Dose-volume analysis and sphincter-related toxicity of radiation therapy for rectal cancer
PO-1102
Abstract
Dose-volume analysis and sphincter-related toxicity of radiation therapy for rectal cancer
Authors: Jullian|, Nicolas(1)*[njullian@ulb.ac.be];Charlier|, Florian(1);Van Gestel|, Dirk(1);Otte|, François-Xavier(1);Moretti|, Luigi(1);
(1)Institut Jules Bordet, Radiotherapy, Bruxelles, Belgium;
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Purpose or Objective
The purpose of this study was to evaluate the dose delivered to the anorectal sphincter and to evaluate its impact on sphincter toxicity/fecal incontinence after preoperative chemoradiation for locally advanced rectal cancer.
Material and Methods
We reviewed 36 patients with a locally advanced rectal adenocarcinoma treated between 2013 and 2015 with preoperative chemoradiation (45-50Gy+5FU) followed by sphincter-sparing surgery.
Four different structures were delineated on the dosimetry/simulation CT-scan: the levator ani muscle (LAM), the pubo-rectal muscle (PRM), the external anal sphincter muscle (EAS), and the internal anal sphincter muscle (IAS).
The correlation between the dose delivered to these sphincter structures and the significance of fecal incontinence was evaluated using the CTCAE v5.0 incontinence grade score and the Low Anterior Resection Syndrome Score (LARS Score)
Results
The median age at the time of the study was 67 year (IQ 25-75: 64-74), the majority were men (64%), and the most represented cTNM was T3N1 (56%).
All patients received preoperative chemoradiation with at least 45Gy delivered to the CTV, most (72%) benefited from an integrated boost (50Gy) to the GTV.
Mean doses (Dmean) (IQ 25 – 75) were 45Gy (44.2 – 46.7) for the PRM, 48.4Gy for the LAM (46.5 – 48.8), 45.1Gy (42 – 47.7) for the EAS, and 45.6Gy (44.1 - 47.5) for the IAS.
There was a linear correlation between the dose delivered to the IAS and the distance from the IAS to the inferior part of the tumor.
The majority of patients (64%) had some degree of fecal incontinence (CTCAE) with 30% of patients having grade I incontinence, 28% grade II, and 6% grade III. Thirty-six percent of patients had a major LARS, 17% a minor LARS, and 47% had no LARS.
The Spearman correlations performed to evaluate the relationship between the LARS Score and the different dosimetric parameters (Dmean, D0.01cc) of each muscle were inconclusive graphically (r <0.4). However, the p value was significant (p<0.05) for EAS and IAS Dmean and for LAM D0.01cc.
Conclusion
No anal sphincter dose-volume relationship was found for the development of LARS, although limitations in sample size may have prevented a statistically significant clinical correlation.
Nevertheless, this study proved particularly informative in terms of dose received by the different muscles.