3079 - MRI as a Biomarker for Pelvic Floor Atrophy in Rectal Cancer Patients Undergoing Chemoradiation Therapy

R. J. Thomas¹, L. M. Andring¹, T. J. Forbes², S. Palmquist³, and E. Holliday¹; ¹Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, ²University of Texas Houston School of Medicine, Houston, TX, ³Department of Radiology, The University of Texas MD Anderson Cancer Center, Houston, TX

Purpose/Objective(s): Pelvic floor dysfunction is a common complication in rectal cancer patients following chemoradiation. This study explores the utility of MRI as a biomarker for assessing pelvic floor atrophy in this population. There is a paucity of literature evaluating MRI for pelvic floor dysfunction. Materials/

Methods: Fifteen rectal cancer patients undergoing definitive chemoradiation therapy were evaluated. Staging/baseline MRI and surveillance MRI were obtained. 2D measurements at the widest cross section of the levator ani muscles were obtained from pre-treatment MRI scans and compared to surveillance MRI. Pelvic floor anatomy/changes were evaluated and compared to validated patient-reported outcome measures (LARS and FiQOL). Percent change was calculated, and we compared patients with =30% vs <30% muscle loss. Dosimetric parameters were analyzed, including mean dose to the anal canal and V50 to the anal canal.
Results: A significant difference in FiQOL Self Perception measure was observed between patients with =30% vs <30% muscle loss (Figure 1). Additionally, a higher median change in LARS score was noted in patients with =30% muscle loss (p=.0.048, Figure 2). Dosimetric parameters, such as mean dose to the anal canal (47.8 Gy for patients with <30% muscle loss, 51.3 Gy for patients with >30% muscle loss) showed a trend as potential predictors of pelvic floor atrophy. V50 to anal canal was significantly different between the two groups. (7.4 cc for patients with <30% muscle loss, 15.5 cc for patients with >30% muscle loss) (p=.03, Figure 3).
Conclusion: MRI demonstrates potential as a biomarker for pelvic floor dysfunction in rectal cancer patients undergoing chemoradiation therapy. This information could aid in identifying patients who may benefit from pelvic floor physical therapy intervention. Further research with larger cohorts is warranted to validate these findings.