Assessment of radiation doses to the para-aortic, pelvic, and inguinal lymph nodes delivered by image-guided adaptive brachytherapy in locally advanced cervical cancer

PURPOSE: This study evaluated the dose delivered to lymph nodes (LNs) by brachytherapy (BT) and the effect of BT image-guided optimization on the LN dose. METHODS AND MATERIALS: Twenty-five patients with locally advanced cervical cancer were retrospectively analyzed, 16 patients of them had LN involvement. The patients received whole pelvis intensity-modulated radiation therapy (45-50 Gy/25-30 fx) to whole pelvis and two fractions of MRI pulsed-dose-rate BT. The delineated LN groups were para-aortic, inguinal, common iliac (CI), external iliac, internal iliac, obturator, and presacral. For each LN group, D-98%, D-50%, and D-2% (the dose that covers 98%, 50%, and 2% of the volume, respectively) were evaluated for optimized and standard BT plans. The correlation between total reference air kerma (TRAK) and D-50% of the LN groups was evaluated. RESULTS: BT contributed considerable dose (mean D-50% was 3.8-6.2 Gy equivalent total dose in 2-Gy fractions) to the pelvic LN (external iliac, internal iliac, obturator, and presacral) in optimized plans, whereas less-dose contribution to CI, para-aortic, and inguinal (mean D-50% was 0.5-1.9 Gy equivalent total dose in 2-Gy fractions) was observed. Optimized plans delivered less dose to the LNs as compared with standard plans, although differences only amounted to a mean of 0.2-0.9 Gy (D-50%). TRAK showed a significant correlation with LN D-50% for all LN groups except CI, although only 19-38% of the dose variation could be explained by the TRAK. CONCLUSIONS: BT contributes considerable dose to pelvic LNs and should be considered in the evaluation of total LN doses. (C) 2015 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.