Re-Irradiation of Recurrent Buccal Mucosa Cancer Utilizing Customized Intraoral Mold-Based HDR Brachytherapy

Abstract

Feasibility of re-irradiation in recurrent buccal mucosa squamous cell carcinoma after definitive external beam radiation therapy utilizing customized intraoral mold HDR brachytherapy, An 82-year-old male with a 3-year history of right buccal mucosal lesions, diagnosed as moderate dysplasia with inability to rule out invasion, was referred to radiation oncology as he was not a surgical candidate. Examination demonstrated extensive erythematous lesions involving the right oral commissure, gingivobuccal sulcus, right anterior tonsillar pillar, and soft and hard palate. He received 70 Gy in 35 fractions with a complete treatment response; however, 6 months later, he presented with stomatalgia and oral mucosa bleeding. Physical examination revealed new ulcerations of the right lower vermillion lip and exophytic plaque-like lesions along the posterior right maxillary alveolar ridge extending to the gingivobuccal sulcus and along the buccal mucosa and hard and soft palate. Biopsy of the tumor demonstrated hyperplastic squamous epithelium with mild to moderate dysplasia. Initially, the patient declined surgical treatment but returned as the tumors became more symptomatic. Subsequently, decision was made to treat with intraoral HDR brachytherapy as this was a previously irradiated field. Impressions were made and a customized mold was embedded with UV exposed low-Z shielding, which allowed for kV CT treatment planning. Eight 6-French catheters were inserted into the mold and a CT scan was obtained to determine the mold composition and needle placement. Modifications were made and a fitting test was conducted to assess reproducibility and comfort. A neck brace was constructed to secure the mold placement. Two CT simulations were obtained: one with contrast to delineate the extent of the tumor, and the other without contrast but with addition of radiopaque markers inside catheters to digitally reconstruct the source path. Rigid registration fused the two CT scans and the clinical target volume (CTV) and mandible were delineated. We prescribed 30 Gy in 10 fractions using the following criteria: CTV target, V90% ≥90% (28.6 Gy2/2) and mandible, D0.1cc < 28.6 Gy2/2 was a hard constraint. HDR plan produced a CTV V90%= 90.7%, V200% = 2.4 cc. Mandible D0.1cc received 25.9 Gy2/2. Prior to fraction 6 of 10, the plan was modified to address medial soft palate contours as a result of tumor shrinkage. Adaptive planning on new image data sets used the same criteria as the original plan. Soft palate D0.1cc was reduced by 9%. Patient completed treatment without complications or interruptions. Four months after treatment, he had no evidence of disease recurrence. This report demonstrates the design and use of non-invasive intraoral mold brachytherapy as a promising treatment modality for complex tumor recurrences within the oral cavity.