Clinical Introduction of Stem Cell Sparing Radiotherapy to Reduce the Risk of Xerostomia in Patients with Head and Neck Cancer

Abstract

Background/Objectives: Studies have shown that dose to the parotid gland stem cell rich (SCR) regions should be reduced to lower the risk of xerostomia after radiotherapy (RT). This study aimed to assess whether stem cell sparing (SCS)-RT can be adopted in routine clinical practice. Methods: Multiple planning studies were performed to compare SCS-RT with standard (ST)-RT using 30 head and neck cancer patients. Shifts in mean dose to the SCR regions (Dmean,SCR) and other organs at risk and their estimated impact on normal tissue complication probability (NTCP) for side-effects were compared using Wilcoxon signed-rank test. A multicenter study was performed (eight institutions, three patients) to test the generalizability of SCS-RT using the Friedman test. Results: Using photons, Dmean,SCR was reduced with median 4.1/3.5 Gy for ipsilateral/contralateral (p < 0.001). The largest reductions were when the SCR regions overlapped less with target volumes. Subsequently, NTCPs for xerostomia decreased (p < 0.001). Using protons, Dmean,SCR was also reduced (2.2/1.9 Gy for ipsilateral/contralateral, p < 0.002). Nevertheless, SCS-RT did not further decrease NTCPs for xerostomia (p > 0.17). Target coverage and prevention of other side-effects were not compromised. However, increased mean oral cavity dose was observed in some patients. Lastly, in the multicenter study Dmean,SCR could be reduced by slightly adjusting the standard optimization. Contralateral Dmean,SCR reductions differed between centers (p = 0.01), which was attributed to differences in ST-RT plans. Conclusions: Stem cell sparing radiotherapy can be clinically introduced by making small adjustments to the optimization strategy and can reduce the risk of xerostomia.