Multicentre evaluation of a novel vaginal dose reporting method in 153 cervical cancer patients

Abstract

© 2016 Elsevier Ireland Ltd Background and purpose Recently, a vaginal dose reporting method for combined EBRT and BT in cervical cancer patients was proposed. The current study was to evaluate vaginal doses with this method in a multicentre setting, wherein different applicators, dose rates and protocols were used. Material and methods In a subset of patients from the EMBRACE study, vaginal doses were evaluated. Doses at the applicator surface left/right and anterior/posterior and at 5 mm depth were measured. In addition, the dose at the Posterior–Inferior Border of Symphysis (PIBS) vaginal dose point and PIBS±2 cm, corresponding to the mid and lower vagina, was measured. Results 153 patients from seven institutions were included. Large dose variations expressed in EQD2 with α/β = 3 Gy were seen between patients, in particular at the top left and right vaginal wall (median 195 (range 61–947) Gy/178 (61–980) Gy, respectively). At 5 mm depth, doses were 98 (55–212) Gy/91 (54–227) Gy left/right, and 71 (51–145) Gy/67 (49–189) Gy anterior/posterior, respectively. The dose at PIBS and PIBS±2 cm was 41 (3–81) Gy, 54 (32–109) Gy and 5 (1–51) Gy, respectively. At PIBS+2 cm (mid vagina) dose variation was coming from BT. The variation at PIBS−2 cm (lower vagina) was mainly dependent on EBRT field border location. Conclusions This novel method for reporting vaginal doses coming from EBRT and BT through well-defined dose points gives a robust representation of the dose along the vaginal axis. In addition, it allows comparison of vaginal dose between patients from different centres. The doses at the PIBS points represent the doses at the mid and lower parts of the vagina. Large variations in dose throughout the vagina were observed between patients and centres.