2210 - Head and Neck Parotid Gland Sparing Techniques: Small Volume, Big Change

B. M. Anderson¹, D. V. Fried², M. Hawkins², S. K. Das³, M. C. Repka¹, C. Shen¹, and X. Chen³; ¹Department of Radiation Oncology, University of North Carolina, Chapel Hill, NC, ²Department of Radiation Oncology, University of North Carolina at Chapel Hill, Chapel Hill, NC, ³University of North Carolina, Chapel Hill, NC

Purpose/Objective(s): We hypothesize that the inclusion of a simple parotid optimization structure (dose to this structure is reduced below specified constraints during treatment planning) will result in significant reduction of dose to the overall parotid in patients with head and neck cancer (HNC) receiving intensity modulated radiation therapy (IMRT), compared to those treated without the optimization structure. Materials/

Methods: We retrospectively extracted data from 1228 patients who had previously undergone IMRT for HNC at our institution from 2020 to 2024. Of these, 79 had the parotid optimization region-of-interest (ROI), crafted to include the parotid duct, accessory parotid, and the anterosuperior parotid gland within 1.5cm of the mandible. The planning goal for the optimization ROI was set to 50% volume (D50%) receiving less than 8-12 Gy, depending on the proximity of high-dose PTV. We compared the relative dose-volume histograms (DVHs) of whole parotids, stratified into standard, intermediate, and high-risk groups based on the maximum parotid dose. These groupings are important to fairly compare parotids based on their proximity to target volumes.
Results: Whole parotid mean dose and D50% were significantly improved in the standard risk (maximum parotid dose 48-56Gy) and intermediate risk (maximum parotid dose 56-64Gy). These results are summarized in the table below. There was no significant difference in the high-risk group (64-72Gy).
Conclusion: Selective sparing of the anterosuperior parotid using a simple optimization structure can have a significant impact on the overall parotid dose. This benefit is most pronounced when the parotid is adjacent to the elective or intermediate dose levels, but less so when high-dose level or gross tumor is nearby, suggesting that existing optimization techniques already offer maximal parotid sparing in these cases. Further research is needed to understand whether this dosimetric benefit translates into clinical improvement in xerostomia. Abstract 2210 – Table 1

		W/o Opt ROI	With Opt ROI	p-value
Standard risk (48-56Gy)	Dmean	25.3 ± 10.4	17.5 ± 6.4	0.0006
	D50%	22.1 ± 13.7	11.9 ± 7.8	0.0003
Intermediate risk (56-64Gy)	Dmean	29.9 ± 10.6	24.5 ± 8.8	6E-05
	D50%	27.1 ± 15.0	20.0 ± 11.3	0.00005
High risk (64-72Gy)	Dmean	33.7 ± 11.8	31.3 ± 8.1	0.199
	D50%	30.9 ± 16.1	27.7 ± 12.7	0.250