ESTRO 2020 Abstract Book

S611 ESTRO 2020

patients with stable PCa post radical radiotherapy (RT), patients with PCa progression post-RT, and patients with metastatic PCa at presentation Material and Methods 19 patients from the PROMPT research cohort were identified with pre-treatment prostate biopsies suitable for analysis: 6 patients with stable PCa following RT (74Gy in 37 fractions) treatment of localised PCa; 5 patients with PCa progression post-RT; 8 patients with metastatic PCa at presentation. Pathology review of biopsies and tumour outlining enabled macro-dissection of multiple slides pooled to a single sample per patient. RNA samples were processed and sequenced with Quantseq 3' mRNA library kit and Illumina Novaseq platform.12 samples (4 per group with optimal RNA from Nanodrop) were analysed in parallel using NScN analysis. Bioinformatic analysis was performed using R 3.52 packages DESEQ2 and EDGER. nSolver analysis software 4.0 was used for NSnC Results Following 3'RNAseq all samples bar one (5%) were sufficient for downstream analysis. All 12 samples selected for NSnC generated sufficient quality data. Upon bioinformatic analysis, differential gene expression between patients with PCa progression post-RT compared to those with stable PCa revealed >600 genes with significant differential expression (p<0.05) adjusted by Benjamini & Hochberg method (DESeq2). Unsupervised hierarchical clustering of gene expression highlighted commonalities between patients with PCa progression post-RT and those with baseline metastatic PCa (Figure 1). Similar findings were found in a separate analysis (EDGER). Gene expression analysis using NSnC confirmed differential gene expression in multiple gene pathways e.g. chromatin remodelling (Figure 2), between patients with stable PCa post-RT and those with PCa progression.

Conclusion This study demonstrates that 3’RNAseq (95%) and NSnC (100%) are technically feasible in FFPE diagnostic PCa biopsies, generating analysable data. Over 600 genes are identified by 3'RNAseq as differentially expressed between patients with PCa progression post-RT and those with stable disease with differences between these patient groups also seen on NSnC analysis. Further work is on-going to identify a predictive RT response signature. Similarities in gene expression appear to exist between baseline metastatic PCa and patients with post-RT PCa progression. PO-1161 The first study in outcomes and toxicity of definite VMAT for prostate cancer in Southeast Asia P. Wongsuwan 1 , S. Vanitchpongphan 1 , K. Tantisiriwat 1 , K. Sooksatian 1 , W. Sittiwong 1 , P. Dankulchai 1 1 Faculty of Medicine- Siriraj Hospital- Mahidol University, Division of Radiation Oncology- Department of Radiology, Bangkok, Thailand Purpose or Objective Volumetric-modulated arc radiation therapy (VMAT) has been well-demonstrated for improved plan quality and treatment-related side effect in prostate cancer. This study aims to report the treatment outcome and complication in prostate cancer patients treated with definite VMAT. This is the first report of VMAT in prostate cancer in Southeast Asia. Material and Methods This is a retrospective data analysis of patients with prostate cancer who received definite VMAT in conventional fractionation (2 Gy/F) to moderate hypo- fractionation (3-3.1 Gy/F) during 2012 to 2018. Biochemical failure was determined by using Phoenix definition which defined by a rise of >2 ng/ml above the nadir PSA. Biochemical progression-free survival (bPFS), locoregional recurrence free survival (LRRFS), distant metastatic-free survival (DMFS), and overall survival (OS) were analyzed by Kaplan-Meier survival analysis. Acute and late genitourinary (GU) and gastrointestinal (GI) toxicity were assessed according to Common terminology criteria for Adverse Event (CTCAE) version 5.0. Results A total of 324 patients were analyzed. Median follow up time was 3.4 years. 305 patient (94.1%) were delivered 2- Gy/F VMAT with a total dose of 72-78 Gy. Androgen deprivation therapy was prescribed in 307 patients (94.7%). 3-year bPFS, LRRFS, DMFS, and OS were 93.7%, 96.9%, 95.2% and 99.2% respectively and 5-year bPFS, LRRFS, DMFS, and OS were 90.9%, 95.3%, 93.1% and 97.8% respectively. bPFS stratified by NCCN risk group was