Dosimetric changes and interfraction anatomical variations during high dose rate brachytherapy of cervical cancers- Can replanning be avoided?

Abstract

Background: Interfraction variations occur due to tumour regression during cervical intarcavitary brachytherapy (ICR) requiring replanning with every fraction. This study aimed to determine the correlation of interfraction variations in positioning of applicator and its relationship with relative dosimetry if the dwell time and source positions of the plan of first fraction were applied to other subsequent fractions. Materials and Methods: This is a retrospective review of the orthogonal radiographs of cervical cancer patients treated from 2013 to 2016 in our institute, receiving ICR with the same dose prescription to point A using a tandem and two ovoids applicators. A hypothetical second and third plan were obtained by applying the same source positions and dwell time as in the first fraction plan. The dose delivered to point A, point B, cervical point, bladder point and rectal point were determined. The actual doses in the treated second and third fractions were compared with these hypothetical plans for any significant change in relative dosimetry. Statistical differences between groups were analysed using 2 tailed paired t test.Results: There was consistant increase in the doses to the point B, bladder point and rectal point in all the hypothetical plans with statistically significant difference observed for point B (p=0.001), rectal point (p=0.000) and bladder point(p=0.041). Conclusion:The conception of avoiding the replanning if similar interfraction conditions are achieved looks promising but the significant findings observed in this study warrants strongly to continue as per current recommendation of replanning with every fraction of brachytherapy.