ESTRO 2020 Abstract book

S1068 ESTRO 2020

paraspinal mass, >3mm gap between edge of the lesion, 2 contiguous spine levels with <50% body involvement & No spinal instability. All patients underwent S board rigid fixation / body fix immobilization, advanced image guidance using 6 DOF corrections on C-arm Linac. Fractionation used for treatment was either 16 / 1 Frc. or 24gy/3 Frc based on the clinical scenario, goals of treatment & projected life expectancy. All patients underwent limited metabolic imaging Pre- treatment and Post-treatment PET-CT scans up to 3 months. Post SBRT first PET-CT scan was scheduled at 48 hours and serial PET CT scans were done at 10, 30, 60 and 90 days post treatment. PET-CT images were reviewed in order to determine the pre- and post- treatment maximum standardized uptake value (m-SUV) of the lesion, including “complete resolution” of FDG- avidity. Corresponding morphologic changes in the target lesions and surrounding normal bony were studied on the PET-CT images during the 3 moth evaluation period. Results All the 5 patients showed nearly consistent serial regression patterns in metabolic activity post treatment. The observed metabolic regression was between 60%-65% (median 50%) 48 hrs after treatment, 70% metabolic regression ( median – 70%) was observed 10 days post treatment. A median SUV increase of 1.7 was observed in all 5 pts in the first and second month scan when compared with 10th day post Treatment scan. At 3rd month, 4 out of 5 patients had FDG non-Avid disease. During the evaluation period (first 3 months) there was no significant change in bony architecture but the paraspinal mass lesions morphologically decreased at 3rd month scan. Conclusion Early metabolic response post Spine SBRT was seen at 48 hours post treatment & maximum metabolic response was seen at 3 monrths post SBRT. This is the first study reported in literature which looked into the serial metabolic trending in first 3 months post Spinal SBRT for spinal oligometastatic disease. PO‐1823 New insights into cellular dose‐response in vitro from high‐throughput time‐lapse AI assays R. Koch 1,2,3 , I. Dokic 2,3,4 , M. Alber 1,2,3 , E. Bahn 1,2,3,5 1 Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Germany ; 2 Heidelberger Institut für Radioonkologie HIRO, Quantitative klinische Strahlenbiologie, Heidelberg, Germany ; 3 National Center for Tumor Diseases NCT, Integrative Radiation Oncology, Heidelberg, Germany ; 4 German Cancer Research Center DKFZ, Clinical Cooperation Unit Translational Radiation Oncology, Heidelberg, Germany ; 5 German Cancer Research Center DKFZ, Clinical Cooperation Unit Radiation Oncology, Heidelberg, Germany Purpose or Objective Assaying the response of cells to radiation in vitro is a widely used radiobiological tool in radiotherapy. Despite occasional criticism, cell colony growth (CG) is commonly used as a surrogate to quantify the deleterious effect of radiation. Today, automation allows the acquisition and analysis of image data as a time series on a large scale. We took this as an opportunity to investigate the potential benefit of extracting statistical and time-dependent dynamical information. Material and Methods Cells of three different strains (ACHN, RENCA, H3122) were seeded onto multiwell plates, irradiated with single doses of 0-10 Gy X-rays and placed into an incubator with automated phase-contrast image acquisition in 3 h Poster: Radiobiology track: DNA damage response

tumour immune microenvironment effects of clinically relevant HF-RT doses delivered to two pre-clinical immunocompetent PCa models. Material and Methods 3x5Gy HF-RT was delivered to 100mm 3 TRAMP-C1 and MyC- CaP subcutaneous flank tumours in syngeneic mice using a Gulmay 320 irradiator (300kV, 10mA) at a dose rate of 2.25Gy/minute. Tumour growth delay and tumour immune microenvironment cellular infiltrates were analysed post- treatment, compared to untreated control tumours, using calliper measurement and flow-cytometry (FACS) analysis respectively. Results 3x5Gy HF-RT caused a significant tumour growth delay in TRAMP-C1 and MyC-CaP tumours compared to untreated control tumours. The mean growth delay to 400mm 3 was greater in TRAMP-C1 than MyC-CaP (27 vs 12 days), suggesting that TRAMP-C1 may be a more radio-sensitive tumour than MyC-CaP. Tumour immune microenvironment changes in TRAMP-C1 at 7 days following initiation of 3x5Gy HF-RT included an increased CD45+ cell infiltrate, comprising primarily tumour-associated macrophages (TAMs) and dendritic cells (DCs) on FACS. At tumour regrowth to 400mm 3 post-3x5Gy HF-RT the tumour immune microenvironment had normalised on FACS compared with control tumours. In contrast, 3x5Gy HF-RT did not cause an increased CD45+ cellular infiltrate in the MyC-CaP tumour immune microenvironment, but resulted in a significantly reduced CD4+helper T-cell infiltrate. Conclusion Clinically relevant 3x5Gy HF-RT resulted in a significant tumour growth delay in both TRAMP-C1 and MyC-CaP pre- clinical PCa allograft models, however this dose of ionising radiation was sublethal with eventual tumour regrowth in both models. 3x5Gy HF-RT resulted in changes within the TRAMP-C1 tumour immune microenvironment at the 7-day time-point, with increased infiltration of TAMS and DCs. However, this effect was not seen in MyC-CaP tumours. Taken together, these results suggest that clinically relevant HF-RT doses can change the immune cellular content of the TRAMP-C1 flank tumour immune microenvironment. Experiments to test the possibility that these immune cell changes may be harnessed in a multi- modality approach to treating high-risk locally advanced PCa in this model are ongoing. PO‐1822 PET‐CT based metabolic regression velocity following SBRT for spinal oligometstases H. Vyas 1 , S. Vangipuram 1 , A. Bhange 1 , D. Patel 2 , B. Patneedi 1 , K. Ar 1 1 HCG Cancer Centre, Radiation Oncology, Mumbai, India ; 2 Geetanjali Medical College and Hospital, Radiation Oncology, Udaipur, India Purpose or Objective SBRT, predominantly, causes indirect cell kill through (1) Ceramide induced vascular apoptosis which starts few hrs after treatment & peaks around 3rd day (2) immunological alteration in the host tumor microenvironment, a process which starts around 3rd day post-treatment & peaks at 10-12 days. Routine Post SBRT follow up imaging is advocated after 3 months. Present study evaluated the clinicoradiobiolgic response of single or multi-fraction spine SBRT post-treatment for spinal oligometastases with serial FDG PET-CT scans. Material and Methods Five patients with localized spinal metastases with primaries from lung-2, breast - 2, kidney - 1 were included in this proof-of-concept study. Patients were having lesions anywhere from C1 to L5, had less than 5 cms Poster: Radiobiology track: Radiation and tumour metabolism