 Landeskrankenhaus Klagenfurt, Strahlentherapie und Radioonkologie, Klagenfurt, Austria ; 2 Emory University School of Medicine- Winship Cancer Institute, Department of Radiation Oncology, Atlanta- GE, USA ; 3 Universita´ La Sapienza Roma- Ospedale Sant´ Andrea, Department of Neurosciences- Mental Health and Sensory Organs / Department of Clinical and Molecular Medicine, Rome- RM, Italy ; 4 Markey Cancer Center- University of Kentucky Lexington ky, Department of Radiation Medicine, Lexington KY, USA ; 5 Thomas Jefferson University- Philadelphia, Department of Radiation Oncology, Philadelphia- PA, USA ; 6 Research Institute of Clinical Medicine- Tbilisi- Georgia- and BioIRC- R&D Center for Biomedical Research- Kragujevac- Serbia, Department of Radiation Oncology, Tbilisi, Georgia Purpose or Objective Patients with unresectable bulky NSCLC continue to be a therapeutic dilemma because the radical conventional radiotherapy (RT) techniques including SBRT are technically difficult to apply to such a large lesions due to the limited surrounding normal tissue tolerance. The immunomodulatory effects of RT have been questioned by many scientists in the era of immunotherapy (IT), with a renewed focus on the immune-mediated abscopal effects (AE) as well as on the depletion of lymphocytes. RT-induced lymphopenia may be limiting the success of therapy and could also negatively affect the ability of immune system in mediating the bystander effect (BE) and AE. A novel SBRT-based PArtial Tumor irradiation of HYpoxic clonogenic cells (SBRT-PATHY) for induction of the tumoricidal BE and AE by sparing the peritumoral immune microenvironment and regional circulating lymphocytes has been developed at our institute to enhance RT therapeutic ratio of unresectable bulky NSCLC. The aim of this retrospective review of prospectively collected mono-institutional phase 2 study was to compare the outcomes between unconventional SBRT-PATHY and standard of care in unresectable bulky NSCLC. Material and Methods 60 patients with stage IIIB/IV bulky NSCLC considered inoperable or unsuitable for radical radio-chemotherapy were treated at our cancer center with: SBRT-PATHY to the bulky NSCLC (group I, n=20 patients), recommended standard of care CHT (group II, n=20 patients), and conventional palliative 3Gy x 10 RT to the bulky NSCLC (group III, n=20 patients). For the purpose of SBRT-PATHY planning each bulky tumor was divided into 4 segments using a combination of contrast-enhanced CT and FDG- PET: 1) peripheral hypervascularized-hypermetabolic („normoxic“) bulky segment, 2) central necrotic („anoxic”) tumor region, 3) hypovascularized- hypometabolic (SUVmax<3, „hypoxic“) segment, 4) peri- tumoral immune microenvironment created by adding a uniform 1 cm margin around the GTV. SBRT-PATHY dose of 10-12Gy x 1-3 (based on bulky site and volume) was delivered to hypoxic segment 3 considering the following dose constraints for segment 4: Dmin<1Gy/fraction, Dmax<5Gy/fraction, Dmean<3Gy/fraction. Results

Conclusion The lack of survival difference between retreatment and matched cohorts provide indirect evidence of the benefit of a second curative-intent thoracic radiotherapy course in NSCLC patients with locoregional recurrence and second primary. Prospective trials are needed to standardise