Timing of Contact X-ray Brachytherapy in organ-preserving treatment of rectal cancer

Than, Ngu ORCID: 0000-0003-4991-5431, Pritchard, D Mark, Duckworth, CA, Hughes, David M and Myint, Arthur Sun (2024) Timing of Contact X-ray Brachytherapy in organ-preserving treatment of rectal cancer. In: ESTRO 2024, 2024-5-3 - 2024-5-7, Glasgow, UK.

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Abstract

Timing of Contact X-ray Brachytherapy in organ-preserving treatment of small rectal cancer Objective For patients with early rectal cancer, who are either at high risk for or refuse surgery, a planned organ preservation treatment involving a combination of external beam radiotherapy (EBRT) and Contact X-ray Brachytherapy (CXB) can be offered as an alternative option to surgery. (1-3) However, the ideal sequence of treatment for small rectal tumours (≤3cm), whether to administer CXB first or after EBRT, has not yet been well established, leading to variable sequences of this organ-preserving treatment being used.(3-5) This study has compared the oncological outcomes between the two treatment approaches using propensity score matching and inverse probability treatment weighting (IPTW) analysis to evaluate whether starting with CXB confers any benefits to patients. Method We analysed patients who had undergone both EBRT and CXB with curative intent, regardless of the treatment sequence, from the prospectively collected database at Clatterbridge Cancer Centre (2008-2019). Only patients who had well to moderately differentiated rectal adenocarcinoma (cT1-3, cN0-1, cM0) and small tumour size (≤ 3cm) were included. The variables of age, sex, fitness for surgery, performance status, tumour stage, nodal stage, EBRT regimen and CXB total dose, were considered possible confounders of the association between treatment regimen and outcomes. The balance of covariates before and after propensity matching and IPTW was assessed by examining the standardised mean difference (SMD) between the groups (Figure 1). The oncological outcomes based on the treatment sequence were first assessed in an unadjusted analysis followed by an adjusted model analysis considering all variables as confounders. Then, we performed propensity score matching (nearest-neighbour method, calliper= 0.25) and calculated IPTW to weigh the full cohort in each regression model. Statistical analysis was performed in R 4.3.1. The primary outcome measures were overall survival (OS) and disease-free survival (DFS). Secondary outcome measures consisted of the local regrowth rate, organ preservation rate, and presence of post-treatment rectal bleeding. Results A total of 251 eligible patients, who received either EBRT (n=103) or CXB (n=148) as their initial treatment with curative intent were included in the study. Patients received a CXB dose of 90-110Gy in 3-4 fractions over 4-6 weeks (each fraction two weeks apart) either before or after EBRT. EBRT was administered either as long-course chemoradiotherapy (45-50Gy/25 #/35 days), long-course radiotherapy alone (45Gy/20#/28days), or short-course radiotherapy (25Gy/5#/5 days). Following treatment, a watch-and-wait policy was adopted for patients who achieved a clinical complete/near response. The median follow-up was 37 [IQR:18-56] months for the EBRT-first group and 32 [IQR:16-54] months for the CXB-first group. In the unadjusted analysis, a higher risk of grade-1(26%) and grade-2(6%) rectal bleeding (p=0.008) was observed in patients who started with CXB, but no significant differences in any of the survival parameters were found. Analysis using the adjusted, propensity matching, and IPTW models, demonstrated a significant improvement of OS (p=0.04, HR (95%CI): 0.69 (0.48-0.98) and a higher risk of grade 1-2 rectal bleeding (p=0.01, OR (95%CI): 2.35(1.16-4.76) in those patients who had been received CXB as their initial treatment (Figure 2). However, DFS (p=0.87), local regrowth rate (p=0.70), and organ preservation rate (p=0.80) were not significantly different between the two groups. Conclusion Small rectal cancer (≤3cm), commencing treatment with CXB, as opposed to EBRT, was associated with improved overall survival, despite an increased risk of grade 1 and 2 rectal bleeding. However, there was no statistically significant improvement in terms of disease-free survival, local regrowth rate, or organ preservation rate with this treatment strategy.

Item Type:	Conference or Workshop Item (Unspecified)
Uncontrolled Keywords:	Contact X-ray Brachytherapy, Organ preservation, Propensity score
Divisions:	Faculty of Health and Life Sciences Faculty of Health and Life Sciences > Institute of Systems, Molecular and Integrative Biology
Depositing User:	Symplectic Admin
Date Deposited:	03 Jun 2024 09:44
Last Modified:	03 Jun 2024 09:44
Related URLs:	Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3181907