Sparing the contralateral submandibular gland in oropharyngeal cancer patients: A planning study

Background and purposeThe submandibular glands are proposed to be important in preventing xerostomia in head-and-neck cancer patients. We investigated the feasibility of sparing the contralateral submandibular gland (cSMG) by reducing the dose to the contralateral planning target volume (PTV) and by reducing the clinical target volume (CTV)-to-PTV margin.Materials and methodsTen oropharyngeal cancer patients with a contralateral elective PTV were included in this planning study, using intensity modulated radiotherapy (IMRT). The effect on the mean dose to the cSMG of reducing the dose coverage to the contralateral elective PTV from 95 to 90% of the prescribed dose (54 Gy in 1.8 Gy daily fractions) was determined. The influence of reducing the margin for position uncertainty from 5 to 2 mm was investigated.ResultsThe mean dose to the cSMG was reduced from 54 Gy to approximately 40 Gy if the dose coverage to the contralateral PTV was reduced to 90% of the prescribed dose. The estimated normal tissue complication probability (NTCP) was reduced below 50%. Reducing the margin from 5 to 2 mm resulted in a decrease in the mean dose to the cSMG of approximately 6 Gy.ConclusionsReducing the mean dose to the cSMG below 40 Gy is possible with a reasonable dose coverage of the contralateral elective PTV.