Use of an intravaginal spacer in young girls treated with brachytherapy for bladder neck rhabdomyosarcoma: Dosimetric impact for organs at risk sparing and acute tolerance.

ABSTRACT

PURPOSE: Interstitial brachytherapy is indicated as part of a conservative strategy for children with bladder and/or prostate rhabdomyosarcoma (RMS), providing high local control probability with acceptable functional results. Vaginal and/or rectal complications were however reported, due to the close proximity to the implanted volume. We investigated the dosimetric impact of a vaginal spacer in terms of rectal and vaginal doses. METHODS AND PATIENTS Medical records of 12 consecutive female patients with bladder neck RMS, median age 32 months (range 1.3-6 years), were reviewed. Five patients were treated prior to 2017 without a vaginal spacer and seven patients treated after 2017 had their brachytherapy delivered with a vaginal spacer placed at time of implant. RESULTS: Minimal doses delivered to the most exposed 2cm3, 1cm3, and 0.5cm3 of the rectum were all statistically significantly lower among patients treated with a vaginal spacer, as compared to those treated without a spacer. Median rectal D2cm3 was 22GyEQD2 versus 38GyEQD2 (P=0.02), D1cm3 was 29GyEQD2 versus 51GyEQD2 (P=0.013), and D0.5cm3 was 32GyEQD2 versus 61GyEQD2 (P=0.017), with and without the vaginal spacer, respectively. The posterior vaginal wall D0.5cm3 dose was also significantly decreased, with median D0.5cm3 of 92GyEQD2 versus 54GyEQD2 (P<0.0001), with and without the spacer, respectively. Acute tolerance was excellent in all patients, with no need for replanning and no acute complication. CONCLUSIONS: The use of vaginal spacers in brachytherapy of female pediatric patients with bladder neck RMS resulted in significantly decreased doses to the rectum and the posterior vaginal wall. Though the clinical impact of such dose reduction remains undemonstrated, routine utilization of a vaginal spacer could be a method to decrease long-term morbidity in these patients.