Intermediate dose-volume parameters and the development of late rectal toxicity after MRI-guided brachytherapy for...

The dose delivered to the most exposed 2 cm³ [Formula: see text] of the rectum and bladder is predictive of late rectal and bladder toxicity in cervix cancer patients. We investigated the predictive value of intermediate doses to the rectum and bladder for late rectal/bladder toxicity after MRI-guided brachytherapy for patients with locally advanced cervix cancer.

Toxicity was prospectively graded using Common Toxicity Criteria for Adverse Events v4.0 and retrospectively verified for women with Stage IB-IVA cervix cancer treated consecutively with MRI-guided brachytherapy between 2008 and 2013. The minimum equivalent dose in 2 Gy fractions delivered to 0.1, 1, 2, 5, and 10 cm³ of the rectum and bladder and the absolute volume of the rectum receiving 55, 60, 65, 70, and 75 Gy₃ (V_55-75) were collected. The association between dose-volume parameters and Grade 2+ rectal/bladder toxicity was examined using logistic regression.

With a median followup of 44 months, cumulative incidences of Grade 2+ rectal and bladder toxicity among the 106 patients were 29% and 15% at 3 years, respectively. All the dose-volume parameters were significantly associated with late Grade 2+ rectal and bladder toxicity (p < 0.05), except for bladder [Formula: see text] . On multivariable logistic regression, both [Formula: see text]  > 70 Gy₃ and V₅₅ > 11 cm³ (p < 0.05) were predictive of late Grade 2+ rectal toxicity, with improved model fitting and higher area under the curve compared with the model with [Formula: see text]  > 70 Gy₃ alone.

In this study, V₅₅ was predictive of late Grade 2+ rectal toxicity. Adding V₅₅ to  [Formula: see text] improved prediction accuracy.