Dose coverage comparison between "interstitial catheter-only" and "hybrid intracavitary-interstitial brachytherapy" for early stage squamous cell carcinoma of the buccal mucosa

Purpose: When squamous cell carcinoma of the buccal mucosa (BSCC) extends surrounding anatomical sites such as gingiva, retromolar triangle, or hard palate, it might be challenging to ensure adequate tumor coverage by sole interstitial brachytherapy due to the complexity of catheter implantation. By combining interstitial catheters with an enoral placed, individually assembled “oral spacer plus embedded catheters” device (hybrid of intracavitary-interstitial brachytherapy), it should be easier to deliver the necessary tumoricidal dose to irregular-shaped tumor volumes (clinical target volume – CTV) with improved conformity. The purpose of this analysis was to compare the dose distribution created by the hybrid of intracavitary-interstitial brachytherapy (HBT) with the dose distribution of an interstitial catheter only-approach, based on the interstitial catheters used for HBT (ISBT-only) by evaluating respective treatment plans (HBT plan vs. ISBT-only plan) for the treatment of early stage BSCC. Material and methods: A retrospective analysis was performed for patients with localized BSCC treated between April 2013 and October 2017. All patients received sole HBT without additional external beam radiation therapy or planned neck dissection. Dosimetric parameters taken into account for comparison between actual HBT and virtual ISBT-only were CTV D90, CTV V100, CTV V150, CTV V200, mandible D2cc, and mucosal surface D2cc. Results: Dosimetrically, HBT showed a trend toward better CTV D90 compared to ISBT-only. In addition, HBT demonstrated statistically better CTV V100 coverage compared to ISBT-only. There was no statistically significant difference with respect to CTV V150, CTV V200, and mucosal surface D2cc, while a trend was seen in better mandible D0.1cc between HBT and ISBT-only. Conclusions: The HBT approach appears to enable improved dose coverage of irregular-shaped enoral tumor volumes compared to ISBT-only for patients with early stage BSCC