Vaginal dose of radical radiotherapy for cervical cancer in China: a multicenter study

The posterior-inferior border of symphysis (PIBS) point system is a novel vaginal dose-reporting method and is a simple and reliable method proposed by the Medical University of Vienna proposed for both external-beam radiotherapy (EBRT) and brachytherapy (BT). In this multicenter study, we sought to first evaluate the vaginal radiation dose in Chinese cervical cancer patients according to the PIBS point system and then to analyze the factors influencing the dose distribution.

We collected data from the medical records of 936 cervical cancer patients who underwent concurrent radiochemotherapy at 13 different institutions in China. Radiation doses at points A, PIBS+ 2 cm, PIBS and PIBS-2 cm, International Commission on Radiation Units (ICRU)-R and ICRU-B were measured.

The median total doses in EQD2_{α/β = 3} at points PIBS+ 2 cm, PIBS and PIBS-2 cm were 82.5 (52.7-392.1) Gy, 56.2 (51.4-82.1) Gy and 2.6 (0.9-7.4) Gy, respectively. The median total doses in EQD2_{α/β = 3} at ICRU-R and ICRU-B were 77.5 (54.8-132.4) Gy and 79.9 (60.7-133.7) Gy, respectively. The mean vaginal reference length (VRL) was 4.6 ± 1.0 cm (median, 4.5 cm). In patients with VRL ≤4.5 cm, the mean total doses in EQD2_{α/β = 3} at points PIBS+ 2 cm, PIBS and PIBS-2 cm were 128.5, 60.7 and 0.8 Gy, respectively. In patients with VRL > 4.5 cm, the mean total doses at these three points were 68.9, 0.5 and 54.5 Gy, respectively. Classification of patients revealed significant differences (P < 0.05) between these two groups.

With the PIBS point system, Chinese patients with a shorter VRL of < 4.5 cm received higher radiation doses at the PIBS+ 2 cm, PIBS and PIBS-2 cm points than European and American patients. Further studies are required to establish the dose-effect relationships with these points as references. The study was registered as a clinical trial (NCT03257475) on August 22, 2017.