Abstract book - ESTRO meets Asia

S10 ESTRO meets Asia 2018

33.3) and 4.4(2.2 to 45.6) in FFPE blocks. After treatment, 3 of 4(75%) patients were ctDNA free and achieved complete response, while 1 of 4 patients still could detect ctDNA and had residual tumor. For 6 patients who received post-operative radiotherapy,4 of 6(66.7%) were ctDNA negative and showed no evidence of residual tumor, while 2 of 6 patients(33.3%) detected ctDNA at baseline and were proved with residual tumor.In our cases, TMB varied heavily from 2.2 to 45.6, and we did not find a clear relationship between TMB and treatment response. Table1

risk. Further, the investigation also looked into the influence of 39 selected genetic variants on their risk for acute normal tissue adverse reactions in breast cancer patients by performing Taqman genotyping assay or PCR- RFLP. All the selected genes were involved in either DNA damage recognition-repair, oxidative stress response, xenobiotics metabolism or cell cycle. Results Our results suggested that the γ-H2AX assay can detect the variation in radiosensitivity among healthy and individuals with cancer. The XRCC6 rs2267437 (p = 0.0340) and LIG4 rs1805388 (p = 0.0250) were associated with cellular radiosensitivity in healthy individuals. Further, the individuals susceptible to radiation-induced toxicity or cancer risk indicated problems in one or all the aspects of DNA damage response, including spontaneous DSB damage, induced damage, and percentage residual damage. In association study including rs8193 (CD44) was associated (p = 0.027; OR 2.52, CI 1.10-5.75) with the increased risk of acute skin toxicity. Further, there was an association between the total number of risk alleles; rs8193-rs2282367 interaction and the acute skin adverse reaction in breast cancer patients. Conclusion The insight gained from this investigation may be helpful for the detection of radiosensitive individuals in a healthy population as well as in cancer patients undergoing radiotherapy and may have implications for radiation protection. PV-026 Treating left breast cancers with ABC device without patient selection criteria and coaching C.Y. Koh 1 , J. Tang 2 1 National University Health System, Radiation Oncology, Singapore, Singapore 2 National University Health System, Radiaion Oncology, Singapore, Singapore Purpose or Objective Deep inspiration breath hold (DIBH) using the Active Breathing Control (ABC) device (Elekta Oncology, Stockholm, Sweden) has been shown to be advantageous for left breast cancer (LBC) patients because it reduces lung and heart dose. ABC device works by achieving temporary and reproducible immobilization of respiratory motions using DIBH. Patient’s breathing cycle is monitored and a breath hold can be implemented at a predefined stage by the patient upon verbal instructions. Previous studies have described ABC device with coaching and training sessions with patients prior to its use during CT-Simulation and radiation treatment (RT). Patients are also selected based on their ability to hold their breath between 15-25 seconds for the use of ABC device. Some studies indicated patient selection criteria such as being able to follow commands, non-English speaking, claustrophobia, poor lung function and age. The main objective of this study is to demonstrate that LBC can be treated safely without pre-treatment coaching and patient selection criteria. Material and Methods We conducted a retrospective single centre study in Radiotherapy Centre, National University Hospital. The inclusion criteria were patients with left breast cancers who had undergone CT-Simulation and RT using ABC device without implementing pre-treatment coaching and patient selection criteria from January 2018 to April 2018. Poster viewing: Doseplanning and verification (RTT)

Conclusion In this preliminary analysis, we fond that ctDNA held great potential as a minimally-invasive biomarker to evaluate the treatment outcomes for patients receiving definitive radiation, and could help us identify residual tumor after surgery.The relationship between TMB and the patient's pathological features and clinical outcomes needs further investigation. OC-025 Evaluating the Risk of Normal Tissue Toxicity Using DNA Repair and Genetic Variant Analysis K.D. Mumbrekar 1 , H.V. Goutham 1 , K. Sharan 2 , B.S.S. Rao 1 1 School of Life Sciences- Manipal Academy of Higher Edu cation, Radiation Biology and Toxicology, Manipal, India 2 Shiridi Saibaba Cancer Hospital- and Research Centre- M anipal Academy of Higher Education, Radiotherapy and Oncology, Manipal, India Purpose or Objective Non-homogeneous response to ionizing radiation may lead to variation in the radiation-induced adverse health effects like normal tissue toxicity, cancer, etc. Developing a predictive biomarker to estimate the risk of radiation- induced health effects may be of prime importance in radiation protection, as well as for disease prediction. The objectives of the study were, to understand the variation in radiosensitivity among healthy individuals and to in the identity the variants which may control this variation; to predict the radiotherapy induced normal tissue toxicity based on DSB repair parameters and selected genetic variants; to identify the individuals at cancer risk based on their DNA repair capacity in response to a challenge dose of radiation. Material and Methods We studied the cellular radiosensitivity in normal healthy subjects (n=100) and cellular and clinical radiosensitivity in the breast, head, and neck cancer individuals (n=205) undergoing curative radiotherapy. The study was undertaken after Institutional Ethics Committee approval and informed consent from all the study subjects. Peripheral blood lymphocytes exposed to a challenge dose of 2Gy were analyzed by the γ-H2AX assay. Various DNA- damage parameters like baseline damage, initial damage, and repair kinetics were investigated for its association with radiation-induced normal tissue toxicity and cancer