Dose to pelvic lymph nodes in locally advanced cervical cancer during high-dose-rate brachytherapy with tandem-ring applicators

Purpose
The present study aimed to assess the correlation between dose to pelvic lymph nodes and to point B with tandem-ring (TR) applicators for intra-cavitary brachytherapy treatment of locally advanced cervical cancer.

Material and methods
Cervical cancer patients treated at brachytherapy department of Lucien Neuwirth Cancer Center, from 2015 to 2018, were included. Target delineation was performed in compliance with GEC-ESTRO guidelines. Revised American Brachytherapy Society (ABS) point A was determined (ARN (right) and ALN (left)) as well as Manchester point B. Prescription dose was 25-35 Gy in 5 fractions. Pelvic lymph nodes were delineated, then dose to points A and B, and dose-volume histogram (DVH) parameters of delineated lymph nodes were extracted. Significant relationships or correlations between lymph nodes reference points, dosage to points B, and their DVH parameters were investigated.

Results
The mean dose and mean percentage of the prescription dose to the left and right points B were 4.6 ±0.18 Gy and 82.08 ±0.72%, respectively. Pearson correlation coefficient R = 0.81 (p-value = 0.00) between dose to ARN and ALN points and prescription dose was obtained. Negative correlation between CTVHR volume and difference between French and ABS prescription points was found.

Conclusions
Dose to point B can be a moderate surrogate for maximum, minimum, and median dose to the internal iliac and presacral lymph node, but cannot be for maximum dose to the obturator lymph node. Points B cannot be a reliable substitute for common and external iliac chains.