Introduction Diarrhoea is common during pelvic chemoradiotherapy and is multifactorial in origin. Previous studies show a rate of 26% small intestinal bacterial overgrowth (SIBO) and 15–44% lactose intolerance during the acute toxicity phase. However radiotherapy treatment has developed to provide more targeted treatment to the tumour, and spare organs at risk such as the small bowel. We aimed to determine the rate of SIBO and lactose intolerance in patients receiving newer techniques at our centre.

Method This study was part of a trial evaluating the use of a gastrointestinal intervention for patients with cervical and bladder cancer receiving pelvic chemoradiotherapy. When patients developed lower gastrointestinal symptoms, hydrogen-methane breath tests were performed using the Quintron Breathtracker to detect SIBO and lactose intolerance. Demographic and treatment data were recorded in the trial documentation.

Results Twenty patients had hydrogen methane breath testing for SIBO and 17 for lactose intolerance. Nine of these patients had cervical cancer and 11 had bladder cancer. Of the patients with bladder cancer, 10 were male. All patients received 20 fractions of radiotherapy over 4 weeks. See Table 1for full demographics.

Glucose hydrogen methane breath testing was performed a median of 19 days after the start of radiotherapy and lactose hydrogen methane breath testing a median of 27 days after. SIBO was diagnosed in 21% (4/19) (1 test was inconclusive) by a rise in hydrogen in all cases. Of patients with cervical cancer 38% (3/8) had SIBO compared with 9% (1/11) patients with bladder cancer.

Lactose intolerance was diagnosed in 29% (5/17) patients by a rise in hydrogen in all cases. Of the bladder group 30% (3/10) had lactose intolerance while 29% (2/7) of the cervix group tested positive.

Conclusion The prevalence of SIBO and lactose intolerance in this study is similar to that previously described despite recent advances in radiotherapy treatment suggesting that new techniques do not reduce the risk of small bowel bystander effects.

Disclosure of interest K. White Grant/ Research Support from: This poster presents independent research funded by the National Institute for Health Research (NIHR) under its Research for Patient Benefit (RfPB) Programme (Grant Reference Number PB-PG-0211–10024. The views expressed are those of the author (s) and not necessarily those of the NHS, the NIHR or the Department of Health., C. Henson: None Declared, J. Glennon: None Declared, S. Burden: None Declared, S. Lal: None Declared, S. Davidson: None Declared, J. McLaughlin: None Declared.