Lumbosacral plexus delineation, dose distribution, and its correlation with radiation-induced lumbosacral plexopathy in cervical cancer patients

BACKGROUND: To evaluate the dose distribution to the lumbosacral plexus (LSP) and its correlation with radiation-induced lumbosacral plexopathy (RILSP) in patients with cervical cancer treated with intensity-modulated radiotherapy (IMRT) and high-dose-rate brachytherapy. MATERIALS AND METHODS: After meeting eligibility criteria, 50 patients with cervical cancer were selected who were treated with IMRT and high-dose-rate brachytherapy, and the LSP was contoured. Mean volume; percentages of LSP volume absorbing 40, 50, 55, and 60 Gy (V30, V40, V50, V55, and V60) and point doses (P1, P2, P3, P4, P5, P6, P7, P8, P9, and P10); and RILSP incidence were calculated. RESULTS: At 60 months of follow-up, four patients (8%) were found to have grade 2/3 RILSP. The mean maximal LSP dose in patients with RILSP was 59.6 Gy compared with 53.9 Gy in patients without RILSP (control; P=0.04). The mean values of V40, V50, V55, and V60 in patients with RILSP versus control were 61.8% versus 52.8%, 44.4% versus 27.7%, 8.0% versus 0.3% and 1.8% versus 0%, respectively (P=0.01, 0.001, 0.001, and 0.001, respectively). CONCLUSION: The delineation of the LSP during IMRT planning may reduce the risk for RILSP. The mean values of V40, V50, V55, and V60 for LSP should be less than 55%, 30%, 5%, and 0.5%, respectively; however, further studies are warranted.