MRI-guided brachytherapy in locally advanced cervical cancer: Small bowel [Formula: see text] and [Formula: see text] are not predictive of late morbidity.

PURPOSE: To establish dose-volume effect correlations for late small bowel (SB) toxicities in patients treated for locally advanced cervical cancer with concomitant chemoradiation followed by pulsed-dose rate MRI-guided adaptive brachytherapy.

METHODS AND MATERIALS: Patients treated with curative intent and followed prospectively were included. The SB loops closed to CTV were delineated, but no specific dose constraint was applied. The dosimetric data, converted in 2-Gy equivalent, were confronted with the occurrence of late morbidity assessed using the CTC-AE 3.0. Dose-effect relationships were assessed using mean-dose comparisons, log-rank tests on event-free periods, and probit analyses.

RESULTS: A total of 115 patients with a median followup of 35.5 months were included. Highest grade per patient was: Grades 0 for 17, 1 for 75, 2 for 20, and 3 for 3. The mean [Formula: see text] and [Formula: see text] were, respectively, 68.7 ± 13.6 Gy and 85.8 ± 33.1 Gy and did not differ according to event severity (p = 0.47 and p = 0.52), even when comparing Grades 0-1 vs. 2-4 events (68.0 ± 12.4 vs. 71.4 ± 17.7 Gy; p = 0.38 and 83.7 ± 26.4 vs. 94.5 ± 51.9 Gy; p = 0.33). Log-rank tests were performed after splitting the cohort according to four [Formula: see text] levels: >80 Gy, 70-79 Gy, 60-70 Gy, and <60 Gy. No difference was observed for Grades 1-4, Grades 2-4, or Grades 3-4 (p = 0.21-0.52). Probit analyses showed no correlation between the dosimetric parameters and probability of Grades 1-4, 2-4, or 3-4 events (p = 0.19-0.48).

CONCLUSION: No significant dose-volume effect relationships were demonstrated between the [Formula: see text] and [Formula: see text] and the probability of late SB morbidity. These parameters should not limit the pulsed-dose rate brachytherapy optimization process.