MRI-guided brachytherapy in locally advanced cervical cancer: Small bowel D 0.1 cm 3 and D 2 cm 3 are not predictive of late morbidity

Abstract 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 D 2 cm 3 and D 0.1 cm 3 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 D 2 cm 3 levels: >80 Gy, 70–79 Gy, 60–70 Gy, and 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 D 2 cm 3 and D 0.1 cm 3 and the probability of late SB morbidity. These parameters should not limit the pulsed-dose rate brachytherapy optimization process.