Estimation of pelvic lymph node dose contribution from HDR ICBT in cervical cancer

Context: Dose received to each pelvic group of lymph nodes, namely obturator (OB), internal iliac (II), and external iliac (EI), is less certain. This study is conducted to evaluate the dose delivered to these nodal groups so that this can be considered while planning external beam radiotherapy external beam radiation therapy (EBRT) boost in patients with gross pelvic lymph nodes. Aims: This study aimed to estimate the dose contribution to pelvic lymph nodes in three-dimensional high-dose-rate intracavitary radiotherapy (HDR-ICRT) of cervical cancer patients. Settings and Design: This was a single-arm retrospective observational study among 25 locally advanced carcinoma cervix patients treated with definitive chemoradiation. Materials and Methods: EI, II, and OB groups of lymph nodes were delineated on computed tomography data sets of selected 25 patients, and D100, D50, and D2cc to each lymph node were analyzed. The dose received by each pelvic lymph node group from all the 3 fractions of HDR-ICRT, corresponding equivalent 2 Gy dose, and percentage of brachytherapy (BT) contribution to each pelvic lymph node were calculated. Results: Mean D100 received by EI, II, and OB lymph node groups after summation across 3 fractions was 1.1 Gy, 2.34 Gy, and 3.11 Gy, respectively. Mean 2 Gy equivalent doses (D100) were 1.66 Gy, 3.41 Gy, and 4.53 Gy, respectively. Corresponding percentage of the dose received by EI, II, and OB was 4.89%, 10.43%, and 13.83% when 7.5 Gy per fraction for 3 fractions was prescribed to Point A. Conclusions: There is a significant contribution from HDR intracavitary BT to the pelvic lymph nodes in the radical treatment of cervical cancer. The dosimetric results given in this work can be used by a radiation oncologist to estimate BT doses to affected lymph nodes and integrate them into the preceding EBRT planning phase.