ESTRO 37 Abstract book

ESTRO 37

S578

2 Queen Elizabeth Hospital- Woolwich, Department of Surgery, London, United Kingdom 3 The Royal Liverpool and Broadgreen University Hospitals NHS Trust, Department of Colorectal Surgery, Liverpool, United Kingdom 4 University of Liverpool, National Institute for Health Research- Collaborations for Leadership in Applied Health Research and Care- North West Coast NIHR CLAHRC NWC-, Liverpool, United Kingdom 5 Castle Hill Hospital, Queen's Centre for Oncology & Haematology, Hull, United Kingdom 6 Royal Surrey County Hospital, St Luke's Cancer Centre, Guildford, United Kingdom 7 Glan Clwyd Hospital, North Wales Cancer Treatment Centre, Rhyl, United Kingdom 8 University of Liverpool, Department of Public Health and Policy, Liverpool, United Kingdom 9 The Clatterbridge Cancer Centre, Clinical Oncology, Merseyside, United Kingdom Purpose or Objective When the circumferential resection margin is threatened over 80% of patients with rectal cancer in some series do not achieve a clinical complete response (cCR) to chemoradiotherapy, and are consequently not eligible for watch and wait (WW) management. Contact X-ray Brachytherapy (CXB) enables high doses of radiation to be delivered directly to the tumour with minimal damage to adjacent tissue, and can be used in addition to external beam radiotherapy (EBRT) to increase the proportion of patients who achieve a cCR. CXB may therefore avoid the need for surgery and the associated mortality and morbidity, including stoma formation. However, the long- term cost-effectiveness has not been evaluated. Consequently, we aim to evaluate the cost-effectiveness of CXB boost when used in addition to standard chemoradiotherapy to increase the cCR rate as part of a WW strategy in patients who would ordinarily have chemoradiotherapy before undergoing curative surgery in Decision analytical modelling and a Markov simulation were used to compare long-term costs, quality-adjusted life years (QALYs), and cost-effectiveness from a third- party payer (NHS) perspective for treatment strategies following chemoradiotherapy; WW with CXB when a cCR was not initially achieved following EBRT (WW CXB ), WW with EBRT alone (WW EBRT ), and radical surgery for all patients (RS). The effect of uncertainty in model parameters and patient demographics was investigated. Results WW CXB had a higher QALY-payoff than both RS and WW EBRT and was less costly in most scenarios and demographic cohorts. In all plausible scenarios WW CXB was most cost- effective at a threshold of £20,000/QALY. This finding was insensitive to uncertainty associated with model parameters. Table: Summary of the results of cost-effectiveness analysis standard UK practice. Material and Methods

insertion of 2 days (ITQ: 0-2). Ten other patients (4.4%) developed hematuria requiring urinary catheter insertion ± continuous bladder irrigation. Except for one, all patients with hematuria were catheterized on the day of the procedure. Total median time with urinary catheter was 3 days (ITQ: 2-55). Prior use of ADT, alpha-blockers or 5α-reductase inhibitors was statistically associated with urinary retention in the univariate logistic regression analysis. Odds ratio and p-value are shown in Table 2. In multivariate analysis, only use of alpha-blocker remained significant (OR: 3.86, p=0.01) for urinary retention, with ADT showing a tendency for significance (OR: 2.89, p=0.053).

Conclusion The rate of acute urinary retention and hematuria post HDR-BT was approximately 10% and 4%, respectively. Previous use of alpha-blocker was found to associate with urinary retention and likely reflects the higher degree of obstructive urinary function in this population. IPSS was not found to be a predictor, however only 130 patients (58%) had IPSS reported and the score value registered may be confounded by concomitant use of alpha- blockers. Neo-adjuvant ADT may independently associate with urinary retention post-BT.

Poster: Brachytherapy: Anorectal

PO-1029 Contact x-ray brachytherapy for rectal cancer following chemoradiotherapy is cost-effective C. Rao 1,2 , F.M. Smith 3 , A.P. Martin 4 , A.S. Dhadda 5 , A. Stewart 6 , S. Gollins 7 , B. Collins 8 , T. Athanasiou 1 , A. Sun Myint 9 1 Imperial College London, Department of Surgery and Cancer, London, United Kingdom