The value of systematic contouring of the bowel for treatment plan optimization in image-guided cervical cancer high-dose-rate brachytherapy.

PURPOSE: To investigate the dose-volume histogram metrics and optimization results of the contoured bowel in cervical cancer brachytherapy.

METHODS AND MATERIALS: Treatment plans of cervical cancer patients treated with image-guided high dose rate were retrospectively analyzed with institutional review board approval. In addition to the clinical target volume, rectum, bladder, and sigmoid, the bowel was contoured at the time of planning (Group 1) or at the time of this analysis (Group 2).

RESULTS: Thirty-two patients treated with 145 insertions were included. Before optimization, mean ± 1 standard deviation overall bowel minimum dose to the most irradiated 2 cm3 volume of an organ (D2cc ) was 67.8 Gyα/β3 ± 13.7 Gyα/β3 (Group 1: 72.6 ± 13.2 Gyα/β3 ; Group 2: 57.3 ± 8.0 Gyα/β3 ). Before optimization, one patient in Group 1 presented a bowel D2cc metric exceeding 100 Gyα/β3 . After optimization, bowel D2cc mean ± 1 standard deviation was 59.4 ± 6.7 Gyα/β3 (Group 1: 61.4 ± 6.0 Gyα/β3 , p < 0.001; Group 2: 55.2 ± 6.5 Gyα/β3 , p = 0.026).

CONCLUSIONS: Given the potentially high doses and the benefit of optimization in reducing dose to the organs at risk, we recommend consideration of systematic contouring of the bowel when bowel is present in the pelvis.