Volumetric image guidance for intravaginal brachytherapy: A dosimetric and clinical study

Background: The present retrospective dosimetric and clinical study aims to explore the subset of patients who will benefit from volumetric image guidance in intravaginal brachytherapy (IVBT). Materials and Methods: Sixty-three consecutive patients who underwent IVBT using single-channel intravaginal cylinder were analyzed. The most common IVBT dose protocol was 1100 cGy in two fractions (with external beam radiotherapy [EBRT]) and 2200 cGy in four fractions (when used alone). The factors affecting the dose to organs at risk (OARs) (such as treated length, orientation of applicator, EBRT) and target volume were analyzed. Local control rate and late toxicities were reported. Results: There was a statistically significant increase in equivalent dose at 2 Gy per fraction (EQD2) doses of all OARs with the addition of EBRT. In 39.4%, EQD2 D2cc dose of rectum was more than 65 Gy. There was a statistically significant positive correlation with increasing treated length in D5cc (Gy) of rectum and D5cc (Gy) of urethra (Pearson's correlation coefficient of 0.375, P = 0.002 and Pearson's correlation coefficient of 0.394, P = 0.001, respectively). There was a statistically significant increase in D2cc and D5cc of rectum with posterior orientation. Air gaps were noted in 81% of applications. Median duration of follow-up was 30 months. One patient had vaginal recurrence in lower third of vagina. One patient was recorded with grade 2 hemorrhagic radiation proctitis. Conclusion: Computed tomography (CT)-based volumetric planning is an effective method to evaluate doses to OARs and confirm the adequacy of dose coverage, and we recommend routine use of the same. Image guidance is most beneficial in patients being treated with a combination of IVBT and EBRT, posterior orientation, and those who are treated for the entire length of vagina.