Abstract book - ESTRO meets Asia

S128 ESTRO meets Asia 2018

radiosensitivity in different oxygen level, showing the possible directions in developing personalized radiotherapy.

shorten the overall treatment time and subsequently reduce the potential error in patient or organ movement. This is particularly beneficial in Stereotactic Body Radiotherapy (SBRT) which usually delivers higher fractionation dose. However, the high dose rate of FFF mode treatment raised out the concern of radiobiological effect. The topic is still controversial and some researchers are still hypothesized that FFF mode have a more pronounced cell killing effect to both tumour and normal cells. In this study, irradiation of lung cell lines at FFF mode high dose rate and conventional mode dose rate were compared and evaluated in in-vitro setting by clonogenic assay analysis. Material and Methods Human lung cancer (Adenocarcinoma) A549 cell line, lung cancer (Squamous cell carcinoma) H2170 cell line and normal lung fibroblast CCD-19Lu cell line were prepared for this study. The cell lines were put in separate culture disks and positioned into a simple geometry phantom. 7- fields IMRT plans were computed and to ensure a homogeneous dose gradient over the cell samples. The cell lines were irradiated by single fraction of 2, 4, 6, 8, 10, 12 ,14, 16, 18 and 20 Gy by 10MV photon beam at FFF mode dose rate (2400 MU/min.) and conventional mode dose rate (400 MU/min.) respectively in the In-vitro setting. The irradiated cell lines were detached with trypsin-EDTA solution and cultured on petri dish with plate setting: 100,000 seeds per dose parameter, each seed contain 250 cells. The cell lines were incubated for 14days. The final clonogenic cell survival data were counted and the individual cell line survival curves were plotted and analyzed. Results All cell lines showed no significant difference (P value >0.05) in cell survival after irradiation at 400 MU/min and 2400 MU/min. Cell survivals of lung cancer cells and normal cell line were not influenced by high dose rate irradiation up to single fraction of 20 Gy. (The calculated alpha/beta ratio of A549, H2170 and CCD-19Lu at 2400 MU/ min FFF mode were 15.11, 19.25 and 3.83 respectively; The calculated alpha/beta ration of A549, H2170 and CCD-19Lu at 400 MU/ min conventional mode were 15.94, 20.00 and 4.02 respectively). Conclusion Although the dose rate of FFF mode is 6 times higher than that of conventional mode. All lung cell lines showed no difference in cell survival after irradiation. Cell survival of lung cell irradiation is found to be independent of dose rate at single fraction of given doses. We conclude that up to these doses, there are no radiobiological differences that could limit the clinical use of high dose rate FFF beams in lung radiotherapy. PO-312 Influence of PEG coated Bi2O3 nanoparticles on radiation dose enhancement for MV photon beams W.N. Rahman 1 , R. Ab Rashid 1 , K. Abdul Razak 2 , S. Zainal Abidin 3 , F.W. Mohd Salim 1 1 Universiti Sains Malaysia, School of Health Sciences, Kubang Kerian, Malaysia 2 Universiti Sains Malaysia, School of Materials and Mineral Resources Engineering, Nibong Tebal, Malaysia 3 Universiti Sains Malaysia, Advanced Medical and Dental Institute, Kepala Batas, Malaysia Purpose or Objective In recent years, application of nanomaterials has been extensively investigated to enhance radiotherapy efficacy. In this study, bismuth oxide (Bi 2 O 3 ) nanoparticles coated with different concentration of polyethylene glycol (PEG) were evaluated for their applicability as radiation dose enhancer in clinical radiotherapy.

Radiobiology: Immuno-radiobiology

PO-310 Intestinal radiation plays a pivotal role in CTLA-4 Ab induced an autoimmune enteritis mouse model J. Wan 1 , Z. zhang 1 , J. cheng 2 1 Fudan University Shanghai Cancer Center, radiation oncology, Shanghai, China 2M emorial Sloan Kettering Cancer Center, Pharmacology, New York, USA Purpose or Objective Checkpoint inhibitors have been approved in specific types of cancers. While the results are promising, severe immunotherapy-related adverse events (irAEs) have been reported. The one of the most common grade 3/4 adverse events was enterocolitis. However, there are currently no mouse models that develop robust autoimmune enterocolitis following checkpoint inhibitors. The aim of the study was to set up a robust CTLA-4 Ab induced autoimmune enteritis mouse model. Material and Methods C57BL/6J mice were injected intraperitoneally (i.p) with 200µg of anti-CTLA-4 mAb every 3 days. In order to deplete CD4+ and CD8+ T cells, CD4 and CD8 antibodies were injected at 200µg/mice 4 days before anti-CTLA4 treatment. Two different tumor models were used: (1) for subcutaneous injection 2.5 ×10 5 melanoma B16 F10 cells in 100 µl PBS were injected into the right flank, (2) for intravenous injection 5 × 10 4 melanoma B16 F10 cells in 100 µl PBS were injected into the tail vein of the animals. Mice received 1100 cGy intestinal irradiation as a split dose with 3 hours interval. The whole small intestine was stained with terminal deoxy transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL), CD3 and hematoxylin and eosin. Results Intestinal epithelial villous apoptosis was induced after injection of CTLA-4 Ab. But, there was no enteritis even after 11 doses of CTLA-4 Ab. 11Gy intestinal radiation alone induced intestinal epithelial crypt apoptosis, not villous apoptosis. However, radiation can increase CTLA-4 Ab induced villous apoptosis, which can be wiped out by CD4 and CD8 antibodies. Tumor bearing can also enhance CTLA-4 Ab induced villous apoptosis. But neither combination of CTLA-4 Ab with intestinal radiation nor combination of CTLA-4 Ab with tumor bearing can induce enteritis. Finally, combination of CTLA-4 Ab, intestinal radiation and tumor bearing induced enteritis. There were morphological changes and neutrophil and T lymphocytes infiltration in jejunum. Conclusion Combination of CTLA-4 Ab, intestinal radiation and tumor bearing established an autoimmune enteritis mouse model. PO-311 Clonogenic Survival Study of Lung Cell Lines by Flattening Filter Free Photon Irradiation H.M. Hung 1 1 Pamela Youde Nethersole Eastern Hospital, Clinical Oncology, Chai Wan, Hong Kong SAR China Purpose or Objective Flattening filter free (FFF) mode linear accelerator has been implemented for clinical use for several years. It can deliver a higher dose rate (6 times higher than the conventional one) during the radiotherapy. Hence, Radiobiology: Miscellaneous