SU‐GG‐J‐95: Feasibility to Use Daily Cone‐Beam‐CT to Determine Dose‐Surface Histogram of Oral Mucosa in Radiotherapy of H&N Cancer

Purpose: to develop a novel approach for estimating dose delivered to the oral mucosa — dose‐surface histogram (DSH)‐ to facilitate assessment of radiation induced mucositis from radiotherapy for head and neck (H&N) cancer. Method and Materials: Mucositis, Xerostomia, and dental caries are common oral complications from radiotherapy. We hypothesized that an improved method for describing dose distribution to oral mucosa and parotid glands would better enable prediction of these dose‐limiting effects. Due to large uncertainties related to mobility of oral tongue and month, we used daily CBCT to delineate the oral cavity and the gum, which were then expanded by 1‐mm. The shell of the expended 1‐mm should represent the mucosal layer. A dose‐surface‐histogram (DSH) was then calculated from the difference between the DVHs for the oral cavity from the 1‐mm expansion. In addition, the daily CBCT would also allow us to calculate the DVHs to the parotid glands that could be displaced and shrunken during the course of treatment. Results: We have successfully applied this method to two patients currently receiving IMRT for H&N cancer. The absolute mucosal surface area receiving a high dose (>80% of prescription dose) is significantly different from the volume within the oral cavity. Conclusion: DSH for oral mucosa is achievable using daily CBCT images. The dose distribution to the mucosa may provide us with a more robust predictor of radiation‐induced mucositis and Xerostomia.