Abstract Book

ESTRO 37

S355

Purpose or Objective To determine the effect of probiotic combination on radiation-induced oral mucositis in nasopharyngeal cancer (NPC) patients with concurrent chemoradio- therapy. Material and Methods Experimental Design: Fifty one NPC patients were enrolled in the clinical trial who were randomized into two groups: radiotherapy + chemotherapy + placebo (RCP), radiotherapy + chemotherapy + probiotic combination (RCPC).The occurrence of oral mucositis, tumor response, immune function, and microbial diversity of intestinal microbiota were monitored and analyzed. Results We found that RCPC patients showed significant reduction of oral mucositis, while the tumor response was similar to the patients in the RCP group. Further, we found that the RCPC group had an enhanced number of lymphocytic cells (P< 0.05), CD4+T cells (P< 0.05), CD8+T cells and CD3+T cells (P< 0.05). High-throughput sequencing results indicated that the uptake of probiotic combination greatly enhanced the population of Bacteroides, Escherichia-Shigella, Parabacterodies, while reducing the abundance of Prevotella and Catenibacterium in the gut microbiome. The abundance of Bifidobacterium, Enterococcus and Lactobacillus in the RCPC group was 2-fold, 13-fold and 4-fold higher than that in the RCP group. Conclusion Our results indicate that probiotic combination signify- cantly enhance the patients' immune response and reduce the incidence of oral mucositis through modification of the gut microbiota. PO-0698 Severe and late dysphagia after head and neck cancer IMRT without residual disease E. Ibrahim 1 , A. Biswas 2 , A. .Mirza 2 , M. Sivaramalingam 2 1 The Christie Hospital NHS Trust Manchester, Clinical Oncology, Manchester, United Kingdom 2 Rosemere Cancer Centre- Royal Preston Hospital, Clinical Oncology, Preston, United Kingdom Purpose or Objective Feeding Dependency (TFD) following HN cancer radiotherapy is an extreme form of swallowing dysfunction. H&N cancer (local and international) protocols advocate Organ at Risk (OAR) radiotherapy dose constraints however, the incidence of toxicities are not well documented. We assessed patients with TFD after definitive HN cancer Radiotherapy treatment that are diseases free at time of the assessment. Material and Methods Retrospective hard copy notes and electronic case notes review for patients treated at Rosemere Cancer Centre at Royal Preston Hospital between 02/01/2013-30/06/2016 was undertaken. We identified a cohort of patient with severe and late dysphagia as defined as TFD beyond 6 month after the completion of treatment. This cohort of patients was split in to 2 groups, one with and the other without evidence of residual disease after definitive treatment. Radiotherapy induced TFD without evidence of residual disease was selected for further analysis. Patient who had definitive and adjuvant radiotherapy were identified. Radiotherapy induced dysphagia documented as grade 3 or above (Dysphagia defined in common toxicity criteria v4) that need needed TFD were analysed. Pharyngeal constrictors (PC) as OAR were contoured in the planning CT scans retrospectively for this cohort of patients. Dose calculation for OAR was split into 3 groups: The whole PC muscle (S+M+L), Superior PC muscle (Sup), and middle + lower PC muscle (M+L). Tumour stage (T), nodal status (N), Planned Target

Poster: Clinical track: Head and Neck

PO-0696 Plasma Cell Free HPV-16 DNA as a Biomarker for HPV-associated Oropharyngeal Squamous Cell Cancers B. Chera 1 , K. Sunil 2 , A. Robert 3 , J. Weiss 2 , J. Grilley- Olson 2 , A. Zanation 2 , T. Hackman 2 , S. Patel 2 , M. Weissler 2 , W. Mendenhall 2 , G. Gupta 2 1 The University of North Carolina, Radiation Oncology, Chapel Hill NC, USA 2 University of North Carolina School of Medicine, Radiation Oncology, Chapel Hill, USA 3 University of Florida School of Medicine, Radiation Oncology, Gainesville, USA Purpose or Objective To quantify HPV-16 copies in circulating tumor DNA (ctDNA) extracted from the plasma of patients with favorable risk, HPV-associated oropharyngeal squamous cell carcinoma (OPSCC) during the receipt of de- intensified chemoradiotherapy (CRT) on a prospective phase II clinical trial (NCT02281955). Material and Methods The major inclusion criteria were: 1) T0-T3, N0-N2c, M0, 2) HPV or p16 positive (tumor sample), and 3) minimal/moderate smoking history. Treatment was limited to 60 Gy intensity modulated radiotherapy with concurrent weekly intravenous cisplatin (30 mg/m 2 ). Blood specimens were collected at baseline and weekly during CRT and processed for plasma circulating nucleic acid extraction (Qiagen). A Taqman assay using a locked nucleic acid probe targeting the HPV-16 E6 gene was developed and implemented on the Bio-Rad QX100 droplet digital PCR platform. Sample quality was confirmed by amplification of an independent genomic locus. Results Plasma HPV-16 ctDNA was analyzed for 47 patients who completed 6 weeks of de-intensified CRT. At baseline, plasma HPV-16 ctDNA assessment identified three strata of patients: those with undetectable (10/47 patients), low (mean 47 copies/mL, 12/47 patients), and high levels (mean 1605 copies/mL, 25/47 patients). Baseline, 3 week, and 6 week HPV-16 copies in plasma ctDNA did not correlate with T stage, N stage, or smoking status. Disease free survival was worse in patients with low/undetectable pretreatment HPV-16 ctDNA versus those with high pre-treatment levels (65% vs. 100%, p = 0.046). Three patients had regional nodal persistence and one had a distant failure. Conversion to undetectable HPV ctDNA was observed in 33%, 58%, and 83% of patients at weeks 4, 5, and 6 of CRT. Conclusion Plasma HPV-16 ctDNA is detectable in the majority of favorable risk HPV-associated OPSCC. Heterogeneity in the baseline levels and clearance kinetics of HPV-16 ctDNA during CRT does not correlate significantly with pre-treatment clinical factors. Patients with undetectable/low baseline plasma HPV-16 ctDNA levels had worse cancer control. We identify a subset of favorable risk patients who have undetectable HPV-16 ctDNA two weeks prior to completion of de-intensified CRT. PO-0697 Probiotics reduces oral mucositis for nasopharyngeal cancer patients in a randomized clinical trial C. Jiang 1 1 JiangXi Cancer Hospital, Radiation Oncology, Nanchang, China