Integrating submandibular gland transfer with proton therapy to preserve salivary function

Submandibular gland (SMG) transfer to the submental space in patients undergoing head and neck radiation therapy was historically performed to decrease radiation-associated xerostomia in the era of 2D/3D radiotherapy. In this study, we evaluated the dosimetric significance of SMG transfer with intensity modulated proton therapy (IMPT).

We reviewed patients with oropharyngeal carcinoma who received curative intent definitive radiation and had contralateral (C/L) SMG transfer. We registered the baseline diagnostic computed tomography (CT) scan of these patients with the CT simulation images and delineated pre-transfer and post-transfer SMG locations. IMPT pre-transfer plans were generated, taking into consideration the initial reference SMG position, and then re-optimized based on the post-transfer SMG position. Each patients' dosimetric parameters from both plans were compared for mean SMG doses, target coverage and other OAR doses.

Seventeen patients were included in the analysis. All patients received definitive radiation (66-70 Gy/30-35 fractions). Pre-transfer plans had a C/L SMG mean dose of 32.92 Gy (range [R]: 17.82-47.6 Gy), which decreased to 20.22 Gy (R: 9.75-38.87 Gy), p < 0.001 on re-optimization. Post-transfer plans met the mean dose constraints more often than pre-transfer plans. The difference in C/L SMG mean dose with gland transfer was 12.02 Gy (95% CI: 9.46-14.59 Gy; p < 0.001). There was no significant difference in target coverage, ipsilateral SMG, and any other OARs between the plans.

This pilot study demonstrates that SMG transfer enables better C/L SMG dose sparing during IMPT. Future prospective studies with larger patient cohorts are warranted to support clinical translation.