MSS05 Presentation Time: 4:05 PM: HDR Brachytherapy for Pediatric Vaginal Rhabdomyosarcoma: Two Case Reports with Long-Term Follow Up

Abstract

<h3>Purpose</h3> Rhabdomyosarcomas (RMS) are the most common soft tissue tumor in children with over 400 cases diagnosed each year. Vaginal RMS is exceedingly rare, accounting for 4% of all RMS and 10% of female RMS. Outcomes are favorable with 10-year overall survival rates estimated to be over 90%. Current standard of care requires multidisciplinary approach involving chemotherapy and local therapy. To limit late effects from treatment, local therapy has advanced from radical surgeries to no local treatment in those with complete response or favoring radiation therapy for those with residual disease following chemotherapy. There is limited data on modern brachytherapy techniques for the management of vaginal RMS. Here we report two cases of pediatric vaginal RMS treated with HDR intracavitary brachytherapy at our institution and long-term follow up. <h3>Methods and Materials</h3> Following IRB approval, we identified two pediatric patients who were treated at our institution with HDR brachytherapy for RMS between 2017 and 2019 and had follow up data available. We collected demographics, presenting information, treatment data including chemotherapy, surgery if applicable, brachytherapy plans, and outcomes. <h3>Results</h3> Both patients presented at outside hospitals at the age of 2 with a prolapsing vaginal mass. Biopsies were consistent with botryoid vaginal RMS. They were referred to our institution for consideration of radiation therapy after completion of 12 weeks of VAC-based chemotherapy. Post-chemotherapy MRIs were obtained to assess extent of residual disease and a vaginal applicator was placed at the time of MRI for HDR brachytherapy planning. Both patients had good response with small areas of residual thickening along the vaginal wall. The first patient underwent exam under anesthesia, vaginal dilation and removal of visualized gross disease prior to brachytherapy. A 2.2 cm Syed obturator was used with a straight central tandem positioned at the proximal end of the obturator for central loading with 2 additional flexible catheters placed in the posterior grooves of the Syed obturator. The 3 channels allowed for coverage of the posterior and proximal vaginal disease seen on her post-chemotherapy MRI. On her last fraction, she was noted to have vaginal swelling and difficulty with inserting the Syed obturator, therefore, a 2 cm Varian single channel cylinder was used for her last fraction. For the second patient, a custom designed vaginal cylinder was made by machining a hole through a 1.3 cm vaginal dilator with a catheter inserted and affixed in the central canal. Both patients were prescribed 4.9 Gy x 6 fractions treated three times weekly with the goal of obtaining an equivalent total dose of 36 Gy with 45 Gy to the vaginal surface. The first patient was prescribed to 5mm depth and the second patient to 3mm depth based on extent of residual disease. Both patients tolerated treatment well with minimal bleeding on cylinder insertion and expected acute side effects including cystitis, dysuria and acute vaginal discomfort that resolved with sitz baths and barrier ointments. With 4 and 3 years follow up, respectively, both patients have no evidence of disease on MRI imaging and no evidence of long-term toxicities related to their brachytherapy. <h3>Conclusions</h3> Vaginal RMS is a rare cancer and thus there is limited modern experience with HDR brachytherapy as a means for local control in this patient population. Here were present two cases where devices relatively common in gynecologic brachytherapy practices can be used and customized to cover small tumors in pediatric patients. Our experience has shown that for select patients, HDR brachytherapy can be a safe, tolerable, and efficacious treatment modality for vaginal RMS.